The Similarities in Microbial and Chemical Patterns of Fermentation in Two Open Environments were Promoted by Using 150-Year-Old Nukadoko as Starters.

Nukadoko, a fermented rice bran employed in traditional Japanese pickling, uses lactic acid bacteria to ferment vegetables. Here, we report the microbial and chemical data of a mixture of matured 150-year-old nukadoko and commercially available rice bran placed in two open environments over 29 days. Across the two environments, Loigolactobacillus was identified as the dominant microbial genera in the later stages of fermentation in nukadoko. The period of increase in the relative abundance of Loigolactobacillus correlated with a decrease in pH and Oxidation-Reduction Potential (ORP) values. While the two environments showed a difference in the rate of change in microbial diversity, they shared the common process through which Loigolactobacillus outcompeted adventitious bacteria in nukadoko, as indicated by the alpha and beta diversity index. Thus, the similarities in microbial and chemical data across two open environments during fermentation using starters indicate that starters contribute to the stability of fermentation in open environments.

Direct contact of fermented rice bran beds promotes food-to-hand transmission of lactic acid bacteria.

The skin microbiome, which varies widely between individuals, plays a crucial role in human health. It also interacts with the environment in various ways, including during the preparation of fermented food. Nukadoko is a pickle and traditional fermented food in Japan that utilizes lactic acid bacteria to ferment vegetables. When preparing or maintaining Nukadoko, it is mixed with bare hands. Despite the known interaction between Nukadoko and human skin, no studies have explored its impact on Nukadoko quality or skin microbiome changes. This study examines these effects during Nukadoko maintenance. Three participants were asked to stir commercially available late-stage Nukadoko for 14 days and not stir it for the remaining 14 days to examine microbial settlement and shedding. Microbiome analysis was performed on human skin and Nukadoko. We found that microorganisms from rice bran beds can temporarily settle on human skin but are shed quickly. Stirring rice bran beds by hand may have short-term effects on the skin microbiome. This study provides insights into the communication between human and food microbiomes in traditional Japanese fermented foods.