Which of the following microbes is(are) important to cheese-making? a. lactic acid bacteria b. clostridium acetylbutylicum c. desuflovibrio d. propionibacterium e. lactic acid bacteria and propionibacterium

E. Lactic acid bacteria & Propionibacterium

Explanation:

Propionibacterium freudenreichii is the most important species.These are gram positive anaerobic and grow only within cheese. The main function of this bacteria is lactate metabolization produced by starter bacteria to form propionate, acetate and carbon dioxide in Swiss type cheese e.g. Emmental and Comte. Propionic acid is used as fungicidal agent for making bread and bakery products and can be made by whey fermentations using ssp. shermanii strains.Whole whey is typically used and the fermentation must proceed under sterile conditions at around 30 °C and pH 6.5–7.5. Propionate production is increased by nutritional supplements & a typical yield of about 40% of lactose fermented is achieved after 60-70 h. The culture fluid is sprayed in a dried form  to extract a powder containing acid & whey proteins.

Lactic acid bacteria : They are most important class of microorganisms which help in the food fermentation process. They have their main contribution in taste and texture of food products and impede food spoilage bacteria by the production of growth impeding substances and large amount of lactic acid. Lactic acid bacteria is responsible for creating fresh acidic flavour of unripened cheese and is significant in coagulation of milk casein which is completed by the combination action of rennet(an enzyme) & lactic acid formed by microbes.

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