Analysis Of Antifungal Compounds Produced By Lactobacillus Casei AST18and Its Antifungal Effect

Lb. casei AST18was screened in our laboratory because of its excellent antifungal activity. In thisresearch, we used a series of separation and purification methods and obtained several antifungalfermentation parts. Then we used UPLC-Q-TOF to detect the antifungal substances in the separatedparts. On this basis, we use the metabolomics technology to collect the data of the culture with differentfermrntation time. Then we used multivariate statistical analysis to analyze the main difference betweenthe fermentation culture, in order to obtain the information of the antifungal substances. We analyzedthe antifungal spectrum and the effect of Lb. casei AST18to the growth morphology of P.chrysogenum, which was used as indictor fungals. Double flat antagonize method was used to study theantifungal activities of Lb. casei AST18. SEM and TEM were used to study the ultrastructure inside thefungal and to speculate the action mode of Lb. casei AST18on P. chrysogenum. We used N+Implantation Mutation Breeding (IMB) to process Lb. casei AST18in order to obtain a stain with betterantifungal effect and use the strain in the actual production industry. At last, we used the mutant strainas adjunct fermentation culture in Cheddar. We analyzed the main physicochemical and sensoryqualities of the cheese during the storage period. The antifungal activities of Lb. casei AST18（1-3）as aadjunct culture in Cheddar was evaluated. This experiment lay a theoretical foundation of antifungalLAB in the cheese production industry.The main conclution were as follows:(1) There are serveal low molecular substance exist in fermentation culture of LAB except lacticacid; the main antifungal substance in the culture detected by UPLC-Q-TOF was organic acid,nitrogen-containing small molecule compounds and small molecule esters. The antifungal activities ofLAB was a synergistic effect of all this substances. The antifungal substances detected in thisexperiment which have been reported was: Lactic acid, acetic acid, citric acid, benzoic acid, cinnamicacid, salicylic acid, azelaic acid, succinic acid, sialic acid and phenyllactic Acid.(2) Through the analysis of antifungal activities and the metabolic footprinting, the increasedantifungal activities of the fermentation culture during the prophase was caused by lactic acid; after thestable period, the increased antifungal activities was caused by Nitrogen-containing small moleculecompounds and other orginic acid..(3) Lb. casei AST18caused the autophagic death of P. chrysogenum. The main changes weobserved during the process was as follows:The vacoule enlarged to the entire cell; part of the cytoplasmic aggregated and the color wasdeepened; autophagosomes contained cytoplasm entered into the vacoule; and then the autophagosomeswas digested in the vacoule; when the color of colony was grayish brown, there was no organelles left inthe cell, only bilayer structure left; the autophagic death should be verified by genetic level.(4) The use of Lb. casei AST18（1-3）as adjunct culture in Cheddar has little effect on the sensoryquality of the cheese. It can increase the degree of hydrolysis and Lactobacillus count, and also it has a good antifungal effect in the cheese.