Relationship of Protease Activity to Shelf-Life of Skim and Whole Milk

Pseudomonas spp. and Hafnia alvei growth in UHT milk at cold storage

“…However, the specific growth rates of both milk spoilage bacteria were higher in LFUM than in WUM. A similar result was reported by Janzen et al (1982), who showed that whole milk stored between 4.5 C and 7 C had a significantly longer shelf-life than skim milk. The reduction of fat and protein in the inoculated milk might be due to the elaborate proteases and lipase enzymes of Pseudomonas sp., since it is assumed that the production of these enzymes has a significant effect on the growth kinetics of the organism (Yagoub, Bellow, & El Zubeir, 2008).…”

“…The different component of UHT milk also affected pH value after cultured with spoilage bacteria. This may be caused by the relative protease activity from Pseudomonas spp, which is significantly higher in skimmed milk than in whole milk stored at 7 C (Janzen, Bishop, & Bodine, 1982). Janzen et al (1982) had reported a higher protease activity may partly account for the decreased shelf-life of skim milk.…”

Spoilage patterns of skim and whole milks

“…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.…”

“…Higher levels of proteolysis have been reported in skim than whole milks (Janzen et al 1982 ;Hsu, 1984). Janzen et al (1982) suggested that this may be due to the production of higher protease activity in the skim milk, although Griffiths (1989) concluded that the different rates of spoilage were not due to the different amounts of protease produced by bacterial contaminants in skim and whole milks.…”

“…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 ; …”