Quality and microbial change of radish Paocai by variable temperature fermentation

Temperature is an important factor affecting the fermentation and storage quality of Paocai. Radish Paocai was prepared by two methods: constant-temperature fermentation (continuous fermentation at 25 ℃ for 18 d) and variable-temperature fermentation (fermentation at 25 ℃ for 3 d and then transferred to 5 ℃ for further fermentation for 15 d). The physiochemical and microbial indicators, texture and color parameters of the two groups of samples during the fermentation process were measured to explore the effect of changing the fermentation temperature on the quality of radish Paocai. The results showed that compared with constant-temperature fermentation, the pH (3.63) and lactic acid content (6.09 mg/ml) of variable-temperature fermented radish Paocai were higher, while the total acid (0.37 g/100 g) and acetic acid (0.91 mg/ml) contents were lower. The lactic acid bacteria count [6.75 lg (CFU/ml)], the total colony count [6.42 lg (CFU/ml)] and yeast count [4.57 lg (CFU/ml)] in the variable-temperature fermented radish Paocai were all higher than those in the constant-temperature fermented radish Paocai. The dominant fungal genus of both groups of samples was Kazakhstania, but the relative abundance of the variable temperature fermented radish Paocai was higher (77.7%), and the relative abundance of Candida was lower (20.5%). The variable-temperature fermented radish Paocai had better hardness, chewiness and a brighter color state. In conclusion, variable-temperature fermentation not only enabled Paocai to mature quickly and promote its aroma formation, but also maintained the quality of Paocai during subsequent storage or transportation.