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Simple membrane filtration method for estimating numbers of Paenibacillus spp. spores in raw milk, using β-galactosidase activity as a selection criterion
- Ohkubo, Yoshiaki, Uchida, Kenji, Motoshima, Hidemasa, Katano, Naoya
- International dairy journal 2019 v.96 pp. 10-14
- Paenibacillus amylolyticus, enzyme activity, microfiltration, porosity, raw milk, spore-forming bacteria, spores, Japan
- Paenibacillus spp. are spore-forming bacteria that adversely affect the quality of dairy products. There is currently no appropriate method for enumerating Paenibacillus spp. spores. We developed a simple membrane filtration method to enumerate Paenibacillus spp. spores in raw milk, using β-galactosidase activity as a selection criterion. Although Paenibacillus spp. spores are relatively small, use of a membrane filter with 0.65-μm pore size allowed us to easily filter raw milk with sufficient recovery. The membrane was put on plates containing X-gal, and detection of β-galactosidase-positive colonies enabled selective enumeration of Paenibacillus spp. spores. We investigated Paenibacillus spp. spore levels in raw milk from six different areas in the Tokachi region, Hokkaido, Japan over 1 year. There were ≤10 spores 100 mL−1 throughout the year, with no significant differences between areas or seasons. Paenibacillus amylolyticus and Paenibacillus odorifer were the predominant species, accounting for 50.6% and 27.4% of the total spores, respectively.