Study On The Inhibitory Effect Of The Volatile Substances Produced By Bacillus Sp.on Aspergillus Flavus

The use of antagonistic bacteria to control the contamination of Aspergillus flavus and its toxin has become a hot research spot in recent years.It is safe,efficient and environmental friendly to control Aspergillus flavus in food by antagonistic bacteria.The volatile compounds produced by Bacillus has good antifungal effect and low molecular weight and easy to spread,which leads to application value in mould control of grain storage.In this paper,Bacillus producing antifungal volatile compounds were screened and identified,and then solid-state fermentation process was optimized to improve the antifungal effect.The volatile compounds were identified and its antifungal mechanism was studied.The purpose is to provide a theoretical basis for developing a new type antifungal agents for paddy.The main results in the paper are as follows.Four Bacillus were isolated from various materials,and their inhibitory rates on Aspergillus flavus were determined by flat plate buckle method.The results showed that the strain R2 has the highest inhibition rate for Aspergillus flavus,which was 73%.Through morphological,physiological and biochemical identification and 16S rDNA identification,the strain R2 was finally identified as Bacillus mycoides.Based on the basic culture medium,solid-state fermentation process of producing antifungal volatile compounds was optimized through single factor test and orthogonal test.It was determined that the optimum fermentation temperature of the strain was 32 ℃,and the best initial pH was 7.The best ratio of the medium is:soluble starch 20 g/L,peptone 10 g/L,NaCl 10 g/L,Na2HPO4 1g/L and MgSO4 0.4 g/L.Under the optimum solid-state fermentation,the inhibition rate of strain R2 to Aspergillus flavus reached 85.2%,which was 16.7%higher than that before.The effects of volatile compounds on spore germination,mycelial growth,mycelia morphology and pigment synthesis of Aspergillus flavus were studied and the antifungal mechanism of volatile compounds was preliminarily discussed.In the presence of volatile compounds,Aspergillus flavus spore germination and mycelial growth were significantly inhibited.The results of light microscope and scanning electron microscope showed that the volatile compounds could cause abnormal morphology of Aspergillus flavus,and the main characteristics are hyphae distortion,abnormal adhesion,hyphae collapse and no conidia formation.The volatile compounds produced by strain R2 can completely inhibit the pigment synthesis of Aspergillus flavus.The volatile compounds was analyzed by SPME-GC-MS and 18 different components were identified,including alkanes,alcohols,aldehydes and esters.The paddy inoculated with Aspergillus flavus and strain R2 were co-cultured in the closed conical flask to study the effect of volatile compounds on the prevention and control of Aspergillus flavus and aflatoxin.The number of moulds,AFTBi content and fatty acid value of paddy in 3,5,7 d treatment and control groups were tested respectively.The results showed that the volatile compounds could not only effectively inhibit the growth of Aspergillus flavus in paddy,but also has significant effect on controlling the content of AFTB1 and the acid value of paddy.It indicates that the volatile compounds has further research value for developing antifungal agents for paddy.