Reduction of Bacillus cereus spores in sikhye, a traditional Korean rice beverage, by modified tyndallization processes with and without carbon dioxide injection

Abstract

Aims: The objective of this study was to inactivate Bacillus cereus spores in sikhye using a modified tyndallization process involving injection with carbon dioxide (CO2). Methods and Results: Heat tolerance of B.similar to cereus spores in tryptic soy broth and sikhye was evaluated. The D95 degrees C values of the B.similar to cereus spores were 2.84.9 min, dependent of type of heating medium or inoculum level. The lethality of conventional heat treatment and modified tyndallization with or without CO2 injection against B.similar to cereus spores in sikhye was determined. The order of effectiveness was modified tyndallization with CO2 > modified tyndallization without CO2 > conventional heat treatment. Modified tyndallization with CO2 reduced the number of B.similar to cereus spores in sikhye by 5.8 log CFU ml-1. The increased CO2 concentration and decreased pH of sikhye resulting from CO2 injection rapidly reverted to near-normal values after heat treatment. Conclusions: Modified tyndallization with CO2 was more effective than conventional heat treatment or modified tyndallization without CO2 in reducing B.similar to cereus spores in sikhye. Significance and Impact of the Study: Results of this study will be useful when developing strategies to control B.similar to cereus spores in sikhye and may have application to other beverages.