Inhibiting Mechanism Of ?-poly-L-lysine·HCL Against Black Spot Diseases In Sweet Cherry And Its Application In Postharvest Preservation

Fungal diseases are the important cause of decay on sweet cherry during postharvest storage and transportation.In order to improve effectively commercialization processs of sweet cherry,reduce postharvest losses and prolong the shelf life,the dominant mould species causing postharvest decay of sweet cherry were clarified and ?-poly-L-lysine?HCl(?-pL·HCl)as a new-type,safeand effective natural preservative was screened and identified,whose antibacterial mechanism,and application in sweet cherry preservation were analyzed and evaluated.The main results were as follows:1)In this project,the pathogens were isolated and identified from "Hongdeng" sweet cherries during storage and transportation by internal transcribed spacer sequence analysis and typical morphology.Six strains were isolated from sweet cherries postharvest during transportation and low-temperature storage.They were Alternaria alternate NCPS1,Alternaria alternate NCPS2,Alternaria sp.NCPS3,Penicillium expansum NCPS4,Cladosporium herbarum NCPS5 and Sarocladium terricola NCPS6.Biological characteristics and pathogenicity analysis showed that NCPS1 was the most low-temperature-resistant and most pathogenic strain in six strains.2)This study clarified the inhibitory effects of ?-pL·HCl on black spot infecting sweet cherry and its mechanisms.The results showed that ?-pL·HCl of 150 mg/L can completely inhibit A.alternate NCPS1 colony expansion and spores germination on PDA med ium.?-pL·HCl of 50mg/L can notably inhibit NCPS1 spores germination in PDB medium.?-pL·HCl can also destroy the morphological structure of NCPS1,causing the mycelium to dry out,entangle,and aggregate,losing the original smooth and healthy shape.Electrical conductivity results confirmed that ?-pL·HCl can destroy the mycelium structure and lead internal dissolution leakage.In addition,?-pL·HCl can also destroy the integrity of the plasma membrane of the spores,leading to cell leakage and death.3)?-pL·HCl showed good effect on maintaining the quality of sweet cherry after harvest.?-pL·HCl of 300-700 mg/L showed the better preservation effect on sweet cherry at room temperature around 25?.?-pL·HCl of 500 mg/L showed the best fresh-keeping effect,leading that decay rate and weight loss rate were the lowest.It also effectively maintained the hardness and vitamin C(Vc)amounts of sweet cherry fruits.4)?-pL·HCl combining with electrolyzed water effectively entended the sweet cherry preservation period.The results showed that the decay rate and weight loss rate of sweet cherry fruits were the lowest after the fruits were treated with the electrolyzed-oxidizing water of pH5.5,current 10 A(Oxidation-reduction potential,ORP was 932.8 m V;Available chlorine concentration,ACC was 50 mg/L)by soaking time for 5 min,combining with 500 mg/L ?-pL·HC l.The hardness and gloss were kept,effectively reducing the decline in TSS and Vc amounts.It can also increase the enzyme activity of Peroxidase(POD),Polyphenol Oxidase(PPO),and ?-1,3 Glucanase(GLU)to improve resistance.Finally,the combined method is better than a single treatment.Therefore,?-pL·HCl combined with electrolyzed water technology can effectively maintain the quality of sweet cherry fruit s and delay their physiological metabolism,which is expected to be widely used in sweet cherry preservation field.