Aflatoxin production by Aspergillus parasiticus and its stability during the manufacture of Korean soy past (doenjang) and soy sauce (kanjang) by traditional method

Abstract

Aflatoxin (AF) production and its stability on meju (crushed Korean soybean cake) by a pure culture of Aspergillus parasiticus and a mixed culture of A. parasiticus, A. oryzae and Bacillus subtilis (fermentation 1) during the manufacture by traditional methods of Korean soy past (doenjang) and soy sauce (kanjang) were studied. There was a difference in the amount of aflatoxin production on different varieties of soybeans, but the pattern of toxin production was similar. During fermentation, more total aflatoxins were produced under the mixed culture condition. Aflatoxin G1 (AFG1) production was highly stimulated though it degraded quickly, whereas aflatoxin B1 (AFB1) synthesis was low. The exposure of the meju to sunlight during fermentation had no effect in reducing aflatoxin synthesis. When the meju fermented under natural conditions (fermentation 2) with a contamination by A. parasiticus, high levels of aflatoxins were still produced. After a month of ripening of the fermented meju with charcoal in brine, more AFG1 than AFB1 was degraded in both the pure and mixed culture samples (degradation %; B1: 2-69%, G1: 31-84%). When the meju was ripened in water, most of the aflatoxins were degraded (B1: 95-99%, G1: 100%) in a month, accompanied by a significant increase in pH (p < 0.05). A greater amount of aflatoxins (96-100%) was detected in the meju when it was ripenend in brine, however, lower amounts (25-85%) of aflatoxins remained in meju ripened in water. During three months of ripening in brine, 83-98% of AFB1 and 98-100% of AFG1 were degraded in fermentation 1, but the degradation rate was slower (B1: 63%, G1: 98%) following fermentation 2. The total levels of aflatoxins remaining were significantly (p < 0.05) reduced when charcoal was added to the mixture.