Bacillus cereus in Refrigerated Milk Submitted to Different Heat Treatments

Abstract

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.

Bacillus cereus food poisoning: international and Indian perspective

“…In the dairy industry, B. cereus group spp., especially psychrothrophic strains, are recognized to limit the keeping quality of pasteurized milk (Svensson et al 2004;Hanson et al 2005;Barbano and Santos 2006;Aires et al 2009). …”

Microflora of biofilm on Algerian dairy processing lines: An approach to improve microbial quality of pasteurized milk

“…Different potential contamination sources of pasteurized milk are reported: raw milk (Bartoszewicz et al, 2008;Lin et al, 1998;), equipment surfaces (Salutiano et al, 2009;Sharma and Anand, 2002;Svensson et al, 2004) and packaging materials (Petrus et al, 2010;Simon and Hanson, 2001;Zygoura et al, 2004). Temperatures used for the pasteurization processes are also reported to affect processed milk shelf life (Aires et al, 2009;Hanson et al, 2005;) as well as the somatic cell count of raw milk (Barbano et al, 2006). Nevertheless, among these limiting factors, pasteurization process appears to be a key step with regard to spore-forming bacteria because the role of temperature on spore activation.…”

Evaluation of the psychrotrophic specific signatures for cspA gene and 16S rDNA on the phenotype of Bacillus cereus sensu strictu

“…; Cronin and Wilkinson ; Aires et al . ). Some strains can also multiply at refrigeration temperatures (García‐Armesto and Sutherland ; Larsen and Jorgensen ; Guinebretière et al .…”