Course:FNH200/Lesson 09

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Food Preservation with Biotechnology

Overview In this lesson we will consider the use of microorganisms, mainly in fermentation processes, in the production of foods in Canada and in other countries. You will learn about the wide variety of foods that are produced with the aid of microorganisms and future applications of biotechnological processes in food processing and preservation.

Objectives Upon completion of this lesson you should be able to:

  • Define the term "biotechnology"
  • Describe the beneficial role that microorganisms have in the production of fermented foods and of food ingredients or additives
  • Outline the sequence of microbiological, chemical and physical changes that are involved in the conversion of milk to cheese
  • Explain and compare the terms "biotechnology-derived foods" and "genetically modified foods", and describe the position of the Canadian government on these foods.
  • Articulate a personal set of values pertaining to use of biotechnology in foods


Required Readings Excerpts from the Health Canada and the Canadian Food Inspection Agency websites, related to "novel foods" and "genetically modified foods"

(Part one only) http://www.hc-sc.gc.ca/fn-an/gmf-agm/fs-if/index-eng.php


Microorganisms in Food Preservation

Microorganisms have been employed for centuries in food preservation. Early practitioners of food fermentations were not aware that preservation of food was aided by the actions of microscopic organisms growing in the agricultural or fisheries commodities and producing preservative agents such as acids, alcohols and substances with antimicrobial properties.

Biotechnology

According to Health Canada: http://www.hc-sc.gc.ca/fn-an/gmf-agm/fs-if/index-eng.php:

"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)"



Biotechnology is a term that began to be used in the 1980s and 90s, to describe the integrated use of biochemistry, microbiology and engineering sciences to utilize microorganisms and cultured animal and plant tissue cells and cell components in the production of desirable products. The definitions given above, from the websites of Health Canada and the Canadian Food Inspection Agency, indicate that "biotechnology-derived foods" includes food products obtained through a very broad spectrum of tools and techniques.

In the food industry the desirable products are food products, ingredients and additives including, and no way limited to:

  • Beverages such as wine, beer, and sake
  • Dairy products such as yogurt and cheeses
  • Meat products such as salami, bologna, and prosciutto
  • Many other traditional foods such as sauerkraut, soy sauce, tempe, and miso

Vitamins, enzymes, biopolymers (xanthan gum, alginates as introduced in Lesson 2), and amino acids (such as methionine, glutamic acid) are examples of food ingredients and additives produced by biotechnology. More specifically,

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 production of xanthan gum, specific isolates of the bacteria are grown in large fermenters under conditions designed to maximize production of the bacterial slime that is then harvested and purified for use as a thickening and stabilizing agent.
Flavouring ingredients for use in foods are produced by plant cell cultures. Cells of specific plants are cultured in fermentation vessels under conditions that favour production of specific flavour compounds and are then extracted from the culture after the culture has been cultivated for the appropriate period of time.
Natural bovine rennin or chymosin are enzymes used in the production of cheese is in short supply. 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.


FNH200 Lesson09 Fermentation.jpg

Fermentation

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.

When we speak of fermented foods we are speaking of 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 microbially 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 (see the above explanation of genetic engineering and compare it to the definition of fermented foods).

Preservation Principle

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.

Fermentation of foods leads to the formation of chemicals (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.


Benefits of Fermentation

Fermented foods in many cases can be more nutritious than the unfermented original materials.

  • This is particularly true of 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.


Fermented foods add variety to our food supply, which adds to our diet a group of nutritious products. Microorganisms used in the production of fermented foods increase the variety of foods in our diet. A number of fermented foods listed below may not be familiar to you as the list represents fermented foods produced throughout the world.

  • Lactic acid bacteria convert:
cucumbers to dill pickles and sour pickles
olives to green olives and ripe olives
cabbage to sauerkraut and kimchi
dough and milk to kishk
coffee cherries to coffee beans
meat to meat sausages such as salami
dairy to sour cream and yogurt
  • Lactic acid bacteria with propionic acid bacteria convert:
dairy products to Swiss, Emmenthaler, and Gruyère cheeses
  • Lactic acid bacteria with mould convert:
vegetable products to tempeh and soy sauce
dairy products to Roquefort, Camembert, Brie and Blue cheeses
  • Acetic acid bacteria convert:
grape to vinegar
  • Yeasts convert:
malt to beer, ale, and stout
fruit to wine and vermouth
wines to brandy
rice to sake
bread doughs to bread
  • Yeast with lactic acid bacteria convert:
ginger plant to ginger beer
beans to vermicelli
  • Moulds convert:
soybeans to miso and soy sauce

You will note that several foods or food ingredients, such as dill pickles, olives, sauerkraut, coffee beans, vanilla, meat sausages and dairy products, are produced by fermentation with lactic acid bacteria. Lactic acid bacteria are used alone or in combination with other microorganisms in the production of a variety of foods.

Acetic acid bacteria oxidize ethanol to acetic acid. This phenomenon forms the basis for the production of food grade acetic acid (vinegar). If you have attempted to produce your own alcoholic beverages, you may have had the unfortunate experience of having what you hoped would be a great wine or beer turned to a fruit or barley vinegar by acetic acid bacteria contaminants in your fermentation vessels.
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.
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.

Microbial Changes in Fermented Foods

Microbial changes in foods that undergo fermentation fall into certain categories as shown in the table below. Conditions in the food to be fermented are controlled to favour growth and desirable metabolic activities of the microorganisms used in the fermentation process. As you can guess, control of conditions for production of fermented foods can be a complicated operation involving many variables.

Raw Materials Agents Products
Lactose, glucose Lactic acid bacteria Lactic acid
Glucose, other fermentable carbohydrates Yeasts Ethanol
Ethanol Acetic acid bacteria Acetic acid
Lipids Microbial lipases Free fatty acids, aldehydes, ketones
Proteins Microbial proteinases Polypeptides, peptides, free amino acids, amines (cause textual and flavour changes in foods)
Cellulose Mould cellulases Oligosaccharides, glucose


Factors Affecting Fermentation in Foods

Factors that are controlled in the production of fermented foods include:

  • Acids
  • Alcohol
  • Starter cultures
  • Temperature
  • Oxygen
  • Salt


Acids

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.

Alcohol

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.

Starter Cultures

Modern food fermentation (biotechnology) employs the use of microbial cultures specifically selected and maintained for desirable trait(s): e.g. acid production; alcohol production; production of flavour compounds; production of specific enzymes; rate of growth. In current food fermentation practices, the starter cultures are grown under specific conditions and the harvested cells are added in a specific proportion to the food to be fermented. Cultures may be grown within the food processing plant or may be purchased as frozen or dehydrated cultures.

You may also have used starter cultures in your home:

  • If you have baked bread in your home, you have no doubt used dehydrated yeast as your starter culture for the bread dough. The food industry uses dehydrated starter cultures in a similar manner, but on a much larger scale.
  • If you maintain a sourdough culture in your refrigerator, you use some of the techniques employed in industry to maintain the vigor of the culture, although in industry the numbers and types of organisms in the starter cultures are constantly monitored.
  • 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.


How does a starter culture work?

Starter cultures are used in 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).

Of special concern to commercial users of starter cultures is the potential presence of microbial viruses (phage) in the food that could infect the culture and inactivate it. The fermentation industry constantly evaluates and selects starter cultures for their phage resistance and vigour in producing the desirable end products of metabolism. Likewise the purity of starter cultures is maintained through sterile handling techniques and strict attention to processing plant sanitation.

Other fermented foods, such as olives, salt stock cucumbers and sauerkraut, are produced by creation of conditions favourable to growth of desirable microorganisms which are part of the normal microbial flora of the starting plant materials (cabbage, cucumbers, olives). Environmental conditions such as salt concentration and temperature are strictly controlled to maximize growth of the desirable microorganisms while suppressing growth of undesirable microorganisms.

Fermented foods, such as yogurt, contain in excess of one billion lactic acid bacteria per gram of product. Many people shudder at the thought of consuming bacteria, but in the cases of "the good" microorganisms, no harmful effects occur to the human body. In fact there is some evidence that certain microorganisms used in food fermentation may have beneficial effects on the digestive function of the human body (Lesson 13).

Temperature

Temperature can be a very important factor in controlling the type of microorganism that grows during food fermentation. For example, temperature is a key factor in ensuring the sequential development of the desirable lactic acid-producing microflora in shredded cabbage during the fermentation of cabbage to sauerkraut. The development of a typical sauerkraut flavour requires the proper succession of lactic acid bacteria starting with Leuconostoc meserenteroides (which requires cool temperatures of about 21°C) and followed in sequence by Lactobacillus cucumeris (32°C) and Lactobacillus pentoaceticus (37°C). If you have made sauerkraut in your home, you have created conditions favourable to growth of these bacteria which are part of the normal microflora of cabbages. You will also have noted that sauerkraut has a much longer storage life than the cabbages from which it was produced but it will eventually become spoiled by acid-tolerant yeasts and moulds, particularly if good sanitary habits are not followed and storage temperature of the finished sauerkraut is too high. This is one of the reasons why sauerkraut is bottled and pasteurized to further extend its storage life.

Oxygen

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.

Salt

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.

The Technology of Fermentation

As discussed before, fermentation leads to the production of a wide variety of food products. In the remaining lesson, the Biotechnology of Cheese will be used as example to demonstrate the technology of fermentation.

Milk is the starting ingredient in the cheese making process. It often takes as much as 10 kg of milk to produce 1 kg of cheese. During cheesing making, most of the water content is removed. The resulting cheeses are therefore rich in protein, fat, calcium and phosphorus, and low in lactose content. The table below shows the proximate composition of cow's milk and Cheddar cheese, in grams per 100 grams edible portion (USDA Nutrient Database)

Milk Cheddar Cheese
Water 88.32 36.75
Fat 3.25 33.14
Protein 3.22 24.90
Lactose 5.26 0.23
Ash (minerals) 0.69 3.93


The fermentation of cheese is a multiple step process. Slight alterations (choice of starter cultures, temperatures, incubation time, salt content, etc) will lead to the production of a variety of cheeses. The fermentation of Cheddar cheese is described below to demonstrate the major principles in cheese fermentation.

Scheme of Cheese Making Process

1. Setting the Milk

Lactic acid-producing culture is added to pasteurized milk at a concentration of 1% (v/v) to ensure that the starter culture is present in much larger numbers than other microorganisms in the pasteurized milk. This is done to ensure that the starter culture becomes the dominant portion of the microbial population in the milk.

Think About: Is cheese produced from "raw milk" (referring to "unpasteurized" milk,and including heat-treated but not pasteurized milk) allowed for sale in Canada?


Colouring is also added at this point. In Canada, annatto and ß-carotene are permitted for use as colourants for Cheddar cheese (Division 8 and Table III of Division 16 in the Food and Drugs Act of Canada http://laws.justice.gc.ca./en/F-27/C.R.C.-c.870/index.html.
Once the inoculated milk becomes mildly acidic, rennet 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. Rennet is a natural mixture of rennin (an enzyme) and other materials found in the 4th stomach of the calf. Rennin, the pure enzyme also known as chymosin, can be produced through commercial preparation.

The rennet 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.

2. Curd Cutting

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.

3. Cooking

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

4. Draining Whey and Curd Matting

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.

5. Salting and Milling

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.


6. Pressing

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 you have some Cheddar cheese in your refrigerator, cut a slice and see if you can see curd junctions in the slice. Gently bend the slice as you look at it.

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.

7. Curing and Ripening

Complex changes occur within the ripening of cheese that lead to desirable flavours and textures of the cheese. After the pressing step, the cheese is placed in a cool room for 3-4 days. In order to prevent mould from growing on the surface of the cheese, the cheese is vacuum packed in flexible film or dipped in hot paraffin.

Can you think of another function of the film/coating? Hint: moisture

During and ripening takes place at 2°C and 85% RH. The ripening stage is continued for at least 60 days. However, as you will note with different kinds of Cheddar cheese, ripening may be continued for 12 months or more if peak flavour and aroma are desired.

FNH200 Lesson09 CheeseQuestions.jpg

Some Common Cheeses

Cheeses are classified as soft, semisoft, hard and very hard, process cheese, and whey cheese. Variations in the cheese making process result in different cheeses, in terms of flavour, texture, appearance, and shelf-life. In addition to the lactic acid cultures, a secondary culture may be used to develop characteristic properties of some of these cheeses. Swiss, blue-veined and Camembert processes are described below.

Optional: If you are interested in more details of cheese making, follow this link to the "Welcome to our Cheese Site" by Professor Arthur Hill at the University of Guelph.

Swiss Cheese

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.

Swiss Cheese: Note the characteristic eyes


Note that a multiple starter is 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. Also note that another bacterium, Propionibacterium shermanii, is used as part of the starter culture since this organism produces propionic acid and carbon dioxide (leading to the formation of eyes/holes in the cheese) from lactic acid. The P. shermanii also produce the amino acid proline which imparts the sweet taste characteristic of Swiss cheese. The starter cultures are very important in the production of a high quality Swiss cheese.

Within the broad classification of microorganisms as "the good, the bad, and the ugly" (as discussed in Lesson 5), the microorganisms used in the production of fermented foods are defined as "the good." These microorganisms produce beneficial effects in foods as a consequence of their growth and metabolism in the food products.

Blue-veined Cheese

The blue veined cheeses are characterized as semi-soft cheeses. There are 4 varieties of blue-veined cheeses; three that are made from cow's milk:

Blue Cheese
Blue Cheese: Note sites of inoculation
  • 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)

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.

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 lipase which breaks down the milk fat to free fatty acids, aldehydes and ketones that contribute to the sharp, distinctive flavour characteristic of the blue veined cheeses. You may remember from earlier lessons that 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. In the blue veined cheeses, however, 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.

Camembert Cheese

Camembert Cheese

You may be a regular consumer of mould-ripened cheese such as Camembert and Brie (soft-type cheeses) or, if you are not, you have undoubtedly seen these types in the cheese counters at the local delicatessen. 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. 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 leads to the formation of the creamy texture characteristic of a good quality Camembert cheese. 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 a mould flavour to the cheese; a mouldy flavour is considered a quality defect.

Genetically Modified Organisms, Novel Foods and Biotechnology-Derived Foods

Start this part of the lesson by completing the following activity:

Activity
Look at the list of ingredients on a package of Cheddar cheese
  • You will note that microbial cultures and rennet and/or pepsin and/or microbial enzymes are listed. The supply of calf rennet falls short of the demand. Some cheese processors use a mixture of rennet and hog pepsin (extracted from the stomachs of slaughtered hogs) or microbial rennets (proteinases with rennet-like properties produced by selected microorganisms). The substitute rennets, however, do not produce Cheddar cheese of as high quality as that produced with calf rennet.
  • A good deal of research worldwide is directed at finding enzymes which could replace calf rennet. This includes production of calf chymosin by genetic engineering of microorganisms.
  • Check out the required additional readings - excerpts from Justice Canada website: Food and Drug Regulations http://laws-lois.justice.gc.ca/eng/regulations/C.R.C.%2C_c._870 Part B Foods, Division 8 Dairy Products, B.08.030 to B.08.033 on cheese and Division 16, Food Additives (Table V Food Additives that may be used as Food Enzymes).
What "shall" cheese consist of? what "may" it contain?
What enzymes are permitted as food additives in cheese?


What are GMOs?

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. Through this technology, a foreign piece of DNA (deoxyribonucleic acid) is inserted into the genetic material of the host organisms.

Genetic modification may enable the host organism to

  • yield a desired product (e.g. bovine chymosin produced by genetically modified bacteria), or
  • 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).


Genetic Engineering and Cheese

Recombinant chymosin
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.

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

Genetically improved starter cultures produced through genetic engineering must go through thorough testing and evaluation to demonstrate their safety prior to approval for their use in foods (they are classified as food additives).

Activity

There is a great deal of public concern and controversy about genetically modified foods and genetically modified organisms (these have been dubbed as Frankenfoods by opponents to the technology and the concept). To make an informed personal decision regarding whether or not you would accept (some or all) GM foods, please visit the following websites:

Canadian Food Inspection Agency (biotechnology page) http://www.tpsgc-pwgsc.gc.ca/ongc-cgsb/programme-program/normes-standards/internet/032-0315/index-eng.html#a6
"Novel Food and Ingredients" page at the Health Canada website: http://www.hc-sc.gc.ca/fn-an/gmf-agm/fs-if/safety-assessment-evalulation-salubrite-eng.php. Guidelines for the Safety Assessment of Novel Foods"


Packaging Requirements for Fermented Foods

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.

Think about the variety of fermented products available in the market.
What other forms of preservation methods are being used along with the fermented product?
Can you list and describe some examples of packaging materials used for fermented products?


Authorship:

FNH 200 Course content on this wiki page and associated lesson pages was originally authored by Drs. Brent Skura, Andrea Liceaga, and Eunice Li-Chan. Ongoing edits and updates are contributed by past and current instructors including Drs. Andrea Liceaga, Azita Madadi-Noei, Nooshin Alizadeh-Pasdar, and Judy Chan.

Some rights reserved
Permission is granted to copy, distribute and/or modify this document according to the terms in Creative Commons License, Attribution-NonCommercial-ShareAlike 3.0. The full text of this license may be found here: CC by-nc-sa 3.0
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