Distribution,OTA-producing And Growth Characteristics Of Aspergillus Niger Aggregates In Stored Paddy Rice In Southern China

Paddy rice is one of the staple foods in southern China.The biggest hazard on paddy rice is mold contamination.The growth of mold causes mildew in paddy rice and loses its edible value.Aspergillus niger is one of the dominant molds in stored paddy rice,which poses a serious threat to the safety of paddy rice due to its strong mildew-inducing ability and mycotoxin production potential.Previous studies have shown that Aspergillus niger is one of 27 species in the Aspergillus niger aggregate,which is a morphologically indistinguishable species,some of which produce Ochratoxin A(OTA).Therefore,it is very important to accurately classify Aspergillus niger aggregates in paddy rice and to clarify their OTA-producing potential and biological characteristics.So far,there has been no systematic study on Aspergillus niger aggregates in paddy rice in China.Therefore,this study took the representative stored paddy rice from ten provinces in southern China as the object to isolate and identify the Aspergillus niger aggregates,and determine their OTA-producing capacity and their growth and oxidation tolerance under different carbon source conditions.The main results of this paper are as follows:1.Through ITS,Ca M amplification and sequencing,107 Aspergillus niger aggregates were collected from the representative grain banks of the main rice producing areas in southern China.They were divided into Aspergillus niger,Aspergillus welwitschiae,Aspergillus tubingensis and Aspergillus neoniger.Phylogenetic analysis has divided them into two branches,Aspergillus niger and Aspergillus welwitschiae belong to the same branch,Aspergillus tubingensis and Aspergillus neoniger belong to another branch.The same species are closely related to each other.The prevalence of Aspergillus niger and Aspergillus welwitschiae increased with the decrease of latitude.2.OTA test on 107 Aspergillus niger aggregates showed that all the strains were not producing OTA.The results of enzyme-linked immunoassay(ELISA)showed that7 strains were positive.However,the 107 strains of Aspergillus niger aggregates were identified as OTA-free strains by high-performance liquid chromatography(HPLC-FLD)and OTA biosynthetic cluster.3.The growth and oxidation tolerance of Aspergillus niger HY2 cultured with different carbon sources were studied.The results showed that when the concentration of H2O2 was 20 m M,only the strains with sucrose,glucose and cellulose as carbon sources grew slowly.When the concentration of H2O2 was 10 m M,the strain with xylose as carbon source had the highest spore production,which reached 1.22×10~7conidia/m L,and the activities of anti-superoxide anion,SOD and GPX were also strong.The contents of H2O2 and MDA in the strains with arabinose as carbon source were lower,and the activities of SOD and CAT were stronger,indicating that the strains cultured under these two carbon sources had better oxidation tolerance.The strain with maltose as carbon source had the lowest spore production,only 3.52×10~6 conidia/m L,and its anti-superoxide anion and CAT activity were also low,indicating that the strain with maltose as carbon source had a weak oxidation tolerance.