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Variations in lactic acid production in milk

Authors: Barbara P. Keogh

Abstract:

Wide variations were found from day-to-day, and between different strains of starter bacteria, in the ability of milk, both raw and heated to 98°C, to support acid production. It was concluded that milk contains both inhibitory and stimulatory substances, that some of these are destroyed or produced by heating and that cultures differ widely in their relative sensitivity to these factors, which themselves vary in proportion from day to day. These variations do not appear to be influenced by weather conditions. A study by various methods of the role of agglutinins and creaming on inhibition shows that with certain cultures creaming, but not agglutination per se, plays a very large part in inhibition in raw whole milk as determined by activity tests. An acetone extract prepared from colostrum was shown to contain agglutinin and peroxidise. Addition of this extract to activity tests performed in heat-treated milk caused inhibition of the same cultures which were inhibited in raw whole milk. There is evidence that the Strept. diacetilactis strains tested are susceptible to yet another heat-liable factor not present in the extract. Detailed and extensive filed observations will be necessary to link these and other recent laboratory findings with occurrences of slow-acid production in cheese and casein factories.

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