Microbes in household products

MICROBES IN HOUSEHOLD PRODUCTS

Dairy Products :

Lactic acid bacteria (LAB) like Lactobacillus are added to milk. It converts lactose sugar of milk into lactic acid.

Milk can be changed into curd, yoghurt and cheese. The starter used in preparation of milk products actually contains millions of LAB.

(a) Curd : Indian curd is prepared by inoculating cream and skimmed milk with Lactobacillus acidophilus at a temperature of about 40°C or less. Curd is more nutritious than milk as it contains a number of vitamins, especially Vit B₁₂ and organic acids.

(b) Yoghurt : It is produced by curdling milk with the help of Streptococcus thermophilus and Lactobacillus bulgaricus. It has a flavour of lactic acid and acetaldehyde.

(c) 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.

(d) Sour Cream : It is inoculated with Streptococcus lactis for producing lactic acid and Leuconostoc cremoris for imparting the characteristic flavour.

(e) Cheese : It is partially degraded concentrate of milk fat and casein, manufactured by activity of microorganisms. There are several hundred varieties of cheese which are prepared by selected types of microorganisms. The quality and characteristic taste of cheese is determined by the biochemical activities of specific microorganisms. Cheese consists of milk curd that has separated from whey or liquid part. 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. Large holed Swiss cheese is ripened with the help of CO₂ producing bacterium called Propionibacterium sharmanii. Roquefort cheese or blue cheese uses Penicillium roquefortii, while Camembert cheese employs Penicillium camembertii for ripening.

Bread :

Selected strains of Saccharomyces cerevisiae (Baker's yeast) grown on molasses are used for this purpose.

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, maltase and zymase.

The leavened dough is baked. Both carbon dioxide and ethyl alcohol evaporates, making the bread porous and soft.

Dosa, Uppma and Idli :

These are fermented preparations of rice and black gram. The two are allowed to ferment for 3-12 hours with Leuconostoc and Streptococcus species of bacteria.

Other Foods :

Tempeh (Indonesia) Tofu (Japanese) and Sufu (Chinese) are fermented foods obtained from soya sauce, is brown flavoured salty sauce fermented from soyabean and wheat.

Tender bamboo shoots can be used as vegetable directly as well as after fermentation. Several types of sausages are prepared by fermentation and curing of fish and meat.

Toddy (Toddy palm-Caryota urens) :

The unopened spadices of palm are tapped to obtain toddy. It is a refreshing drink which can be heated to produce jaggery or palm sugar. Toddy left for a few hours undergoes fermentation with the help of naturally occurring yeast to form beverage containing about 6% alcohol.