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Document Type

Thesis - University Access Only

Award Date

1992

Degree Name

Master of Science (MS)

Department

Dairy Science

First Advisor

Vikram V. Mistry

Abstract

Cultured dairy products gain their identity from the fermentation of lactose, the principal milk carbohydrate, to lactic acid. This fermentation is brought about by the lactic acid bacteria (LAB) which could be native to milk or added as starter culture. Production of lactic acid decreases the pH which helps in the preservation of the product. Other fermentation products like acetic, citric, and propionic acids, diacetyl, acetyl methyl carbinol, acetaldehyde and ethyl alcohol may also be produced which are characteristic of the type of product and provide distinct flavor (43). Lactic acid bacteria commonly used as starter cultures belong to the Lactococcus, Streptococcus, Lactobacillus or Leuconostoc genus (66). Apart from preserving the product LAB also serve other important roles. Cultured dairy products are more easily digested and assimilated than unfermented milk (27). Fermented milks are acceptable to lactose intolerant people who would otherwise have to exclude dairy products from their diets. The LAB in fermented milks possess 8 galactosidase and phospho-8-galactosidase, which are the key enzymes required to utilize lactose (22, 28). Cultured dairy products help in maintaining a healthy normal microflora in the human intestine and prevent enteropathogens from colonizing. The presence of LAB in the intestine promotes the production of the B vitamins and is also believed to activate the immune system and inactivate toxic compounds (22). Bifidobacteria were first isolated by Tissier from infant feces who called them Bacillus bifidus communis (64). The 1st - 4th edition of the Bergey's manual classified these organisms as Bacteroides bifidus; the 5th - 7th editions as Lactobaci1lus bifidus and the 8th edition in 1974 gave them the present classification under the genus Bifidobacterium with 11 species. The 1986 edition of the manual has 24 species listed under bifidobacteria. Interest in this genus grew after it was proposed by Tissier that it could be beneficial to health and even have therapeutic values. Bifidobacteria are gram positive, anaerobic and non-motile rods. They are typically Y-shaped or club or spatulated rods. They ferment lactose to produce acetic and lactic acid in a 3:2 molar ratio. Scardovi (75) in the 1986 edition of the Bergey's manual of systematic bacteriology has defined 24 different species under this genus. Most of the identified species have been isolated from human intestinal microflora though some have been isolated from the intestine of farm animals (64). However, most interest has been centered around a select few species, viz: Bifidobacterium bifidum, Bifidobacterium longum, Bifidobacterium infantis and Bifidobacterium breve; probably due to their beneficial qualities.

Library of Congress Subject Headings

Bifidobacterium bifidum
Bacterial growth
Lactic acid bacteria
Cheddar cheese -- Composition

Description

Includes bibliographical references (pages 39-46)

Format

application/pdf

Number of Pages

74

Publisher

South Dakota State University

Rights

In Copyright - Non-Commercial Use Permitted
http://rightsstatements.org/vocab/InC-NC/1.0/

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