22.4 Microorganisms and biotechnology

Earliest use recorded was around 6000 BC where Sumerians and Babylonians were using yeast to make beer. By 4000 BC the Egyptians were using yeast to make their bread rise.

Defining Biotechnology

Biotechnology - involves applying biological organisms or enzymes to the synthesis, breakdown, or transformation of materials in the service of people.

eg - production of cheese, yoghurt, wine, bread, beer, DNA manipulation to produce genetically engineered microorganisms synthesising drugs like insulin and antibiotics.

Bioremediation - use of biological systems to remove soil and water pollution.

Most commonly used organisms are fungi, especially yeasts and bacteria as they are easier to genetically manipulate.

Use of microorganisms

Most biotech involves using biological catalysts in a manufacturing process and the most stable, convenient and effective form of enzyme if often the whole microorganism.

They are ideal as

  • There are no welfare issues to consider - all needed is optimum conditions

  • There is a large range or microorganisms capable to carrying out different syntheses or degradations.

  • Genetic engineering allows to to artificially manipulate them to carry out synthesis’ reactions - eg human insulin

  • They have a short life cycle and rapid growth rate - grown in short periods of time.

  • Nutrients required to grow them are simple and relatively cheap, can be modified by genetic manipulation to that they utilises materials that would be water, making cheaper.

  • Conditions are relatively low temperature, oxygen, food and removal of waste gas. They provide their own catalysts in enzymes, therefore relatively cheap.

Indirect food production

Microorganisms have an indirect effect, it is their actions on other food that is important.

Few disadvantages for using them in the production of human foods.

  • if conditions are not ideal, they do not grow and work properly, could cause the food to go off and cause disease so the process have to be sterile.

  • Some people have ethical issues with the use of GM organisms.

Example of microorganisms involved in commercial processes.

Baking

-Yeast mixed with sugar and water to respire aerobically. CO2 produced is what makes the bread rise.

  • active yeast mixture is added to flour and other ingredients, mixed and left in a warm environment to rise.

  • dough is knock back (excess air is removed), kneaded, shaped and left to rise again.

  • cooked in a hot oven - the CO2 bubbles expand, so the bread rises more.

    Yeast cells are killed during cooking.

Brewing

-Yeast respires anaerobically to produce ethanol. Traditional yeasts ferment at 20-28 ‘c. GM years ferment at lower and therefore cheaper, temperature, and clump together (flocculate) and sink at the end of the process leaving the beer very clear.

  • Malting - barley germinates producing enzymes that break down starch molecules down to sugars which yeast can use. Seeds then killed by slow heating but enzyme activity retained to produce malt.

  • Mashing - the malt is mixed with hot water (55’c - 65’c) and enzymes break down starches to produce wort. Hops are added for flavour and antiseptic qualities. The wort is sterilise and cooled.

  • Fermentation - wort is inoculated with yeast. Temperature maintained for optimum anaerobic respiration (fermentation). Eventually yeast is inhibited by falling pH, build up of ethanol and lack of oxygen.

  • Maturation - the beer is conditioned for 4-29 days at a temperature of 2-6 ‘c in tanks

  • Finishing - the beer is filtered, pasteurised, and then bottled or canned with the addition of carbon dioxide.

  • The alcohol content varies between 4% - 9%.

Cheese-making

-Bacteria feed on lactose in milk, changing the texture and taste and inhibiting the growth of bacteria which makes the milk go off.

  • the milk is pasteurised (heated to 95’c for 20 seconds to kill off most natural bacteria) and homogenised (the fat droplets evenly distributed through the milk)

  • It is mixed with bacterial cultures and sometimes chymosin enzymes and kept until the milk separates into solid curds and liquid whey.

  • For cottage cheese, the curds are separated from the whey, packaged and sold.

  • For most cheese, the curds are cut and cooked in whey then strained through draining moulds or cheesecloths. They whey is used for animal feeds.

  • The curds are put into steel or wooden drums and may be pressed. They are left to dry, mature and ripen before eating as the bacteria continue to act for anything from a few weeks to several years.

Yoghurt-making

-Bacteria often Lactobacillus bulgaricus that forms ethanal and streptococcus thermophilus (forms lactic acid) Both are extracellular polymers that give yoghurt that smooth thick texture.

  • Skimmed milk powder is added to milk and the mixture is pasteurised, homogenised and cooled to about 47’c.

  • The milk is mixed with 1:1 ratio of Lactobacillus bulgaricus and streptococcus thermophilus and incubated at around 45’c for 4-5 hours.

  • At the end of the fermentation, the yoghurt may be put into cartons at a temperature of around 10’c as plain yoghurt or mixed with previously sterilised fruit.

  • Thick-set yoghurts are mixed and ferment in the pot.

  • Yoghurt has a shelf life of about 19 days if stored at 2-3 ‘c

Direct food production

Best known SCP is Quorn, made from the fungus Fusarium ventetatum, a single celled fungus that is grown in large fermenters using glucose syrup as a food source.

The microorganisms are combined with albumen (egg white) and then compressed and formed into meat substitutes. Quorn is also a healthy choice as it is high in protein and low in fat.

People are very conservative in their food choices and when the new food was launched, no mention was made of the fungi used to produce it, mycoprotein meant that most people didn’t recognise what is was made of.

Other attempts to make proteins have not yet been as successful. Yeasts, algae, bacteria can be used to grow proteins that match animal proteins found in meat as well as plant proteins. They can be grown on almost everything and are relatively cheap and low in fat however none have been proven so successful but people have many reservations about eating food grown on waste. Increasingly single celled proteins are being used to feed animals that we prefer to eat like fish and cattle. → many people may turn to eating food made directly from microorganisms.

Advantages of using microorganisms to produce human food.

  • they reproduce fast and produce protein faster than animals and plants

  • they have a high protein content with little fat

  • can use a wide variety of waste materials including human and animal waste, reducing costs.

  • can be GM to produce the protein required.

  • production of microorganisms is not dependant on weather, breeding cycles - it takes place constantly and can be increased or decreased to match demands.

  • no welfare issues when growing them

  • can be made to taste like anything.

Disadvantages of using microorganisms to produce human food

  • some microorganisms can also produce toxins if the conditions are not maintained at the optimum

  • the microorganisms have to be separated from the nutrient broth and processed to make the food.

  • need sterile conditions that are carefully controlled -adding to costs.

  • often involve GM organisms and many people have concerns about eating GM food.

  • the protein has to be purified to ensure it contains no toxin or contaminants.

  • has little natural flavour, needs additives.