Mycotoxin and microbiome profiling for aflatoxin control in the Korean traditional fermented soybean paste Doenjang

Mycotoxin contamination is an important concern in producing traditional fermented soybean paste, though no effective control strategy has been developed. This study investigated the mycotoxin profiles of the intermediate (fermented soybean brick, known as "Meju" in South Korea) and final soybean paste products ("Doenjang") to identify major contaminants and describe microbial diversity with the mycotoxins. Profiling of 323 Meju and Doenjang samples revealed severe aflatoxin (AF) contamination. Metagenomic analysis revealed that the species richness and phylogenetic diversity were significantly higher in AF-free than in AF-contaminated Meju and Doenjang. Certain Aspergillus and Penicillium species were more abundant in AF-free than in AF-contaminated Meju and Doenjang. To control AF levels, we developed a novel mycotoxin-reduction approach that preserves the indigenous microbiome by backslopping fermentation of Meju in both Aspergillus-dominant and Penicillium-dominant modes. Both treatments reduced AF levels by > 95 % at a backslopping rate of > 2.5 %. Our results suggested that backslopping fermentation can effectively reduce AF contamination in traditional soybean fermentation, maintaining food safety standards and artisanal practices.