Fermented Dairy Products

Fermented Dairy Products

	Fermented Dairy Products - Many products are made through microbial fermentation of milk, including buttermilk, yogurt and many cheeses. Fermentation is primarily carried out by lactic acid bacteria. The lactic acid pathway and the accumulation of lactic acid from the metabolism of milk sugar, lactose are common to the production of fermented dairy products. The differences in the flavour and aroma of the various dairy products are due to additional fermentation products, that may be present in very low concentrations.
1. Buttermilk, Sour cream, Kefir and Koumis. Different products are produced by using different strains of lactic acid bacteria as starter cultures and different fractions of whole milk as the starting substrate. Sour cream uses Streptococcus cremoris or S. lactis for producing lactic acid and Leuconostoc cremoris for characteristic flavour. Cream is starting substrate. Butter is normally made by churning cream that has been soured by lactic acid bacteria. Streptococcus cremoris or S. lactis is used to produce lactic acid rapidly and Leuconostoc citrovorum produces necessary flavors. Kefir and Koumis, popular in Europe are fermentation products of S. lactis, S. cremoris, other Lactobacillus spp and yeasts.
2. Yogurt. It is made by fermenting milk with a mixture of Lactobacillus, bulgaricus and Streptococcus, thermo phi/us at 40°C. Flavour is due to accumulation of lactic acid and acetyldehyde.
3. Cheese. Cheese consists of milk curds that have been separated from the liquid portion of the milk (whey). The curdling of milk is done by enzyme rennin (casein coagulase or chymosin) and lactic acid bacterial starter cultures. Cheeses are classified as soft (high, 50-80% water content), semi hard (about 45% water) and hard (a low water content, less than 40%). They are also classified as unriped if produced by single-step fermentation or ripened if additional growth is required during maturation of the cheese to achieve the desired taste, texture and aroma. Cottage and cream are soft, unripened cheese; Brie, Camembert and Limburger are soft, 1-5 months ripened cheeses; Blue, Brick, Gorgonzola, Monterey, Muenster and Roquefort are semi soft, 1-12 months ripened cheeses, whereas Cheddar and Colby are hard, 3-12 months ripened cheeses.
	Natural production of cheese involves lactic acid fermentation, with various mixtures of Streptococcus and Lactobacillus spp. used as starter cultures. The flavour results from use of different microbial starter cultures, varying incubation times and conditions and the inclusion or omission of secondary microbial species late in the process. Ripening involves additional enzymatic transformations after the formation of cheese curd. Swiss cheese formation involves a late propionic acid fermentation with ripening done by Propionibacteria shermanii. Various fungi are also used in the ripening of different cheeses. The unripened cheese is inoculated with fungal spores.

Blue cheeses are produced by Penicillium spp. Roquefort cheese is produced by using P. roqueforti and Camembert and Brie by using P. camemberti and P. candidum.

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