Predictive modeling of bacterial growth in ready-to-use salted napa cabbage (Brassica pekinensis) at different storage temperatures

The objectives of the current study were to investigate the fate of microbial indicators [aerobic plate counts (APC), total coliforms (TC), and lactic acid bacteria (LAB)] in commercial salted napa cabbages during storage conditions at different temperatures (5, 22, and 30 °C, for up to 72 h) and to develop a predictive growth model using the modified Gompertz equation to determine shelf life. Microbial population sizes (initial log CFU g−1: APC, 5.1; TC, 3.0; LAB, 3.7) remained stable at 5 °C, but rapidly increased by 2-4 log CFU g−1 within 12 h at 22 and 30 °C; furthermore, the pH of salted napa cabbages decreased significantly (P < 0.05: initial pH 6.3; final pH 4.1-4.4) due to LAB fermentation. The pH showed a negative correlation with all bacterial groups and did not prevent the growth of TC during storage. According to the modified Gompertz model (R2 ≧ 0.97), the highest μmax was observed for LAB at 30 °C [0.61 log CFU h−1], while the lowest was noted for TC at 5 °C [0.04 log CFU h−1]. Shelf-life was determined using APC (7.7 log CFU g−1) and LAB (6.0 log CFU g−1) limits; the microbiological acceptability period of salted napa cabbage was predicted to be 12.6 and 9.3 h at 22 and 30 °C, respectively. Thus, consumers should use the product within 12 h of storage at room temperature (more quickly in the summer (9 h)), or store it in a refrigerator. The presented research proposes a shelf-life modeling of commercial salted napa cabbages, which may be used as a scientific basis for product quality control and issuing appropriate guidance for consumer use at home.