HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Juven, B. J. Articles by Laufer, A. Search for Related Content PubMed Articles by Juven, B. J. Articles by Laufer, A.

Changes in Refrigerated Milk Caused by Enterobacteriaceae¹

Division of Food Technology, Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel

ABSTRACT

Laboratory-pasteurized samples of whole raw milk were inoculated with psychrotrophic strains of Citrobacter freundii, Enterobacter agglomerans, Enterobacter cloacae, Escherichia coli, Klebsiella ozaenae, and Serratia liquefaciens and incubated for 7 days at 7°C. All test organisms caused a pH reduction that ranged from .12 (C. freundii) to .69 units (K. ozaenae), but none reduced pH to lower than 6.0. Following growth of E. agglomerans, K. ozaenae, S. liquefaciens, and E. cloacae, the milk coagulated upon heating or upon addition of alcohol; with C. freundii and E. coli the milk did not coagulate. All organisms caused reductions in the redox potential (Eh) of milk, ranging from 20 mV (E. coli) to 152 mV (S. liquefaciens).

All organisms caused an increase in free tyrosine plus tryptophane in milk ranging from 3.5 (E. agglomerans) to 12.5 µg/ml (E. cloacae) as well as an increase in free fatty acids in milk which ranged from .29 (C. freundii) to .89 µeq/ml (K. ozaenae). In spite of the significant proteolytic and lipolytic activities exhibited in milk by some of the organisms, none showed proteolytic activity in skim milk-nutrient agar or lipolytic activity on Tween 80 agar.

¹ Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. No. 203-E, 1980 series.