Investigation Of Grain Processing Contaminants And Preliminary Study Of Aflatoxin B₁ Degrading Strains

Aflatoxin B₁（AFB₁）is one of the fungal toxins,mostly found in cereals,which is recognized as a Class I carcinogen by the World Health Organization and poses a great threat to human health and economic development.The efficient and economic removal of AFB₁has become a widespread concern for researchers,and biodegradation of AFB₁is being focused on because of its low cost,high efficiency and good safety.In this study,we analyzed the current situation of mycotoxins contamination in rice,wheat,corn and their products in some regions of China,screened out AFB₁efficient degrading strains and carried out preliminary identification,optimized their growth conditions,and studied their degradation mechanism and characteristics.The specific results of the study are as follows:By detecting the contents of mycotoxins and heavy metals in rice,wheat,corn and their products in some regions of China,the current status of mycotoxin contamination was statistically analyzed.The results showed that the detection rates of mycotoxins in rice and its products were ZEN>AFB₁>AFB₂>AFG₁>DON>AFG₂in descending order;in wheat and its products,AFB₁and DON toxins showed high positive rates,but the exceedance rate was maintained at a low level;in corn and its products,the detection rate of ZEN was as high as 100.00%and the exceedance rate was 44.44%.The detection rates of heavy metals in rice and rice flour and their products were Cd>Pb>Hg in descending order,with Cd showing a high positive rate,followed by Pb,and Hg not detected in all samples.The strains that could efficiently degrade AFB₁were screened by co-culture with AFB₁.The results showed that 11 strains could degrade AFB₁from 62 strains,among which the degradation rate of MD1 to AFB₁was as high as 99.2%,and the strain MD1 was identified as penicillium herquei by morphology and ITS r DNA gene identification.The degradation rate of AFB₁by penicillium herquei MD1 was improved by optimizing the conditions for the degradation of AFB₁by penicillium herquei MD1.The results showed that the single-factor experiment showed the highest AFB₁degradation rate of strain MD1 when the inoculum was 2%,the speed was 160 r/min,the initial p H of the medium was 7,the incubation time was 72 h,and the incubation temperature was 28℃.The response surface optimization experiment showed that the degradation rate of AFB₁could reach the maximum after co-cultivation of strain MD1with AFB₁for 24 h at the incubation temperature of 28℃,the initial p H of the medium of 8 and the inoculum of 1%,and the measured degradation rate of AFB₁after optimization increased by 11.73%compared with the single-factor optimization（86.84%）.The effective sites of AFB₁degradation by suspension,thalli,spore solution and fermentation solution were investigated by separating the thalli and fermentation solution of penicillium herquei MD1 suspension,and the effective sites of thalli were crushed for further investigation.The results showed that the degradation rate of AFB₁was 98.15%and 28.20%for the suspension of penicillium herquei MD1 and the unbroken thalli after 72 h of culture,and the degradation rate of AFB₁was 55.40%after 24 h of culture for the broken thalli.