processing tech

8/3/2019 Processing Tech

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Food Processing and Preservation Technologies

Syed Rizvi

Professor, Food Process EngineeringDepartment of Food Science

114B Stocking Hall

Cornell University(V) 607-255-7913

(F) 607-254-4868

E-mail: [email protected]

http://www.foodsci.cornell.edu/faculty/rizvi.htm
mailto:[email protected]://www.foodsci.cornell.edu/faculty/rizvi.htmhttp://www.foodsci.cornell.edu/faculty/rizvi.htmmailto:[email protected]


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Food Processing and Preservation Technologies

Food is undeniably most vital to the survival of human beings. Over

the years several processing and preservation technologies have evolved,

mostly by trial and error, for extending the storage life of food. As ourscientific understanding of biological materials has accelerated in recent

years so has the nature of the food industry, from a craft-based industry

to a science-based manufacturing enterprise. Today, it is a big, dynamic,

worldwide industry and undergoing continual change. The basic elements

of a well-developed food-manufacturing infrastructure, linking the farm

to the consumer plate, are shown below.gate

Commodities

-

FOODINGREDIENT

MANUFACTURER

S

Colors

Flavors

VALUE-ADDEDFOOD

PROCESSORS

Cereals

Bread

Cheese

ProcessorsCommodities: milk, proteins, fiber, flour,

Livestock

Su

ar

OilSeeds

Grains

Vegetables

Basic Producers Farmers

Fruits

Fish


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The major aims of the food processing and preservation activities

are to:

Extend the shelf-life of food and

serve as the surge capacity in natures

seasonal cycle. Increase the organoleptic (flavor, color,

texture) quality of food

Provide food with the nutrients required

for enhancing good health, strengthening

bodies and empowering minds.

Help build communities and generate

income for the farmers and manufacturers

The fundamentals of food preservation involve the following two

basic principles:

Destroy or inactivate pathogens found in food.

Reduce or eliminate non-pathogenic microorganisms and

enzymes responsible for spoilage of food.

Control growth through adjunct treatment

12

11

10

9

8

7

6

5

4

3

2

4 8 12 16 20 24 28 32 36 40 44

Time (min.)

Survivor(Log10CFCU)

Thermal death curve for a microorganismin liquid food at 70C

(D-value = time for one-log cycle

(10-fold) reduction in survivors)

D7 0 = 10.5 min

Optimal microbial growth temperatures


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In general, all food processing and preservation operations are

carried out by using a combination of procedures, called unit

operations. These unit operations are used to transform perishables

into stable foods and vice versa and are illustrated below.

Highly Perishable( Keeps for few hours to one week)

Examples:

milk, fish, meat, poultry, many fruits and

vegetables

Stable( Keeps for several months to years)

Examples

cereal grains, oilseeds, nuts, sugar, honey.

Perishable( Keeps for one week to several months)

Examplesapples, citrus, coconuts, dates, fats & oils,

potatoes, root vegetables, pumpkins.

Canning

Freezing

Dehydration

Refrigeration

Pasteurization

Juice

extraction

Hurdle technol

C.atmosphere

e

Flourmilling

Oil pressing

Baking

Brewing

After Bourn 2002

Some of the most common unit operations include:

Thermal processing: cooking, blanching, pasteurization,

canning, etc.

Cold preservation: refrigeration and freezing

Dehydration

Fermentation

Irradiation


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I. THERMAL PROCESSING

It is the application of heat energy to the foods with the following

specific objectives.

1. Cooking

to produce a palatable food

examples: baking, broiling,

roasting, boiling, stewing and

frying etc.

2. Blanching

to inactivate enzymes before freezing, to remove tissue

gases, to wilt the tissue to facilitate packing or to cleanse

the tissue before canning

examples: beans, peas, corn

Pasteurized products require

refrigeratedstorage

3. Pasteurization

to kill pathogenic and selectedspoilage microorganisms in

the foods followed by some

adjunct treatment

techniques: LTLT, HTST, UHT

examples: milk, cider, and juice.

4. Commercial Sterilization (Canning, retorting, etc.)

bacterial destruction is a

logarithmic function, complete

destruction not probable

to make food commercially

sterile for extended shelf-life at

room temperature

examples: beans, soup, cream


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Thermal conditions needed to produce commercial sterility

depends on:

Nature of food such as pH

Storage conditions

Heat resistance of the microorganisms or spore

Heat transfer characteristics of the food, its container &

heating medium

Initial load of viable cells

History of Commercial Sterilization (Canning, Retorting,

Appertization):

1804: Nicholas Appert established a commercial cannery(bottling plant) for preserving foods by the following

processes:

Filling foods to be preserved into bottles

Carefully corking the bottles

Heating the bottles in boiling water for various

periods of time depending upon the type of food

Removing the bottles from the boiling water and

cooling them

1819 UNDERWOOD, who came from England, started the

first American canning operation in Boston. By 1822,

Underwood packed fruits, vegetables and condiments in

bottles.

1856 BORDEN built first canned milk plant in America,

based on his process for condensing milk and filling itinto a hermetically sealed container.

1861 CIVIL WARaccelerated demand for canned goods.

Processing plants for fruits and vegetables were started

in Ohio, Indiana, Illinois and California.


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1874 SHRIVERinvented the retort (pressure cooker),

permitting canners to control temperatures accurately

during heat processing

1921 CANNED CITRUS JUICE was started beingproduced in Florida.

1947 SCRAPED SURFACE HEAT EXCHANGERwastested as a high temperature- short time sterilizer in aseptic

processing of dairy products, baby foods, fruits, vegetables and

custards.

Current Regulations for Commercial Sterilization:

FDA CFR Part 113

Def. "Commercial sterility" of thermally processed

foods means conditions achieved by:

1. Application of heat which renders the food free of viable

(a) microorganisms capable of producing in the food undernormal non-refrigerated conditions of storage and

distribution

(b) microorganisms of public health significance.

OR

2. Control of water activity (aw) and application of heat which

renders the food free of viable(a) microorganisms

distribution

(b) microorganismssignificance


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Design of Commercial Processes

Low Acid Foods: Foods other than alcoholic beverages with a

finished equilibrium pH > 4.6 (pH >= 4.7 for tomato products), aw

> 0.85 Destruction of C. botulinum (12 log reduction, 10

-9survivors)

Clostridium botulinum

Can grow and produce toxin at pH > 4.6

Obligate anaerobe, spore-forming, heat resistant pathogens

Assumed to be ubiquitous in soil

Has several strains. Types A & B are most heat resistant

Ingestion of toxins produced them causes food poisoning

Toxins are destroyed at 100oC for 10 min

Putrefactive anaerobe(PA) 3679 and FS 1518

Non-toxic facultative anaerobe

Resistance to heat similar to C. bot.

Generally used to determine safe thermal processes instead of

C. bot.

Industry classification of foods for thermal processing

High acid foods: pH < 3.7

Acid foods: pH 3.7 - 4.5

Low acid foods: pH > 4.5

Examples:

Acid foods: Apples, blueberries,

peaches, tomatoes, orange, grapefruits,grapes

Low acid foods: Asparagus, beans,

corn, potatoes, cauliflower, cantaloupe,

Canned foods come in containers of

various shapes and sizes and include

ars

watermelons, banana


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2. Acid Food (pH 3.7 4.5)

Thermal processes are based on the destruction of

Bacillus coagulans Bacillus polymyxa

3. High Acid Foods (pH < 3.7)

Thermal processes are based on the destruction of yeasts and

molds.

Spore former do not grow at pH < 3.

II. COLD PRESERVATION

All microbial and biochemical activities are temperature dependant

and slow down as the temperature is reduced. As a rule of thumb,

for every 10oC temperature change, the rate of reaction changes by

a factor of 2 to 3.

1. Chilling and refrigerated storageIn the unit operation of chilling, the temperature of a food is

reduced generally to between -1oC and 7

oC and thus subsequent

storage at refrigerated temperature extends the shelf life of both

the fresh and processed foods. It is also used as an adjunct

process to extend the storage life of mildly processed (e.g.

pasteurized, fermented and irradiated) and low-acid foods. In

the US, refrigerated storage of food is mandated by regulations

at temperatures at or below 7.20C (45

0F). Such foods are also

marketed under refrigeration and labeled as needing

refrigeration. Commercially sterilized and processed foods that

may become contaminated after opening should also be labeled

for refrigerated storage.

Chilling and refrigerated storage prevents the growth of

thermophiles and mesophiles. Psychrophiles, however, can and


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do cause food spoilage during low temperatures storage but

there are some psychrophillic pathogens, see table below, that

need attention.

From Walker (1992)

It is now well recognized that when chilling is combined with

the control of the composition of the gaseous atmosphere

around the product, their preservative effect is greater than that

achieved by using either unit operation alone. In particular,

fresh fruits and vegetables show considerable reduction in their

respiration rate when oxygen concentration is reduced and/or

carbon dioxide concentration is increased in the surrounding

atmosphere. The atmospheric composition is changed by one of

the following two methods.

Pathog enic B acter ia of Conc ern in Refr igerated Food

7 .7 Staphylococcus aureus

7 .1E schir ichia coli

5 .1Salmonella spp.

3.3-5nonproteolyt ic

10-12proteolytic

Clostr idium botulinum4tox in p roduct ion

1B acil lus cereus

1Aerom onas h ydrophi la

-1.3Yersina e nterocoli ta

-0.4Lis ter ia monocytogenes

M in im um G rowth

Tem perature ( C)

Classif ication

Controlled-atmosphere storage (CAS): In this process

the concentrations of oxygen, carbon dioxide and often

ethylene are monitored and regulated all the time.


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Modified-atmosphere packaging (MAP): In this the

composition of gases within a package is replaced with a

known composition mixture and the package is sealed.

Examples of shelf life extension by MA storage (Adapted from

Zeuthen, et al. 1990)

Product

Air storage

Shelf life

(days)

Optimal MAP

composition

CO2:N2

MA storage

shelf life

(days)

French fries


12/19

Recommended temperature and atmospheric composition for

storage of selected fruits (Adapted from Zeuthen, et al., 1990)

Fruit Temperature

( 0C)

Oxygen

(%)

CO2

(%)Apple 0- 4 2 5 1 - 5

Citrus 5 15 10 - 15 4 - 5

Kiwi fruit 0 2 4 - 5

Peach -0.5 0 2 4 - 5

Plum 0 2 4 - 12

2. Freezing and frozen-food storage

The unit operation of freezing involves reduction of the

temperature of a food, packaged or whole, to levels well below

its freezing point, generally in the range of 10 to 200C.

The conversion of water to ice

Frozen foods last many months

without spoiling. Some quality loss

may occur

increases the concentration

of dissolved solutes in unfrozen

water and thus lowers thewater activity of the food.

The concerted effect of

low temperatures, reduced

water activity, and pre-treatment

of blanching prior to freezing

of some products lead to longer

shelf life.

With adequate packaging, the more frozen water that exists, the

less:a. chemical, enzymatic activity

b. microbial activity

c. desiccation occurrence

The freezing process involves the removal of sensible heat to


13/19

lower the temperature of a food to its freezing point followed by

the removal of latent heat of crystallization (fusion) to covert

water within the product to ice. Since most foods contain lots of

water (see table below) which has a high specific heat

(4.2kJ/kg-K) and a high latent heat of crystallization (335kJ/kg),its the freezing of water that dominates the energy

requirements.

Water content and freezing points of foods

As the temperature is lowered, more and more water converts

into ice, as shown in table below, the energy requirement for

freezing also increases:

The quality of frozen food, however, depends not only on the

temperature but also on the rate of freezing. The rate of

Food Water content

(% wt.)

Freezing point

(0C)

Egg 74 -0.5

Milk 87 -0.5

Meat 60 - 70 -1.5 to 2.2

Fruits 85-95 -0.9 to 2.7

Vegetables 76-92 -0.8 to 2.8

P e r c e n t W a t e r i n F r o z e n P r o d u c t

- 8 9- 8 9- 2 0

- 8 8- 8 2- 4

- 8 3- 7 01 5

- 7 1- 3 52 5

- 5 0- 1 02 7

L e a n M e a tI c e C r e a mT e m p e r a t u r e

( 0 F )


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freezing is defined as the time required to reduce the

product temperature from its initial freezing point to a

temperature 5 degrees lower. At higher rates of freezing

smaller ice crystals are formed and vice versa. Large ice

crystals create quality problems such as sandiness in icecream, mushiness in vegetable, to name a few.

Although freezing is a preferred process today for quality

foods, structural changes do occur over time whatever the

rate of freezing. This shows in quality loss with time such as

formation of drip on thawing to ambient temperatures,

moisture loss by sublimation from ice.

Types of Freezing Methods

*1.Air: Blast, Tunnel, Fluidized Bed

*2.Plate: Direct contact with freezer

plates3.Immersion: Contact with low

temperature fluid

*4. Cryogenic: Uses liquid vaporization

to rapidly freeze product

* Most common industrial methods.

The storage life of a few

meat products is shown

in the accompanying

table, illustrating the effects

of storage temperatures.

Methods of freezing

Among the freezing methods available, the most common

and industrially practiced ones are highlighted below.

10842Pork

12843Veal

12+1263Lamb

12+1264Beef

-20 F-10 F0 F10 FProduct

1 Diced products have shorter life

2 Cured products such as ham and bacon can be stored a few

weeks only

Storage Life of Frozen Meats In Months


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III. DRYING / DEHYDRATION

The unit operation of drying generically refers to the application of

heat and removal of water from liquid, semi-solid and solid foods.Dehydration, on the other hand, requires close control of physical

and biochemical changes taking place during the drying

operations. Since most chemical and microbiological activities

require water, dried foods kept in airtight containers can last quite

a long time.

Since todays consumers and producers of food are away from

each other both in time and place, preservation by dehydrationhelps maintain a more continuous food supply. Additionally,

removal of water reduces the weight and bulk of the product and

thus the cost of shipping and storage. Dehydrated foods often offer

convenience not available with their fresh counterparts.

Examples of dehydrated foods include:

Dehydrated products very stable

andlast for months toyears

milk powders, coffee, tea, pasta,

cereals, dehydrated potatoes, dried

fruits and vegetables, dried meats

(like beef jerky), powdered soups

and sauces, instant rice, yeast, cheese

powder, etc.

State of water in foods

The state of water in food represents an energetically complex

continuum. In food processing and preservation, the

thermodynamic measure ofwater activity is often used to describehow water behaves in food systems. Water activity (aw) is defined

as:

aw = ( Pw / Pw0)T

where, Pw = vapor pressure exerted by water in food

Pw0

= vapor pressure of pure water at the same constant

temperature (T)


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For pure water, aw =1 and when there are solutes (like salts, sugar,

proteins, etc.) present in the water, the vapor pressure is lower than

the saturation pressure and awbecomes less than unity. The vapor

pressure exerted by a system also can be used to relate it to relative

humidity in the air surrounding the system. Thus if a food isallowed to equilibrate in a closed environment at a constant

temperature, the % equilibrium relative humidity (%ERH) when

divided by 100 also represents awof the foodat that temperature. It

can be written as

% ERH = 100 . aw = 100. ( Pw / Pw0)T

Labuza (1980) has generalized the role of water activity in food preservation and how different deteriorative reactions and

microbial growth are controlled in food systems by developing a

food stability diagram shown below:

Food stability diagram (Labuza, 1980)


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For convenience and ease of interpretation, in the past the state of

water has been classified into two types, free and bound. Free

water exerts awof unity, is relatively easy to remove and requires

energy similar to that needed for evaporation of pure water. Bound

water gives aw less than unity and takes more energy to evaporate.

Drying Methods

Direct contact dryers: In this type of dryers, hot air is blown

across the foods to provide energy for evaporation of water.

Examples include sun, bin, tray, belt, spray and fluidized bed

dryers.

Indirect contact dryers: In this set of dryers, heat is transferred to

food indirectly through a heat transfer surface. Examples are drum

and freeze dryers.

Infrared and microwave technologies are also used for food drying.

However, uniformity of drying and temperature control becomes

critical in these types of systems.

IV. FERMENTATION

Production of acids and/or alcohols by controlled action of selected

microorganisms is the basis of preservation of foods by

fermentation. Derivative advantages include alteration of texture of

foods and production of aromatic and flavor compounds. It is a

low-energy and low-capital process which generally operates at

mild pH and temperature conditions and thus helps minimizelosses in nutritional qualities of food. Examples of fermented

foods:

1. Acid (Lactic) fermentations

Meat and Meat Products: Pepperoni, salami, bologna

Vegetables: Pickles, sauerkraut, idli

Milk Products: Yogurt, cheese, kefir, buttermilk


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2. Alcoholic (Ethanolic) fermentation

Beer, bread, wine

3. Mixed alcohol-acid Coffee, cocoa, vinegar

V. IRRADIATION

Irradiation prevents food spoilage and destroys microorganisms of

public health significance. The FDA recently approved the

irradiation of beef, and the irradiation of chicken has beenapproved for some time.

Advantages of irradiation

The product does not undergo heating and thus the

organoleptic qualities are preserved.

Packaged and frozen foods may be irradiated

Process is automatic, low-energy and not labor intensive.

Disadvantages

Some loss of nutritional value

Possibility of development of resistance to radiation in

microorganisms

Absence of adequate analytical procedure for detecting

irradiated foods

Public fear of induced radioactivity


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Applications of food irradiation

Example of foods Dose range (kGy) Application

Herb, spices 7 10 Sterilization

Meat Up to 50 Long-term storage

Poultry, meat, frozen shrimp 3 10 Pathogen destruction

Fresh fruits 2 5 Mould control

Pork 0.1 6 Parasite (Trichenella) inactivation

Fruit, grain, flour 0.1 2 Disinfestation, insect control

Potatoes, onions, garlic 0.1 2 Sprout inhibition

Adapted from Ley (1987)

REFERENCES

Bourne, M.C. 2002. Personal communication

Labuza, T. P. 1980. Effect of water activity on reaction kinetics

of food deterioration. FoodTechnol. 34(4):36

Walker, A.P.1992. Chilled Foods Microbiology. In Chilled

Foods: A Comprehensive Guide. C. Dennis and M. Stringer

(Eds.). Ellis Harwood, London.

Zeuthen, P.J.C., et al. (Eds.). 1990. Processing and Quality ofFoods, Vol. 3. Chilled Foods : The Resolution in Freshness.

Elsevier Applied Science, London.

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