Aerobic spore-forming bacteria in raw and pasteurized milks of East-Azarbaijan area: occurrence, quantity and diversity

Growth and proliferation of spore-forming bacteria cause food spoilage or may contribute in foodborne illness through the production of toxins. Aerobic spore-formers are widely distributed in nature and are of greater concern in dairy industry. The aim of this study was to investigate the occurrence, quantity and diversity of spore-forming bacteria in raw and pasteurized milks of East-Azarbaijan area. For this reason, 80 raw milks and 40 pasteurized milk samples were randomly obtained and the populations of mesophilic together with thermophilic spore-formers were estimated. The diversity of the enumerated colonies was determined using routine biochemical assays. According to the results, the occurrence of mesophilic and thermophilic spore-formers in raw milks was 82.5% and 87.5%, and for the pasteurized milk samples it was 77.5% and 82.5%, respectively. Results revealed remarkable loads of spore-formers (ranged 2-8 log cfu/ml) both in raw and pasteurized milks. Moreover, 12 and 8 Bacillus species were identified in raw and pasteurized milks, respectively; amongst B. macerans and B. cereus were the major species which accounted for the overall 76% and 64% of the isolates in raw and pasteurized milk samples, respectively. Results revealed that contamination of milk via environmental sources could be the main reason for the presence of high loads of spore-forming bacteria, so that pasteurization process was not appreciably efficient. It was concluded that the presence of toxin-producing species in pasteurized milks could be considered as a health hazard for the consumers.