| Objective: The purpose of this study was to utilize high quality lactic acid bacteria strains,which was isolated from traditional fermented yak yogurts on the QinghaiTibetan Plateau and had special biological functions,and explore the potential advantages of lactic acid bacteria and their metabolites as natural biological preservative.So as to provide a theoretical and scientific basis for the application of replacing chemical preservatives in the preservation of fruits and vegetables.Methods: Three high quality lactic acid bacteria isolated from traditional fermented yak yogurt on the Qinghai-Tibetan Plateau were selected to carry out different postharvest fruit preservation studies:(1)The fermentation supernatant of Leuconostoc lactis H52 with high ability to produce extracellular polysaccharides was applied to preserve “Red Globe” table grapes,and stored at 25?.At the scheduled storage period(0,5,10,15,and 20 d),the physical and chemical indicators(weight loss rate,decay rate,soluble solids content(SSC),stem browning rate,pH,titratable acid content,total phenol content,and sensory evaluation)and the colony number of microorganisms(aerobic mesophilic bacteria,yeast and molds,and coliform bacteria)on the surface of table grapes were measured.(2)The fermentation supernatant of Leuconostoc lactis H52 with high ability to produce extracellular polysaccharides and Lactobacillus delbrueckii F17 with bacteriocin-producing ability were applied to preserve “Benihoppe” strawberries,and stored at 25?.At 0,12,24,48 and 72 h of storage period,the physicochemical indicators(weight loss rate,decay rate,SSC and pH)of strawberry were determined,and the colony number of microorganisms(aerobic mesophilic bacteria,yeast and molds,and coliform bacteria)on the surface of strawberry was conducted.Meanwhile,Illumina high-throughput sequencing technology(16S rDNA and ITS)on MiSeq platform were used to detect the microbiota community(bacteria and fungi)from the surface of strawberry at each sampling time point,and muthor,R and other software were used to analyze the difference of microbiota community structure and diversity.(3)Fresh-cut “Fuji” apples were treated with the bacterial suspension of Lactobacillus parplantarum BX62,which possessing high antioxidant capacity,and 1% chitosan solution alone or in combination,and stored at 4°C.At each specific storage time(0,2,4,6 and 8 d),physicochemical indicators(weight loss rate,browning rate,DPPH scavenging activity,PPO and POD activity,titratable acid content,SSC and total phenol content)of fresh-cut apples were measured,and colonies were counted for microorganisms(aerobic mesophilic bacteria,aerobic psychrophilic bacteria,lactic acid bacteria,and yeasts and molds)on the surface of fresh-cut apples.Results:(1)Treatment with Lactobacillus H52 reduced the weight loss rate,decay rate and stem browning rate,and delayed the ripening and senescence,and well maintained the total phenol content of postharvest “Red Globe” grapes,the differences were statistically significant(P<0.05);Meanwhile,treatment with Lactobacillus H52 significantly inhibited mesophilic aerobic bacteria,yeasts and molds,and coliform bacteria on the surface of table grapes,the differences were statistically significant(P<0.05);The results of Pearson correlation analysis showed that the weight loss rate,decay rate,stem browning rate,SSC and the number of microbial colonies were highly correlated with the sensory score of fresh grapes(P<0.05).(2)The results showed that treatment with Lactobacillus F17 and H52 did not only reduced the weight loss and decay rate of strawberry fruits,but also delayed the decrease of the SSC and pH,and well maintained the postharvest quality of strawberry fruits,the differences were statistically significant(P<0.05);Meanwhile,treatment with Lactobacillus F17 and H52 obviously inhibited aerobic mesophilic bacteria,yeast and mold,and coliform bacteria on the surface of strawberry fruits,the differences were statistically significant(P<0.05);By comparing the microbiota community composition of the genus level of strawberry samples in the control and two treatment groups at the same storage time,treatment with F17 inhibited Pantoea,Mycospherella,unclassified_Pleosporales,Aureobasidium and Phoma,whereas treatment with H52 inhibited Bacillus,Streptophyta,Mycospherella,Aureobasidium and Phoma,the differences were statistically significant(P<0.05);The results of canonical correspondence analysis revealed that the SSC and pH were positively correlated with bacteria,whereas the decay rate,weight loss rate and SSC were positively associated with fungi;Additionally,Gluconobacter,Podosphaera,Hanseniaspora,Botrytis and unclassified_Pleosporales were positively correlated with strawberry fruit decay and weight loss rate.(3)Treatment fresh-cut apples with bacterial suspension of Lactobacillus BX62 reduced weight loss rate,browning rate,PPO and POD activity,and delayed the reduction of total phenol content,and improved the ability of DPPH scavenging activity,fresh-cut apples of Lactobacillus BX62 treatment exhibited with good sensory characteristics,the differences were statistically significant(P<0.05);The results of microbial colony counts showed that treatment with 1% chitosan solution inhibited mesophilic aerobic bacteria,aerobic psychrophilic bacteria and yeasts and molds on the surface of freshcut apples,the differences were statistically significant(P<0.05),treatment with 1% chitosan solution effectively ensured the food safety of fresh-cut apples during storage;Meanwhile,the results of Pearson correlation analysis showed that Lactobacillus BX62 was highly correlated with the antioxidant capacity of fresh-cut apples(P<0.01),suggesting that Lactobacillus BX62 can be used as a good natural antioxidant to delay the oxidative browning of fresh-cut apples.Conclusion: In conclusion,lactic acid bacteria from Qinghai-Tibetan Plateau and their metabolites are potential sources of good biological preservatives,which can better maintain the quality of postharvest fruits and ensure food safety. |
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