| Grape is dehydrated,threshed and dried during postharvest storage.In addition,the infection of harmful microorganisms can also cause deterioration and loss of commodity and nutritional value,which accounts for about 30% to 40% of grape losses.Therefore,it is very important to preserve the grape during postharvest storage.The main postharp fungal diseases include Coniothyrium diplodiella,Coniothyrium diplodiella and Coniothyrium diplodiella.The highest incidence of white rot was about 30%.Nowadays,chemical fungicides are mainly used to prevent and control postharvest diseases of grapes,but the resistance of pathogenic bacteria to chemical fungicides is becoming stronger and stronger,and the control effect of chemical fungicides is getting worse and worse.Chemical fungicides not only do harm to the environment,but also pose a great threat to human health.Therefore,it is urgent to look for green,healthy,efficient,pollution-free and residue-free methods for grape preservation after harvest.A large number of studies have shown that lactobacillus can produce secondary metabolites that inhibit spoilage bacteria to protect the host from disease.Therefore,it has become an inevitable trend to isolate and screen out the lactic acid bacteria with inhibitory effect on spoilage bacteria so as to reduce the use of chemical fungicides.In this study,white rot of grape was used as the indicator bacteria,and the inhibition effect of lactic acid bacteria was used as the measurement index.Lactic acid bacteria with significant inhibitory effect were screened and isolated from fermented vegetables and their physicochemical properties and 16 SrDNA sequences were determined.The inhibitory spectrum of lactic acid bacteria and the properties of the fermentation supernatant were studied.The fermentation conditions of lactic acid bacteria were optimized by response surface method,and the preservation effect of the fermentation supernatant on post-harvest grape was studied.The research results are as follows:1.A bacterioinhibitory Lactobacillus plantarum was screened and named MG-1.Its morphology was observed under a microscope,and the physicochemical properties and16 S rDNA sequence of Lactobacillus MG-1 were determined.The Genbank number areMG766279.2.The physicochemical properties of the fermentation supernatant were determined by using white rot after grape harvesting.The results showed that the fermentation supernatant of Lactobacillus plantarum MG-1 was stable to heat,and there was no significant change in the diameter of the inhibition zone after treatment at 120? for 30 minutes.For acid stability,the inhibition zone diameter of the lactic acid bacteria MG-1 fermentation supernatant did not change significantly at 25?,pH 2-7 acid-basic range;stable to trypsin and papain,but it is unstable to pepsin and proteinase K;it is stable to ultraviolet radiation,and the diameter of the inhibition zone has no obvious change with the unirradiated control group after being irradiated by 20 W ultraviolet light for 150 minutes.3.The fermentation conditions and medium components of lactic acid bacteria MG-1were optimized by single factor experiment and the fermentation conditions were optimized by the response surface Box-Behnken test.The optimized test results showed that the composition of the medium was sucrose 20 g,beef extract 10 g,dipotassium hydrogen phosphate 5g,distilled water 1L;Lactobacillus plantarum MG-1 optimal fermentation conditions were time 48 h,temperature 36?,initial pH 7 When the inoculation amount is2%,the diameter of the inhibition zone is 22.19 mm and the diameter of the inhibition zone(17.14 mm)before optimization is increased by 29.40%.4.The resistance of grape to white rot fungus induced by lactic acid bacteria fermentation supernatant was studied with "Jufeng" grape as test material.The results showed that 12 days after inoculating the spores of white rot fungus,the fermentation supernatant could effectively inhibit the incidence of grape compared with CK2(inoculating the spores of root rot fungus after stabbing),the incidence of grape was reduced by 16.92%(P<0.05);compared with CK1(adding sterile water after stabbing)and CK2(inoculating the spores of root rot fungus after stabbing),the fermentation supernatant could effectively inhibit the activity of phenylalanine ammonia lyase(PAL)in grape increased by 36.82% and 16.34%(P<0.05);peroxidase(POD)activity increased by 71.68% and 52.92%(P<0.05);pectinase(PG)activity decreased by 19.87% and 12.26%(P<0.05);ascorbic acid peroxidase(APX)increased by 48.10% and 20.60%(P<0.05);chitinase(CHI)increased by 36.89% and22.49%;beta-1,3-glucanase(GLU)extraction increased by 50.50% and 15.15%(P<0.05);the relative conductivity decreased by 5.00% and 1.67%(P<0.05);the free proline increased by17.65% and 9.18%(P<0.05).The results showed that the fermentation supernatant could improve the disease resistance of grape and effectively inhibit the growth of white rot fungus on grape fruits.5.The results showed that the fermentation supernatant could effectively reduce t he weight loss rate and decay rate of grape fruits stored until 28 days.Compared with CK group(sterile water treatment)and fresh-keeping liquid group,the decay rate of f ermentation supernatant group decreased by 34.38% and 4.10%(P<0.05);the weight los s rate decreased by 6.25% and 1.11%(P<0.05);the hardness increased by 32.01% and4.97%(P<0.05);reducing sugar increased by 34.51% and 14.72%(P<0.05);titratable acid increased by 49.80% and 8.12%(P<0.05);vitamin C decreased by 25.28% and 8.30%(P<0.05);soluble solids decreased by 9.93% and 3.53%(P<0.05);malondialdehyde(MDA)decreased by 13.42% and 9.03%(P<0.05);catalase(CAT)activity increased by52.89% and 26.78%(P<0.05);and peroxidase(POD)activity increased by 25.98% an d 3.69%(P<0.05);polyphenol oxidase(PPO)increased by 24.13% and 10.37%(P<0.05);superoxide dismutase(SOD)activity increased by 36.06% and 8.68%(P<0.05);pectinase(PG)activity decreased by 20.64% and 10.78%(P<0.05).The results showed that the fermentation supernatant could effectively improve the disease resistance of grapes,and was beneficial to preservation and preservation,thus prolonging the storage period of grapes. |
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