Saturday, July 17, 2021

Application of microorganisms in food

Microorganisms have been used for preparing food products like bread, yoghurt or curd, alcoholic beverages, cheese for a long time without knowing their involvement in fermentation.

For example, bacteria that cause milk to become sour are used in making cottage cheese, buttermilk, and yogurt. Vinegar and sauerkraut also are produced by the action of bacteria on ethyl alcohol and cabbage, respectively.

In Europe and the Middle East yoghurt is made from milk thickened by heating or the addition of dried milk solids and fermented with Lactobacillus bulgaricus and Streptococcus thermophilus. It has custard like consistency and is often flavored with ground fruit or nuts.

Acidophilus milk is made with Lactobacillus acidophilus. Butter is made from pasteurized cream, to which a lactic acid starter has been added.

Sour-cream butter is made by churning cream that has been ripened by bacterial action with a resultant production of lactic acid. The fat globules are more easily coalesced during the churning, and they take up certain desirable flavors that were produced by the bacteria during the fermentation process.

Kefir is a fizzy beverage made from fermented mares' milk using 'grains' that contain yeasts, streptococci, lactobacilli, and micrococci. The grains are strained off after their action is complete and added to the next batch of milk. Koumiss, also made from mares' milk, is a greyish-white liquid with uncurdled casein, often bottled and allowed to carbonate by the action of the microorganisms.

A culture of yeast is allowed to grow in a dough made of flour and water. As it grows the yeast produces carbon dioxide, which causes the dough to rise or become light. In addition, flavors are produced in the bread by the yeast or certain types of bacteria.

Molds are grown as feed and food and are employed to produce ingredients such as enzymes like amylase used in making bread or citric acid used in soft drinks.

Molds are major contributors in the ripening of many oriental foods. A species of Bothrytiscinerea, is used in rotting of grape for production of wine. Lactic fermentations using molds results in a unique Finnish fermented milk called viili.

Lactic acid bacteria are a heterogenous family of mainly low G+C Gram positive anaerobic, non sporulating and acid tolerant bacteria. They can ferment various nutrients through a homo or heterofermentative route into primarily lactic acid, but also into by products such as acetic acid. Formic acid, ethanol and carbon dioxide. They contribute to rapid acidification of food products, but also to flavous, texture and nutrition.

Since these lactic acid bacteria are tolerant of salt, and since salt exerts a curing action, it is employed in almost all fermented foods. Cucumbers are fermented in brines strong enough to discourage most spoilage micro-organisms, the salt and acid being soaked out before the product is used as food.
Application of microorganisms in food

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