Discuss the role of microbes in the production of houshold products.

Explanation

1. Dairy Products, Lactic acid bacteria (LAB) like lactobacillus are added to milk. It converts lactose sugar of milk into lactic acid. Lactic acid causes coagulation of milk protein casein. Milk is changed into curd, yoghurt and cheese. The starter or inoculum used in preparation of milk products.actually contains millions of LAB. LAB convert milk sugar lactose into lactic acid. Curd is more nutritious as it contains organic acids and vitamin `B_(12)`.
(i) Yoghurt (= yogurt). It is produced by curdling milk with the help of Streptococcus thermophilus and Lactobacillus bulgaricus. The temperature is maintained at about `45^(@)C (40^(@)-46^(@)C)` for four hours. It has a flavour of lactic acid and acetaldehyde. Yoghurt is often sweetened and flavoured with fruit.
(ii) Butter Milk. It is acidulated product which is formed by inoculating skimmed milk with starter culture of Streptococcus cremoris, S. lactis, Lactobacillus acidophilus, Leuconostoc species at `22^(@)C` for 18 hours. Acidulated liquid left after churning of butter from curd is also called butter milk.
(iii) Sour Cream. Cream is inoculated with Sterptococcus lactis for producing lactic acid and Leuconostoc cremoris for imparting the characteristic flavour.
(iv) Cheese. It consists of milk curd that has separated from whey or liquid part. Depending upon water content still present in milk curd, cheese is of three types -soft (50-80% water), semihard (about 45% water) and hard (less than 40% water). The method of preparing cheese with the help of microbes was known in Asia and Europe long before Christ. There are several varieties of cheese with different texture, flavour and taste. Curdling is done with the help of lactic acid bacteria and enzyme rennin (= Casein coagulase.= chymosin), rennet (from Calf.s stomach) or fruit extract of Withania coagulans. In preparation of raw cheese milk is curdled with the help of lactic acid bacteria. The curd is heated gently to separate cheese from whey. Any liquid left in cheese is allowed to drain by hanging it in cloth. Unripened or Cottage cheese is prepared by single step fermentation which involves inoculation of skimmed milk with cheese culture and addition of rennin or rennet after 12 hours. Curd is placed in cloth lined porous containers for draining out whey. Ripened cheese is prepared from unripened cheese by first dipping in brine, wiping and then maturation with different strain of bacteria and fungi. It takes 1-16 months for ripening. Large holed swiss cheese is ripened with the help of `CO_2` producing (causing holes) bacterium called Propionibacterium sharmanii. Roquefort cheese uses Penicillium roqueforti while Camembert cheese employs Penicillium camemberti for ripening.
2. Bread. Selected strains of Saccharomyces cerevisiae grown on molasses are used as Baker.s yeast. The yeast is available in the form of powder (or cake). A small quantity of yeast is added to wheat flour. The same is kneaded. The kneaded flour is kept at a warm temperature for a few hours. It swells up. The phenomenon is called leavening. Leavening is caused by secretion of three types of enzymes by yeast. They are amylase, maltose and zymase. Amylase causes breakdown of a small quantity of starch into maltose sugar. Maltase converts maltose into glucose. Glucose is acted upon by zymase. Zymase is a complex of several enzymes of anaerobic respiration which brings about fermentation. Fermentation of glucose mainly forms ethyl alcohol and carbon dioxide. It leaves the dough. The leavened dough is baked. Both carbon dioxide and ethyl alcohol evaporate making the bread porpus and soft.
3. Dosa, Uppma and Idli. They are fermented pr paration of rice and Black Gram (vern. Urad). The two are allowed to ferment for 3-12 hour, with Leuconostoc and Streptococcus species of bacteria.
4. Other Foods. Tempeh (Indonesia), Tofu (Japanese) and Sufu (Chinese) are fermented foods obtained from soyabean. Soy sauce is brown flavoured salty sauce fermented from soyabean and wheat. Tender bamboo shoots are used as vegetable directly as well as at er fermentation. Several types of sausages are prepared by fermentation and curing of fish and meat.
5. SCP (Single cell protein). It is the production of microbial biomass for consumption as human food or animal feed by growing the same on agricultural and other organic wastes. The .common SCP are Spirulina, Yeast and Fusarium graminearum. Processing is required to remove contaminants and excess nucleic acids. SCP is rich in high quality protein but poor in fat. Besides proving much needed proteins, SCP is useful in reducing environmental pollution by managing industrial and agricultural wastes.