Sonmat, a citizen-science enabled Kimjang kimchi case study on associations between hand and kimchi microbiota

Kimjang kimchi is traditionally made in Korea in autumn to preserve cabbage during colder winter times after the harvest. Kimjang is an important societal tradition in which the whole community collaborates in processing the cabbages into kimchi. Cabbage is kneaded by hand with salt and fermented in large earthenware jars. The origin of the microorganisms that contribute to flavor and safety during fermentation is still unclear. Bacteria present on the raw ingredients are important colonizers of the fermentation. Additionally, in Korean culture, the term “Sonmat“ is often used, which literally translates into 'hand flavor', suggesting a role for the hand microbiota in the kimchi fermentation. In this citizen-science project, we aimed to investigate the impact of the hand microbiome on kimchi fermentation during a special kimchi festival organized in Belgium. Samples were taken from the hand microbiome of the participants after washing just before the start of the salting and kneading of the cabbage. Both individual and group fermentations were carried out and sampled after 48 h fermentation at room temperature. The kimchi fermentations contained mainly lactic acid bacteria belonging to the genera Leuconostoc, Weissella and Latilactobacillus. The hand microbiota was characterized by the presence of Staphylococcus, Corynebacterium, Micrococcus and Enhydrobacter. Only a limited overlap was found between the hand and kimchi microbiome, but 15% of the variation within the kimchi microbiome could be explained by the respective microbiota on the hand of the participant and correlations were found between the relative abundance of Staphylococcus on the hand and relative abundance of Latilactobacillus and Leuconostoc ASVs found in kimchi. In addition, different microbiota were found to dominate the kimchi made following traditional group Kimjang practices compared to individually prepared kimchi. These findings pave the way for future research into how traditional practices and the skin microbiome influence the unique qualities of kimchi, offering exciting possibilities for enhancing fermentation processes and cultural food heritage through citizen science