Preparation of folate-producing nukadoko by artificial inoculation and investigation of their microbial community

In order to increase folate in the nukadoko, the present study was conducted to optimise the fermentation process by artificial inoculation of folate-producing strains of Lactobacillus plantarum Z3 and Pichia myanmarensis J2, and to systematically study the dynamic evolution of microbial communities and their correlation with the physicochemical indexes in the fermentation process. The optimised conditions were as follows: 1:2 (v/v) ratio of Pichia myanmarensis J2 to Lactobacillus plantarum Z3, 6 % inoculum size, 9 % brine concentration, bed thickness of 5–7 cm, fermentation time of 60 days, and addition of 0.1 % ascorbic acid (Vc). Under these optimised conditions, the addition of Vc effectively solved the problem of low folate accumulation rate caused by acidic conditions in the traditional fermentation process. High-throughput sequencing results showed that the diversity of the bacterial community in the nukadoko was higher than that of the fungal community. At the genus level of the bacterial community, Pantoea and Methylobacterium were the dominant genera in the early stage of fermentation (Day0-Day15), and Lactobacillus became the dominant group from Day30 to Day60 with the extension of fermentation time. In contrast, Pichia was always the dominant genus in the fungal community. This study provides a new idea for the development of folate-containing nukadoko, and also lays a preliminary foundation for the preparation of folate-rich nukazuke.