Factors that determine the microbiological quality of ready-to-use salted napa cabbage (Brassica pekinensis): Season and distribution temperature

Abstract

A large outbreak of Escherichia coli O157:H7 in Japan, caused by salt-pickled napa cabbage, highlighted potential hazards posed by this vegetable, which is a ready-to-use form of kimchi or some side dishes that does not undergo heat treatment. Here, microbiological quality of 500 commercial salted napa cabbages were examined (quantitative analysis: Aerobic Plate Count [APC], total coliforms [TC], Bacillus cereus, and E. coli; qualitative analysis: E. coli and seven foodborne pathogens). To identify major factors affecting microbiological quality, we examined the correlation between various production, distribution, and physicochemical factors and the results from quantitative analyses. The overall results revealed that the salinity of salted napa cabbage (average, 3.7%) did not guarantee microbiological quality. Although no pathogenic foodborne bacteria were isolated from the samples, the TC count (an indicator of overall hygiene) reached a maximum of 6.8 log CFU/g. APCs and TC counts were highest in the summer (average, 7.1 and 4.4 log CFU/g, respectively), suggesting that temperature is a significant factor. Indeed, distribution temperature was a major factor (correlation coefficient [r] = 0.7, P <.05) for increased bacteria counts; other factors (i.e., salinity, pH, etc.) did not show a strong correlation with bacterial counts. These results highlight the potential hazard of bacterial growth during distribution. Thus, manufacturers should ensure that both the product and the distribution conditions are suitable: salted napa cabbages should be maintained at < 10 degrees C. Few studies have examined the microbiological quality of salted napa cabbages; therefore, the present study may be useful as a quantitative risk assessment and should help to improve/establish safety regulations. (C) 2017 Elsevier Ltd. All rights reserved.