Isolation of Spore-Forming Bacteria from Dried Sardine Meal and Thermal Death of the Isolated Bacillus amyloliquefaciens Spores in an Ultra-High Temperature and Extremely Short-Time Processor

Abstract

A highly heat-resistant spore-forming mesophilic bacterium was isolated from dried sardine meal (DSM, Iriko) and identified it as Bacillus amyloliquefaciens. The thermal death characteristics of the bacterial spores were evaluated in a laboratory test. To kill such spores contaminated in DSM, we examined the efficiency of a recently developed ultrahigh-temperature and extremely short-time (UHT-est) processor, which was designed for sterilization of powdered food materials. In the processor, such powders were injected into wet heat steam and processed at temperatures of 140, 150 and 160℃ for 0.16 s and then were instantly cooled down to about 60 to 70℃ at an abrupt pressure drop upon passing through a special nozzle. It was found that the survivors obtained after practical operation of the UHT-est processor at those high temperatures were much less than those estimated from D and z values obtained in the laboratory test. After the treatment under even more severe heating conditions, the DSM color was found to change only slightly. It is suggested that the UHT-est processor effectively kills spores present in DSM, seemingly keeping acceptable quality.