The supercooling degree (SD), which refers to the difference between the ice nucleation temperature and freezing point of kimchi, varies depending on the type of kimchi, manufacturer, recipe, and manufacturing season. The aim of this study is to investigate the major influencing factors for the supercooled storage of kimchi and to analyze the possibility of supercooled storage for commercial kimchi. Pearson correlation analysis determined that, in commercial kimchi manufactured between March and July 2018, the SD of kimchi correlated to the number of aerobic bacteria (P < 0.01), however, was not associated with lactic acid bacteria. Moreover, the ice nucleation temperature of saline solution inoculated with aerobic bacteria was reduced from -3.03 ± 0.04 to -6.18 ± 0.11 °C by 10 kGy gamma ray sterilization. Meanwhile, the ice nucleation temperatures of 1.8 kg of commercial red cabbage kimchi and 500 g of white cabbage kimchi manufactured in February 2020 were -3.93 ± 0.06 °C and -3.57 ± 0.06 °C, respectively, and they could be stored at -2.5 °C for 12 weeks without freezing. Additionally, supercooled storage of kimchi at -2.5 °C caused a fermentation delay effect compared to control storage at 1 °C, considering the acidity and amount of lactic acid bacteria. Therefore, if the number of aerobic bacteria is controlled during the manufacturing process of kimchi, supercooled storage at temperatures below -2.5 °C may extend the shelf life of kimchi. PRACTICAL APPLICATION: We have shown that aerobic bacteria are the key influencing factor for ice nucleation of kimchi during supercooled storage. Aside from the initial sterilization process, fermentation of kimchi can also be delayed by lowering the storage temperature below -2.5 °C. Moreover, the method of direct cool refrigeration may have an industrial-level application.
Keywords: supercooled storage, kimchi, lactic acid bacteria, fermentation, direct cool refrigerator.
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