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Food Science And Technology Extended Study

12 Food Science and Technology Extended Study12.1 Functional properties of food components for food production

12.1.1 Water

12.1.2 Carbohydrates

12.1.3 Protein

12.1.4 Fats and Oils (Lipids)

12.2 Industrial food production

12.2.1 Principles

12.2.2 Food Processing

12.2.3 Food Processing Technology and Hygienic Practices

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12 Food Science and Technology Extended Study12.1 Functional properties of food components for food production

12.1.1 Water Nearly all foods contain a certain amount of water. Nutrients present in the food are dispersed in the water. Elements in the form of solids, liquids and gases may be dispersed in water to form either solutions or colloids. The major function of water in food is mainly to provide a medium for the formation of solution and colloids.

(A) Solutions If sugar is placed in water, it dissolves and produces a solution. A solution is homogenous, i.e. its composition is uniform throughout.

A solution is made up of two components; the solute, which is the substance dissolved, e.g. sugar in the above example, and the solvent, the liquid in which the solute is dissolved, e.g. water in the above example. Solutions are not necessarily composed of a solid dissolved in a liquid. Soda water is a solution of a gas (carbon dioxide) dissolved in a liquid (water). Vinegar is a solution in one liquid (acetic acid) dissolved in a second liquid (water).

Dissolved substances will cause an increase in the boiling point and a depression of the freezing point of solutions. The effect of a solute on the boiling point and freezing point of a solution is directly proportional to its concentration. Sugar solution, used in confectionery, has a boiling point well above 100℃, the boiling point of water. Salt is used to lower the freezing point of water to below 0℃ and to prevent ice forming on roads in winter.

Solutions are formed by inorganic compounds, in which particles or ions have an affinity for water. If the particles of a compound have a greater attraction for each other than they have to water, the compound will be insoluble.

(B) Colloids If a substance such as albumin, the protein in egg white, is mixed with water it does not dissolve but forms a colloidal dispersion. This dispersion is not a solution and is not homogeneous, since the molecules of protein do not dissolve. The molecules are dispersed throughout the water producing a heterogeneous or two-phase system. The substance which is dispersed is known as the dispersed phase and it is suspended in the continuous phase. In the above example, protein is the dispersed phase and water is the continuous phase. The particles of the dispersed phase of a colloid are usually

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between 1 and 100 nm in diameter. After a period of time the particles in a suspension settle out as sediment, due to the effect of gravity. Figure 12.1 is a diagram illustrating that Substance A is dispersed in water to form a colloid.

Figure 12.1 Colloid of water and substance A

Substance A Water

There are various types of colloidal system depending on the physical state (solid, liquid or gas) of the two phases. Some of the colloidal systems found in foods are listed in Table 12.2.

Table 12.2 Types of colloidal system

Common name

Foam

Solid foam

Emulsion

Gel

Disperse phase

Gas

Gas

Liquid

Liquid

Continuous phase

Liquid

Solid

Liquid

Matrix Network Solid

Examples

Whipped cream

BreadCake

MilkCream

Gelatin (Clear)Baked egg custard

(Translucent)

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12.1.2 Carbohydrates Carbohydrates are a group of nutrients important in the diet as a source of energy. They contain the elements carbon, hydrogen and oxygen and are produced in plants by the process of photosynthesis. Carbohydrates include monosaccharides, disaccharides, oligosaccharides and polysaccharides.

(A) StarchStarch is the most widely used polysaccharide in food production due to its nutritional value and its functional properties, such as gelatinisation and dextrinisation.

(i) Gelatinisation If starch granules are added into water and heated, the water penetrates the outer layer of the granules and the granules begin to swell. This occurs as the temperature rises from 60℃ to 80℃. The granules may swell until the volume is five times larger than the original. As the size of the granules increases the mixture becomes viscous. At about 80℃, the starch granules break up and the contents become dispersed throughout the water. The long-chain starch molecules begin to unfold and the starch/water mixture becomes more viscous, i.e. the mixture is thickened forming a sol. On cooling, if the proportion of starch to water is sufficiently great, the starch molecules form a network with the water entrapped to form a gel. The entire process is known as gelatinisation and is very important in cooking. For example, it is responsible for the thickening of sauces, soups and gravies by the addition of flour or corn starch.

(ii) Dextrinisation Dextrinisation is the breakdown of starch molecules to smaller, sweeter-tasting dextrin molecules (still a starch fragment) in the presence of dry heat. When starch (in a slurry form) is treated with acid or enzyme, or both, it is a hydrolytic reaction involving liquefaction and saccharification that leads to the breakdown of starch into maltose and glucose (not fructose unless the enzyme glucose isomerase is used).

(B) SugarSugar has the following functions that make it useful in food production.

(i) As Preservatives High concentrated sugar solutions can act as preservatives in food to prevent the growth of bacteria. As foods with very high concentration of sugar have very low water activity, this can prevent the bacteria from accessing the water in the food. The bacteria become dehydrated and stop growing.

(ii) As Caramelising Agents Prolonged heating of sugars can form caramel pigment, this process is known as non-enzymatic browning. When sugars are subjected to heat in the absence of water or heated in a concentrated solution, a series of chemical reactions occurs that finally leads to the formation of caramel which can be used to enhance the food flavour and colour. Caramelisation of sucrose requires a temperature of about 200℃ and heating for at least 35 minutes.

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(iii) As SweetenersSugar can be used as sweeteners in food preparation. Different sugars provide different intensity of sweetness. The table below shows the relative sweetness of several commonly used sugars (Table 12.3):

Table 12.3 Relative sweetness of common sugars

Sugar

Fructose

Sucrose

Glucose

Maltose

Lactose

Honey (mixture of sugars)

Relative sweetness

170

100

70

40

15

100 - 130

(iv) As Crystallising AgentsAnother important characteristic of sugars is their ability to form crystals, the process is called crystallisation. In the commercial production of sugar, crystallisation is an important step in the purification of sugar. The purer a solution of a sugar, the easier it will crystallise. Therefore, mixtures of sugars crystallise less easily than pure sugars. In certain foods, crystallisation is undesirable, such as crystallisation of lactose in sweetened condensed milk or ice-cream.

(v) As TenderisersSugar can also act as a tenderiser in cake making. It competes with gluten-forming proteins for water in the batter and prevents full hydration of these proteins during dough mixing. This prevents the over-development of gluten which may make the dough too rigid.

12.1.3 Protein

(A) Denaturation of protein:Proteins undergo a process known as denaturation when their secondary structure is altered but their primary structure is unchanged. The molecule unfolds and changes shape but the sequence of amino acids remains the same. Denaturation is brought about by various physical and chemical means and involves the breaking of the cross-linkages which maintain the shape of the molecule. It is usually irreversible, by being impossible to regain the original structure of the molecule. As a result of denaturation,

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the properties of the proteins alter; they become less soluble and more viscous. The unfolded molecules tend to bond with each other forming clumps. This results in the hardening or ‘setting’ of the protein food and is known as coagulation. Coagulation can be brought about by various means such as:

(i) Action of heatMany proteins coagulate when heated. For example, when an egg is cooked, the proteins in the white and the yolk coagulate. Egg-white proteins coagulate first at 60 ℃ and the yolk at approximately 66 ℃. This coagulation is used extensively in the preparation of many dishes, e.g. egg custard and sponge cake. The proteins in the muscles fibre of meat coagulate when heated resulting in the shrinkage of meat during cooking.

Denaturated proteins are more readily attacked by digestive enzymes and therefore most protein foods (e.g. eggs, meat) are more digestible when cooked.

(ii) Mechanical actionMechanical action during the whisking of egg white causes a partial coagulation of the protein. The protein molecules unfold and form a reinforcing network round the air bubbles, thus stabilising the foam. This is used in food preparation, e.g. the making of meringues and soufflés.

(iii) Presence of acidWhen milk gets sour, the bacteria present in the milk ferment lactose, producing lactic acid. The pH of the milk is lowered and this causes the milk protein, caseinogens, to coagulate. The starter culture, used in the manufacture of some milk products, such as yoghurt and cheese, consists of lactose-fermenting bacteria. The lactic acid, produced by the bacteria, is responsible for the coagulation or ‘setting’ of the milk and the formation of a curd.

(iv) Addition of saltCertain salts, such as sodium chloride, coagulate some proteins. If salt is added to the cooking water used for boiling eggs, the egg white will not escape as readily if the shell is cracked. During cheese-making, salt is often added to the curd to increase firmness and also to suppress the growth of micro-organisms.

(v) Addition of renninRennin, known commercially as rennet, is an enzyme isolated from the stomach of young cow which coagulates protein. Rennet is used to make junket, which is clotted or coagulated milk. Rennin is also used together with a bacterial starter, to form curd in cheese manufacture.

(B) Emulsification Since part of a protein contains amino acids with hydrophobic side chains and part of the protein contains hydrophilic side chains, the molecule is then able to act as oil-water interface. Thus, protein can serve as an emulsifier to stabilise a mixture of two immiscible phases like oil and water.

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(C) Foaming Protein can act as a foaming agent to produce foam. Foods such as whipped egg white or meringue and marshmallow are examples of protein foam. Protein foam is the dispersion of gas bubbles in a protein solution.

12.1.4 Fats and Oils (Lipids) Fat and oils, also known as lipids, are similar to carbohydrates in that they contain the elements including carbon, hydrogen and oxygen. They are esters of glycerol and fatty acids. Ester is a kind of compound with chemical structure (COOC). Fats and oils are mixtures of triglycerides. Fats and oils have the same general chemical structure. The word ‘fat’ is commonly used to refer to mixtures of triglycerides which are solid at normal room temperature, whereas the word ‘oil’ refers to those which are liquid at the same temperature. The difference between a fat and an oil may be explained by the presence of different fatty acids. Fats contain a large proportion of saturated fatty acids distributed among the triglycerides, and oil a large proportion of unsaturated fatty acids. The presence of unsaturated fatty acids lowers the melting point, i.e. the temperature at which the fat starts to melt.

(A) Emulsification If oil and water are shaken up together and left for a short time, the two liquids will separate with the oil forming a layer on top of the water. Two such liquids which will not normally mix are said to be immiscible. In an occasion that two immiscible liquids are held in a stable colloidal state by means of a third substance is called an emulsion, and that substance present in small quantities is known as an emulsifying agent or emulsifier.

There are two main types of emulsion found in foods:(i) Oil-in-water emulsions (e.g. milk, yoghurt, ice-cream), where the dispersed phase consists of droplets of oil dispersed in the continuous phase, which is mainly water.(ii) Water-in-oil emulsions (e.g. butter, cheese, chocolate), where the dispersed phase consists of droplets of water dispersed in the continuous phase, which is mainly oil.

The structures of these two types of dispersions are shown in Figure 12.4.

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Figure 12.4 Types of emulsion

Oil Water

Water Oil

(i) Oil-in-water emulsion

(ii) Water-in-oil emulsion

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(B) Hydrogenation Hydrogenation is a reductive chemical reaction, in which hydrogen (H

2) is added to a

saturated organic compound. The process constitutes the addition of hydrogen atoms to the double bonds (unsaturated bonds) of a molecule through the use of a catalyst. Figure 12.5 is the chemical equation of hydrogenation.

Hydrogenation is widely applied to the processing of vegetable oils and fats. Complete hydrogenation converts unsaturated fatty acids to saturated ones which results in the conversion of liquid vegetable oils to solids or semi-solid fats, such as those present in margarine. Changing the degree of saturation of the fat changes some important physical properties such as the melting point, which is why liquid oils become semi-solids. Semi-solid fats are preferred for baking because the way the fat mixes with flour produces a more desirable texture in the baked product.

In practice, hydrogenation is not usually carried to completion. Since the original oils usually contain more than one double bond per molecule (that is, they are polyunsaturated), the result is usually described as partially hydrogenated vegetable oil (i.e. some, but usually not all, of the double bonds in each molecule have been reduced). This is done by restricting the amount of hydrogen (or reducing agent) allowed to react with the fat. Since partially hydrogenated vegetable oils are cheaper than animal source fats, they are available in a wide range of consistencies. They have other desirable characteristics such as increased oxidative stability for longer shelf life and are the predominant fats used in most commercial baked goods. Fat blends formulated for this purpose are called shortenings.

Figure 12.5 Chemical Equation of hydrogenation

(C) Rancidity of fatRancidity of fat is the decomposition of lipids due to hydrolysis or oxidation, or both. Hydrolysis will split fatty acid chains away from the glycerol in a triglyceride molecule forming glycerol and free fatty acids. The double bonds of free fatty acids will be further attacked by oxygen, ultra violet wave / light (UV), heat, heavy metals or free radicals (reactive oxygen species) to form lipoperoxides and free radicals. These chemical processes can generate highly reactive molecules in rancid foods and oils, which are responsible for producing unpleasant and noxious odours and flavours. These chemical processes may also destroy nutrients in food. Under some conditions, rancidity, and the destruction of vitamins, occur very quickly.

hydrogenation

H H

H

H H

H

C CC C+ H2 , Ni

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12.2 Industrial food production

12.2.1 Principles

(A) Maintain product qualityQuality of a product means that a product reaches a particular level of excellence or standard. Quality of products can be determined by several aspects including quality of design, quality of manufacture, quality assurance, quality control, quality of raw ingredients and quality of production.

(i) Quality of designGood design is the first stage of ensuring the quality of products. A good design must be easy to make with a clear specification and production process as well as low costs with high profits. In addition, the product must meet the needs of the target group.

(ii) Quality of manufactureThe quality of manufacture is judged by the appearance, the taste and smell of the product as well as the quality of the product including how safe and durable the product is. For an example, the following questions can be asked to check the quality of manufacture of biscuits:❖ Are the biscuits in consistent shapes and thickness?❖ Are the biscuits having the same sweetness and odour?❖ Does the packaging prevent the spoilage and contamination of the biscuits well?❖ Are the biscuits able to withstand the force of machinery and workers during distribution without cracking?These are the questions that can be asked during the production and the controls can be established over these points in the production for controlling the quality.

(iii) Quality controlQuality control is a method to check every stage in the production for maintaining the quality of the final product. The whole process of production should be under control from raw materials to final products. Many questions can be asked in quality control. How are raw materials grown, produced, processed etc.? Is the machinery functioning well? Is the correct amount of ingredients used in every batch of product? Is the packaging sealed correctly? Is there any contamination? These can be checked in the laboratory, by engineers, by assistants with some apparatus including thermometer, metal detector, etc.

(iv) Quality assuranceQuality assurance involves activities of providing evidences for ensuring every stage of the production as well as the final product reaches a preset standard. It covers all activities from design, development, production, installation to documentation. It is to make sure that the process of quality control running at its standard. Documentation is very important in quality assurance. Well-organised

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documentation provides a way to track the source of problem and thus maintain the standard quality of the product.

(v) Quality management system (QMS)Quality management system (QMS) includes a series of policies, processes and procedures required for helping in improving quality, and building up consumer confidence in the products and services. One of the most popular standards for QMS is ISO9000. It is a family of standards providing a framework around to guide the implementation of a QMS. There are a series of standards numbering as ISO 9000:2005, ISO 9001:2000 and ISO 9004:2000. ISO 9000:2005 is a guidance document which describes the fundamentals of QMS and the core of ISO 9000 standards. ISO 9001:2000 includes a list of requirements needed to be fulfilled to achieve customer satisfaction through consistent products and services meeting the needs of customers. ISO 9004:2000 covers continual improvements. This standard gives manufacturers advice on how to enhance a mature system. This standard is not supposed to be used in the stage of implementation. A company or an organisation which is certified to be in conformance with ISO 9001 may publicly state as “ISO 9001 certified” or “ISO 9001 registered”. ISO 9001 does not guarantee the compliance of the end product or service but only the consistency of the process of the system.

Apart from QMS, food manufacturers can promote quality assurance in other ways including using high quality ingredients, implementation of a refunding system to please the consumers, establishing a complaint follow-up system, advertising the company’s policy regarding quality as well as displaying the symbol of quality on all products.

(B) Enhance flavours and coloursDuring the early days of history, people used spices for enhancing the flavour of foods. About 90% of flavours used were natural deriving from spices and essential oils in the late 19th century. About 90% of flavours used were artificial in 1950s due to the advancement in chemical synthesis. In 1980s and 1990s, the proportion of natural flavours used rose again to about 70%.

Food may lose its original flavour and colour through processing, especially thermal processing. In order to maintain the food quality in terms of flavour and colour as well as ensuring the repeatability of the product, flavours, flavour enhancers and colours are added to the food products. Three categories of flavour compounds have been proposed. They include:

(i) Natural flavours and flavouring substances obtained from raw materials(ii) Nature-identical flavours produced by chemical synthesis or from aromatic raw materials(iii) Artificial flavours which are not present in natural products

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The first two categories require considerably less legislative control than the latter one. Many food items covering soft drinks, beverages, baked goods, confectionary products, ice-cream, desserts, etc. contain flavouring compounds.

Apart from flavouring chemicals, there is another group of chemicals which can supplement or enhance the original flavours of the food. They carry the property of umami. Most flavour enhancers are glutamates and nucleotides. Glutamates and nucleotides naturally exist in food. Many vegetables including mushrooms, peas and tomatoes contain high levels of free glutamate. Monosodium glutamate (MSG) is one of the most popular flavour enhancers used. However, it is mainly produced by chemical synthesis. Nucleotides can be found in many types of food including vegetables, meat and mushrooms.

Sweetness is one of the most important sensations for pleasure for humans. In order to increase the sweetness in food, sweeteners are used in many types of food including candies, beverages, soft drinks, etc. There are two categories of sweeteners, the nutritive and non-nutritive sweeteners. Glucose, fructose and sucrose are some commonly used nutritive sweeteners while saccharin and aspartame are some commonly used non-nutritive sweeteners.

Colours are used in foods to make them more attractive to consumers. Colours are especially important in candy and beverage industries. People associate colours with certain flavour. Therefore colour is important in the food acceptability and food flavour. Food with the “wrong” colour (beverage with orange flavour but green in colour) may not be accepted by consumers.

The use of food additives including flavours and colours must be regulated under the law. In Hong Kong, a food additive is banned if it is not mentioned in the food law. The company must check the regulation first before using a particular food additive.

(C) Control product consistencyThe quality consistency of a product is important for building up consumers’ confidence on the product. To control the product consistency is to ensure “identical” products are always being produced. It can be achieved by straight adherence to the production procedures, using the same type of ingredient in every batch, keeping precise measurement including weight, timing, thickness etc and using standard equipment for the production. A flow chart showing each step of the production is needed to determine where to control the process. Assess each step to find out what controls should be placed to ensure consistency of production. Some parameters are difficult to be controlled accurately. Tolerances can be added to the steps. For example, the weight limit of vegetables can be set at 1 ± 0.1 kg. The following table shows an example of some production steps. The letters in bold are the parameters that must be controlled and followed.

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Table 12.6 Examples of steps for ensuring consistency of a product

Process

Preparation

Production

Forming

Heat application

Example 1

Chop carrots to 1cm in length

Cream sugar and butter for 30 seconds, using an electric whisk on speed 2

Feed pasta dough into a pasta machine, set to width 6

Fry potato chips in oil at 180℃ for 8 minutes

Example 2

Shred cabbage using a grating blade of a food processor

Knead bread dough for 4 minutes, using a dough hook of a food processor, set to speed 3

Press 80g of vegetable mix into a burger maker

Pour ice cream mixture into an ice cream machine, leave aside for 20 minutes

The finished products should be randomly tested against the specification for the weight, colour, size, sensory attributes, volume etc. to ensure the consistency of the products.

(D) Improve nutritive valueMany processing methods may cause the loss of nutrients. Here are some examples: (i) Wastage caused by peeling and trimming food(ii) Refining of wheat and rice(iii) Heat treatment(iv) Washing and polishing(v) Oxidation as a result of exposure to air

Protein can be denatured by heat. Overcooking of food may lower the digestibility of protein. If protein and carbohydrate are heated together under high temperature, they may react with each other and lower the nutritive value of the food. Apart from protein, vitamins are suspected to be destroyed during various processing of food. Vitamin B-group and C are water-soluble that are more susceptible to processing loss. Washing and heating are the most destructive processing to vitamins. Water-soluble vitamins may lose in water during washing. Heat treatment including pasteurisation, sterilisation, cooking etc. may destroy water-soluble vitamins especially vitamin C.

To increase the nutritional value and attractiveness of food products, food manufacturers may fortify the food to compensate the loss of nutrients or promoting the nutritive value. Food manufacturers may modify the nutrients of the food by adding extra nutrients according to the trend of the market. For example, when current research shows that

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calcium is good for preventing osteoporosis, many food products that are fortified with calcium appear on the market.

12.2.2 Food Processing

(A) Use of Micro-organisms – Fermentation It was accidentally found in the past that raw foods from plant and animal sources might change to a different and more desirable product with longer stability over a period of storage by fermentation. The technique was then developed for storage of food. Nowadays, over 2000 different fermented foods are available in the world. Many of them are produced in small quantities for some ethnic groups. Some of them are now being produced commercially in a large scale. The popularity of fermented food is increasing worldwide. Food fermentation is a process of converting raw materials into fermented food by the growth and metabolism of some desirable microorganisms. The raw materials can be milk, meat, fish, vegetables, fruits, cereal, grains, seeds and beans. The raw materials are exposed to an environment favouring growth and metabolism of specific microorganisms to produce desirable end-products. These end-products and the un-metabolised components constitute the characteristics of fermented food. Foods can be fermented through natural fermentation, back slopping and controlled fermentation. Natural fermentation is the fermentation involving microorganisms present naturally in the foods. The incubation conditions are to enhance the growth of desirable microorganisms and lower the growth rate of the associated microorganisms which are usually undesirable. Back slopping utilises a portion of a successful fermented food as the starter culture for the production of a new fermented food. Pure culture of single or mixed strains or species of microorganisms is used as the inoculum in controlled fermentation. In this type of fermentation, the incubation conditions are set for the optimum growth of the starter cultures. All conditions including quantity and quality of the product are under control. Other than these three methods, fermentation can be classified into alcoholic fermentation, lactic acid fermentation, mould fermentation and acetic fermentation.

(i) Alcoholic fermentationFermentation involving production of ethanol is one of the most ancient fermentation methods known. In the production of ethanol, the starchy source is first hydrolysed into sugar followed by yeast fermentation. The primitive method to hydrolyse starch is using saliva. Even nowadays, women and children in the Andes region of South America sit together chewing maize kernels which is then removed from the mouth and sundried. It is then allowed to ferment with yeast in crockery with water. The alcohol content of the finished yellow cloudy liquid would be as much as 6%. Later, people discovered that some moulds like Aspergillus, Rhizopus and Mucor can also hydrolyse the starch. Alcoholic beverages can also be produced from plant juice. Pulque is an ancient Mexican alcoholic beverage made by the fermentation of pulp juices from the Agave plant. The alcohol is produced by a yeast, Saccharomyces cerevisiae or a bacterium, Zymomonas mobilis.

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❖ BeerThe word ‘beer’ originated from the Latin word Bibere which means “to drink”. Beer is relatively low in alcohol content. It ranges from 3.9% to 5.1% alcohol by volume (ABV indicates ml of ethanol per 100 ml of beer). The basic raw ingredients for most beers are malted barley, water, hops and yeast. Brewer’s yeast Saccharomyces can ferment sugar into ethanol anaerobically.

C6H12O6 → 2C2H5OH + 2CO2

Sugar Ethanol carbon dioxide

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Barley

Malt

Wort

Beer

Water

Water

Adjuncts(Other sources of starch)e.g. maize rice

Hops

Saccharomyces

Filter, stabilize, package

Maltin

gB

rewin

gF

ermen

tation

and

co

nd

ition

ing

Do

wn

stream p

rocessin

g

and

packag

ing

Figure 12.7 Flow chart of beer production

Process

Steep

Germinate

Kiln

Temp.

14-18℃16-20℃50-110℃

Duration

48h

4-6 days

24h

Process

Store

Mill, mash

Wort separation

Boil

Clarify

Temp.

20℃40-72℃

100℃

Duration

4 weeks

1-2h

1.5-4h

0.75-2h

Process

Fermentation

Maturation

Cold

conditioning

Temp.

6-25℃varies

-2-0℃

Duration

3-14 days

varies

3-48 days

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During the process of brewing, the malted grain of barley is milled to produce fine particles for easier digestion by enzymes. Then it goes through a process called mashing where the particles mix with hot water containing the right amount of salt at around 65℃, when the granules of starch are gelatinised to a form that is more susceptible to enzyme digestion. After about an hour of mashing, the liquid portion of the mash known as wort is recovered. The wort is boiled for the purposes of sterilisation, precipitation of proteins which may cause the cloudiness of the finished beer and driving away unpleasant grainy characters originated from barley. At this stage, adjunct sugars and hops can also be added. The main flavour components contributing in the beer from hops are resins and essential oils. The resins provide the bitterness of beer by changing into compounds called iso-α-acids during the boiling process while the oils provide the hoppy smell of beer. Nowadays, extracts of hops are used instead of the whole pieces of hops. This increases the efficiency and the quality which is easier to be controlled.

(ii) Lactic acid fermentationLactic acid fermentation was found when people started domesticating and milking cows, sheep and goats. People stored the milk in slaughtered animals’ stomach. Milk was then fermented by the naturally-occurring lactic acid bacteria and turned sour rapidly. Sour milk became one of the first fermented foods existing as yoghurts nowadays. The sour milk stored in animal stomach might curdle, lose its whey and became primitive cheeses fermented by other lactic microorganisms in the environment. Cheese is an important part of the diet in humans. Some foods produced through lactic acid fermentation are listed as follows:

❖ SauerkrautSauerkraut is prepared from sound, well-matured heads of cabbage. Cabbage contains 4.69% total sugars including 0.25% sucrose, 2.38% glucose, and 2.05% fructose. Sugars are rapidly converted to lactic acid with some other important products including carbon dioxide, mannitol, acetic acid, and ethanol during fermentation by lactic acid bacteria in the cabbage.

There are two main groups of lactic acid bacteria involved in sauerkraut fermentation: heterofermentative (gas-forming) species such as Leuconostoc mesenteroides and homofermentative (nongas-forming) species such as Lactobacillus plantarum, Lactobacillus brevis as well as Pediococcus cerevisiae. Raw cabbages contain enough bacteria of these two kinds for spontaneous fermentation. Sauerkraut fermentation is a complex microbiological process involving the sequential growth of microorganisms of these two types. Heterofermentative bacteria grow in the early stage of fermentation. At this stage, bacteria produce carbon dioxide to create an anaerobic environment which promotes the growth of desirable lactic acid bacteria and dominate the growth of oxidative fungi. After about 8-day fermentation, most of the bacteria growing would be homofermentative converting the shredded cabbage to sauerkraut of high quality.

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Figure 12.8 Industrial procedure of sauerkraut production

Cabbage delivered to factory by truck

Coring machine

Removing outer leaves and bad spot

Shred the cabbage

Distribute in a fermentation vat

Add salt of 2.25 – 2.5 kg per 100 kg cabbage

Heat in hot brine to above 74℃

Filling fermented cabbage into retail packages (cans, jars or flexible pouches)

Covered with a plastic sheet weighted with water

Sealed containers are water-cooled to 38℃

Cored head

After 4 or more weekslactic acid content reaches 1.5%

Withdrawal of “early brine”

Excess “late brine”

Solid waste

Liquid waste

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The variety of cabbages, fermentation temperature and salt concentration are factors affecting the quality of fermentation. Some cabbages may not be able to undergo normal fermentation due to the presence of growth inhibitors or lack of essential growing factors including nutrients for the growth of lactic bacteria. Higher fermentation temperature gives higher level of lactic acid production as well as higher rate of production. The sauerkraut fermentation reaches its maximum rate at 32℃. However, in general, sauerkraut fermentation under lower temperatures has a better colour, flavour, and character than that under higher temperature. Proper salt concentration is very important for a proper fermentation and inhibition of growth of undesirable microorganisms. A salt concentration of 2.25% favours the growth of desirable bacteria and produces a product with proper salt to acid balance. A salt concentration of less than 2% would produce a softer product due to the activity of pectinolytic enzymes.

❖ OlivesOlive fermentation is similar to that in sauerkraut except that the olives are soaked in a lye solution of 1.6-2.0% which is important in removing bitter factors in olive before brining. Lye on the olives is rinsed out in fresh water. After the removal of lye, the olives are brined in containers where the brine concentration varies from 5-15% depending on the variety and size of the olives. Leuconostoc mesenteroides and Pediococcus cerevisiae are the first group of lactic acid bacteria fermenting the olive followed by the prominent growth of Lactobacillus plantarum and Lactobacillus brevis. The lye treatment may affect the natural microbial flora, therefore, Lactobacillus plantarum may be inoculated to the olives. The fermentation process may last from 2 weeks to several months. The acid content of the final product varies from 0.18-1.27%.

❖ MeatsMeat is a nutrient-rich food. Skeletal bovine muscle contains about 20% of high quality protein, 2-3% lipid, and a small amount of carbohydrate, non-protein nitrogen and inorganic material. A piece of meat contains about 75% water and the pH ranges form 5.6-7.0, which is desirable to the growth of some kinds of bacteria. Therefore, fermentation technique for meat storage is developed. Fermentation of meat has not been investigated as much as fermentation of milk. The use of pure culture is a matter of recent industrial practice. Instead, backslopping was used in the past and even in some of the present food industries. In backslopping, the bacteria in inoculum are already selected for well growing in the environment of sausage which contains salt in high concentration, nitrate and low oxygen level. Those bacteria which cannot survive in such a tough environment are inhibited and are even ruled out in the starter culture. The bacteria in the starter culture in backslopping are heterogenous in nature which consist multiple species and strains. If one strain dies suddenly, other remaining strains can act as a back-up and continues the fermentation. A high portion of inoculum (as high as 20% of the total mass) can be used in backslopping which increases the chance of success of the fermentation. However, backslopping fermentation usually has inconsistent and uncontrollable quality. Therefore in industrial production, short and consistent fermentation time, standardised production procedures and the use of a single, small batch of product are important in maintaining the consistency

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of the quality. After microbial technology has been developed, pure culture of Lactobacillus sp. and Pediococcus sp. are being used for the production of fermented sausage. The production of fermented sausages involves only a few simple steps. The ingredients include meat, sugar, salt, starter culture, curing agents (usually nitrite salts), spices, flavouring, etc., which are selected, weighed, mixed and stuffed into casings. Then the stuffed sausages are held under conditions suitable for the process of fermentation. The sausage is subjected to one or more post-fermentation steps which is to affect the flavour, texture and preservation properties. These steps may take as short as one week to as long as two months depending on the final properties needed for the product.

❖ Cultured dairy productsCultured dairy products can be divided into two kinds: semi-solid and solid-cultured dairy products. Semi-solid cultured dairy products include yoghurt, sour cream, fromage frais (a French cheese) etc. while solid cultured dairy products include cheese, traditional Greek feta etc.

Typical manufacturing protocol for fermented semi-solid dairy food require raw milk selection, milk pretreatments, ingredient blending and standardisation, heat processing, starter addition, and other technological procedures. The milk is pretreated by filtration, clarification by centrifuge and homogenisation by minimising the milk fat globules size. In addition, the milk is pasteurised (Table 6.2.2) to kill most of the microorganisms first before adding the starter culture (Table 6.2.3). Stabilisers, sweeteners, fruits, colourants and flavourings are some other ingredients that can be added into the products.

Table 12.9 Typical heat treatment(s) for the fermented milk preparation of yogurt, sour cream and fromage frais

Product

Yogurt

Sour cream

Fromage frais

Typical heat treatment(s)

90-95℃ for 2-5 min80-85℃ for 30 min

74℃ for 30 min85℃ for 25 min80℃ for 30 min90℃ for 5 min

93℃ for 2 min

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Table 12.9 Typical heat treatment(s) for the fermented milk preparation of yogurt, sour cream and fromage frais

Table 12.10 Typical starter culture for the production of yogurt, sour cream and fromage frais

Product

Yogurt

Sour cream

Fromage frais

Starter culture

Streptococcus thermophilus and Lactobacillus delbrueckii

Lactobacillus lactis and Leuconostoc mesenteroides

Lactobacillus lactis and Leuconostoc mesenteroides

In the production of cheese, milk is coagulated first by rennet enzyme or by acidification. Along with the coagulation of milk, there is a natural tendency to syneresis (giving out water) with contraction and expelling of whey. Lactococcus sp. and Leuconostoc sp. are used as the starter culture. The lactic acid produced by the bacteria promotes the action of rennet enzymes and the acidification of the curd. The milk is coagulated only by the acid produced by the starter culture in the production of sour milk cheese. Another function of lactic acid bacteria is to inhibit the growth of harmful bacteria. Cheese may be consumed as fresh curd or it may undergo ripening. Ripening involves enzymes from the milk, the rennet, and microorganisms in the cheese or on the surface. During ripening, the characterised flavour, consistency and texture of cheese are developed by hydrolysis and metabolism of the organic matters in the cheese. This process may last for months.

(iii) Mould fermentation❖ Soy sauce

Soy sauce is generally accepted as Chinese invention. It is a protein hydrolysate made by fermentation. In the production of soy sauce, soybeans, defatted soybeans or black beans are some proteinaceous materials used while wheat, rice, barley, maize and milo are some starchy materials used for fermentation. These raw materials are steamed and mixed with cultured starter to form the soya koji. Apart from the proteinaceous and starchy sources, salt, sugars, alcohol, chemical seasonings, chemical preservatives are some other raw materials added in the soy sauce in the finished product.

Starter mould should have high unit spore number, high spore germination rate, low foreign mould count, suitable for dry preservation, and abundant secretion of protease. There are two common species of starter mould used in soy sauce fermentation for better utilisation of raw materials: Aspergillus oryzae

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with strong alkali protease and Aspergillus sojae with strong alpha-amylase. Soya koji is made by prolonged cultivation of the mixture of cooked defatted soybean and roasted wheat inoculated with the starter mould. The cultivation period is about 3-4 days with frequent turnover to lower the koji temperature and for better evapouration of moisture. The purpose of making soya koji is to produce a source of strong protease enzymes without offensive odour or taste as well as to minimise the contamination of foreign microorganisms. The protease activity would be the highest when the soya koji is produced at about 25℃. However, the optimum growth of the mould would be achieved at about 33℃. To balance both parameters for the best production, 30℃ is chosen for making the soya koji.

Soya koji is mixed with cold brine (22.5-23.7% sodium chloride) at 0-5℃ which can avoid sedimentation and darkening of soy sauce. After mixing, several kinds of microorganisms summarised in Table 12.11 are responsible for the fermentation. The moulds in soya koji cannot withstand the high salt concentration and anaerobic environment. They will die in three months after the mixing of the mash leaving the enzymes for the hydrolysis. The hydrolysis of protein and starch are very slow and so it takes long time to make soy sauce. The digestion may take 10 months to 1.5 years. After the digestion, the mash can be held in outdoor tanks for maturation process. After maturation, soy sauce is separated out by a process called pressing. The mash is pressed under pressure in nylon bags. The liquid come out from the first filtration is called raw soy sauce and the cake is called raw cake. The raw cake still contains residue soy sauce. Water or diluted brine can be added in the second wash and the mash is pressed again. The filtrate is called secondary soy sauce and the cake is called soy mash cake. After filtration, the soy sauce can then be pasteurised and packaged.

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Types

Moulds

Yeasts

Bacteria

Origin

Soya koji

Soya koji and the environment

Mash and the environment

Microorganisms

Aspergillus oryzae

Aspergillus sojae

Saccharomyces rouxii

Torulopsis versatilis

Pediococcus halophilus

Bacillus subtilis

Bacillus mesentericus

Purpose

Produce protease for hydrolysis of raw materials

Produce amylase for hydrolysis of raw materials

Responsible for the main fermentation. Capable of alcoholic fermentation and hydrolysis of various amino acids into their respective alcohols giving soy sauce its characteristic flavour and odour. Other organic acids such as acetic, lactic and succinic acids are also produced providing the strong odour and bright colour of soy sauce.

Responsible for the maturation stage with the production of soy sauce odour compounds.

Produce lactic acid in the soy sauce

Help in the production of organic acids, amines and esters, creating a more complex flavour.

Table 12.11 Micro-organisms involved in the fermentation of soy sauce

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Soybeans

Selection

Washing

Soaking

Steaming

Wheat

Selection

Washing

Crushing

Mould starter culture

Inoculation

Spreading on trays

Cultivation

Transfer to vessels

Pressing

Addition of salt solution

Unpasteurised soy sauce

Sterilization

Sedimentation

Filtration

Primary product

Residue

Addition of salt

Pressing

Sterilisation

Second grade product

Figure 12.12 Industrial processes for making soy sauce

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(iv) Acetic acid fermentation❖ Vinegar

Primitive alcoholic beverages generally contain some limited amount of acetic acid. When the anaerobic fermentation for the production of ethanol stops and the anaerobic environment is broken down, Acetobacter sp. would become active and a portion of ethanol would be converted into acetic acid which is commonly called vinegar. Vinegar is used as a condiment, a pickling agent or even as a medicinal due to its germicidal properties.

Vinegar production involves two main processes including alcoholic fermentation and acetogenic fermentation. The former process is performed mostly by yeasts under anaerobic conditions while the latter one is performed by acetic acid bacteria under highly aerobic conditions. Distilled ethanol can be used for the production of vinegar, however, ethanol from musts or malt mashes is usually being used due to the fact that flavour and aroma properties of the end product depends mainly on the starting material used.

The most popular groups of acetic acid bacteria used in the production of vinegar are Acetobacter and Gluconobacter. Both of them produce acetic acid from ethanol through oxidative pathways. That means oxygen is needed in the production of acetic acid. There are mainly two steps in the conversion of ethanol to acetic acid. Firstly, ethanol is oxidiseoxidised to acetaldehyde and then the acetaldehyde is oxidiseoxidised to acetic acid. The pathway is summarised as follows:

C2H5OH → CH3COH → CH3COOH Ethanol Acetaldehyde Acetic acid

There are several methods of vinegar production. These are referred to as the open vat method, trickling generator process and the submerged fermentation process.

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Figure 12.13 Vats for vinegar production

Figure 12.14 Tickling generator system

Exhaust air

Recovery for substrate

Wood shaving

Oxidation air Intake

Pump

Product (vinegar)

Wood grating

Collecting Chamber

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Open vat is a method traditionally used for vinegar production. The process relies on the acetic acid bacteria growing on the surface of vats, barrels, jars, or trays (Figure 12.13). Accompanied by the vinegar production, a film of polysaccharides is also produced which is very important for the adhesion of the bacteria on the surface of the vat for successful fermentation. A special barrel is designed for minimising the disturbance from refilling the container with fresh wine. Usually, the barrel is filled with 60-70% wine with the inoculation of a fresh vinegar culture which contains acetic acid bacteria. A small portion of vinegar can be removed from the tap end when the fermentation is completed which takes about two to three weeks. Fresh wine can be refilled to the barrel through the filling device. This can minimise the chance of disrupting the film.

Trickling generator accelerates the vinegar generation (Figure 12.14). In this system, the ethanol substrates are circulated or trickled through the vessels containing wood shaves or other packing materials inoculated with acetic acid bacteria. Air is pumped into the system continuously for efficient oxidation of ethanol into acetic acid. The ethanol and vinegar mixture is sprayed as small droplets onto the wood shave packing. The substrate flows down the packing to the collection tank at the bottom and the ethanol is oxidiseoxidised by the acetic acid bacteria on the wood shaves. When the substrate reaches the bottom tank, it may circulate back to the top for another round of fermentation until almost all the ethanol is converted into acetic acid. Alternatively, a second tank can be used. After the substrate flow through the first tank, it is pumped to another tank of the same setting and then back to the first tank. This can increase the production efficiency. About three days are required to convert 12% (v/v) ethanol solution to a vinegar containing 10-12 % acetic acid.

Submerged fermentation is an advanced biotechnology developed by vinegar industry. The main feature of the submerged fermentation system is that it is able to provide rapid and efficient aeration. Agitators can help the distribution of air throughout the liquid. The starter materials are a combination of ethanol and acetic acid which comes from a prior fermentation. The production capacity can range from 25 liters a day of 10% acetic acid in small scale fermentors to 30,000 liters a day in large scale reactors. After 16 to 24 hours, the acetic acid concentration will increase from 7% to 12% and then half of the contents can be removed as the finished production and replaced with fresh ethanol feedstock.

(B) Use of Food Additives(i) What are food additives?

A food additive is any natural or synthetic substance intentionally added to food in the processing, packaging, transport or storage of food for a technological purpose. According to the Laws of Hong Kong, food additives do not include nutrients such as vitamins and minerals used for enriching food, or seasonings like salt, herbs and spices.

Food additives play a vital role in today's bountiful and nutritious food supply. They allow our growing urban population to enjoy a variety of safe, wholesome

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and tasty foods year-round. They also make possible an array of convenience foods without the inconvenience of daily shopping.

(ii) Why are additives used in foods?Additives perform a variety of useful functions in foods that are often taken for granted. Since most people no longer live on farms, additives help keep food wholesome and appealing while transporting to markets sometimes thousands of miles away from where it is grown or manufactured. Additives improve the nutritional value of certain foods and also make them more appealing by improving their taste, texture, consistency or colour.

Some additives could be eliminated if we are willing to grow our own food, harvest and grind it, spend many hours cooking and canning, or accept increased risks of food spoilage. But most people today have come to rely on the many technological, aesthetic and convenience benefits that additives provide in food.

Additives are used in foods for five main reasons: ❖ To maintain product consistency. Emulsifiers give products a consistent texture and prevent them from separating. Stabilisers and thickeners give smooth uniform texture. Anti-caking agents help substances such as salt to flow freely. ❖ To improve or maintain nutritional value. Vitamins and minerals are added to many common foods such as milk, flour, cereal and margarine to make up for those likely to be lacking in a person's diet or lost in processing. Such fortification and enrichment has helped reduce the problems of malnutrition. All products containing added nutrients must be appropriately labelled. ❖ To maintain palatability and wholesomeness. Preservatives retard product spoi lage caused by mould, air, bacteria, fungi or yeast. Bacterial contamination can cause foodborne illness, including life-threatening botulism. Antioxidants are preservatives that prevent fats and oils in baked goods and other foods from becoming rancid or developing an off-flavour. They also prevent cut fresh fruits such as apples from turning brown when exposed to air. ❖ To provide leavening or control acidity/alkalinity. Leavening agents that release acids when heated can react with baking soda to help cakes, biscuits and other baked goods to rise during baking. Other additives help modify the acidity and alkalinity of foods for proper flavour, taste and colour. ❖ To enhance flavour or impart desired colour. Many spices and natural and synthetic flavours enhance the taste of foods. Colours, likewise, enhance the appearance of certain foods to meet consumer expectations. ❖ To preserve food to extend its storage life and minimise food wastage. Preservatives prevent the growth of micro-organisms, antioxidants reduce the lipid oxidation, both can help extend the storage life of food. Longer storage life means less food are discarded due to spoilage or deterioration.❖ Improve food safety. Preservatives can inhibit the growth of bacteria on foods to improve food safety.

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(iii) Principles of using food additivesFood additives should be used at appropriate levels so as not to affect consumer health.

The use of food additives is justified only when such use has an advantage, does not present a hazard to the health of the consumers, does not deceive the consumers, and serves one or more of the following technological functions and needs, and only where these objectives cannot be achieved by other means which are economically and technologically practicable:❖ to preserve the nutritional quality of the food;❖ to provide necessary constituents for foods manufactured for groups of consumers having special dietary needs;❖ to enhance the keeping quality or stability of a food or to improve its organoleptic properties;❖ to facilitate the processing, packaging, transport or storage of food, provided that the additive is not used to disguise the effects of the use of faulty raw materials or undesirable (including unhygienic) practices of techniques during the course of any of these activities;❖ all food additives should be used under conditions of good manufacturing practice (GMP) as stipulated in the law.

(iv) Advice to the trade and public on the safe use of food additives❖ Advice to the trade

When formulating a food product, food manufacturers are recommended to consider the above principles and should not abuse the use of food additives so as to guarantee the food is fit for human consumption.

Food trade should exercise due care when choosing food additives, only the right type and right amount of food additives should be added, which can serve the desired technological functions.

All food additives should be used under the conditions of GMP, which include the following:✐ the quantity of the additive added to food should be limited to the lowest possible level necessary to accomplish its desired effect;✐ the quantity of the additive that becomes a component of food as a result of its use in the manufacturing, processing or packaging of a food and which is not intended to accomplish any physical, or other technical effect in the food itself, is reduced to extent reasonably possible; and✐ the additive is prepared and handled in the same way as a food ingredient; hygiene and food safety must be observed.

❖ Advice to the public✐ buy food from reputable sources.✐ read the label of prepackaged food carefully, particularly the ingredient list for the food additives added.

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✐ people with allergic condition, such as asthma patients, may experience hypersensitive reaction due to an intake of some food additives like sulphur dioxide. They should be careful in selecting food and seek medical advice when necessary.✐ when choosing foods, avoid as far as practicable those which seem abnormal.✐ report any abnormalities of food to the Centre for Food Safety (CFS) for investigation and follow-up.✐ maintain a balanced diet so as to avoid excessive exposure to certain food additives from a small range of food items.

(v) Benefits of additivesThere are obviously many recognised benefits derived from additives. Some of the major benefits are a safer and more nutritious food supply, a great choice of food products, and a lower-priced food supply.

❖ Safer and more nutritious foodsThere is no question that the preservatives and nutritional additives used in foods increase the safety and overall value of many food products. The use of several antimicrobials is known to prevent food poisoning from various bacteria and moulds. Antioxidants, used to prevent the development of off-flavours, also prevent the formation of potentially toxic oxidation products and maintain the nutritional value of vitamins and lipids. The use of various nutritional additives such as vitamins is also of proven value in preventing nutritional deficiencies.

❖ Greater choice of foodsMost major supermarkets today carry more than 20,000 food items, providing the consumers a wide choice of food products. The availability of additives has allowed the production of numerous out-of-season foods and a variety of new food products. Additives have increased the development of convenience foods, snack foods, low-calories foods and a variety of food substitutes.

❖ Lower-priced foodsFood additives can lower the price of foods by maintaining the quality of foods with reduced cost in high quality packaging or processing procedures, and increase the shelf-life, to ensure a steady food supply.

(vi) Risks of consuming food additivesDespite the benefits attributed to food additives, for several years there were a number of concerns regarding the potential short- and long-term risks of consuming food additives. Critics of additives are concerned with both indirect and direct impacts of using additives. Like many of the benefits mentioned above, there is not always adequate scientific proof of whether or not a particular additive is safe. Little or no data is available concerning the health risks or joint effects of the additive cocktail each of us consume daily.

The indirect risks that have been described for additives are the converse of some of the benefits attributed to their use. While it is accepted that through

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additives, a greater choice and variety of foods have been made available, there is no question that additives have also resulted in the increased availability of food products with a low density of nutrients. These so-called “junk” foods, which include many snack items, can, in fact, be used as substitutes in the diet for more nutritious foods. Recently the food industry has attempted to address this criticism by adding nutritional additives to snack items so that these foods are a source of selected vitamins and minerals. The long-term effectiveness of this is questionable. Obviously, educational programmes are needed to ensure that consumers select nutritious foods. Some scientists, however, feel that there is a place in the diet for foods that provide pleasure even if no direct nutritional benefit can be ascribed to their consumption.

Of greater concern than the indirect risks are the potential direct toxicological effects of additives. Short-term acute effects from additives are unlikely. Few additives are used at levels that will cause a direct toxicological impact, although there have been accidents where this has happened. Of particular concern are the hypersensitivity reactions to some additives that can have a direct and severe impact on sensitive individuals even when the chemicals are used at legally acceptable levels. However, with proper labelling, sensitive individuals should be able to avoid potential allergens.

(vii) Legislative controlWhen food manufacturers intend to use food additives in their products, they have to make sure that the food additives used conform to the legislation in terms of category and quantity.

When using food preservatives, it should be noted whether the preservatives are permitted to be used in that particular type of food while the quantity used should conform to the legislation. Benzoic acid, sulphur dioxide and sodium nitrate are some of the permitted preservatives. However, they can only be used in particular food items at specified amounts.

The usage of food additives in Hong Kong is governed by several by-laws in Public Health and Municipal Services Ordinance (Chapter 132), including Preservatives in Food Regulations (Part BD), Colouring Matter in Food Regulations (Part H), Sweeteners in Food Regulations (Part U) and Food and Drugs (Composition and Labelling) Regulations (Part N).

(viii) Classes of food additivesAccording to Alimentarius Commission (codex), food additives are grouped under their technological functions which are more meaningful and easily understood by the consumers. There are a total of 23 class titles and they are listed below:

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Table 12.15 23 classes of food additives

1. Acid

2. Acidity regulator

3. Anti caking agent

4. Anti foaming agent

5. Antioxidant

6. Bulking agent

7. Colour

8. Colour retention agent

9. Emulsifier

10. Emulsifying salt

11. Firming agent

12. Flavour enhancer

13. Flour treatment agent

14. Foaming agent

15. Gelling agent

16. Glazing agent

17. Humectant

18. Preservative

19. Propellant

20. Raising agent

21. Stabiliser

22. Sweetener

23. Thickener

Additives may be:❖ Natural substances, which have been produced biologically and have been extracted from natural products. For example, lecithin, which is used as an emulsifier, is extracted from soybeans.❖ Synthetic compounds, which are ‘nature identical’. These have been synthesised either chemically or biologically to match naturally occurring counterparts. For example, L-ascorbic acid (vitamin C), which is used as an antioxidant, can be made synthetically. ❖ Artificial compounds, which are synthesised chemically and have no naturally occurring counterpart. For example, azodicarbonamide, which is used as a flour treatment agent, does not occur naturally and is synthesised by chemical methods.

(ix) Types of food additives and their applicationsThe above mentioned food additives group can be classified into 4 groups according to their application on foods, including preserve product quality, enhance sensory characteristics, control product consistency and Improve or maintain nutritive value.

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❖ Preserve product qualityMaintaining product quality is one of the most important concerns in food manufacturing. Without the addition of extra chemicals, it is very difficult to maintain a good product quality in long shelf-life food. Therefore, some food additives are added to packaged foods to make sure the quality is maintained.

✐ PreservativesPreservatives are probably the most important class of additives, which prevent or slow down the growth of micro-organisms (e.g. bacteria, yeast and mould) in food. Preservatives play an important role in today’s supply of safe and stable foods. Increasing demand for convenience foods and longer shelf life of processed foods result in the use of chemical food preservatives. Preservatives can also improve food safety and avoid wastage of seasonal surplus by extending the storage period. Some of the chemicals shown the Table 12.16 are natural, e.g. propionic acid in some cheese, benzoic acid in plums, cranberries and cloves.

Table 12.16 Some common preservatives

Preservative

Sulphite

Nitrite

Propionic acid

Sorbic acid

Benzoic acid

Target organism(s)

Yeasts

Bacteria

Moulds

Moulds

Yeasts and moulds

Example of use

Dehydrated fruit and vegetables

Bacon

Bread

Cheese, wine

Soft drink, ketchup

The use of chemicals to preserve food in Hong Kong is controlled by the Preservatives in Food Regulations (Chapter 132BD, Laws of Hong Kong). Permitted preservatives in Hong Kong are generally safe to consume. As all preservatives permitted in Hong Kong must go through rigorous safety assessment and approval procedures and are recognised by the joint Food Agriculture Organisation/ World Health Organization Expert Committee on Food Additives (JECFA), which is responsible for collecting and evaluating scientific data on food additives including preservatives to provide reference points for the safe use of food additives.

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✐ AntioxidantsAntioxidants reduce the oxidative deterioration that leads to rancidity, loss of flavour, colour and nutritive value of foodstuffs. Fats, oils, flavouring substances, vitamins and colours can all oxidise spontaneously with oxygen when exposed to air. The rate of deterioration can vary considerably and is influenced by the presence of natural antioxidants and other components, availability of oxygen, and sensitivity of the substance to oxidation, temperature and light etc. Oxidation can be avoided, or retarded, removal of oxygen with glucose oxidase, incorporation of UV-absorbing substances in transparent packaging materials, cooling, and use of an adequate shelf-life for some foods. Thus antioxidants are used to retard oxidative deterioration and extend shelf-life. Some antioxidants actually remove oxygen by self-oxidation, e.g. ascorbic acid, whilst others interfere in the process of oxidation, e.g. tocopherols (vitamin E), gallic acid esters, butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT). All have specific properties, making them more effective in some applications than in others. Often a combination of two or more antioxidants is more effective than any one used simply because of their synergistic effects. The presence of sequestering agents, such as citric acid, may also has a synergisitic effect, by reducing the availability of metallic ions that may catalyse oxidation reactions. The use of the powerful synthetic antioxidant BHA, BHT and the gallic acid esters is restricted. Tocopherols, which can be either natural or synthetic, are less effective in production of processed foods. Antioxidant cannot restore oxidiseoxidised food; they can only retard the oxidation process. As oxidation is a chain reaction process, it needs to be retarded as early as possible. The most effective use of antioxidants is therefore in the fats and oils used in the manufacturing process.

✐ AcidAcid as food additives serves dual purpose, as acidity regulators and as preservatives. Phosphoric acid is used in cola soft drinks to reduce the pH. Acetic acid is used to provide tartness in mayonnaise and salad dressings. A similar function in a variety of other foods is served by organic acids such as citric, tartaric and lactic acid.

❖ Enhance sensory characteristics✐ Colours

Colours are used to enhance the visual properties of foods. Their use is particularly controversial, partly because colour is perceived by some as a means of deceiving the consumer about the nature of the food, but also because some of the most brightly coloured products are those aimed at children. As with all additives, their use is strictly controlled and permitted only where a case of need is proven, e.g. to restore that is lost in processing, such as in canning or heat treatment; to ensure consistency of colour; and for visual decoration. The use of colour in food has a long and noble tradition in China. Adding colour to food may appear to some to be an unnecessary cosmetic, which is not in the consumer’s interests, there can be no doubt that the judicious use of colour enhances the attractiveness of many foods. Some retailers tried introducing ranges

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of canned vegetables and fruits such as strawberries and peas without adding back the colour leached out by the heat processing. Colour is important in consumer perception of food and often denotes a specific flavour. Thus, strawberry flavour is expected to be red and orange flavour orange-coloured. Consumer expectation is therefore a legitimate reason for adding colour.

✐ SweetenersSweeteners perform an obvious function. They come in two basics types – “bulk” and “intense”, and are permitted in foods that are either energy-reduced or have no added sugar. They are also sold directly to consumers as “table-top” sweeteners – well-known to dieters and the diabetic. Intense sweeteners, such as aspartame, saccharin and acesulfam K have, as their name suggests, a very high sweetening property, variable from type to type but generally several magnitudes greater than that of sucrose. (For example, aspartame is approximately 200 times sweeter than sugar; saccharin 300-500 times; and acesulfam K 130-200 times.) Bulk sweeteners, such as sorbitol, xylitol and maltitol are less sweet, but provide volume and mouthfeel. Both types of sweetener are useful in low-calorie products, and are increasingly sought after by many consumers, and for special dietary products such as for diabetics.

✐ Flavour enhancersThis is a group of additives that has attracted adverse attention, in particular monosodium glutamate (MSG), which is widely blamed for an intolerance reaction that became known as “Chinese Restaurant Syndrome”.

Flavour enhancers are substances which have no pronounced flavour or taste of their own but bring out and improve the flavours in the foods to which they are added. Although salt has a distinctive taste of its own and is not classed as a food additive, it is in fact the most widely used flavour enhancer. The next best known is glutamic acid and its salts, most commonly found in the form of monosodium glutamate, which has been used for several centuries as condiment in savoury products. It is a normal constituent of all proteins, an essential amino acid and present in the body. The alleged intolerance reaction was never confirmed in sound scientific studies. Anyone showing a reaction to MSG used as an additive would necessarily also react to foods that contains it naturally in high quantities, such as tomatoes and cheese.

✐ FlavouringsAlthough flavour enhancers are categorised as additives, flavourings are technologically different and regulated separately, even though they are defined as imparting odour and/or taste to foods and are generally used in the form of mixtures of a number of flavouring preparation and defined chemical substances. Some 2,800 such substances have recently been identified and included in a European register. These do not include edible substances and products intended to be consumed as such, or substances that have exclusively a sweet, sour or salty taste, i.e. ordinary

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food ingredients such as sugar, lemon juice, vinegar or salt. In addition to the types of flavouring such as process flavours or smoke flavours, there are three distinct classes of flavouring substances: natural, e.g. citral; nature-identical, e.g. vanillin; and artificial, e.g. ethyl vanillin. Then there are flavouring preparation, e.g. vanilla extract. Many flavourings are sold as a complex mixture of individual preparations and flavouring substances, generally confidential to the company that has produced the flavouring.

Some flavourings are sold directly to the consumers for domestic culinary use. Vanilla and peppermint are amongst the best known, as well as the popular brandy and rum essences. Citrus and orange oils, for example, are amongst the most common natural source materials used in flavouring preparation and substances.

❖ Control product consistency✐ Anticaking agents

Anticaking agents are used in foodstuffs such as table salt to keep the product from forming lumps, making it better for packaging, transport, and for the consumers. An anticaking agent in salt is denoted in the ingredients for example, sodium aluminosilicate which is a man-made product. This product is present in many commercial table salts as well as dried milk, egg mixes, sugar products, and flour. In Europe, sodium ferrocyanide and potassium ferrocyanide are more common anticaking agents in table salt. Natural anticaking agents used in more expensive table salt include calcium carbonate and magnesium carbonate.

Anticaking agents must be insoluble in water. They function either by adsorbing excess moisture or by coating particles and making them water repellent. Calcium silicate (CaSiO3), a commonly used anticaking agent, added to e.g table salt, adsorbs both water and oil.

✐ Emulsifiers and stabilisersThe purpose of emulsifiers and stabilisers is to facilitate the mixing together of ingredients that normally would not mix, namely fat and water. This mixing of the aqueous and lipid phase is then maintained by stabilisers. These additives are essential in the production of mayonnaise, chocolate products and fat spreads, for example. The manufacture of fat spreads (reduced-fat substitutes for butter and margarine), has made a significant contribution to consumer choice and dietary change, and would not be possible without the use of emulsifier and stabilisers. Other reduced-and low-fat versions of a number of products are similarly dependent on this technology.

✐ Acidity regulators (pH control agents)Acidity regulators, or pH control agents, are food additives added to change or maintain pH (acidity or basicity). They can be organic or mineral acids, bases, neutralising agents, or buffering agents. Acidity regulators are simply listed as "food acid" in the food ingredient list. Commonly used acidity regulators are citric, acetic and lactic acids.

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✐ ThickenersThickeners or thickening agents, are substances which, when added to a mixture, increase its viscosity without substantially modifying its other properties, such as taste. They provide body, increase stability, and improve suspending action.

Food thickeners are frequently made from polysaccharides (starches or vegetable gums) or proteins (egg yolks, demi-glaces, or collagen). Common examples are agar, carageenan, cornstarch, gelatin, guar gum, pectin and xanthan gum. Starch is a natural thickener, which provides a strong gelling property. Starch is commonly added to sauces to increase the viscosity. Soups can also be thickened by adding grated starchy vegetables. Egg yolk is another natural thickener, which has a rich flavour and offers a velvety smooth texture. Pectin is used as a gelling agent for jams and jellies.

When using a thickening agent, care must be taken not to overcook the food. Some starches lose their thickening quality when cooked for too long or at too high a temperature, and thickened food may burn more easily during cooking.

❖ Improve or maintain nutritive value ✐ Nutrients / Nutritive additives

Sometimes foods are fortified by the addition of some nutrients. Those nutrients serve to supplement the nutrients loss during food processing or improve the nutritional values of foods. For example, iodine is added to salt, as a supplement to people who lack iodine. Vitamin D and calcium are added to milk to produce fortified milk to prevent osteoporosis. Iron and vitamin B complex are added to cereal products. Docosahexaenoic acid (DHA) and arachidonic acid (AA) are added to baby formula.

Table 12.17 Summary of different food additives

Acids

Acidity regulators

Anticaking agents

Antifoaming agents

Function of additives:

Food acids are added to make flavours "sharper", and also act as preservatives and antioxidants. Common food acids include vinegar, citric acid, tartaric acid, malic acid, fumaric acid, lactic acid.

Acidity regulators are used to change or otherwise control the acidity and alkalinity of foods.

Anticaking agents keep powders such as milk powder from caking or sticking.

Antifoaming agents reduce or prevent foaming in foods.

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Function of additives:

Antioxidants such as vitamin C act as preservatives by inhibiting the effects of oxygen on food, and can be beneficial to health.

Bulking agents such as cellulose are additives that increase the bulk of a food without affecting its nutritional value.

Colourings are added to food to replace colours lost during preparation, or to make food look more attractive.

In contrast to colourings, colour retention agents are used to preserve a food's existing colour.

Emulsifiers allow water and oil to remain mixed together in an emulsion, as in mayonnaise, ice cream, and homogenised milk.

Flavours are additives that give food a particular taste or smell, and may be derived from natural ingredients or created artificially.

Flavour enhancers enhance a food's existing flavours. They may be extracted from natural sources (through distillation, solvent extraction, maceration, among other methods) or created artificially.

Flour treatment agents are added to flour to improve its colour or its use in baking.

Humectants prevent foods from drying out.

Preservatives prevent or inhibit spoilage of food due to fungi, bacteria and other microorganisms.

Stabilisers, thickeners and gelling agents, like agar or pectin (used in jam for example) give foods a firmer texture. While they are not true emulsifiers, they help stabilise emulsion.

Sweeteners are added to foods for flavouring. Sweeteners other than sugar are added to keep the food energy (calories) low, or because they have beneficial effects for diabetes mellitus and tooth decay and diarrhoea.

Thickeners are substances which, when added to the mixture, increase its viscosity without substantially modifying its other properties.

Antioxidants

Bulking agents

Food colouring

Colour retentionagents

Emulsifiers

Flavours

Flavour enhancers

Flour treatment agents

Humectants

Preservatives

Stabilisers

Sweeteners

Thickeners

(Adapted from http://vm.cfsan.fda.gov/~lrd/foodaddi.html)

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(x) What is International Numbering System (INS)?The names of many food additives are long and complex. The International Numbering System for Food Additives (INS) was prepared by the Codex Alimentarius Commission (Codex) for the purpose of providing an agreed international numerical system for identification of food additives.

In Hong Kong, the Food and Drugs (Composition and Labelling) Regulations require prepackaged food to declare details of the food additives used in their labels. As required by such provision, food labels should identify food additives both by their exact names and by their functional classes so as to provide consumers with accurate and meaningful information on the exact type of additives present and their functions in the food. For example, Tartrazine when used as a colour in food should be declared as “Colour (Tartrazine)” on the food label. In many cases, names of the food additives are lengthy as they often involve complex chemical structures. The adoption of INS makes it less cumbersome to identify food additives, e.g. “Thickener (Sodium Carboxymethyl Cellulose)” can be labelled as “Thickener 466”.

❖ Composition of the INSThe INS is a means of identifying food additives on a world-wide basis. Notwithstanding some chemicals are present in the INS, their use in food for sale in Hong Kong is still subject to the regulations prescribed in the local legislation. The INS does not include flavours, chewing gum bases, and dietetic and nutritive additives. Enzymes which function as food additives are included in the INS along with the technological functions they perform. It is not possible to insert these enzymes in the INS in close proximity to other food additives with similar functions (e.g. flour treatment agents). They have therefore been included together in an 1100 series.

❖ Layout of the INS✐ Functional Class of Food Additives

For labelling purposes, the technological functions are grouped under more descriptive functional class titles, which are intended to be meaningful to consumers. 23 class titles which have been endorsed by the Codex are listed in the section on “Functional Class of Food Additives”, along with simple definitions of the function performed.

A single food additive can often be used for a range of technological functions in a food and it remains the responsibility of the manufacturer to declare the most descriptive functional class on the food label. For example, Sulphur Dioxide may function as either a preservative or an antioxidant in foods and may therefore be declared as “preservative 220” or “Antioxidant 220”, as appropriate.

✐ List of Food Additives“List of Food Additives” tabulates the INS in numerical order. The three columns in the list describe the identification number, the name of the food additive and the technological function. The identification number for labelling purposes

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usually consists of three or four digits such as 100 for Curcumins and 1001 for Choline Salts and Esters. However in some instances the number is followed by an alphabetical subscript, for example, 924a identified Potassium Bromate, 924b identifies Calcium Bromate, and so on. Therefore, the numbers including any alphabetical subscripts are for use on labels.

Under the column listing the name of the food additive, some additives are further subdivided by numerical subscripts, such as (i), (ii), etc. For example, Curcumins are subdivided into (i) Curcumin and (ii) Turmeric. These identifications are not for labelling purposes but simply to identify sub-classes (in this case of Curcumins) which are covered by separate specifications. The various technological functions performed by the food additives are included in the INS in a third column. The functions listed are indicative rather than exhaustive and are not intended for labelling purposes.

❖ Open Nature of the INSGiven its primary purpose of identification, the INS is an open list subject to the inclusion of additional additives or removal of existing ones on an ongoing basis.

12.2.3 Food Processing Technology and Hygienic Practices

(A) Food technology(i) Pasteurisation

Pasteurisation is a method to deliver a mild heat treatment to food commodities, especially to liquid food, for the purpose of eliminating specific undesirable components and microorganisms. This method is commonly used in the production of milk for minimising vegetative pathogens, in the production of fruit juices for inactivating enzymes, in the production of beer for reducing the population of spoilage microorganisms etc. A more recent use of pasteurisation is the removal of microorganisms such as Salmonella and Listeria in raw eggs. Since the thermal condition of pasteurisation is very mild, undesirable matters can be minimised without much changing in the texture and flavour of food commodities. The time for the pasteurisation can be shorter if a higher temperature is used (high temperature short time, HTST). However, both too much time and too much heat may destroy the quality of liquid food. Therefore a balance between temperature and time is needed. A temperature of 71.5℃ for 15 seconds is often used in HTST pasteurisation of milk.

(ii) Ultra-heat treatmentUltra-heat treatment (UHT) is utilising very high temperature, usually over 120℃ using steam injection heating under pressure, for a very short period of time which is usually less than 1 minute before flash cooling to a relatively low temperature. Under such thermal conditions, the microorganism count is significantly reduced and the shelf-life of the liquid food can be extended. In addition, the quality attributes of the liquid food is mostly retained. Most tetra-pak products are using UHT as the sterilisation process.

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(iii) BlanchingBlanching is a method to deliver a mild heat treatment to inactivate specific enzymes in a solid food product. Enzymes naturally occurring in foods may cause self-decomposing of food even under refrigeration or freezing. Through the process of blanching, enzymes are inactivated and therefore achieving better storage stability. In addition, blanching is sufficient to reduce vegetative microorganisms and enhance the colour of most vegetables and fruits.

(iv) CanningCanning is a method for preservation of food by first sealing the food in air-tight jars, cans or pouches and then heating it to a temperature that kills all microorganisms in it. The most concerning bacteria in heat sterilised food is some spore-forming thermo-resistant microorganisms such as Clostridium botulinum which produces botulism causing chronic intoxication in humans. Spores of C. botulinum can resist boiling at 100℃ for more than 300 minutes. The chance of survival of the microorganisms decreases exponentially as the temperature increases. General speaking, heating the containers with food up to 121℃ holding for about 30 minutes is enough for killing all microorganisms. The most commonly used material for canning is tin-coated steel. Modern double seams provide an airtight seal to the tin can. The body of the can is mainly cylindrical in shape and the two ends are attached to the tin can body by double seam method through operation of rollers in a seamer. Double seam is used for the attachment of the lid to the cylindrical body. Double seam consists of two operations involving two groups of rollers. The first operation (figure 12.18a) involves pressing the end curl against the flange towards the body. The flange is also bent downward. The end of the cover and the body are loosely joined together in the first operation. In the second operation (figure 12.18b), the end curl of the cover and the flange of the body are pressed tightly together leaving no space and the can is then sealed tightly. After the seaming process, the edge of the can is formed by five layers named as end, body hook, cover hook, body and countersink.

Figure 12.18 The two operations in double seam method. (a) First operation (b) Second operation

(a) (b)

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(v) Modified atmosphere packagingModified atmosphere packaging (MAP) is a packaging method that changes the storage atmosphere in the packaging for preserving the quality of the food. It can be achieved by either flushing preselected gas mixture before sealing or allowing the product itself changing the gas mixture in the package. The composition of gas is varied in order to achieve the desirable shelf-life. This method of packaging must be used in the accompany of the right packaging material. Fish, meat and poultry do not respire. Meat is usually packed in high oxygen mixtures for maintaining a bright red colour and inhibiting the growth of micro-organisms. For these types of food products, a barrier packaging material is chosen for reducing the permeability of gas in and out of the package. Fruits and vegetables are still ‘alive’ and continue to respire after they have been harvested. They use up oxygen in the packing and release carbon dioxide. This may establish an anaerobic condition in the pack of food. Therefore, materials permeable to gas should be used in the packing of fruits and vegetables. Some products such as cheese absorb the gas (carbon dioxide) in the pack and result in the shrinking of the packing.

(vi) Freeze-dryingFreeze-drying is a method for dehydration of food by removing moisture from ice to vapour via sublimation. The freeze-drying process involves initial freezing followed by sublimation of ice under conditions of heat and vacuum. The drying process consists of two stages: primary and secondary stages. The primary stage is the removal of ice by sublimation while the secondary stage is the removal of unfrozen liquid water. Freeze-drying is a better drying method over others. The structure and the flavour of foods are retained well in freeze-drying. Freeze-dried foods are considered to be higher in quality compared to the foods dried by other methods. However, the cost of freeze-drying is rather high. Not many products use this drying method. Nowadays, some high quality instant coffee is freeze-dried for reserving the best quality.

(B) Hazard analysis and critical control point (HACCP)systemHazard analysis and critical control point (HACCP) system was developed by The Pillsbury Company working alongside National Aeronautics and Space Administration (NASA) and the United States Army Laboratories at Natick. The system was originally developed to ensure the microbiological safety of foods for astronauts.

HACCP is a useful tool for identifying, evaluating and controlling hazards which may affect the quality of food based on the following seven principles according to the guidelines from National Advisory Committee on Microbiological Criteria for Foods (NACMCF):

(i) Conduct a hazard analysis. A HACCP team is set up to analyse and identify potential hazards that may occur in the production process.(ii) Determine the critical control points (CCPs). CCP is a point, step, or procedure at which control can be applied and a food safety hazard can be prevented, eliminated, or reduced to acceptable levels.

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(iii) Establish critical limits for each identified CCP.(iv) Establish monitoring procedures for each CCP. Set up procedures for using the data from monitoring to adjust the process and control under the limit set.(v) Establish corrective actions to be taken when monitoring indicates that there is a deviation from the critical limit occurred. (vi) Establish verification procedures to verify the effectiveness of the HACCP system.(vii) Establish record-keeping and documentation procedures so that records can be tracked for any incidents.

A flow chart of production procedure is constructed prior to identifying the CCPs. Figure 12.19 shows a flowchart on how to decide whether a step in the production design is a CCP or not. Figure 12.20 shows an example of a flowchart of beef stew with critical control points. In the procedures of making beef stew, the steps of cooking, cooling and reheating have the chance of getting contamination and are irreversible. Therefore, control is important at these stages.

After determining the CCPs, critical limits have to be set in accordance with the CCPs. Critical limits define the boundaries between safe and unsafe products. Therefore, critical limits are the guidelines for setting corrective measures for the hazards. Critical limits can be chemical limits, physical limits, procedural limits and microbiological limits. When there is deviation from the critical limits, actions are taken for minimising the hazard. Lowering or rising the temperature of ovens, checking the machines by engineers, throwing away the batch of products etc. are some examples of corrective measures. All information in running a HACCP system including procedures, parameters checking, and actions taken should be well documented for future references.

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Figure 12.19 Decision tree for finding critical control point (CCP)

Q1. Is there any control measures suitable for the identified hazard?

Q2. Does the step eliminate or reduce the hazard to an acceptable level?

Q3. Could contamination at this step occur or increase to unacceptable level?

Q4. Will a subsequent step, prior to consumption of the food, eliminate or reduce the hazard to an acceptable level?

Is control necessary for safety at this step?

Modify the step, process of product

Not a CCP

This is a CCP

NO

NO

NO

NO

NO

YES

YES

YES

YES

YES

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Ingredients:prime rib, vegetables, beef stock, roux (flour/butter)

Storage:✧vegetables, beef stock and butter (4℃ or below)✧flour (keep dry)

Preparation:Wash hands, sauté vegetables, add prime rib and beef stock

Cooking:✧Add roux when boiling✧Add seasonings✧Cook to 74℃ or above

Cooling:Cool from 60℃ to 20℃ within 2 hours and then to 4℃ within 4 hours

Reheat:Reheat to 74℃ or above

Serve:Serve at 60℃ or above

Figure 12.20 Flow chart with indication of CCP in the production of beef stew

CCP

CCP

CCP

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(C) Food packaging materials and legal requirementsPackaging is very important for preserving the food and well presenting the food to customers. Packaging materials can be roughly classified as follows:(i) Metal(ii) Glass bottles, jars and jugs(iii) Plastics (rigid, semi rigid/flexible, films)(iv) Paper, cellulose and wood containers

There are four main types of metals used in food packaging: i.e. aluminium, chromium, steel and tin. Cans can be made by different metals including aluminium, iron, steel etc. coated inside with tin or with an organic compound to prevent chemical reactions between food and metal. There is a rubber compound between the metal in the cap of the can and the metal of the body of the can to ensure the complete sealing of the can.

Glass is transparent in nature that allows for better shelf displays. Glass can be moulded into any shape, size as well as being given any colour to meet the needs of the customers. Glass containers are microwavable and they are reusable and recyclable. However, glass containers are usually quite heavy and they may be broken easily. The foods in glass containers are susceptible to light destruction since it is transparent.

Plastic is a by-product from the petroleum industry refining process. In general, plastic containers are inexpensive, light in weight, flexible and can be moulded into different shapes meeting the requirement of customers. However, most of the plastic materials are not biodegradable.

Raw materials for producing paper and paper products are woods from the forest. Kraft bags, waxed paper, glassine and cellophane are some derivatives of paper materials. Most paper materials are renewable and biodegradable. They are used directly for wrapping fresh food produces, or secondary containers such as bags, cartons or cases and tote boxes.

Six items are required to be shown on the food labels according to Hong Kong food law. They are the name of the food, list of ingredients, shelf life of the food, statement of special conditions for storage or instructions for use, name and address of manufacturer or packer and count, weight or volume of the food. The name of the food must be easy for customers to know the nature and type of the food. If the food contains allergic effects, it should be indicated in the name. Additives added in the food must be labelled for its functional class and its exact name or its identification number under the International Numbering System (INS) for Food Additives with a prefix “E” or “e”.

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Category of food

(A) Prepackaged food which is highly perishable and is therefore likely to constitute an immediate danger to human health from the microbiological point of view after a short period.e.g. pasteurised fresh milk, eggs in a pack and ham sandwiches, etc.

(B) Prepackaged food which is not included in category (A) abovee.g. candies, canned beverages, etc.

Words for indication

Use byIf the “use by” date is shown in arabic numbers, the day shall be indicated by the words “DD”, ”dd”, “D”, or “d” in English lettering and “日” in Chinese character; the month shall be indicated by the words “MM”, ”mm”, “M”, or “m” in English lettering and “月” in Chinese character; and the year shall be indicated by the words “YY”, ”yy”, “Y”, or “y” in English lettering and “年” in Chinese character, and the day, month and year can appear in any order.

Best beforeIf the “best before” date is shown in arabic numbers, the day shall be indicated by the words “DD”, ”dd”, “D”, or “d” in English lettering and“日” in Chinese character; the month shall be indicated by the words “MM”, ”mm”, “M”, or “m” in English lettering and“月” in Chinese character; and the year shall be indicated by the words “YY”, ”yy”, “Y”, or “y” in English lettering and “年” in Chinese character, and the day, month and year can appear in any order.

Marking of Date in Arabic Numerals

DD MM (e.g. 25 04, i.e. 25 April)

DD MM YY(e.g. 25 04 06, i.e. 25 April 2006)

DD MM YY(e.g. 25 06 2007,i.e. 25 June 2007) or

For date of not more than 3 months

More than 3 but not more than 18 months

More than 18 months

DD MM(e.g. 25 04, i.e. 25 April)

end MM YY(e.g. end 06 2007, i.e. up to June 2007)

end MM YY(e.g. end 12 2007, i.e. up to December 2007)orend YY(e.g. end 2007, i.e. up to the end of 2007)

Table 12.21 Legal statements of using “use by” and “best before”

(Adapted from Food and Environmental Hygiene Department, HKSAR)

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(D) Environmental issuesFood packaging materials especially plastics cause serious environmental problems. According to the data from Environmental Protection Department, Hong Kong Special Administrative Region (HKSAR), there were about 1064 tonnes plastic bags equaling to about 33 million plastic bags disposed to landfills everyday in 2005 and 2006. Most plastic materials cannot be degraded in the nature and left in landfills for years. This has been discussed for decades on how to minimise the use of plastics. In recent years, retailers try to reduce the use of plastic bags or use some biodegradable plastic bags instead.

Apart from using biodegradable packaging materials, some packaging materials can be recycled to be used again and again. Aluminium can, glass containers etc. are some examples that can be recycled. Some plastics, but not all, can be recycled. There is a code on plastic materials identifying the type of plastics used. Table 12.23 shows the coding system, the properties of the plastics, common uses and the recycled end-products. Hong Kong government used to encourage people to throw rubbish according to their type for easy recycling. The government established a slogan “blue for paper, yellow for aluminium cans, brown for plastic bottles” and set up three recycling bins in blue, yellow and brown respectively in different areas. This policy raises people’s consciousness of environmental protection by recycling wastes.

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Type of plastic

PET PolyethyleneTerephthalate

PE-HDHigh DensityPolyethylene

PVCUnplasticisedPolyvinylChloridePVC-U

Plasticised PolyvinylChloridePVC-P

PE-LDLow DensityPolyethylene

Properties

Clear, tough, solvent resistent, barrier to gas and moisture soften at 80℃

Hard to semiflexible, resistant to chemicals and moisture, waxy surface, opaque, softens at 75℃, easily coloured, processed and formed

Strong, tough, can be clear, can be solvent welded, soften at 80℃

Flexible, clear, elastic, can be solvent welded

Soft, Flexible, waxy surface, translucent, softens at 70℃, scratches easily

Common uses

Soft drink and water bottles, Salad domes, biscuits trays, salad dressing and peanut butter containers

Crinkly shopping bags, freezer bags, milk bottles, ice cream containers, juice bottles, shampoo, chemical and detergent bottles, buckets, rigid agricultural pipe, milk crates

Cosmetic containers, electrical conduit, plumping pipes and fittings, blister packs, wall cladding, roof sheeting, bottles

Garden hose, shoe soles, cable sheathing, blood bags and tubing, watch straps

Glad wrap, garbage bags, squeeze bottles, black irrigation tube, black mulch film, garbage bins

Recycled in

Pillow and sleeping bag filling, colthing, soft drink bottles, carpet

Recycling bins, compost bins, buckets, detergent containers, posts, fencing, pipes

Flooring, film and sheets, cables, speed bumps, packaging, binders, mud flaps and mats

Rubbish bin liners, pallet sheets

Table 12.23 The plastic identification code

Symbol

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Common uses

Dip pottles and ice- cream tubs, potato chip bags, straws, microwave dishes, kettles, garden furniture, lunch boxes, blue packing tape

CD cases, plastic cutlery, imitation ‘crystal glassware’, low cost brittle toys, video cases

Foamed polystyrene hot drink cups, hamburger take-away clamshells, foamed meat trays, protective packaging for fragile items

Car parts, appliance parts, computers, electronics, water cooler bottles, packaging

(Data adapted from Plastics New Zealand. Available: http://www.plastics.org.nz)

Properties

Hard but still flexible, wazy surface, soften at 140℃, translucent, withstands solvents, versatile

Clear, glassy, rigid, brittle, opaque, semi-tough, softens at 95℃. Affected by fats and solvents.

Foamed, light weight, energy absorbing, heat insulating

Includes all other resins, and multi-materials(e.g. laminates)

Properties dependent on plastic or combination of plastics

Type of plastic

PP Polypropylene

PSPolystyrene

PS-EExpanded Polystyrene

OTHERLetters below indicate ISO code for plastic typee.g. SAN, ABS, PC, Nylon

Recycled in

Pegs, bins, pipes, pallet sheets, oil funnels, car battery cases, trays

Coat hangers, coasters, white ware components, stationery trays and accessories

Car parts, concrete aggregate, plastic timber

Symbol

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Not for SaleThe copyright of the materials in this booklet belongs to the Education Bureau. The materials can be used by schools only for educational purpose. Written prior permission of the Education Bureau must be sought for other commercial uses.

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