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UBC Theses and Dissertations

Fermentation of milk by Lactobacillus bifidus. Brown, Charles Dwight

Abstract

Bacteria, belonging to the Lactobacillus bifidus group, were isolated from rectal swabs obtained from healthy babies receiving breast milk. The fermentation properties of these bacteria in cow's milk were studied. Strains potentially suitable for fermentation in a food product were selected according to their ability to produce lactic acid and no gas from lactose, as well as adhering to characteristics common to the bifidus group (Gram positive, catalase negative and blanching morphology). The five strains chosen for intensive study produced 1.14 to 1.25% lactic acid and less than 0.05% volatile acid. The latter organisms could be cultured readily and coagulated milk in less than 24 hr when using a 5% inoculum. Repeated subculture resulted in a change from the branched to the unbranched bacterial morphology. This transformation, which is not unusual among bifid bacteria, was accompanied by a change in ability to produce lactic acid, but no gas was produced by branched or unbranched strains. A great deal of variability in morphology, growth consistency, and acid production was observed among the more than 500 bacterial strains isolated. However, the bifid populations from Caucasian babies was not noticeably different from those of native Indian babies. All of the five strains selected utilized inulin, dextrin, mannitol, and melezitose. A 24 hr culture of fermented milk yielded a product with a mild pleasant natural flavour which could conceivably be altered, if desired, by adding sweeteners or flavouring agents

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