SOLVED QUESTION PAPER 2008-09FOOD BIOTECHNOLOGY

Q1. Discuss the principles of preservation of food by drying and freeze drying. Why freezing and irradiation of food increases the self life of the food?

Q1. A) Food preservation is a process by which certain foods like fruits and vegetables are pre-vented from getting spoilt for a long period of time. The colour, taste and nutritive value of the food are also preserved.

DRYING

The word dehydration means removing water or moisture from foods. The home method of de-hydration is sun drying. We will now discuss this method in some more detail. Some foods are dried as they are, eg, green leafy vegetables (methi, pudina, corrianderetc.) cauliflower, grapes, amla, onion, raw mango, etc. Some foods are cooked and then dried. For example potato chips, papad, banana, chips, wadis, etc. The most appropriate weather to dry foods is when the air is dry and there is strong sunshine. Let us understand the basic method of dehydration before we learn to apply it to individual foods.

Step 1 Clean all tins, plates, etc, to be used to dry and store the food. Dry in sun. Storage tins should have airtight lids.

Step 2 Wash the vegetables/fruits to be dehydrated. Cut, if required. Remove the stem, seeds, skin. Remove any decaying por-tions.

Step 3 Blanch vegetables, i.e., put them in boiling water. Time for blanching varies with hardness of fruit/vegetables. Remove when the food is soft (blanching reduces enzymed activity).

Step 4 Put vegetables in cold water containing salt and potassium metabisulphite(kms) for 5-10 minutes. This prevents black-ening of foods. Green leafy vegetables and other dark veg-etables should not be put in this solution.

Step 5 Spread on a clean cloth in the sun. Cover with a thin cloth to avoid dust and flies getting into the food.

Step 6 When the food is dry, (test by looking at hardness), cool to room temperature. Store in an air tight container. When you want to use dehydrated fruits and vegetables, wash and soak in water for

some time.

FREEZE DRYING

Using low temperature to preserve foods works on the principle that low temperature slows microbial and enzyme action. The food is thus prevented from spoilage. Are you using this method of preservation

at home? Yes, if you have a refrigerator you can use it because a refrigerator works on this principle. Foods can be preserved at low tem-perature by:–

The duration for which the food can be preserved by using low temperature varies with the type of food and the temperatures. The lower the temperature, longer is the dura-tion for which food can be preserved. Of the three methods, freezing uses the lowest temperature.

Q1) b) Discuss the role of different classes of microorganisms in food spoilage. Mention three methods commonly used to prevent microbial spoilage of food?

A1) b) In the 1960s, most food-related illnesses were attributed to one of five major groups of pathogenic bacteria. These were associated with particular foods, commodities, or processes and were classified as infectious or toxin-producing. These five groups, described below, remain major causes of food-borne illness. See also: Bacteria Salmonella and Shigella

The primary infectious bacterium associated with foods is Salmonella. These organisms cause gastroenteritis with symptoms of fever, diarrhea, and vomiting 12–36 h after ingestion. Salmonellosis is usually self-limiting, but it can be fatal in the old, young, or medically compromised individuals.

Salmonella are commonly found on meats, especially poultry and eggs. Salmonella are easily killed by cooking. However, items contacted by the contaminated raw meat can transfer the Salmonella to food that is ready to eat (cross contamination) and cause illness. The seasonal increase in Salmonella isolations illustrates how food-borne illness increases in warm summer months.

Shigella are related organisms which produce a similar infectious syndrome. They are usually transmitted by a fecal-oral route or through feces-contaminated water rather than through foods.

Clostridium botulinum The most dreaded toxin-producing organism is Clostridium botulinum. It excretes a potent neurotoxin that causes weakness, double vision, slurred speech, paralysis, and often death if ingested. The vegetative reproductive form of C. botulinum is heat-sensitive, lives only in the absence of air, does not compete well with other bacteria, and is rarely a problem in fresh foods. Clostridium botulinum spores are killed only through severe heating, such as in canning.

Historically, botulism has been associated with foods canned at home. If canned foods receive inadequate heat processing, competing bacteria are killed, air is expelled, and the botulinal spores germinate.

Fortunately, botulinal toxin is often destroyed by heat when the food is cooked before serving; hence the standard advice is to boil home-canned foods before eating.

Modern commercial canning is designed to destroy C. botulinum spores. Reported outbreaks of botulism caused by pot pies, potatoes, and fried onions have been caused by temperature abuse, that is, the holding of foods at warm temperatures that promote bacterial growth. Clostridium botulinum can also be a problem in processed meats, such as hams and sausages. In this case, its growth is controlled through the use of nitrite, salt, and refrigeration. One type of C. botulinum is associated with fish. See also: Botulism;

Toxin

Clostridium perfringens and Bacillus cereus These are spore-forming, toxin-producing bacteria that cause illness when foods are heated enough to kill competing bacteria but not enough to kill the spores. When large volumes of foods are prepared cooked, and then kept warm until they are served, spores can germinate. In the case of C. perfringens, which is associated with meats, the ingested cells release toxin in the digestive tract, resulting in cramps and diarrhea. Bacillus cereus, found in meats, dried foods, and rice, produces two different types of toxins: the diarrheal toxin, which has an etiology similar to C. perfringens, and the emetic (vomiting) toxin, which causes symptoms similar to those produced by staphylococcal toxins.

Staphylococcus aureus This bacterium produces toxins that are very resistant to heat. Staphylococcus aureus is found in the nose and throat of many healthy people and is transferred to food by inadequate hygiene. When foods are temperature-abused, the bacteria grow and produce toxin. Subsequent heating of the food kills the bacteria but does not inactivate the toxin. The toxin causes severe vomiting and diarrhea from ½ to 4 h after ingestion. The microorganism grows well at salt and sugar concentrations that inhibit many competing bacteria. Foods high in protein, such as cured meats, custards, and cream-filled bakery goods, pose special hazards for staphylococcal food poisoning. See also: Staphylococcus

Methods used to prevent microbial spoilage of food

Temperature

The most important environmental condition is temperature. Most food-borne pathogens are mesophiles; that is, body temperature is optimal for growth. With a doubling time of 20 min at 98.6°F (37°C), one bacterium generates 1 million progeny in less than 7 h; at 32°F (0°C) the doubling time increases to 1200 min and the 1 million cell count is not reached for 16 days. Keeping hot foods hot (>145°F or 63°C) and cold foods cold (<45°F or 7°C), combined with rapid heating and cooling to get rapidly beyond the growth- promoting temperature range (45–145°F or 7–63°C), prevents most food-borne illnesses. Psychrophylic (cold-loving) bacteria such as Listeria monocytogenes are exceptions.

Acidity

A food's acidity, quantified as pH, is another major environmental factor. The pH range for bacterial growth is 4–9, with fastest growth at neutrality (pH 7). Changing a food's acidity can change the rate of bacterial growth. Meats, fish, poultry, and most dairy products are near pH 7, which is ideal for bacterial growth; fermented foods and fruits have pH less than 4. Many yeasts and molds grow in acidic environments and spoil acidic foods. The pH value of 4.6 has special significance because C. botulinum can grow and produce toxin above this value. Canned foods with pH above 4.6 are legally classified as low-acid and must be processed in retorts under steam at 240–280°F (116–138°C) to kill C. botulinum spores. Foods with pH below 4.6 are legally high-acid and are processed in open pans of boiling water. In this case, C. botulinum need not be killed because it cannot grow at low pH. See also: pH

Water activity

The amount of water available for microbial growth, that is, water activity (aw), is the third major factor influencing microbial competition. Water activity is the equilibrium relative humidity generated by afood in a closed chamber divided by 100 to give a 0 to 1.00 scale. Salad dressings and honey, which both contain 50% water, are microbiologically quite different. The dressing separates into a 100% free-water phase (aw = 1) and supports bacterial growth, while the sugar in honey binds water so tightly that it is unavailable for microbial growth. Most bacteria grow only at aw = 0.90–1.00. Fresh meats, vegetables, fruits, and perishable foods have water activity in this range. Most yeasts can grow at slightly lower values. Staphylococcus aureus is the pathogen most insensitive to water; it grows at aw = 0.86. Since no pathogenic bacteria grow below aw = 0.85, this value has special significance in the regulations defining low-acid foods. Foods having an aw value below 0.85 are legally considered high-acid, regardless of their pH. Most molds grow at aw values as low as 0.8 and compete well in foods such as flour, cakes, beans, rice, and cereals. Some xerophilic molds and yeasts grow at aw values as low as 0.6. Dehydrated foods, with even less available water, are completely recalcitrant to microbial spoilage.

Q1. C) Mention the characteristics of a suitable food yeast. Briefly discuss the process of food yeast production by submerged fermentation.

A1. C) Food yeast was produced from several sources in Germany, the most important being sugars obtained by the hydrolysis of wood, Sugars were made by complete hydrolysis, as in the Scholler ( 33) or Bergius ( 1 ) process; from a prehydrolysis of woods such as beech, the residue of which was then used for the production of pulp; and as a byproduct of the hydrolysis that occurs in the sulfite pulping of wood. At the end of the war, five plants were producing food yeast from sugar obtained by acid hydrolysis of wood (25 ). They were the Bergius wood -sugar plants at Regensburg and Mannheim and the Scholler plants at Dessau, Holzminden, and Tornesch. Their production was about 9,000 tons per year. Hydrolysate from 1 ton of wood produced 200 to 400 pounds of yeast. A plant for the prehydrolysis of wood or straw at Wittenberg had a rated capacity of 20,000 tons of yeast per year. Four tons of straw treated in this way were expected to yield 1 ton of high alpha pulp and one-half ton of yeast. The organism used most frequently for food-yeast production was a strain of Torula utilis. After acclimatization, this organism uses hexose and pentose sugars, acetic acid, and possibly other organic compounds. Other strains used in Germany were Torula pulcherima , Monilia candida ,

and Candida arborea . Considerable advan-tage was claimed for the latter because the new yeast buds adhere to the parent cell, making the aggregate larger and therefore easier to separate from the spent solutions.

When food yeast is produced on any form of wood hydrolysate, aeration produces excessive foaming. Two yeast propagators were designed to control the foaming. The Vogelbush propagator was a discontinuous type provided with external tubes extending from the bottom to the top of the yeast container. Air introduced into the tubes at intervals circulated the media and broke the foam. At Holzminden, antifoam was required in amounts equivalent to about 10 percent of the weight of the yeast produced. The Waldhof continuous propagator made use of a draft tube in the center. Air was introduced through a spinner, which also served as an agitator to circulate the media. In this propagator advantage was taken of the foaming tendency to obtain intimate contact between the air and the media. The contents of the propagator foamed to about three times the actual liquid content. In this condition equilibrium was reached and good foam control achieved without the use of antifoam Sugar solution with nutrients was introduced continuously and yeast and spent liquor were removed con-tinuously. The yeast was defoamed in a centrifugal foam breaker, separated in a yeast separator, washed, and dried. The Waldhof propagator, thus, appeared to be the more satisfactory of the two types for food-yeast production. Yeast propagation from wood sugars in the Waldhof-type propagator in Germany required 1.1 kilowatt of electricity, 2.7 pounds of steam, and about 10 gallons of cooling water for each pound of dry yeast produced.Preliminary Selection of Organism for Yeast Growth Peterson and coworkers (22) conducted tests with several organisms to determine those best suited for propagation on wood sugar. The sugar solution was made neutral and 0.05 percent sodium sulfite added and then heated and filtered. Nutrients were added and the solution diluted to about 1.5 percent concentration. Table 1 gives the results of the preliminary study. The most promising strains were selected for acclimatization. The results of acclimatization in shake flasks for 12 transfers are shown in table 2. Preparation of the Sugars

Hydrolysis of Wood

Following a study of the kinetics (26 , 29 ) of wood saccharification, several changes were made in the procedure for producing wood sugar (9 ). These changes made possible higher yields of fermentable sugars and a reduction of the time required for the hydrolysis. The improved process (fig. 1) consists of pumping a stream of 0.5 percent sulfuric acid through a charge of shavings, sawdust, or chipped wood waste at temperatures gradually increasing from 150° to 180° C. The resulting sugars are neutralized to approximately pH 4, cooled, and filtered. The yield of reducing material calculated as glucose averages about 50 percent of the dry, bark-free wood substance. The sugars are present in about 5 percent concentration and are a mixture of pentoses and hexoses. The yield and type of sugars from various woods are shown in table 3. In the table, sugars fermentable to ethyl alcohol are designated as hexoses and the remainder as pentoses. Sugars remaining in the hydrolysate after alcoholic fermentation may also be used for the production of yeast (12 ). When Douglas -fir hydrolysate containing material calculated as glucose was about 0.9 percent. If the residual liquors are subjected to yeast propagation, 0.3

percent of reducing material remains. Since these residues after yeast production do not show the presence of sugars by osazone tests, it is concluded that reducing material other than sugar is responsible for this

residual reducing material. If the sugars present in the liquor are corrected for non-sugar reducing material, 87 percent of the sugars present are fermentable to alcohol and are hexoses and 13 percent are pentoses. Hydrolysate from southern red oak contains about 16 percent of nonsugar reducing substances. After correcting for these substances, the sugars present are 75 percent hexoses and 25 percent pentoses. Organic acids in the hydrolysate, such as acetic acid, are utilized for the production of yeast.

Sulfite Waste Liquor

Pulping of wood by the sulfite process yields a pulp representing about 50 percent of the dry wood substance. Softwoods, such as spruce or hemlock, are usually pulped by this process. These woods contain about 67 percent of carbohydrate, 27 percent of lignin, 5.5 percent of extractives, and 0.5 percent of ash. On the basis of carbo-hydrate about 17 percent of the wood, or 25 percent of the total carbohydrate, is converted into simple sugars or other substances during the process. About half of the hydrolyzed carbohydrate appears as simple sugars in the recovered waste pulping liquor in concentration of 2 to 2.5 percent reducing sugars. These waste pulping liquors are steamed to remove the excess sulfur dioxide and then treated with lime to bring the pH of the solution to 4. Sugars in sulfite waste liquor from spruce or hemlock are about 65 percent fermentable to alcohol. The sulfite waste liquor produced annually contains about 500,000 tons of dissolved sugar.

Prehydrolysis of Wood or Straw Used for Pulp Production

In alkaline pulping processes carbohydrates are also converted into soluble non-pulp products. In the presence of alkali at pulping temperatures the carbohydrates are converted to reversion products that are nonfermentable and not useful for yeast production. When it is desired to produce a pulp with high alpha cellulose content by an alkaline process from wood or straw, the material may be subjected to a pre -hydrolysis with 0.3 to 0.5 percent acid at 30 to 50 pounds per square inch of steam pressure for about 1/2 hour. Hemicelluloses representing 15 to 20 percent of the wood and up to 30 percent of straw are made water -soluble. These are extracted in some type of countercurrent extractor designed to give high recovery of the soluble material in as high a concentration as possible. Frequently the hemicellulose is only partially converted to simple sugars. In order to complete the inversion, acid is added until the solution has a pH of 1.2 to 1.5, and it is then given a secondary hydrol-ysis at 20 to 30 pounds per square inch of steam pressure for 30 minutes. Lime is then added to give the solutions a pH of 4. Calcium sulfate and other precipitated material are removed by filtration. Sugars representing 15 to 20 percent of wood and 25 percent of straw in concentrations of 6 to 8 percent may be recovered from pre-hydrolysis. Sugars from prehydrolyzed softwoods, such as pine, are about one

-half hexoses and one-half pentoses, and those of hardwoods, such as maple or beech, are 20 percent hexose and 80 percent pentose.

Q2. A) Write a short note on the fermented food. How fermentation increases the nutritive value and self life of food?

A2. A) Fermented foods, whether from plant or animal origin, are an intricate part of the diet of people in all parts of the world. It is the diversity of raw materials used as substrates, methods of preparation and sensory qualities of finished products that are so astounding as one begins to learn more about the eating ha- bits of various cultures. The preparation of many indigenous or “traditional” fermented foods and beverages remains today as a household art. The preparation of others, e.g., soy sauce, has evolved to a biotechnological state and is carried out on a large commercial scale.

Soy Sauce

The written records of the Chinese show that they have been using soy sauce for over three thousand years (YONG and WOOD, 1974). Production of soy sauce in Japan probably was a result of the introduction of Buddhism from China and the consequent change to a vegetable diet in 552 A.D. (HESSELTINE, 1965). SMITH (1961) published a report on various methods of using soybeans as foods,

including soy sauce, in China, Japan, and Korea. YOKOTSUKA (1960), YONG and WOOD (1974) and HESSELTINE (1983) have subsequently reviewed soy sauce fermentation in considerable detail. The technology of soy sauce preparation was at one time a closely guarded family art passed on from one generation to the next. While there are still unique formulae used on a domestic level, the major steps involved in the manufacture of soy sauce are no longer a secret. There is, however, much to be learned about the bio- chemical changes which occur during fermentation and lead to desirable as well as undesirable sensory qualities in the finished product.

Two distinct basic processes can be used to prepare soy sauce (BEUCHAT, 1984). The first involves fermentation with microorganisms and the second, i.e., chemical method, in- volves the use of acids to promote hydrolysis of ingredient constituents. The latter method will not be discussed here mainly because it cannot be considered as traditional or indigenous, but also because there are many who consider the end product to be inferior and not in a class deserving of recognition as a substitute for the fermented product.

Q2. B) What do you mean by lactic acid bacteria? Discuss with examples preservation of food by lactic acid bacteria.

A2. B) Lactic acid bacteria are a group of related bacteria that produce lactic acid as a result of carbohydrate fermentation. These microbes are broadly used by us in the production of fermented food products, such as yogurt (Streptococcus spp. and Lactobacillus spp.), cheeses (Lactococcus spp.), sauerkraut (Leuconostoc spp.) and sausage.

These organisms are heterotrophic and generally have complex nutritional requirements because they lack many biosynthetic capabilities. Most species have multiple requirements for amino acids and vitamins. Because of this, lactic acid bacteria are generally abundant only in communities where these requirements can be provided. They are often associated with animal oral cavities and intestines (eg. Enterococcus faecalis), plant leaves (Lactobacillus, Leuconostoc) as well as decaying plant or animal matter such as rotting vegetables, fecal matter, compost, etc.

Lactic acid bacteria are used in the food industry for several reasons. Their growth lowers both the carbohydrate content of the foods that they ferment, and the pH due to lactic acid production. It is this acidification process which is one of the most desirable side-effects of their growth. The pH may drop to as low as 4.0, low enough to inhibit the growth of most other microorganisms including the most common human pathogens, thus allowing these foods prolonged shelf life. The acidity also changes the texture of the foods due to precipitation of some proteins, and the biochemical conversions involved in growth enhance the flavor. The fermentation (and growth of the bacteria) is self-limiting due to the sensitivity of lactic acid bacteria to such acidic pH.

The metabolic activities of lactobacilli are responsible for their therapeutic benefits.

Lactobacilli cultured in milk medium perform the following activities:

1. Proteolysis:

Proteins are broken down into easily assimilable components.

These activities of lactobacilli in the gastrointestinal tract make protein ingested by the host easily digestible, a property of great value in infant, convalescent and geriatric nutrition.

2. Lipolysis:

Complex fat is broken down into easily assimilable components.

This property is useful in the preparation of dietetic formulations for infants, geriatrics and convalescents.

Evidence from preclinical and clinical trials has revealed that lactobacilli can break down cholesterol in serum lipids. Lactobacilli also assist in the deconjugation of bile salts. Both of these findings have clinical significance.

3. Lactose metabolism:

Lactic acid bacteria have the enzymes b- galactosidase, glycolases and lactic dehydrogenase (LDH) which produce lactic acid from lactose. Lactic acid is reported to have some physiological benefits such as:

a) Enhancing the digestibility of milk proteins by precipitating them in fine curd particles.

b) Improving the utilization of calcium, phosphorus and iron.

c) Stimulating the secretion of gastric juices

d) Accelerating the onward movement of stomach contents

e) Serving as a source of energy in the process of respiration.

The levels of optical isomeric forms of lactic acid produced depend upon the nature of the culture. The structural configurations of these isomers are as follows :

D(-) levorotatory lactic acid         L(+) dextrorotatory lactic acid

In humans, both isomers are absorbed from the intestinal tract. Whereas L(+) lactic acid is completely and rapidly metabolized in glycogen synthesis, D(-) lactic acid is metabolized at a lesser rate, and the unmetabolized acid is excreted in the urine. The presence of unmetabolized lactic acid results in metabolic acidosis in infants. L. acidophilus produces the D(-)- form and is therefore of disputable clinical benefit, although it has earlier been the probiotic of choice in various therapeutic formulations. L. sporogenes* on the other hand produces only L(+)- lactic acid and hence is preferred.

The ability of lactobacilli to convert lactose to lactic acid is used in the successful treatment of lactose intolerance. People suffering from this condition cannot metabolize lactose due to lack or dysfunction of the essential enzyme systems. Lactic acid, by lowering the pH of the intestinal environment to 4 to 5, inhibits the growth of putrefactive organisms and E. coli, which require a higher optimum pH of 6 to 7. Some of the volatile acids produced during fermentation also possess some antimicrobial activity under conditions of low oxidation-reduction potential.

Production of bacteriocins:

Bacteriocins are proteins or protein complexes with bactericidal activities directed against species which are closely related to the producer bacterium. The inhibitory activity of L. sporogenes* and lactobacilli towards putrefactive organisms is thought to be partially due to the production of bacteriocins.

Some of the bacteriocins isolated from lactobacilli are listed in Table 2.1:

Table 2.1 : Bacteriocins isolated from different Lactobacillus species.

Substance Producing species

Acidolin L. acidophilus

Acidophilin L. acidophilus

Lactacin B L. acidophilus

Lactacin F L. acidophilus

Bulgarin L. bulgaricus

Plantaricin SIK-83 L. plantarum

Plantaricin A L. plantarum

Lactolin L. plantarum

Plantaricin B L. plantarum

Lactolin 27 L. helveticus

Helveticin J L. helveticus

Reuterin L. reuteri

Lactobrevin L. brevis

Lactobacillin L. brevis

Production of other antagonistic substances:

Lactic acid bacteria also inhibit the growth of harmful putrefactive microorganisms through other metabolic products such as hydrogen peroxide, carbon dioxide and diacetyl.

The metabolites of lactic acid bacteria that exert antagonistic action against putrefactive microorganisms and their mode of action are summarized in Table. 2.2:

Table 2.2 : Antagonistic activities caused by lactic acid bacteria

Metabolic product Mode of antagonistic action

1.Carbon dioxide Inhibits decarboxylation? Reduces membrane permeability?

2. Diacetyl Interacts with arginine-binding proteins.

3. Hydrogen peroxide / Lactoperoxidase Oxidizes basic proteins.

4. Lactic acid

Undissociated lactic acid penetrates the membranes, lowering the intracellular pH. It also interferes with metabolic processes such as oxidative phosphorylation.

5. Bacteriocins Affect membranes, DNA-synthesis and protein synthesis.

Synthesis of B- vitamins

Experiments on fermented milk products have revealed that lactic cultures require B- vitamins for their metabolic activities. However, some lactic cultures synthesize B-vitamins16. Friend et al. reported that the B-vitamin content of fermented milk products was a function of species as well as the strain of lactic acid

bacteria used in their manufacture. Similarly, vitamins are synthesized by the lactic cultures in the gut microflora, in symbiosis with other flora.

It has been observed that the diet of the host influences the nature and levels of beneficial intestinal microflora, such as lactobacilli. The presence of dietary fructooligosaccharides was found to enhance the healthful effects of intestinal lactic acid bacteria. These compounds, found naturally in foods such as onion, edible burdock and wheat, are effectively employed as non-nutritive sweeteners (Neosugar, Meiologo). They have the advantage of being indigestible by humans and farm animals, rendering them valuable in dietetic products. They are, however, selectively utilized by intestinal lactic acid bacteria, especially bifidobacteria, thereby enhancing the healthful effects of these beneficial intestinal flora.

Q4. A) Wrute the method of production of Sour Kraut by fermentation. What are sour kraut spoiling microorganisms?

A4. A) Sauerkraut is very healthy food. Finish researchers discovered that Sauerkraut prevents of cancer. It’s also very good for a diet. A hundred grams only have 26 calories and a portion of fat of 0,3 g. The fermentation of white kraut produces choline. This substance controls the human digestion.

List of contents:

o vitamins o minerals (iron, calcium) o trace elements o roughage o lactic acid

Production

Plantation

Important parameters: the choice of the species, the method of cultivation and the time of harvesting. For the production of sauerkraut to be cut, particularly large cabbages (5 to 12 kg) are needed, without any green leaves. After the seedlings have been planted in hot houses or under plastic material, they are planted outside as from March/April. They are planted in different portions to avoid having to harvest and process the entire quantity at the same (which would be impossible due to lacking storage capacity). Up to the harvest, i.e. between the beginning of August to the end of November, the farmers carefully check the growth of the cabbages, so that the it will conform with the quality requirements.

The harvest

The cabbage is harvested manually, cleaned carefully and loaded onto carts. The rough product is then supplied to the producers of Sauerkraut.

Preparation of cabbage

Reception and unloading

Here the cabbage is thoroughly checked. Apart from external visual checks, the internal values are also carefully inspected and registered in a protocol and the cabbage is then transported to the hall on a large conveyor belt.

Cutting

Before the cabbage is cut, the core of each plant has to be drilled out to ensure that there are no tough and unappetising slices. For this purpose, a special machine is used. Loose leaves as well as the drilled cores are collected separately and returned to the suppliers. After removing the cores, the cabbage is finely sliced in an appropriate machine. Before the sliced cabbage is stored in the fermentation silo, it is salted and sometimes a mix of spices is added.

Fermentation

Lactic acid bacteria are the primary group of organisms involved in sauerkraut fermentation. They can be divided into three groups according to their types and end products:

Leuconostoc mesenteroides an acid and gas producing coccus

Lactobacillus plantarum and bacilli that produce acid and a small amount of gas

L. Cucumeris

Lactobacillus pentoaceticus acid and gas producing bacilli(L. Brevis)

In addition to the desirable bacteria there are a range of undesirable micro-organisms present on cabbage (and other vegetable material) which can interfere with the sauerkraut process if allowed to multiply unchecked. The quality of the final product depends largely on how well the undesirable organisms are controlled during the fermentation process. Some of the typical spoilage organisms utilise the protein as an energy source, producing unpleasant odours and flavours

The fermentation process

Shredded cabbage or other suitable vegetables are placed in a jar and salt is added. Mechanical pressure is applied to the cabbage to expel the juice, which contains fermentable sugars and other nutrients suitable for microbial activity. The first micro-organisms to start acting are the gas-producing cocci (L. Mesenteroides). These microbes produce acids. When the acidity reaches 0.25 to 0.3% (calculated as lactic acid), these bacteria slow down and begin to die off, although their enzymes continue to function. The activity initiated by the L. mesenteroides is continued by the lactobacilli (L. plantarum and L. Cucumeris) until an acidity level of 1.5 to 2% is attained. The high salt concentration and low temperature inhibit these bacteria to some extent. Finally, L. pentoaceticus continues the fermentation, bringing the acidity to 2 to 2.5% thus completing the fermentation.

The end products of a normal kraut fermentation are lactic acid along with smaller amounts of acetic and propionic acids, a mixture of gases of which carbon dioxide is the principal gas, small amounts of alcohol and a mixture of aromatic esters. The acids, in combination with alcohol form esters, which contribute to the characteristic flavour of sauerkraut. The acidity helps to control the growth of spoilage and putrefactive organisms and contributes to the extended shelf life of the product. Changes in the sequence of desirable bacteria, or indeed the presence of undesirable bacteria, alter the taste and quality of the product.

Effects of temperature on sauerkraut process

The optimum temperature for sauerkraut fermentation is around 21ºC. A variation of just a few degrees from this temperature alters the activity of the microbial process and affects the quality of the final product. Therefore, temperature control is one of the most important factors in the sauerkraut process. A temperature of 18º to 22º C is most desirable for initiating fermentation since this is the optimum temperature range for the growth and metabolism of L. mesenteroides. Temperatures above 22ºC favour the growth of Lactobacillus species.

Effects of salt on the sauerkraut process

Salt plays an important role in initiating the sauerkraut process and affects the quality of the final product. The addition of too much salt may inhibit the desirable bacteria, although it may contribute to the firmness of the kraut. The principle function of salt is to withdraw juice from the cabbage (or other vegetable), thus making a more favourable environment for development of the desired bacteria.

Generally, salt is added to a final concentration of 2.0 to 2.5%. At this concentration, lactobacilli are slightly inhibited, but cocci are not affected. Unfortunately, this concentration of salt has a greater inhibitory effect against the desirable organisms than against those responsible for spoilage. The spoilage organisms can tolerate salt concentrations up to between 5 and 7%, therefore it is the acidic environment created by the lactobacilli that keep the spoilage bacteria at bay, rather than the addition of salt

In the manufacture of sauerkraut, dry salt is added at the rate if 1 to 1.5 kg per 50kg cabbage (2 to 3%). The use of salt brines is not recommended in sauerkraut making, but is common in vegetables that have a low water content. It is essential to use pure salt since salts with added alkali may neutralise the acid.

Use of starter cultures

In order to produce sauerkraut of consistent quality, starter cultures (similar to those used in the dairy industry) have been recommended. Not only do starter cultures ensure consistency between batches, they speed up the fermentation process as there is no time lag while the relevant microflora colonise the sample. Because the starter cultures used are acidic, they also inhibit the undesirable micro-organisms. It is possible to add starters traditionally used for milk fermentation, such as Streptococcus lactis, without adverse effect on final quality. Because these organisms only survive for a short time (long enough to initiate the acidification process) in the kraut medium, they do not disturb the natural

sequence of micro-organisms. On the other hand, if Leuconostoc mesenteroides is added in the early stages, it gives a good flavour to the final product, but alters the sequence of subsequent bacterial growth and results in a product that is incompletely fermented. If gas producing rods (for example L pentoaceticus) are added to the sauerkraut, this disturbs the balance between acetic and lactic acids - more acetic acid and less lactic acid are produced than normal - and the fermentation never reaches completion. If lactic acid, non-gas producing rods (L. Cucumeris) are used as a starter, again the kraut is not completely fermented and the resulting product is bitter and more susceptible to spoilage by yeasts.

It is possible to use the juice from a previous kraut fermentation as a starter culture for subsequent fermentations. The efficacy of using old juice depends largely on the types of organisms present in the juice and its acidity. If the starter juice has an acidity of 0.3% or more, it results in a poor quality kraut. This is because the cocci which would normally initiate fermentation are suppressed by the high acidity, leaving the bacilli with sole responsibility for fermentation. If the starter juice has an acidity of 0.25% or less, the kraut produced is normal, but there do not appear to be any beneficial effects of adding this juice. Often, the use of old juice produces a sauerkraut which has a softer texture than normal.

Emptying the silo

Once the fermentation is completed, the water bag is removed and the sauerkraut is lifted out of the silo by means of a crane and then filled into smaller containers for further treatment.

Treatment after fermentation

Packing

The raw or cooked sauerkraut is packed into pouches of 500 g or 750 g. Each pouch is checked individually with regard to its weight. Too light and too heavy units are eliminated automatically. The loose sauerkraut is packed in 5kg, 10 kg or 25kg buckets.

Pasteurisation

After the weight has been checked, all the pouches are pasteurised by means of continuous pasteurisation machines. As these facilities heat the goods up rapidly and chill them again quickly in a single operation, thereby preserving the precious ingredients.

Packing in containers for transport

After the pasteurisation, the pouches are checked individually for tightness and for the correctly-declared contents, after which they are packed in containers for transport.

Q4. B) Write note on vinegar production by “quick method”.

A4. B) Quick vinegar method

Because the Orleans process is slow, other methods have been adapted to try and speed up the process. The German method is one such method. It uses a generator, which is an upright tank filled with beechwood shavings and fitted with devices which allow the alcoholic solution to trickle down through the shavings in which the acetic acid bacteria are living. The tank is not allowed to fill as that would exclude oxygen which is necessary for the fermentation. Near the bottom of the generator are holes which allow air to be drawn in. the air rises through the generator and is used by the acetic acid bacteria to oxidise the alcohol. This oxidization also releases considerable amounts of heat which must be controlled to avoid causing damage to the bacteria.