Enterobacter cloacae, Citrobacter freundii, Serratia liquefaciens and Escherichia coli were the predominant Enterobacteriaceae species isolated from raw milk samples collected from refrigerated bulk tank trucks at the entry of a milk processing plant. About half of the 181 Enterobacteriaceae isolated were psychrotrophs and these included 80% of E. cloacae, 80% of Klebsiella ozaenae and 62% of S. liquefaciens. S. liquefaciens grew in raw and in pasteurized milk at refrigeration temperatures, causing significant pH reduction but only slight lipolytic changes. The significant proteolytic activity of S. liquefaciens in refrigerated milk samples is assumed to have been the cause of the unclean flavor detected.

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1Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel No. 107-E, 1979 series.