Bacillus cereus in refrigerated milk submitted to different heat treatments.
The possibility of the survival, germination, and multiplication of Bacillus cereus in extended-shelf-life milk prompted research into the occurrence of the bacteria in refrigerated milk submitted to different heat treatments. Samples were submitted to ultrapasteurization (138 degrees C for 2 s), "superpasteurization" (96 degrees C for 13 s), and pasteurization (74 degrees C for 15 s) and stored under refrigeration at 4 +/- 2 degrees C for up to 6 weeks. The milk was analyzed for its sensory quality and for the quantitative determination of mesophilic and psychrotrophic B. cereus in the vegetative form at incubation temperatures of 7 and 30 degrees C, in addition to standard plate counts and psychrotrophic counts. In the three experimental trials, the psychrotrophic B. cereus counts were below the detection limit of the methodology (<10 CFU/ml) in all of the samples analyzed, independent of the heat treatment and storage period. The count of mesophilic B. cereus was restricted to samples of superpasteurized and pasteurized milk from a single trial, reaching 4.0 x 10(1) and 7.0 x 10(5) CFU/ml, respectively. Although the pasteurized milk had higher populations of mesophilic B. cereus after the second week of storage, flavor defects resulting in sensory rejection of the product did not appear before the fourth week of storage. The results of this research indicate that superpasteurization and ultrapasteurization are adequate for maintaining the product at refrigeration temperatures for 6 weeks. Pasteurized milk produced under clean conditions should have a shelf life limited to less than 2 weeks.
Aires
Georgiana S B
GS
Department of Food Technology, Faculty of Food Engineering, CP 6121, State University of Campinas (UNICAMP), 13083-862, Campinas, São Paulo, Brazil.
Walter
Eduardo H M
EH
Junqueira
Valéria C A
VC
Roig
Salvador M
SM
Faria
José A F
JA
D000818:Animals; D001409:Bacillus cereus / Q000254:growth & development* / Q000302:isolation & purification; D015169:Colony Count, Microbial; D003258:Consumer Behavior; D003257:Consumer Product Safety; D005506:Food Contamination / Q000032:analysis*; D005511:Food Handling / Q000379:methods*; D005516:Food Microbiology; D006358:Hot Temperature; D006801:Humans; D008892:Milk / Q000382:microbiology* / Q000592:standards; D012034:Refrigeration; D013171:Spores, Bacterial / Q000254:growth & development; D013649:Taste; D013997:Time Factors