Antimicrobial effects of vinegar against norovirus and Escherichia coli in the traditional Korean vinegared green laver (Enteromorpha intestinalis) salad during refrigerated storage

Abstract

In Korea, edible seaweeds are potentially regarded as high-risk foods with respect to enteric norovirus (NoV) and non-pathogenic generic Escherichia coli. This study investigated the antimicrobial effects of 5%, 10%, and 15% vinegar (6% acetic acid) on the survival of murine norovirus-1 (MNV-1), a human NoV surrogate, and E. coli, a fecal indicator in experimentally contaminated raw fresh green lavers (Enteromorpha intestinalis) during a 7-d storage period at 4°C. Both MNV-1 titers and E. coli counts significantly (p<0.05) decreased with stepwise increase in vinegar concentration and storage time, except in E. coli of the 0% vinegar-containing lavers; however, MNV-1 was more resistant to vinegar than E. coli. The overall average MNV-1 titers were significantly (p<0.05) higher in 0% vinegar-containing lavers (3.6log₁₀PFU/ml) than in 5-15% vinegar-containing lavers (3.3-3.1log₁₀PFU/ml) throughout the 7days of storage. A 1-log reduction in the MNV-1 titer was observed in 0% vinegar-containing laver samples after 5days of storage and 5-15% vinegar-containing laver samples after 3days of storage. The overall E. coli count was also significantly (p<0.05) decreased in the 15% (6.8log₁₀CFU/g) vinegar-containing lavers than in the 10% (7.3log₁₀CFU/g) and 5% (7.6log₁₀CFU/g) vinegar-containing lavers. A >1-log reduction in the E. coli count was observed in 10-15% vinegar-containing laver samples just after 1day of storage. A 2-log reduction in the E. coli count was also observed in 10-15% vinegar-containing laver samples after 5days of storage. Using the non-linear Weibull model, this study showed that the d_R-values (1-log reduction) of MNV-1 were 4.90days for 0%, 4.28days for 5%, 3.79days for 10%, and 2.88days for 15% vinegar-containing lavers, whereas those for E. coli were 1.12day for 5%, 1.03day for 10%, and 0.90day for 15% vinegar-containing lavers stored at 4°C. Vinegar with over the storage time can be used as an antimicrobial ingredient against NoV and E. coli in Korean conventional foods. Specifically, this study suggests that ~1day of storage is required for 1-log reduction in the E. coli count in the vinegar-containing (5-15%) lavers, whereas 3-5days of storage at 4°C is adequate for 1-log reduction in the MNV-1 count in the vinegar-containing and non-vinegar-containing lavers.

Keywords: E. coli; Fresh green laver; Murine norovirus-1; Storage; Vinegar.