The Research Of Lactic Acid Bacteria With Inhibition Of Postharvest Pathogens In Pepper And Fresh-keeping Effect

Pepper has the characteristics of seasonality,regionality and perishability,so it is not easy to store after picking.Among them,infectious disease is the main reason for the decline of postharvest quality of pepper,accounting for about 50% to 90% of the total loss.Phytophthora capsici Leonian is one of the common pathogens causing postharvest diseases of pepper.However,at present,there is no research on the biological control of Phytophthora capsici in postharvest pepper,which leads to huge economic losses in postharvest pepper.Currently,the physical fresh-keeping technology and equipment commonly used for postharvest preservation of hot pepper is expensive and energy-consuming,so it is not suitable for large-scale application.Chemical antistaling agents are easy to cause drug resistance of pathogenic bacteria and have potential safety risks to the ecological environment and human health.Meanwhile,Chemical antistaling agents can easily lead to drug resistance of pathogenic bacteria,and at the same time have potential safety risks to ecological environment and human health.Therefore,the environment-friendly,pollution-free and efficient biological fresh-keeping technology has a broad research space and development prospect for the preservation of postharvest pepper.Lactic acid bacteria are a kind of probiotic Generally Recognized as Safe(GRAS).Their bacteria and metabolites are considered to be natural preservatives to inhibit the growth of food fungi.At present,lactic acid bacteria and their metabolites have been used in the study of postharvest bacteriostasis and preservation of many kinds of fruits and vegetables,but there are few researches on postharvest antibacterial and fresh-keeping of peppers.In this experiment,Phytophthora capsici was used as indicator,and the inhibitory effect of lactic acid bacteria on Phytophthora capsici was measured.A strain of lactic acid bacteria with significant antibacterial effect on Phytophthora capsici was isolated from fermented vegetables,and the strain identification and biological characteristics of the lactic acid bacteria were analyzed.The inhibitory effect of the fermentation supernatant of the strain on Phytophthora capsici,the physicochemical properties and the antibacterial spectrum of the fermentation supernatant were determined.On this basis,the effect of fermentation supernatant on postharvest antibacterial and fresh-keeping of pepper was studied.The main research results are as follows:1.A strain O2 with good inhibitory effect on Phytophthora capsici was screened from 8strains of lactic acid bacteria by solid dilution method,and the inhibition rate of its fermentation supernatant to Phytophthora capsici was 87.18%.Strain O2 was identified as Lactobacillus plantarum with Genbank accession number of OL616071 by physiological and biochemical characteristics identification and 16 S rDNA sequence homology data analysis.2.Phytophthora capsici was used as an indicator to determine the physical and chemical properties of the supernatant of Lactobacillus plantarum O2 fermentation.The results showed that Lactobacillus plantarum O2 fermentation supernatant was not sensitive to catalase,proteinase K,trypsin and pepsin,and the antibacterial substances were stable in the temperature range of 40 to 120 °C,15 W UV lamp irradiation for 30 to 150 min and pH(27)5.The minimal inhibitory concentration(MIC)and minimal bactericidal concentration(MBC)of Lactobacillus plantarum O2 supernatant against Phytophthora capsici were determined by double dilution method,which were 12.8mg/mL and 25.6mg/mL,respectively.The inhibitory effect of supernatant of Lactobacillus plantarum O2 fermentation on Phytophthora capsici,Colletotrichum gloeosporioides,Colletotrichum nigrum and Rhizopus spp.in postharvest pepper was determined by solid dilution method.The results showed that the supernatant of O2 fermentation had significant inhibitory effect on Phytophthora capsici and Colletotrichum gloeosporioides,and the inhibition rate were 87.18% and 31.43%.The inhibitory effect of supernatant of Lactobacillus plantarum O2 fermentation on common foodborne pathogens Escherichia coli,Salmonella,Shigella,Listeria monocytogenes,Shigella and Enterobacter sakazakii was determined by Oxford cup method.The results showed that the supernatant of Lactobacillus plantarum O2 fermentation had significant inhibitory effect on Escherichia coli,Salmonella,Shigella and Enterobacter sakazakii,and the diameter of the inhibition zone was 11.06±1.33 mm,10.06±0.58,18.40 ±0.54 mm and 13.20±0.23 mm,respectively.3.The inhibitory effect of supernatant of Lactobacillus plantarum O2 fermentation on the incidence of Phytophthora capsici and its resistance to Phytophthora capsici were studied with "Xiangyan NO.15" pepper as experimental material.The results showed that after 12 days of inoculation,No disease was found in CK1 group(inoculate sterile water after stabbing),the incidence of Phytophthora capsici in CK2 group(inoculated with Phytophthora capsici spores after stabbing)and fermentation supernatant group was 30.00% and 18.33%,respectively.Compared with CK2 group,The incidence of Phytophthora capsici in the fermentation supernatant group(inoculated with Phytophthora capsici spores after stabbing,and then the supernatant of O2 fermentation was sprayed)decreased by 38.90%.The relative electrical conductivity of CK1,CK2 and fermentation supernatant group was 21.97%,26.18%and 24.69%,respectively.Compared with CK2 group,the relative conductivity of fermentation supernatant group decreased by 5.69%.Compared with CK2 group,fermentation supernatant group increased PAL activity by 14.03%,POD activity increased by9.17%,PPO activity increased by 29.67%,proline content increased by 7.73%,TP content increased by 7.69%,flavonoid content increased by 9.09% and MDA content decreased by13.13%.The results showed that the supernatant of Lactobacillus plantarum O2 fermentation had a good inhibitory effect on the postharvest rot of pepper caused by Phytophthora capsici.By improving the physiological activity of defensive enzymes,the supernatant of O2 fermentation can enhance the tolerance of pepper under stress,thus slowing down the damage caused by Phytophthora capsici.4.The fresh-keeping effect of supernatant of Lactobacillus plantarum O2 fermentation on postharvest pepper was studied with "Xiangyan NO.15" pepper as experimental material.The results showed that after 20 days of storage,compared with the blank control group,the weight loss rate,decay index,relative electrical conductivity,chlorophyll content and vitamin C content of the fermentation supernatant group decreased by 18.10%,64.27%,26.15%,33.03% and 20.47%(p<0.05);the L* value of the fermentation supernatant group was significantly lower than the blank control group,the a* value was not significantly different from that of the blank control group,and the b* value of the fermentation supernatant group was significantly different from blank control group(p<0.05).Except for the relative electrical conductivity,there was no significant difference between the fermentation supernatant group and the 1%(m/v)chlorine dioxide positive control group(p<0.05).It shows that Lactobacillus plantarum O2 fermentation supernatant has the effect of reducing the postharvest quality loss and rot of pepper,and can alleviate the damage caused by environmental conditions to pepper cells to a certain extent,but the damage inhibition effect on infective diseases is poor.At the same time,it can achieve the preservation effect of1%(m/v)chlorine dioxide positive control group.