Application of gamma radiation for the reduction of norovirus and the quality stability in optimally ripened cabbage kimchi

Abstract

Optimally ripened commercial cabbage kimchi is considered the main cause of enteric norovirus (NoV) outbreaks in Korea. This study investigated the effect of 1–10kGy gamma radiation on the inactivation of murine norovirus-1 (MNV-1; initial inoculum of 5–6log10PFU/ml), used as a human NoV surrogate, in kimchi. The effects of gamma radiation on the pH and acidity were also examined to address the index of quality and fermentation, respectively. Titers of MNV-1 significantly reduced (p<0.05) in kimchi subjected to increasing gamma radiation doses: MNV-1 titers in kimchi after 1, 3, 5, 7, and 10kGy were 4.82 (0.34-log10 reduction), 4.45 (0.71-log10 reduction), 4.18 (0.98-log10 reduction), 3.71 (1.45-log10 reduction), and 3.40 (1.76-log10 reduction) log10 PFU/ml, respectively. However, the values of pH (4.5–4.6) and acidity (0.6–0.7%) were not significantly different between non-irradiated and irradiated kimchi (p>0.05). The D-value (1-log reduction) for MNV-1 in kimchi, calculated using first-order kinetics, was 5.75kGy (R2=0.98, RMSE=0.10). Therefore, this study suggests that the use of ≥5.75kGy gamma radiation in the kimchi manufacturing industry could be very effective in reducing NoV contamination by >90% (1 log), without causing changes in quality and fermentation.