Aerobic spore-forming bacteria in bulk raw milk : factors influencing the numbers of psychrotrophic , mesophilic and thermophilic Bacillus spores

Abstract

Psychrotrophic, mesophilic nd thermophilic spore concentrations o/ Bacillus spp. were determined on a weekly basis in bulk raw milk samples obtained front a central processing facility, ovel one calendar year. These data were coruelated with concentrations of metal ions, fi"ee amino acids and somatic cell counts obtainedfrom the same samples, as well as locl meteorological mean temperature and relqtve humidity mea.sur"enxents relating to the sqme test period. A heat treatment of 80"Cfor 20 minllowed by the addition of L-lanine to the milk at 0.I o/o w/v and incubation at 5 5 "Cfor 7 dys gave optimal recovery conditions r thermophilic spores. Free amino acids, metal ions, somatic cell cotmts, temperture, and relative huruidity measurements were each significantly correlatedwith the recovery of spores o/Bacillus spp. from bulk raw milk, although no singlefactor was shown to demonstrute a consistent ffict with the psychrotrophic, ntesophilic and thermophilic spore groups studied.

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