Inhibitory Effect Of Peptides Produced In Tea Fermented By Bacillus On OTA Producing Fungi

The post-fermented tea is one of the most popular beverages in the world,but it often suffers from fungal toxin contamination.As harmful fungal toxins have various types and strong toxicity,they cause significant losses in the yield and quality of tea products.One of the most harmful fungal toxins is ochratoxin A(OTA),which is widely distributed,highly contaminating,water-soluble,and hard to degrade.OTA has strong liver and kidney toxicity,and can cause mutations,cancers,and immunosuppression.Currently,there are three methods for OTA detoxification,including physical,chemical,and microbial detoxification.Physical and chemical detoxification methods are simple,inexpensive,but have limited detoxification effects,nutrient loss,and safety issues.By contrast,the use of beneficial microorganisms to inhibit toxin-producing fungi and OTA can not only achieve effective detoxification and guarantee safety but also prevent nutrient losses in source products.Therefore,microbial detoxification will be the future direction of research on OTA detoxification.This paper focuses on how to improve the inhibition of beneficial bacteria and their antibacterial substances against OTA to ensure the safety of human consumption.Using Brevibacillus Brevis and its fermented tea(produced by the natural fermentation method in the laboratory)as experimental materials,the study explores the regularities of the effects of Brevibacillus Brevis fermentation liquid and fermented tea extract on Aspergillus carbonarius and Aspergillus ochraceus.Based on this,the antibacterial mechanism was studied using computer molecular simulation technology.The experimental results showed that:(1)Brevibacillus Brevis is a biocontrol bacterium with strong inhibition activity,and its strain 101 fermentation liquid and crude peptide extract have obvious inhibitory effects on Aspergillus ochraceus and Aspergillus carbonarius.(2)When the Brevibacillus Brevis 101 fermentation liquid was diluted 6 times,the concentration of peptides was 0.27 mg/m L,and the inhibition zone was 19.5±0.70 mm.The inhibition effect against Aspergillus carbonarius was the best.When diluted 1 time,the peptide concentration was 0.19 mg/m L,and the inhibition zone was 21±2.82 mm.The inhibition effect against Aspergillus ochraceus was the best.(3)The crude peptide extract of Brevibacillus Brevis fermentation liquid has a significant inhibitory effect on Aspergillus ochraceus and Aspergillus carbonarius,which helps to damage the integrity of the cell membrane and cell wall.(4)High concentration of peptides can effectively inhibit Aspergillus ochraceus,but there is no obvious pattern of inhibition against Aspergillus carbonarius at different peptide concentrations.(5)Infrared,ultraviolet,and fluorescence spectral scans of peptides showed that they are amino acid-like substances.(6)The quantity of Brevibacillus Brevis during the tea fermentation process is related to the cultivation time,and the number of Brevibacillus Brevis bacterial population in tea leaves cultured for 16 days(1.0×10~5 cfu/g)was much higher than that in tea leaves cultured in other six periods.(7)The content of tea polyphenols,catechins,and soluble sugars showed a significant decreasing trend with the increase of cultivation time,while free amino acids did not show an obvious pattern with cultivation time.(8)The tea peptide fermentation liquid(3～10 KDa)prepared by mixing Brevibacillus Brevis in the culture can effectively inhibit the activity of Aspergillus ochraceus and Aspergillus carbonarius.By using HPLC-MS/MS technology to determine the peptide sequence in the tea peptide extract,25 peptides were selected with high scores,and their molecular weights were between600～1300 Da,and the length was between 7 and 11.Based on this,molecular simulation was conducted on peptides and proteins with Pdbid:3A58,and it was found that 5 of the 25 smallpeptides can bind to the active site of GTPase,indicating that they may have inhibitory effects on GS activity,which microscopically reveals the antibacterial mechanism of tea peptide extract.(9)With the increase of cultivation time,the activity of GS enzyme of tea peptide fermentation liquid against Aspergillus carbonarius decreased,while there was no same trend against Aspergillus ochraceus.In addition,the DPPH free radical scavenging rate decreased with the increase of cultivation time.In view of the inhibitory effect of Bacillus and its antibacterial peptides on ochratoxin A(OTA)produced by animals and plants,the active development of antibacterial peptides and peptide substances will have important influence and broad prospects in agricultural and chemical industries.Finally,it will play a positive role in promoting the safety of human health.