BIOTECHNOLOGY AND FOOD
Biotechnology is very important in a number of ways to the food both humans and animals consume in the following ways:
LACTIC ACID FERMENTATION
Anaerobic bacteria that can ferment carbohydrates to lactic acid are widely used in the food industry. They lack the enzymes of the citric acid cycle and the respiratory chain, and so ferment carbohydrates into lactic acid - this process is called fermentation.
In making yoghurt
Yoghurt is basically milk (cow, goat or ewe) that is fermented by bacteria. Although it originated in Western Asia and Eastern Europe, it is now eaten all over the world. To make yoghurt, a starter culture of the lactic acid bacteria Lactobacillus bulgaricus and Streptococcus thermophilus is added to whole or skimmed milk. The bacteria multiply and ferment lactose, the disaccharide sugar in the milk, producing lactic acid. As you will know if you have ever added lemon juice to milk, acid causes the milk to curdle. Separation of the acidified milk into solid curds gives yoghurt its taste and texture.Yoghurts can be pasteurised to destroy the fermentation bacteria but if this is not done, the result is 'live' yoghurt. Pasteurisation of milk involves heating it to 60°C so that most of the bacteria in it are killed, but the taste is not unduly affected. Sterilised milk has been heated to 100 °C to kill all the bacteria, which is why it keeps much longer. However, at this temperature, some of the proteins in it are denatured and this changes the taste of the milk - many people dislike the new taste and sterilised milk has never been popular for drinking.
Many supermarkets now sell yoghurts they describe as 'bio-yoghurts'. These have been produced in the usual way, left unpasteurised, and then extra bacteria added. Bio-yoghurts usually contain live Lactobacillus acidophilus and Bifidobacterium bifidum.
Various health claims are made for these yoghurts, but whether they actually do keep you healthy or not is still an open question.
In cheese-making
This is one of the oldest biotechnologies in the world. Cheese-making dates back at least 5 000 years and the basic method used has changed very little over that time. Three main ingredients are needed: • milk, • a source of the protein-degrading enzyme chymosin, which causes the milk proteins to clump together - traditionally, this was added in the form of calf rennet (chymosin can also be called rennin), but non-animal sources of this enzyme are now available and can be used in the manufacture of cheese suitable for vegetarians; • a starter culture of lactic acid bacteria.In many ways, cheese-making is similar to yoghurt-making. The lactic acid starter culture is added to the milk to convert the lactose to lactic acid, which helps to preserve the cheese. Chymosin causes the milk to set, producing hard cheese. Once bacterial fermentation stops, the maturation of the cheese then begins. As the bacteria die, they are digested by their own enzymes - a process called autolysis. This process produces more enzymes including peptidases, that produce the strong flavours that we associate with a 'good' cheese. Some strains of bacteria produce carbon dioxide during maturation - this makes the holes in cheeses such as Gouda and Emmental.
A fungus of the Penicillin genus (Penicillium roquefortii) is used to inoculate fermented curd to produce blue cheeses such as Stilton and Danish Blue. This fungus grows through the cheese during the maturation process, producing the characteristic blue-green veins.
FERMENTATION USING YEAST
Yeast is an essential microorganism in the production of bread, wine and beer. Under the right conditions, yeast will ferment carbohydrates to release carbon dioxide and alcohol in a series of chemical reactions.
Bread-making
Bread is basically a mixture of flour, water and a little fat that is baked. Some breads are still produced like this (pitta bread, for example) but yeast fermentation is usually used to cause the dough to rise, so that a lighter, less dense loaf can be made. As the flour, water and yeast are mixed, enzymes called amylases that are present in the flour break down the starch into the disaccharide maltose.Other enzymes break this down into glucose, which is then fermented by the yeast to carbon dioxide and alcohol. In bread, the alcohol evaporates during baking, but the carbon dioxide bubbles become trapped in the sticky dough, causing the baked loaf to have lots of tiny pockets.
Wine and beer
In wine-making, the fermentation of grape juice is a complex process that involves yeasts, bacteria and filamentous fungi - but the yeasts have the starring role. During fermentation, yeasts use the sugars and other components of grape juice and convert them into ethanol, carbon dioxide and other end-products that contribute to the chemical composition and taste of wine.Fermentation stops when the yeast becomes poisoned by its waste - the alcohol - which is why drinks made by fermentation only are no stronger than about 14 per cent alcohol by volume. Spirits such as whisky and gin, which have a much higher alcohol content, are distilled from a fermented mixture.
Most wine makers are more interested in the alcoholic by-product of yeast fermentation, but a brewer producing beer needs both the alcohol and the carbon dioxide made by the yeast. Carbon dioxide gives the beer its characteristic fizziness.
The brewing industry uses barley as the source of the food that the yeast ferments to make the alcohol in beer, However, barley stores food in the form of starch - which yeast cannot use directly. In order to solve this, the brewer allows the barley grains (seeds) to germinate. During germination, enzymes in the barley convert the starch into maltose sugar, which the yeast can ferment. This process is called malting.
Beer production is made as efficient as possible by providing the best possible conditions for yeast to grow and ferment. This means that the temperature, oxygen supply and amount of glucose must be carefully controlled, and unwanted microorganisms must be kept out. The easiest way to make sure that this happens throughout the fermentation is to set up all the conditions at the start, together with the raw materials, and then to leave the whole system closed and untouched till the fermentation is complete. This has the disadvantage that production is only possible in batches rather than a continuous process.
I'll quickly discuss on what a metabolite is, its types and roles in culturing.
A metabolite is a general term for a compound made by an organism's metabolism. Primary metabolites are made during an organism's main growth period while the Secondary metabolites are made after an organism's main growth period.
This is significant when culturing microbes for their products. If the desired product is a primary metabolite (for example, transgenic bacteria making insulin) then a continuous culture is best. This is where the microbes are kept in their main growth phase by constantly adding nutrients and drawing off products. If the desired product is a secondary metabolite (for example, many antibiotics) then it's usually best to have a batch culture, where the microbes are allowed to pass through their main growth phase. The whole culture is then extracted and the product purified before repeating the process again.
USING OTHER MICROORGANISMS AS A FOOD SOURCE
Biotechnology has been used in the past few years to make foods that are as rich in protein as meat, but that are much cheaper. Pruteen™ is one example, mycoprotein (for example, Quorn™) is another. Both can be eaten by vegetarians. Pruteen™ is a microbial protein produced by bacteria that can break down methanol.
Pruteen™ is the trade name for microbial protein produced by growing Methylophilus methylotrophus bacteria on methanol, which is derived from methane or natural gas. Since the product is a low-value commodity, large quantities have to be manufactured to make profits. Usually very large (about 3000 m3) airlift fermenters are used with a diameter of 7m and a height of 60m. These can be run for 100 days at a time
Mycoprotein has the following nutritional advantage over meat:
• it has no animal fat, little overall fat and no cholesterol; • it has a high protein content (as high as that of skimmed milk); • it is high in fibre; • it contains useful amounts of trace elements and B vitamins.Mycoprotein is produced by the fungus Fusarium graminearum, which is related to mushrooms and truffles. Mycoprotein is made by a filamentous fungus-one that produces lots of thin strands called hyphae. This fungus can use the carbohydrate present in cheap, readily available carbohydrates like the wheat in the UK, potato in Ireland, and cassava, rice or sugar in tropical countries, for example. Mycoprotein contains 45 per cent protein and 13 per cent fat, a composition similar to that of grilled beef. It is also high in fibre and has a complete amino acid content.
The industrial fermenters currently being used to manufacture mycoprotein are 40 metres high. They run continuously for 6 weeks, after which there is a 2-week period for cleaning and preparing the fermenter for the next run. After production, the mycoprotein looks like pastry, but it is then mixed with binding agents and colours to form a product that looks like different kinds of meat.
OTHER FERMENTED FOOD PRODUCTS
Sauerkraut
Sauerkraut is a German delicacy that is now popular in other parts of the world, particularly the USA. It is made by fermenting cabbage that has been salted.
Soya products
Biotechnology is also used to process soya beans to give the following food products:• Textured vegetable protein (TVP):-This is a type of soya flour that has been freed of fat and moisture to produce a substance resembling a meat but with a soft, light and porous surface. It is processed by shedding the soya's skin and extracting its oil before being later pulverized into soft powder. The soft powder is afterwards emulsified with water and the remnant is textured after the soluble carbohydrate must have been extracted through a process known as spinning.
• Tofu:- This is a type of soya bean that's made from solidified soya milk. The process is by first soaking the soya beans, then compressing them to release the milk. Afterwards, either calcium chloride or its sulphate is dropped into the milk to serve as a thickening agent. The ensuing soya curd is then squeezed to give tofu. Tofu may be fried, sauteed, and added to salads and casseroles. Tofu is very rich in protein, iron, calcium and vitamins.
• Tempeh: - This is a type of soya bean paste that has been made to ferment by injecting an already cooked soya beans with the fungus Rhizopus oligosporous. Tempeh has a very nice and unique flavour and can be used in place of meat.
• Miso: - This is a fermented ingredient gotten from soya beans, grains, salt and water. The miso is produced by subjecting polished rice through intense heat and then adding the fungus Aspergillus oryzae. By leaving the steamed rice with the fungus to ferment will produce a new product called koji, not konji oh......lol .Miso has varieties of colour, aroma and texture. It is majorly used as flavour in soups and casseroles.
• Soy sauce:- A true soy sauce is also called shoyu. It is produced by fermenting soy beans added with roasted wheat, salt and then water.
It can take up to a year before shoyu can be fully fermented. So, what this translates to is that,larger percentage of the soy sauce sold in supermarkets is not real soy sauce but is gotten from the chemical hydrolysis of fatty-shedded soya flour and corn syrup without going through any fermentation process whatsoever.
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