title: Evaluation of high-intensity ultrasonication for the inactivation of endospores of 3 bacillus species in nonfat milk.
abstract: Endospores of Bacillus licheniformis [American Type Culture Collection (ATCC) 6634], Bacillus coagulans (ATCC 12245), and Geobacillus stearothermophilus (ATCC 15952) were spiked in sterile nonfat milk, and subjected to high intensity batch ultrasonication treatment at different amplitudes (80 or 100%) and durations (1 to 10 min). Increasing the amplitude from 80 to 100% did not result in enhanced inactivation of G. stearothermophilus endospores. However, an increase in the duration of ultrasonication from 1 to 10 min significantly increased the inactivation of endospores of all 3 species. About 48.96% of the G. stearothermophilus endospores were inactivated by ultrasonication alone, whereas ultrasonication and pasteurization combined increased the inactivation to 65.74%. Inactivation of endospores could be further enhanced to 75.32% by ultrasonication and higher heat (80 °C/1 min) combination. Endospores of B. licheniformis and B. coagulans were inactivated to a lesser extent compared with G. stearothermophilus spores. Ultrasonicated B. licheniformis endospores germinated in higher numbers when compared with untreated endospores resulting in their greater inactivation during the combined treatment. During microstructure imaging of ultrasonicated endospores, although no structural damage was noticed, they showed irregular shrinkage and wrinkles with surface coarseness. This may also have contributed to their reduced thermal resistance, in addition to sporulation.
authors.affiliation: Midwest Dairy Foods Research Center, Dairy Science Department, South Dakota State University, Brookings 57007.
authors.forename: Som Nath
authors.initials: SN
authors.lastname: Khanal
authors.affiliation: Midwest Dairy Foods Research Center, Dairy Science Department, South Dakota State University, Brookings 57007. Electronic address: Sanjeev.anand@sdstate.edu.
authors.forename: Sanjeev
authors.initials: S
authors.lastname: Anand
authors.affiliation: Department of Agricultural and Biosystems Engineering, South Dakota State University, Brookings 57007.
authors.forename: Kasiviswanathan
authors.initials: K
authors.lastname: Muthukumarappan
mesh_terms: D000818:Animals; D001407:Bacillus / Q000528:radiation effects*; D001411:Geobacillus stearothermophilus / Q000528:radiation effects*; D050296:Microbial Viability; D008892:Milk / Q000382:microbiology*; D061352:Pasteurization / Q000379:methods*; D013010:Sonication / Q000662:veterinary*; D013171:Spores, Bacterial / Q000528:radiation effects*; D013997:Time Factors
keywords: endospore; nonfat milk; sporeformers; ultrasonication