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Method of quantifying the loss of acidification activity of lactic acid starters during freezing and frozen storage

Published online by Cambridge University Press:  01 February 2000

FERNANDA FONSECA
Affiliation:
INRA Laboratoire de Génie et Microbiologie des Procédés Alimentaires, Institut National Agronomique Paris-Grignon, F-78850 Thiverval-Grignon, France
CATHERINE BÉAL
Affiliation:
INRA Laboratoire de Génie et Microbiologie des Procédés Alimentaires, Institut National Agronomique Paris-Grignon, F-78850 Thiverval-Grignon, France
GEORGES CORRIEU
Affiliation:
INRA Laboratoire de Génie et Microbiologie des Procédés Alimentaires, Institut National Agronomique Paris-Grignon, F-78850 Thiverval-Grignon, France
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Abstract

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We have developed a method to quantify the resistance to freezing and frozen storage of lactic acid starters, based on measuring the time necessary to reach the maximum acidification rate in milk (tm) using the Cinac system. Depending on the operating conditions, tm increased during the freezing step and storage. The loss of acidification activity during freezing was quantified by the difference (Δtm) between the tm values of the concentrated cell suspension before and after freezing. During storage at −20 °C, linear relationships between tm and the storage time were established. Their slope, k, allowed the quantitation of the decrease in acidification activity during 9–14 weeks of frozen storage. The method was applied to determine the resistance to freezing and frozen storage of four strains of lactic acid bacteria and to quantify the cryoprotective effect of glycerol.

Type
Research Article
Copyright
Proprietors of Journal of Dairy Research 2000