curd
The starter or inoculum used in preparation of milk products containing millions of lactic acid bacteria (LAB) like Lactobacillus are
added to skimmed or cream milk at a temperature of about 40°C or less. They convert lactose sugar of milk into lactic acid. Lactic
acid causes coagulation of milk protein casein. Milk is changed into curd.
Besides the conversion of milk into lactic acid, the LAB also improve its nutritional quality by increasing vitamin B 12. Curd is more
nutritious than milk as it contains a number of vitamins and organic acids. LAB present in curd also check growth of disease causing
microbes in stomach and other parts of digestive tract. Indian curd is used either as such or in other forms such as mattha, chhach
or lassi.
Yoghurt and butter milk
Yoghurt is produced by curdling milk with the help of Streptococcus thermophilus and Lactobacillus bulgaricus. Butter milk 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.cheese
Cheese is known to be the oldest food item in which microbes are used. There are two groups of cheese, fresh or unripened cheese
and ripened cheese. The unripened cheese are made up of milk coagulated by acid or high heat e.g., cottage cheese, while ripened
cheese are made through lactic acid bacterial fermentation and coagulated by an enzyme preparation.
A large number of microorganisms play a role in the ripening process and different varieties of cheese are obtained depending
upon the microorganisms used in production. The CO 2 producing culture of Propionibacterium sharmanii is essential for
giving swiss cheese its eye or holes, and flavour. Roquefort cheese uses Penicillium roqueforti while camembert cheese
employs P.camemberti for ripening.
• Soft cheese is ripened by the enzymes from yeast and other fungi that grow on the surface.
• Hard cheese is ripened by lactic acid bacteria which grows throughout the cheese, die, autolyse and release hydrolytic
enzymes.
• The semisoft cheese is ripened by proteolytic and lipolytic organisms which soften the curd and give it a flavour.dough for making food items
Numerous food items such as ‘dosa’, ‘idli’, ‘jalebi’ and ‘bread’ are prepared by fermentation process in which one or more kinds of
microbes are used.
Dosa, uppma and idli are fermented preparation of rice and black gram. The ‘dough’ which is used for making dosa and idli is
allowed to ferment overnight for 10 to 12 hours. The bacteria, which come from atmosphere (particularly Leuconostoc mesenteroides,
Streptococcus faecalis) cause fermentation so that the dough increases in volume and gets sour. Increase in the volume of dough is
due to carbon dioxide gas (CO 2 ) that is released as a result of fermentation.Bread is made from flour obtained by grinding cereal grain usually wheat. Selected strains of Saccharomyces cerevisiae grown on
molasses are used as baker’s yeast. A small quantity of yeast is added to wheat flour and kneaded. The kneaded flour is kept at 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. 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. The two cause swelling or leavening of dough. The leavened
dough is baked. Both carbon dioxide and ethyl alcohol evaporate making the bread porous and soft.
single cell proteins
A relatively new food source is single cell protein (SCP). Its production began in the late 1960s. The term refers to protein obtained
from the large scale growth of microorganisms such as bacteria, yeasts and other fungi, and algae. The protein may be used for
human consumption or animal feed. It may also be a useful source of minerals, vitamins, fats and carbohydrates. The common SCP
are obtained from Spirulina, yeast and Fusarium graminearum. SCP is rich in high quality protein but poor in fat.
other household products
Coconut water is fermented to produce a refreshing drink called toddy. It is a traditional drink in some parts of Southern India. The
term toddy is also applied to sweet exudation got by tapping unopened spadix of coconut. Palm sugar or jaggery is produced by