Comparison of the murine norovirus-1 inactivation in cabbage Kimchi with two different salinities during storage

Abstract

Enteric noroviruses are occasionally detected in Kimchi, which is a traditional dish made of fermented vegetables. This study was aimed at examining the effects of two levels of salt concentrations on the survival of murine norovirus-1 (MNV-1), a human norovirus surrogate, in experimentally contaminated cabbage Kimchi stored at 5°C for 10weeks. The number of total aerobic bacteria (TAB) and lactic acid bacteria (LAB), MNV-1 titer pH, and acidity were measured every week. The titers of MNV-1 in both low (1.17%) and normal (2.22%) salinity cabbage Kimchi were significantly (P<0.05) decreased with increase in storage time. The overall reduction was 1.75log10plaque-forming unit (PFU)/mL in normal salinity cabbage Kimchi and 1.24log10PFU/mL in low salinity cabbage Kimchi. The time required to reduce the titer by >1log10PFU/mL in normal and low salinity cabbage Kimchi were 4 and 8weeks, respectively. The pH value under both salinities significantly (P<0.05) decreased until 4weeks. The maximum acidity was 0.83% and 0.79% in normal and low salinity cabbage Kimchi, respectively, during the 10weeks. The population of TAB and LAB reached up to 7.33log10colony-forming unit (CFU)/g as a maximum population during the storage period of 3weeks in normal salinity cabbage Kimchi. However, the population of TAB and LAB in low salinity cabbage Kimchi reached to 6.99 and 7.04 log10CFU/g at 5 and 4weeks, respectively. Through these findings, fermentation factors such as TAB, LAB, pH, and acidity of cabbage Kimchi were influenced by salt concentration. The inactivation of MNV-1 in normal salinity cabbage Kimchi was much faster than that in low salinity cabbage Kimchi because the fermentation in normal salinity cabbage Kimchi progressed more quickly than that in low salinity cabbage Kimchi. However, both salinity cabbage Kimchi were able to infect cells for 70days even though the MNV-1 was reduced over 1 log10 during fermentation. Therefore, the way to protect cabbage Kimchi from norovirus must be considered.