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

摘要

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. cereus spores in tryptic soy broth and sikhye was evaluated. The D_{95 degrees C} values of the B. cereus spores were 2.8-4.9 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. 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. 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. cereus spores in sikhye. Significance and Impact of the Study. Results of this study will be useful when developing strategies to control B. cereus spores in sikhye and may have application to other beverages