Microbial characterization of the Japanese traditional pickle senmaizuke produced by two different manufacturing...

Senmaizuke, a traditional turnip pickle, prepared in Kyoto, Japan, is produced via two types of manufacturing processes: with and without vinegar for fermentation. The aim of this study was to reveal the microbial community and growth behavior in the products and manufacturing processes of two types of senmaizuke. Microbial growth analysis of commercial senmaizuke products showed that both types harbored 10²-10⁸ colony forming units (CFU)/g of lactic acid bacteria (LAB) and 10²-10⁴ of yeast. The fermented-type products showed successive growth of LAB during the pickling and ripening processes, whereas LAB in vinegar-type products showed growth only at the preliminary pickling step before vinegar addition; however, the bacteria were viable at the ripening step. LAB in the vinegar-type products showed growth when the pH of the pickle was neutralized, indicating that acidification via vinegar retards LAB growth. Metagenomic sequencing showed that the fermented-type products harbored Lactobacillus, Leuconostoc, and other halophilic and psychrophilic bacteria, with a higher bacterial diversity than in the vinegar-type products. In the vinegar-type products, Lactobacillus, Leuconostoc, or both were predominant. Culture tests using LAB isolates and turnip medium suggested that a change in the dominance of Leuconostoc to Lactobacillus members observed in the fermented-type products during pickling and ripening processes was attributed to the low pH sensitivity of Leuconostoc as well as a relatively long lag phase of growth for adapting to the pickling environment. The findings of this study will be useful for the appropriate quality control and assurance procedure of senmaizuke.