Food Preservation with Biotechnology

Question 1

What is biotechnology?

Answer 1

“Biotechnology is an umbrella term that covers a broad spectrum of tools and techniques, ranging from fermentation (bread, wine, cheese) to plant and animal breeding, cell and tissue culture, antibiotic production and genetic engineering.

The traits of every organism are encoded in its genetic material (DNA or RNA) which is organized into individual units called genes. Genetic modification is achieved by changing the code or organization of the genetic material of an organism.

This includes, but is not limited to, moving a gene or genes from one organism to another (this is commonly called genetic engineering)”

Question 2

Is food fermentation the same as biotechnology?

Answer 2

Although the word biotechnology is a new term, biotechnology has in fact been practiced in the agriculture/food industries for thousands of years: Yogurt production in India, bread, and beer in Egypt. Thus, in the current vernacular, food fermentation would be referred to as food biotechnology- a new name for an old process.

Question 3

What are the functions of adding salt to cheese?

Answer 3

• to draw the whey out of the curd;
• to flavour the final cheese;
• to inhibit growth of proteolytic and lipolytic spoilage-causing microorganisms that may be associated with the newly formed milled curd;
• to provide conditions favourable to the proteolytic action of the rennet and of the proteinases of the lactic acid starter during ripening of the cheese.

Question 4

Describe how microorganisms may be used in biotechnology.

Answer 4

• Microorganisms are used for the production of fermented food products
• Microorganisms are cultivated as sources of enzymes and flavouring ingredients used in food systems.

Question 5

Describe the production of xanthan gum.

Answer 5

Xanthan gum, a stabilizer used in a variety of food systems, is extracted from bacteria (Xanthamonas campestris) that in nature cause slime rot of cabbages.

During the production of xanthan gum, specific isolates of the bacteria are grown in large fermenters under conditions designed to maximize production of the bacterial slime.

Then the cells are harvested and gum is purified for use as a thickening and stabilizing agent

Question 6

Bovine rennin or chymosin used in the production of cheese is in short supply. Describe how cheese production gets around this issue.

Answer 6

Researchers in several countries have shown that it is possible to transfer the gene which codes for rennin in the dairy cow to a bacterial cell.

The implanted gene is replicated with the bacterial genetic material each time the bacterial cells divide.

The implanted rennin gene permits the bacteria to produce bovine rennin.

Rennin produced by means of bacterial fermentation is used widely in cheese production in Canada, the United States, and other countries.

Question 7

Is food fermentation the same as biotechnology?

Answer 7

Although the word biotechnology is a new term, biotechnology has in fact been practiced in the agriculture/food industries for thousands of years: Yogurt production in India, bread, and beer in Egypt.

Thus, in the current vernacular, food fermentation would be referred to as food biotechnology- a new name for an old process.

Question 8

What is fermentation?

Answer 8

Fermentation, in the strictest sense, means “the breakdown of carbohydrates under anaerobic (absence of oxygen) conditions.”

However, in a broader sense, fermentation is often used to describe the anaerobic and aerobic breakdown of carbohydrates and carbohydrate-like materials by microorganisms.

In fermented foods, proteins and lipids may be hydrolyzed and metabolized by microorganisms involved in the fermentation process.

Question 9

Are fermented foods genetically engineered?

Answer 9

When we speak of fermented foods, we are referring to the foods which have been produced with the aid of microorganisms.

The changes that occur, may not be solely to the carbohydrate component of the foods, but will also likely involve microbial induced changes to the proteins and lipids in the foods to create the desired colours, flavours and textures characteristic of fermented foods.

Most fermented foods are not genetically engineered

Question 10

What is microbial antagonism?

Answer 10

The basis of preservation of foods by fermentation is the encouragement of growth and metabolism of alcohol and acid-producing microorganisms to suppress the growth and metabolic activities of proteolytic and lipolytic, spoilage-causing microorganisms.

This condition forms the basis of microbial antagonism that is the principle of preservation of foods by microorganisms specifically cultured for the production of fermented foods.

Microorganisms, when cultured in foods, produce a variety of end products including acids and alcohols which act as antimicrobial agents.

Question 11

What forms during fermentation?

Answer 11

Fermentation of foods leads to the formation of chemicals ( e.g. acetic acid, citric acid, lactic acid) that are commonly added to foods as preservatives. In this case, preservatives are formed in situ.

In addition, other microorganisms, especially the bacteria that produce lactic acid, also produce as yet unidentified substances that have antimicrobial activity, particularly toward spoilage- and disease-causing microorganisms.

Foods in which acids are produced, especially when the pH is lowered to 4.6 or lower, will not support the growth of pathogenic bacteria such as Clostridium botulinum.

Products such as sauerkraut, wine, yogurt and cheese are more stable forms of the low acid food materials that were used at the start of the fermentation process.

Question 12

Why are fermented foods often more nutritious than their non-fermented counterparts?

Answer 12

• This is particularly true for mould fermented foods where the moulds synthesize B-vitamins. Food products such as miso, and tempeh have higher levels of B-vitamins than the soybeans that are used to produce those fermented foods.
• Microorganisms also liberate nutrients from parts of plants that are normally undigestible in the human gastrointestinal tract. The availability of minerals and vitamins that are usually biologically unavailable is thereby increased.
• Fermentation can enhance the nutritional value of foods by microbial hydrolysis of cellulosic materials that are undigestible in the human digestive tract. This renders the fermented foods more digestible than their unfermented counterparts.

Question 13

What microorganism ferments the following foods (and what is produced)?

Cucumbers

Olives

Cabbage

milk

Coffee cherries

Vanilla beans

Meat

Dairy

Answer 13

Lactic acid bacteria

Dill pickles, sour pickles
Green olives, ripe olives
Sauerkraut & Kimchi
Kishk
Coffee beans
Vanilla
Meat sausages (salami)
Sour cream, yogurt

Question 14

What does acetic acid bacteria do?

Answer 14

Acetic acid bacteria oxidize ethanol to acetic acid.

This phenomenon forms the basis for the production of food grade acetic acid (vinegar).

Question 15

What does Lactic acid bacteria with propionic acid bacteria ferment?

Answer 15

Dairy products to produce :

Swiss

Emmenthaler

Gruyère cheeses

Question 16

What does Lactic acid bacteria with mould ferment?

Answer 16

Vegetable products and dairy products into

Tempeh, soy sauce
Roquefort, Camembert,
Brie, Blue cheeses

Question 17

What does acetic acid bacteria ferment?

Answer 17

Grapes to produce vinegar

Question 18

What bacteria ferments the following foods (and what food do they produce)?

Malt
Fruit
Wines
Rice
Bread dough

Answer 18

Yeasts

Beer, ale, stout
Wine, vermouth
Brandy
Saké
bread

Question 19

What does Yeast with lactic acid bacteria ferment?

Answer 19

Ginger plants, and beans to produce ginger beer and vermicelli

Question 20

What does mould ferment?

Answer 20

Soy beans to produce soy sauce and miso

Question 21

What do yeasts do?

Answer 21

Yeasts are used widely in the production of alcoholic beverages and breads.

Yeasts with lactic acid bacteria are used in the production of sourdough breads and pancakes and in the conversion of beans to vermicelli.

Question 22

What does mould do?

Answer 22

Moulds are used in the production of many foods, particularly in Asia, as well as in the production of well known cheeses such as Roquefort, Brie and Camembert.

Question 23

What are factors controlled in the production of fermented foods?

Answer 23

Starter cultures, Formation of Metabolites ( e.g Acids, Alcohol), Temperature, Oxygen and Salt.

Question 24

Give examples of using starter cultures at home.

Answer 24

• If you have baked bread in your home, you may have used dehydrated yeast as your starter culture for the bread dough.
• If you maintain a sourdough culture in your refrigerator, you use some of the techniques employed in industry to maintain the vigour of the culture.
• Similarly, if you have made yogurt in your home, you have probably used part of a previous batch of yogurt or a commercially produced yogurt as the source of the starter culture.

Question 25

Describe the formation of metabolites in fermentation.

What are the most common metabolites?

Answer 25

Metabolites are products resulted from metabolism by the organism.

In fermentation, the desired microorganisms or more specifically the starter culture is grown to produce the desired metabolites.

These compounds vary depending on the type and condition of growth of the microorganisms.

The most common metabolites are acids and alcohols.

Question 26

Discuss acids in fermentation.

Answer 26

Foods can be preserved by the addition of acids to lower the pH or by the encouragement of growth of acid-producing microorganisms used in food fermentations.

Milk and meat are treated in such a manner that the lactic acid-producing bacteria, added as a starter culture, will grow rapidly and produce lactic acid in sufficient quantities to suppress growth and metabolism of spoilage and disease-causing microorganisms.

Cheese, yogurt, and fermented sausages must be stored under refrigeration with or without vacuum packaging to delay growth of the acid-tolerant psychrotrophic yeasts and moulds.

Question 27

Discuss alcohol in fermentation.

Answer 27

Alcohol, like acid, in sufficient concentrations functions as a preservative.

Alcohol in wines and beer is not of sufficient concentration to inhibit growth of ethanol-oxidizing bacteria.

Wines and beer must be further processed by pasteurization or filtration through membranes with pore diameters smaller than the spoilage-causing microorganisms.

Fortified wines with alcohol contents above 20% do not require further preservation treatments.

Question 28

Discuss temperature in fermentation.

Answer 28

Temperature can be a very important factor in controlling the type of microorganism that grows during food fermentation.

Question 29

Discuss oxygen in fermentation.

Answer 29

Oxygen may be desirable or undesirable in fermentation processes.

Microorganisms used in fermentation processes have different oxygen requirements for growth and fermentation activity.

An example is baker’s yeast (Saccharomyces cerevisae).

This yeast will grow better under aerobic conditions; however, the yeast ferments sugars more rapidly under anaerobic conditions.

Therefore, oxygen requirement conditions may differ and may change during the different steps of the fermentation process.

Question 30

Discuss salt in fermentation.

Answer 30

Adding salt to cabbage, olives and some meats favours the growth of lactic acid-producing bacteria while inhibiting the growth of normal spoilage- and disease-causing microorganisms.

Salt also tends to draw moisture and the water-soluble nutrients from tissues making them available for use by the fermentative microorganisms.

This important function is one of the purposes of using salt in sauerkraut, olive and pickle production.

Salt also acts as a means of controlling the growth of undesirable microorganisms that may not be inhibited by the acid produced during the fermentation process.

The acid and salt together produce a food system more inhibitory to disease- and spoilage-causing microorganisms than the salt or acid alone at the same concentrations.

Question 31

How does a starter culture work?

Answer 31

Starter cultures are used in the production of fermented dairy products, meats, wines, beer and other alcoholic beverages.

The starter culture, upon addition to the food to be fermented, begins to grow rapidly under the favorable conditions provided by the food processor and to produce desirable products of metabolism (acid, alcohol, flavour compounds, enzymes).

Question 32

In cheese production, what happens once the inoculated milk becomes mildly acidic?

Answer 32

Rennet or enzyme is added.

The combination of acid and rennet causes the caseins to coagulate and form a gel very much like that found in a carton of yogurt.

The commercial rennin preparation is known as “rennet”, which is obtained from the 4th stomach of the calf and contains rennin and other small amounts of other materials.

Rennin (also called chymosin) is a pure enzyme.

Question 33

What does rennet do?

Answer 33

The enzyme hydrolyzes a portion of the k-casein from the casein micelle, changing the micelles from a calcium-stable to a calcium-sensitive state that leads to the formation of the coagulum with the aid of the lactic acid produced by the starter culture.

The whey is trapped within the three-dimensional network created by the aggregating casein micelles and forming a gel.

Question 34

What is curd cutting in cheese production?

Answer 34

The curd is cut into cubes to promote efficient removal of whey from the curd.

During this phase, the lactic acid culture continues to produce lactic acid which also aids in expression of the whey from the casein curd by causing the aggregated micelles to aggregate even further.

Question 35

Why is cheese cooked during production?

Answer 35

The cut curds are cooked at 38°C to accelerate lactic acid production and further expulsion of whey from the curd.

Question 36

Discuss draining whey and curd matting in cheese production.

Answer 36

The curd cubes settle and the whey is drained from the cheese vat.

Matting of the curd leads to fusion of the curd pieces to form a rubbery slab.

This fusion is promoted by attractive interactions between the casein micelles along the curd edges.

During matting and Cheddaring, the lactic acid bacteria continue to produce lactic acid which aids in curd fusion and shrinkage, leading to further expulsion of the whey.

Cheddaring involves cutting the matted curd into blocks, turning the blocks every 15 minutes, and piling the blocks on one another.

This process allows whey to be further squeezed from the curd.

Question 37

What is the purpose of salting and milling during cheese production.

Answer 37

The matted, Cheddar curd is cut (milled) and salted. The functions of the salt are:

• to draw the whey out of the curd;
• to flavour the final cheese;
• to inhibit growth of proteolytic and lipolytic spoilage-causing microorganisms that may be associated with the newly formed milled curd;
• to provide conditions favourable to the proteolytic action of the rennet and of the proteinases of the lactic acid starter during ripening of the cheese.

Question 38

What is the purpose of ‘pressing’ during cheese production.

Answer 38

The curd is pressed and hooped before curing.

During curing, the curds knit together such that the curd junctions cannot be seen in a good quality Cheddar cheese.

If the curd has not completely knit together, the cheese will fracture along the junction lines.

Cheese in which the junctions are clearly visible tends to have a crumbly rather than a smooth texture.

During ripening, proteinases of the lactic acid bacteria and the rennet continue to hydrolyze the casein to produce peptides and free amino acids that contribute to the typical Cheddar cheese flavour.

Question 39

What is the secondation bacterial culture in the production of swiss cheese?

What is the starter bacteria?

Answer 39

The production of Swiss cheese (characterized as a hard-type cheese) begins much like that of cheddar cheese except that an extra (“secondary”) bacterial culture, Propionibacterium shermanii, is added to the milk along with the lactic acid starter bacteria.

Question 40

Why is Streptococcus thermophilus used during Swiss cheese production?

Answer 40

Note that multiple starters are used for production of Swiss cheese and that one of the starters, Streptococcus thermophilus, is heat-tolerant so that acid can still be produced at the higher cooking temperatures employed during production of Swiss cheese.

Question 41

Why is Propionibacterium shermanii used in Swiss cheese production?

Answer 41

Also note that another bacterium, Propionibacterium shermanii, is used as part of the starter culture since this organism produces propionic acid and carbon dioxide from lactic acid.

The P. shermanii also produce the amino acid proline which imparts the sweet taste characteristic of Swiss cheese.

Question 42

What creates the characteristic flavour of Swiss cheese, and what forms the holes?

Answer 42

The propionic acid contributes to the characteristic flavour of Swiss cheese while the carbon dioxide forms the holes (eyes) in the cheese during aging.

Question 43

What are four varieties of blue veined cheese?

Answer 43

• Blue cheese (Denmark, U.S.)
• Stilton (England)
• Gorgonzola (Italy)
• And one (perhaps the most famous) made from ewes’ (sheep’s) milk: Roquefort (Roquefort region of France)

Question 44

How are blue veined cheeses produced?

Answer 44

The production procedure for the blue veined cheeses is similar to that of Cheddar cheese except that the curd is inoculated with a mould, Penicillium roquefortii, which grows within the hooped curd producing the characteristic flavour and colour of the blue veined cheeses.

After it is hooped and pressed, the cheese curd is pierced in order to provide channels for the oxygen, required for mould growth, to enter the cheese.

Question 45

What creates the blue colour in blue veined cheese?

Answer 45

The blue colour is due to the mould spores that are formed during growth of the mould along the lines where the cheese curd was pierced.

Penicillium roquefortii is an active producer of the enzyme lipase which breaks down the milk fat into free fatty acids, aldehydes and ketones that contribute to the sharp, distinctive flavour characteristic of the blue veined cheeses.

Question 46

In most food preservation situations, great efforts are made to impede the action of lipolytic enzymes since lipolysis is generally considered to be a sign of spoilage.

Why then, is lipase necessary for blue cheese production?

Answer 46

In the blue veined cheeses, lipolysis of the milk fat is a necessary part of proper flavour development.

Part of the flavour of the blue cheeses is a musty, somewhat mouldy flavour that is contributed by the mould mycelia.

Question 47

Describe production of Camambert cheese.

Answer 47

The curd is produced through the use of a lactic fermentation much like that used for Cheddar cheese.

In this case the surface of the pressed cheese curd is also inoculated with spores of Penicillium camembertii (or Penicillium candidum).

Vigorous growth of the mould leads to the formation of a layer of mycelia that form the white, velvet-like coating on the outer layer of the cheese.

The mould is highly proteolytic and the mould proteinases diffuse into the cheese curd, hydrolyzing the casein into long-chain peptides which do not contribute much flavour to the cheese.

Question 48

What creates the creamy texture characteristic of a good quality Camambert cheese?

Answer 48

The hydrolysis of the casein

If the Penicillium culture is too proteolytic or if curing takes place too long, bitter tasting short-chain peptides, free amino acids and ammonia are formed.

A good quality Camembert cheese has a mild flavour, is not bitter, and has a characteristic creamy texture.

With Camembert cheese, the mould should not contribute to a mouldy flavour to the cheese; a mouldy flavour is considered a quality defect.

Question 49

Why has the traditional mould used for Camambert cheese been replaced in Normandy, France?

Answer 49

For the past few years in Normandy, France, the mould Penicillium candidum has been commonly used instead of P. camembertii.

The reason for replacing the ‘traditional’ mould was that P. camembertii was sometimes responsible for causing ‘blue moisture’ on the cheese.

Question 50

What creates the white surface of Camambert cheese?

Answer 50

The cheese surface is inoculated with mould spores.

A layer of mycelia forms the white, velvet-like coating on the surface of the cheese

Question 51

What are GMOs?

Answer 51

Genetically Modified Organisms (“GMOs”) are plants, animals and microorganisms in which there is a change to the heritable trait(s) of the organism by intentional manipulation.

This intentional manipulation includes but is not limited to the use of modern gene technologies such as recombinant nucleic acid technology.

Genetically engineered organisms are more specific and through this technology, a foreign piece of DNA (deoxyribonucleic acid) is inserted into the genetic material of the host organisms.

Question 52

What may genetic modification allow the host organism to do?

Answer 52

• yield a desired product (e.g. bovine chymosin produced by genetically modified bacteria)
• possess a desired characteristic (e.g. tolerance to a specific herbicide in genetically modified canola plants, insect resistance in corn genetically modified to produce the insect toxin produced by Bacillus thuringensis, Bt; canola plants genetically modified to produce oil with specific compositional characteristics)

Question 53

What is recombinant chymosin?

Answer 53

• Recent developments have enabled transfer of the gene from calves that encodes for the enzyme chymosin to specific microorganisms selected for enzyme production.
• The microorganisms are cultured in large fermenters and produce the chymosin which is then isolated, purified and sold to the dairy industry for cheese making.
• Microbially produced bovine chymosin is an approved food additive in Canada.
• Chymosin is the principle milk-clotting enzyme in bovine rennet extracts that have traditionally been used in cheese making.

Question 54

Research is also being conducted to improve fermentative capabilities of lactic acid bacteria and other bacteria and moulds used in cheese making.

What does this research involve?

Answer 54

Some of that research involved genetic engineering where genes encoding for increased resistance to bacterial viruses (bacteriophage, a potentially serious problem in cheese making which can cause starter culture failure), improved enzymatic activity (lactose utilization; production of desirable proteinases involved in cheese ripening) are transferred into bacteria used as starter cultures.

Question 55

Discuss packaging considerations for fermented foods.

Answer 55

In order to extend their shelf life, fermented foods require “additional” forms of preservation such as pasteurization and refrigeration.

Packaging also plays an important role as it should protect the food from re-contamination, oxidative reactions, etc.