Comparative shelf‐lives of skimmed, semi‐skimmed and whole milks

Abstract

The comparative microbiological shelf‐lives of skimmed, semi‐skimmed and whole milks were studied under controlled conditions. No difference in shelf‐life between the milks was observed whatever the conditions of storage or contamination. The factors that were established to affect shelf‐life, irrespective of fat content, were the presence or absence of post‐pasteurization contamination and the temperature of storage.

Spoilage patterns of skim and whole milks

“…For both the uninoculated commercial milks and those inoculated with spoilage pseudomonads, the bacterial growth patterns in skim milk were not significantly different from those in whole milk. This is consistent with the results of other researchers who observed similar rates of growth in skim and whole milks (Janzen et al 1982 ;Brown et al 1984 ;Chandler et al 1990). It also supports their conclusions that the different shelf lives of skim and whole milks cannot be attributed to different bacterial growth rates.…”

“…In the first part of this work, the rates of flavour deterioration of refrigerated, commercial pasteurised skim and whole milks during storage were not significantly different, which is at variance with several reports and anecdotal evidence from industry sources. However, when spoilage bacteria from these milks were inoculated into freshly pasteurised skim and whole milk, the inoculated skim milks reached an unacceptable score before the corresponding whole milks during subsequent cold storage, supporting previous reports (Langlois et al 1966 ;Janzen et al 1982 ;Brown et al 1984).…”

“…The gross spoilage end-point at which the spoilage bacteria were isolated was set at a lower level than that used in other investigations (Brown et al 1984 ;Chandler et al 1990). This is evident in the total aerobic count data.…”

“…This is evident in reports from various countries (Langlois et al 1966 ;Janzen et al 1982 ;Brown et al 1984 ; Pieper & Tims, 1987 ;Griffiths, 1989 ;Heo, 1989), and in complaints received by some dairy companies. Janzen et al (1982) reported that the average shelf lives of skim milks stored at 4n5 and 7 mC were less than those of the corresponding whole milks by 2n3 d and 1 d, respectively, although at 10 mC, there was no difference.…”

“…Some workers have assumed that the difference in spoilage rates is due to different rates of growth of psychrotrophic bacterial contaminants in the different milks. However, it has been shown that the bacterial numbers in the different milks after incubation under identical conditions are not significantly different (Janzen et al 1982 ;Brown et al 1984 ;Allen et al 1989 ; …”