Lecture_19___fermented_dairy_products

Lecture_19___fermented_dairy_products - Fermented Dairy...

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1 Fermented Dairy Products Carmen I. Moraru Cornell University How are they made? - Fermented milk products are obtained as a result of the fermentation of lactose in milk by fermentative microorganisms (mostly bacteria) - Types of lactic fermentations: - Homolactic fermentation - Heterolactic fermentation Do you remember the reactions involved?
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2 Homolactic fermentation - Main end product is lactic acid – max. 1.5% in milk - Produced by homofermentative lactic bacteria from the N streptococci group: Str.cremoris , Str.lactis , Str.diacetylactis - Net reaction: 1 molecule of lactose 4 molecules of lactic acid - For Str. thermophilus and Lb. bulgaricus - a nother pathway: - Net reaction: 1 molecule of lactose 2 molecules of lactic acid - Produced by some Lactobacillus or Leuconostoc , which lack the enzyme that can break glucose in 2 three carbon units Lactose Lactate + Ethanol + CO 2 + H 2 O Heterolactic fermentation Str. thermophilus and Lb. bulgaricus form diacetyl Str. diacetylactis and Leuconostoc cremoris can also oxidize pyruvic acid to diacetyl, and they can also form some pyruvic acid from citric acid Formation of aroma compounds 2 CH 3 -CO-COOH + O CH 3 -CO-CO-CH 3 + 2 CO 2 + H 2 O
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3 Starter cultures Functions of lactic starters: - Production of lactic acid from lactose (main role), which contributes to: - Product preservation - Formation of product texture - Product flavor - Production of flavor and aroma compounds, and sometimes of alcohol - Proteolytic and lipolytic activities (important mostly in cheese making) - Inhibition of undesirable organisms Starter cultures – contd. - According to the optimum growth temperatures , there are: - Mesophilic cultures – optimal growth temperatures of 20° to 30°C - O cultures - contain only acid-producing strains - LD cultures - contain citrate-fermenting bacteria - Thermophilic cultures – optimal growth temperatures of 40° to 45°C - According to their composition , cultures may be: - Single-strain - Multiple-strain (a mixture of several strains, each with its own specific effect)
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4 Examples of lactic starters Mesophilic - Lactococcus lactis subsp. cremoris - Lactococcus delbrueckii subsp. lactis - Lactococcus lactis subsp. lactis biovar diacetylactis - Leuconostoc mesenteroides subsp. cremoris Thermophilic - Streptococcus salivarius subsp. thermophilus ( S.thermophilus ) - Lactobacillus delbrueckii subsp. bulgaricus - Lactobacillus delbrueckii subsp. lactis - Lactobacillus casei
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This note was uploaded on 05/02/2009 for the course FDSC 4250 taught by Professor Moraru during the Spring '09 term at Cornell University (Engineering School).

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Lecture_19___fermented_dairy_products - Fermented Dairy...

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