Bacillus cereus in Refrigerated Milk Submitted to Different Heat Treatments

Authors: Aires, Georgiana S.B.¹; Walter, Eduardo H.M.¹; Junqueira, Valéria C.A.²; Roig, Salvador M.¹; Faria, José A.F.¹

Source: Journal of Food Protection®, Volume 72, Number 6, June 2009 , pp. 1301-1305(5)

Publisher: International Association for Food Protection

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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°C for 2 s), "superpasteurization" (96°C for 13 s), and pasteurization (74°C for 15 s) and stored under refrigeration at 4 ± 2°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°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 × 10¹ and 7.0 × 10⁵ 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.

Document Type: Research article

Affiliations: 1: Department of Food Technology, Faculty of Food Engineering, CP 6121, State University of Campinas (UNICAMP), 13083-862, Campinas, São Paulo, Brazil 2: Institute of Food Technology (ITAL), Av. Brasil 2880, 13070-178, Campinas, São Paulo, Brazil

Publication date: 2009-06-01

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First published in 1937, the Journal of Food Protection^®, is a refereed monthly publication. Each issue contains scientific research and authoritative review articles reporting on a variety of topics in food science pertaining to food safety and quality. The Journal is internationally recognized as the leading publication in the field of food microbiology with a readership exceeding 11,000 scientists from 70 countries. The Journal of Food Protection^® is indexed in Index Medicus, Current Contents, BIOSIS, PubMed, Medline, and many others.

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Bacillus cereus in Refrigerated Milk Submitted to Different Heat Treatments

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