Screening Of Fungal Toxins-producing Fungi From Contaminated Corns And Chemical Investigaiton On Seconday Metabolites

Food quality and safety are directly related to the country's food supply,people's health,and social development and stability.Approximately 25%of the world's food is contaminated by mycotoxins each year.Food mycotoxin contamination is particularly prominent in China.In order to effectively prevent toxin-excess food from entering the human food chain,timely and accurate detection method for the mycotoxins in food is necessary.The preparation of mycotoxins standard materials is relatively lagging behind in China,and most of mycotoxins standard have long been dependent on imports and are restricted by foreign countries,which seriously affects our country's food security.Therefore,conducting chemical research on toxin-producing fungi in contaminated grain can not only discover some potential mycotoxins,to provide theoretical basis for further control of food security;but also develop some mycotoxin standard substances to satisfy the mycotoxins detection.In this study,fifty fungi were isolated from twenty-five contaminated grains collected in five provinces of China.Based on mycotoxin anaylsis by HPLC,five strains producing mycotoxins were obtained and identified from contaminated grains,including Fusarium sp(L1278)producing zearalenone(ZEA),deoxynivalenol(DON)and 3-acetyl deoxynivalenol(3-ADON),Fusarium clavum(L1293)producing zearalenone(ZEA),Aspergillus westerdijkiae(L1295)producing ochratoxin A(OTA),Aspergillus tennesseensis(XZ155)producing sterigmatocystin(STE)and Fusarium verticillioides(Fv WT)producing fumarin B₁ and B₂.In order to obtain the standard substance of ochratoxin A,L1295 was fermented and its secondary metabolites were investigated.Totally sixteen compounds were isolated from this fungus,including two new cyclopeptides(1,2)and fourteen known compounds(3-16).Biological activities of cytotoxicity,antibacterial,and?-glucosidase inhibitory activities were assayed for the isolated compounds.Compound 5 had weak inhibitory activity against Escherichia coli,Bacillus subtilis,Staphylococcus aureus and showed weak cytotoxicity on 293T,K562 and Hep G2;Compounds 12 and 14 showed inhibitory effect on 293T at the dose of 100?mol;Compounds 3 and 13 had inhibitory activity on?-glucosidase,with IC₅₀ values of 138.9±6.3?mol and 429.9±17.5?mol,respectively;Compound 2 showed stronger inhibition against NO release from LPS-activated macrophage at 100?m.In this study,the content of ochratoxin A in the crude extract of L1295 was determined to be 115.5 mg/g of extract.This article provides high-yield strains for the preparation of mycotoxins through the isolation,identification and screening of toxin-producing strains.Through the study of the secondary metabolites of Aspergillus westerdijkiae,two new cyclic tetrapeptide compounds were discovered,and the content of ochratoxin A in the crude extract of Aspergillus westerdijkiae was clarified,which provided a basis for the preparation of ochratoxin A standard substances.