Aflatoxin control strategies for traditional Korean doenjang: Fermentation process improvements and industrial application

Abstract

Meju, a raw material used in fermented soybean paste, doenjang, is often contaminated with aflatoxins; thus, controlling aflatoxin contamination in meju and doenjang is crucial. A one-variable-at-a-time (OVAT) approach revealed an inhibitory effect on aflatoxin production by Aspergillus flavus in cooked soybeans treated with soaking solutions containing NaCl (≥ 5 %) and vinegar (≥ 1 %). Additionally, a fermentation temperature (40 °C) negatively affected aflatoxin production. Based on OVAT and response surface methodology, three soaking solutions: I (0.1 % vinegar + 2.5 % salt), II (0.1 % vinegar + 3.75 % salt), and III (0.1 % vinegar + 5 % salt) were prepared and applied at the industrial level of meju production. Meju prepared from soybeans treated with these soaking solutions, coded Meju-I, Meju-II, and Meju-III, respectively, exhibited significant reductions (96.03–100 %) in aflatoxin production compared with control meju (Meju-C). Similar microbial counts and genus-level microbial diversity were observed in Meju-C and Meju-I, with Bacillus, Enterococcus, Klebsiella, and Aspergillus as the predominant microbial genera. Furthermore, sensory analysis of doenjang prepared from Meju-C and Meju-I yielded no significant differences, supporting the applicability of soaking solution I to regulate aflatoxin levels in meju and doenjang at industrial scale.