Aflatoxin Reduction and Retardation of Aflatoxin Production by Microorganisms in Doenjang during a One-Year Fermentation.

Vishal Kumar,Ashutosh Bahuguna,Jong Suk Lee,Myunghee Kim,Sung Soo Han,Hyang Sook Chun,Srinivasan Ramalingam

doi:10.3390/jof8020190

Abstract

Meju, a raw material for doenjang preparation, is highly vulnerable to aflatoxin-producing fungi. The aim of this study was to evaluate the effect of a one-year fermentation on aflatoxins and aflatoxin-producing fungi in doenjang spiked with aflatoxins B1, G1, B2, and G2 and inoculated with toxigenic Aspergillus flavus. A significant reduction in aflatoxins was observed after a year of fermentation, measuring 92.58%, 100%, 98.69%, and 100% of B1, G1, B2, and G2, respectively. After a year of fermentation, 6.95 ± 3.64 µg/kg of total aflatoxin was detected, which represents a 97.88% reduction in the total aflatoxin compared with the initial value (328.83 ± 36.60 µg/kg). Several aflatoxin-degrading fungi (Aspergillus versicolor, Cladosporium subcinereum, Aspergillus ochraceus) and bacteria (Bacillus albus, Bacillus velezensis) isolated from doenjang were identified as the major contributors to the reduction of aflatoxin. Furthermore, it was observed that most of the aflatoxin contamination in doenjang occurred during the meju stage, and this stage was found to be most susceptible to A. flavus contamination and growth. These findings reveal that native microorganisms mediate aflatoxin clean-up in doenjang during fermentation and support the use of such microorganisms as a starter culture for the preparation of aflatoxin-free doenjang.

Highlights

Soybean-based fermented foods are an integral part of the diet in many Southeast Asian countries, including Korea, China, and Japan [1,2,3]
We examined the presence of aflatoxins B1, G1, B2, and G2 in doenjang samples during 12 months of fermentation
A non-considerable (Table S1) amount of aflatoxins was traced in a few samples (Table S2), which spontaneously disappeared with the fermentation time

Summary

Introduction

Soybean-based fermented foods are an integral part of the diet in many Southeast Asian countries, including Korea, China, and Japan [1,2,3]. Examples of soybean-based fermented foods include thua nao from Thailand, sufu from China, natto from Japan, tempeh from Indonesia, and doenjang from Korea. Doenjang is made of meju and salt and is naturally fermented by diverse microbial communities. Both aerobic and anaerobic fermentation take place during doenjang-meju preparation. In the exterior part of doenjang-meju, aerobic fermentation takes place, whereas in the interior part, anaerobic or microaerophilic fermentation is predominant. Microbial communities vary greatly in the interior and exterior parts of doenjang-meju fermentation. The Korea Food and Drug Administration limits total aflatoxin and aflatoxin B1 levels in doenjang to 15 μg/kg and 10 μg/kg, respectively, to ensure safe consumption

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Results