| Due to the property of both heat-resistant and acid-tolerant,Alicyclobacillus acidoterrestris can germinate and outgrow in pasteurized juice,which can produce undesirable odors such as guaiacol and halophenol resulting in spoilage and deterioration of juice.So serious threats and challenges were posed to the quality and safety of fruit juices and beverages.And it is imperative to search for a natural and effective antibacterial agent.The purpose of this study was to screen lactic acid bacteria from kimchi and jiangshui that can inhibit A.acidoterrestris.Antibacterial effect and the composition of antibacterial substances were determined.The resulting lactic acid bacteria was used to ferment apple juice to determine the potential to withstand spoilage by A.acidoterrestris.In order to provide a bio-protective adjunct culture in the fermented juice.The main results of the study were as follows:(1)As an indicator,A.acidoterrestris was used to screen 50 strains of lactic acid bacteria isolated from kimchi and jiangshui.And the Lactobacillus plantarum L10 had the greatest antibacterial activity.The antibacterial activity of L10 cell-free supernatants(CFS)was growth-dependent.L10 CFS began to have antibacterial activity in the logarithmic phase.And the maximum antibacterial effect was obtained in 48 hours.Then the antibacterial property remained steady.The minimum inhibitory concentration(MIC)and maximum bactericidal concentration(MBC)of L10 CFS for A.acidoterrestris were 62.5 μL/m L.L10 had a broad-spectrum of inhibition with a strong inhibitory capacity against Penicillium paspalum.(2)The temperature,p H and enzyme stability for L10 CFS were determined.And the main components in the CFS were measured by GC-MS.The characterization results showed that the antibacterial substances produced by L10 had good temperature stability.In connection with p H,the antibacterial activity could disappear when the p H was greater than 6.And the antibacterial properties of L10 were mainly due to acids,such as lactic acid,malic acid,oleic acid,phenyllactic acid and so on.And the L10 also could produce cyclic dipeptides,Cyclo(leu-l-pro)and Cyclo(gly-l-pro),and proteinaceous bacteriostatic substances.All the substances played a bacteriostatic effect through synergistic action.(3)The effects of L10 CFS on the bacterial growth,spore germination and heat resistance were studied.Scanning electron microscopy(SEM)was used to observe its effects on the morphology of A.acidoterrestris.The results revealed that the L10 bacteriostatic substances could kill the A.acidoterrestris cells,inhibit the germination of spores and increase the thermal sensitivity of spores.Furthermore L10 metabolites could cause severe damage to the cell wall and cytoplasmic membrane resulting in cell rupture and bacterial death.(4)L.plantarum L10 could adapt to the apple juice fermentation substrate and grow and reproduce quickly.During the course of fermentation apple juice began to have antibacterial activity and gradually increased after 20 hours.L.plantarum L10 and A.acidoterrestris were co-inoculated into apple juice.L10 grew rapidly that could inhibit the growth of A.acidoterrestris might by the mechanism of the competition of nutrients,the production of antibacterial substances and the quorum-sensing signal molecules.(5)The total acid content in the apple juice increased first and then decreased while the p H was opposite during the fermentation by L.plantarum L10.The contents of malic acid and citric acid decreased.But lactic acid,quinic acid and acetic acid’s content increased significantly(P<0.05).While the change of succinic acid was not obvious.During the fermentation process,fifty-one volatile components and aroma active compounds were monitored by GC-MS.The content and type of the majority of aroma in the fruit juice increased,which indicated that L10 fermentation could enrich the flavor of the fermented juice. |
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