THE ROLE OF BACILLUS CEREUS IN SWEET CURDLING OF FLUID MILK

Abstract

Twenty-eight percent of commercially pasteurized milk samples procured from various plants throughout Tennessee exhibited sweet-curdling within 10 days on refrigerated storage. Psychrotrophic Bacillus cereus was isolated as a causative organism from these milk samples. The isolates differed from the type culture organism only in their ability to grow and bring about sweet curd formation in skimmilk at refrigeration temperature. These isolates exhibited marked differences in their response to heat activation temperatures as well as to the initial excessive growth of Pseudomonas species in raw milk. Spores of three isolates exhibited greater activity after activation at 80 C for 15 sec than at the standard pasteurization temperature of 71.5 C for 15 sec. Excessive growth of Pseudomonas fragi or Pseudomonas fluorescens in raw skimmilk before processing had a stimulatory effect on two of three psychrotrophic Bacillus cereus isolates in combination with heat-activation especially with activation at 80 C for 15 sec.