Yeast, Enzymes and Yoghurt NEET Notes | EduRev

Biology Class 12

NEET : Yeast, Enzymes and Yoghurt NEET Notes | EduRev

The document Yeast, Enzymes and Yoghurt NEET Notes | EduRev is a part of the NEET Course Biology Class 12.
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"Biotechnology may be defined as use of micro-organism, animals, or plant cells or their products to generate different products at industrial scale and services useful to human beings."

A powerful industry based on microbes has been developed in recent time. A careful selection of microbial strains, improved method of extraction and purification of the product, have resulted in enormous yields.

The use of living organisms in systems or process for the manufacturer of useful products, It may involve algae, bacteria, fungi, yeast, cells of Higher plants & animals or subsystems of any of these or Isolated components from living matter.

Old biotechnology are based on the natural capabilities of micro organisms. e.g. formation of Citric acid, production of penicillin by Penicillium notatum New biotechnology is based on Recombinant DNA technology. e.g. Human gene producing Insulin has been transferred and expressed in bacteria like E.coli.

In,modern biotechnology, different types of valuable products are produced with help of microbiology, biochemistry, tissue culture, chemical engineering and genetic engineering, molecular biology and immunology.


A common example is the production of curd from milk. Micro-organisms such as Lactobacillus and others commonly called lactic acid bacteria (LAB) grow in milk and convert it to curd. During growth, the LAB produce acids that coagulate and partially digest the milk proteins. A small amount of curd added to the fresh milk as inoculum or starter contain millions of LAB, which at suitable temperatures multiply, thus converting milk to curd, which also improves its nutritional quality by increasing vitamin B12. In our stomach too, the LAB play very beneficial role in checking disease causing microbes.

The dough , which is used for making foods such as dosa and idli is also fermented by bacteria. The puffed-up appearance of dough is due to the production of CO2 gas. Similarly the dough, which is used for making bread, is fermented using baker's yeast (Saccharomyces cerevisiae). A number of  traditional drinks (e.g. ''Todi' prepared from sap of palms) and foods are also made by fermentation by the microbes.Microbes are also used to ferment fish, soyabean and bamboo shoots to make foods. Cheese, is one of the oldest food items in which microbes were used. Different varieties of cheese are known by their characteristic textur flavour and taste, the specificity coming from the microbes used. For example, th large holes in 'Swiss cheese' are due to production of a large amount of CO2 by a bacterium named Propionibacterium sharmanii. The 'Roquefort cheese' are ripened by growing a specific fungi on them, which gives them a particular flavour.


Louis Pasteur showed in the middle of nineteenth centuary that beer and butter milk are product of fermentation brought about by "yeast". It is a microscopic single celled organism –Saccharomyces cerevisiae.

Presently however yeast product for human and animal consumption are produced on commercial scale. "Alcoholwas the first product of ancient biotechnology"

There are basically two types of yeasts (i) Baker's yeast (ii) Alcohol yeast or Brewer's yeast Baker's yeast generally utilize during the preparation of food materials to increase the taste of food, flavour in food and nutrients in food. It is also utilized as "leavening agent".

By the incomplete degradation of complex organic compounds [sucrose] by yeast fermentation, alcohol is formed.

Yeast, Enzymes and Yoghurt NEET Notes | EduRev

Some other common products of yeast fermentation are – 

[i] Beer – It is produced from Hordeum Vulgare[Barely] malt and alcohol content is 4-8%

[ii] Wine – Produced from grapes, alcohol content is 10-20%.

[iii] Brandy – Produced by distilation of wine and alcohol content is 43-57%

[iv] Gin – Produced from European Rye-Scale cereal.

[v] Rum – Produced from Molasses of Sugarcane and alcohol contents is 40%

Note – Another yeast which supplies nutritional rich food for Man and animals is Torulopsis utilis.

Yeast, Enzymes and Yoghurt NEET Notes | EduRev

Yeast, Enzymes and Yoghurt NEET Notes | EduRev  

Industrial utilization of biotechnology involve three steps – 

[i] Laboratory scale process

[ii] Pilot plant scale

[iii] Manufacturing unit The development from laboratory scale to manufacturing unit is "Scaling up to industrial production"

[i] Laboratory Scale – In this process for the production of desirable product, proper micro organism searched and then suitable strain is selected and multiplied. Proper medium also find out on which selected strain, produce best and more amount of product.

Many number of experiments performed in lab for the analysis and selection of strains and medium. All the equipment are utilized in lab i.e., glass apparatus. All the parameters of the process worked out and precaution are also not down for the smooth running of process such as – proper sterlization of nutrient and microbesstrain, required - pH, suitable aerator, disposal of CO2 if evovled, temperature, by product or product inhibition or stimulation, time of optimum production, separation of product and its purification etc. Ultimately, the laboratory scale process finalized and transfer at pilot plant scale.

[ii] Pilot plant Scale – It is the intermediate stage where working of laboratory scale process is tested. At this stage cost and quality of product throughly checked. Glass apparatus are replaced by stainless steel equipment/containers is called "bio reactor".

To produce in large quantities, the development of bioreactors. where large volumes (100-1000 litres) of culture can be processed, was required. Thus, bioreactors can be thought of as vessels in which raw materials are biologically converted into specific products, individual enzymes, etc., useing microbial plant, animal or human cells. A bioreactor provides the optimal conditions for achieving the desired product by providing optimum growth conditions (temperature, pH, substrate, salts, vitamins, oxygen).

The most commonly used bioreacters are of stirring type

Yeast, Enzymes and Yoghurt NEET Notes | EduRev

Yeast, Enzymes and Yoghurt NEET Notes | EduRev

A stirred-tank reactor is usually cylindrical or with a curved base to facilitate the mixing of the reactor contents.

The stirrer faciliates even mixing and oxygen availability throughout the bioreactor. Alternatively air can be bubbled through the reactor. The bioreactor has an agitator system, an oxygen delivery system and a foam control system, a temperature control system, pH control system and sampling parts so that small volumes of the culture can be withdrawn periodically.

Micro organisms can be grown in bioreactors in two ways :

(a) Support growth system – In this method microorganisms are growing as a thin layer or film in the solid medium.

(b) Suspended growth system – By suspending cells or mycelia in the liquid medium is called suspended growth system.

[iii] Manufacturing unit – During the designing of bioreactor for  the process often very large size so that it accomodate huge amount of medium.

Downstream Processing – After completion of the biosynthetic stage, the product has to be subjected through a series of processes before it is ready for marketing as a finished product. The processes include separation and purification, which are collectively referred to as downstream processing. The product has to be formulated with suitable preservatives.

Such formulation has to undergo through clinical trials as in case of drugs. Strict quality control testing for each product is also required. The downstream processing quality control testing vary from product to product.

Some important biotechnological products which are produced with the help of organisms as follows –


Total known enzymes 2,200 and only 1–1.5% are used

(i) Rennet – Manufacturing "Cheese"

Old days cheese had been prepared either using the layer of stomach of Goat or Sheep OR the sap of Fig. tree, containing special enzyme–Ficin. In 1874 a Danish Chemist – Christian Hansen extracted pure rennet enzyme from Calf's stomach for industrial production of cheese. First of all diastase enzyme was identify by payen and persoz (1933) Cheese is mainly two different types.

I. Unripened cheese – Ripened from out side–soft

II. Ripened cheese– It is hard and ripened externally as well as internally.

Manufacturing cheese involve following steps.

(i) Milk is inoculated with starter culture of bacteria – Streptococcus lactis or S.cremoris and warmed at 380C. If higher temperature [500C or more] then S.thermophilus combined with Lactobaccilus lactis, L.bulgaricus or L.helveticus.

(ii) When a certain acidity reached in milk by the activity of species of bacteria then rennet enzyme is added. Curdling of milk occurs within half an hour to one hour.

(iii) The curd is removed and liquid separates out which is called whey [contain 93% water and 5% Lactose].

Lactose of whey is used for the manufacture of Lactic acid – First fermented acid.

If the cheese is used at this stage is calledcottage cheese(unripened stage).

(iv) The salts mixed with cottage cheese and put into the frames and pressed so as to allow removal of whey.

Salts hastens the removal moisture and prevent the growth of undesriable microbes. The frames are removed as soon as the cheese has set sufficiently to maintin its shape.

The ripening period varies from 1–16 months but which is very tasty and nutritious. This is hard and ripened cheese contains about 20-30% fats, 20-35% proteins and small amount of minerals and vitamins. [Cheese which prepared at homes with the help of lemon juice is called Raw cheese] Nearly 400 varieties of cheese available which can be classified into following type –


Type of Cheese

Micro Organisms used




  1. Camembert
  2. Limburger

Penicillium camemberti , Brevibacterium ,Streptococcus liquifaciens ,Brevibacterium

Ripend by action of microorganisms on the surface of curd



  1. Roquefort
  2. Hue

Penirilliim roqueforti

Combination of surface and interior growths



  1. Swiss
  2. Cheddar

Propionibacterium sp Geotrichum

Inoculating the organisms throughout the curd


(ii) Proteases – This enzyme obtained from Aspergillus orizae and Bacillus subtilis, Bacillus licheniformis and utilized from the formation of detergents in detergent industry [For removing proteinous strains on clothes]. The bottlejuices are clarified by the use of pectinases and protease.

(iii) Amylases – It works on starch and used in Beer, Bread and Textiles industries.

(iv) Amylase, Gluco amylase and Gluco isomerase – By the action of all these enzymes corn (maize) starch transformed into fructose corn syrup. This syrup is more seeter than sucrose and used in beverage industry to flavoursoft drinks and in baking industry to sweeten biscuits and cakes.

(5) Tissue Plasminogen Activator [TPA] or Streptokinase – This enzyme utilized in medicinal field.

Streptokinase produced by the bacterium Streptococcus and modified by genetic engineering is used as a clot buster for removing clots from the blood vessels of patients who have undergone myocardial infraction leading to heart attack.

Uses Of Enzymes : 

(1) Detergents (i) Proteases (ii) -Amylase (iii) Cellulases (iv) Lipases 

(2) Leather Industry 

(3) Wool Industries 

(4) Glucose from Cellulose 

(5) Food, Dairy, Juice and Beverages Industries 

(6) Production Of  Glucose Syrup Bioactive molecule, cyclosporinA, that is used as an immunosuppressive agent in organ-transplant patients, is produced by the fungus Trichoderma polysporum.

Statins produced by the yeast Monascus purpureus have been commercialised as blood -cholesterol lowering agents. It acts by competitively inhibiting the enzyme responsible for synthesis of cholesterol.


For production of curds or yoghurt pasteurized milk is inoculated with a mixture ofStreptococcus thermophilus andLactobacillus bulgaricus and its lactose is fermented by keeping it at 400C. The peculiar or characteristic taste and flavour of curds are due to presence of lactic acid and acetaldehyde. Curdling or coagulation of milk is also caused by lactic acid which is formed. In India, curds are not generally commercially produced but in developed countries large scale manufacture of yoghurt is done. In U.S.A. alone about 75 lakh kilogram of yoghurt is manufactured every year.

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