Screening and inhibition mechanism of lactic acid bacteria against Aspergillus niger using 96-well microtiter plates

Objective: To isolate lactic acid bacteria (LAB) with outstanding inhibitory activity against Aspergillus niger.Methods:LAB with inhibitory activity against A. niger was screened using 96-well microtiter plates. Research on effect factors of antibacterial was analyzed by p H test, heat-treated test. Research on the antimicrobial substances of the contents of organic acids were analyzed by the gas chromatography. Research on the antibacterial mechanism of the integrity of cellular of spores was observed by scanning electron microscope.Results: Lactobacillus plantarum DL3 isolated from traditional northeast Suancai had strong anti-fungal activity against A.niger, and its inhibitory rate reached 92.28%.Antimicrobial substances were effective within p H2.5~6.5 and heat stable, which was declined by 5.71% after incubation at 121 ℃ for 30 min. The contents of lactic acid, acetic acid, propionic acid and phenyl lactic acid in CFS of strain DL3 were 5.743, 1.635, 0.033 and 0.085 μg/m L using gas chromatography analysis, respectively.In addition, the inhibition rate of lactic acid and acetic acid to A.niger were 91.69%and 92.04%, respectively.Therefore, antimicrobial substances produced by strain DL3 were preliminary determined as organic acids.The propionic acid and phenyl lactic had no inhibition against A.niger.The scanning electron microscope images revealed that the membrane of the spores of A.niger treated with CFS of strain DL3 was damaged and dissolved, resulting in the leakage of intracellular material from spores. Conclusion: Lactic acid and acetic acid were the main inhibitory substances produced by strain DL3, which could be used as starting strain of biological fungicide in rice and flour products.