A study was conducted to investigate the use of bacterial numbers
and metabolites for their Value in predicting potential shelf-life of
pasteurized fluid milk. The study consisted of two phases. In the first
phase, chemical inhibitors were evaluated for their ability to allow
growth of gram-negative psychrotrophic bacteria while inhibiting growth
of gram-positive organisms. Crystal violet, benzalkonium chloride, a
mixture of crystal violet and benzalkonium chloride, and alkylaryl
sulfonate were tested. These were incubated with milk samples separately
inoculated with gram-negative and gram-positive bacteria, at 2l°C for 18
hours. Alkylaryl sulfonate allowed growth of gram-positive organisms.
Crystal violet inhibited gram-positive organisms but was not as effective
as the mixture of crystal violet and benzalkonium chloride, The inhibitor
of choice was benzalkonium chloride as it inhibited growth of all gram-positive
organisms tested and allowed growth of the gram-negative
psychrotrophic organisms.
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