| Over the years,chemical synthetic fungicides are widely used to control postharvest decay and prolong caducity for the pepper.However,it has caused the concern of consumers because of the side-effects of synthetic fungicides such as leaving residues,environmental pollution,in addition to causing the resistance of pathogens and the risk of human health.It has become a priority to search for a safer and eco-friendly alternatives for the fresh-keeping of pepper.At present,it has promising prospects of development and application that plant extracts and edible coating on keeping-fresh of pepper.This experiment took Fusarium oxysporum,Collet totrichum nigrum,Colletotrichum gloeosporioides,Rhizopus spp.for test material and studied antifungal activity 9 alcoholic extracts of Syzygium aromaticum,Cinnamonmu m cassia,Zanthoxylunm bungeanum by method of mycelium growth rate.Screening and optimizing studies on fresh-keeping activities of 7 film-forming agent based on weight of loss and rot rate,such as guar gum,Pullulan polysaccharide,xanthan gum.Based on the single factor experiment results,optimize complex preservatives consisting of plant extracts,film-forming agent by response surface methodology.It was investigated that fresh-keeping effects by plant extracts composite film-forming agent.The main results are as follows:1.This paper was intend to isolate,purify,and identify four pathogens from pepper.This experiment took Fusarium oxysporum,Colletotrichum nigrum,Colletotr ichum gloeosporioides,Rhizopus spp.for test material and studied antifungal activity of 9 alcoholic extracts by the mycelium growth rate method,such as Syzygium aromaticum,Cinnamomum cassia,Zanthoxylunm bungeanum etc.The results showed that the inhibition rate of Syzygium aromaticum and Cinnamomum cassia extracts were 100%.The minimal inhibitory concentrations(MIC)and minimum bactericidal concentration(MBC)of Syzygium aromaticum and Cinnamomum cassia extracts were tested on the 4 fungi above by the dilution spread plate method.The results showed that the MIC of Syzygium aromaticum and innamomum cassia extracts on Fusarium oxysporum,Colletotrichum nigrum,Colletotrichum gloeosporioides,Rhizopus spp was 1.25 mg/mL,2.50 mg/mL,2.50 mg/mL and 5.00 mg/mL,respectively.The MBC of Syzygium aromaticum and Cinnamomum cassia extracts on Fusarium oxysporum,Colletotrichum nigrum,Colletotrichum gloeosporioides,Rhizopus spp.was 2.50 mg/mL,5.00 mg/mL,5.00 mg/mL and 10.00 mg/mL,respectively.2.Screening and optimizing the concentration and ratio of Syzygium aromaticum,Cinnamomum cassia extracts,the category,concentration and ratio of film-forming agent and soaking time based on weight of loss and rot rate on the pepper(Xiangyan NO.15).The results showed that the concentration of Syzygium aromaticum and Cinnamomum cassia extracts was 0.025 g/L,0.10 g/L,respectively,the ratio of Syzygi um aromaticum and Cinnamomum cassia extracts was 1:2(v/v),the categories of film-forming agent were guar gum and Pullulan polysaccharide,the concentration and ratio of guar gum and Pullulan polysaccharide were 0.5%(m/v)and 3:1(m/m),the soaking time was 30 s.Based on the single factor experiment results,response surface methodology was employed to optimize the composite concentration of Syzygium aromaticum,Cinnamomum cassia extracts was 0.05 g/mL(m/v),the composite concenentration of guar gum and Pullulan polysaccharide was 0.55%(m/v),the soaking time was 30 s.Compared with CK1(water)and CK2(no-treatment group),under the optimized conditions,the weight of loss and rot rate of pepper coating with antistaling agent consisting of Syzygium aromaticum,Cinnamomum cassia extracts,guar gum and Pullulan polysaccharide decreased by 31.80%,30.94% and 72.13%,68.27%,respectively.3.The effects of induction of resistance in pepper(Xiangyan NO.15)against Rhizopus spp.infection by antistaling agent consisting of Syzygium aromaticum,Cinnamomum cassia extracts,guar gum and Pullulan polysaccharide were investigated.The results showed that the incidence and lesion diameter in pepper fruits caused by Rhizopus spp were decreased by the antistaling agent after 8 d storage.Compared with CK2(inoculation of conidial suspension of Rhizopus spp.),the incidence and lesion diameter of pepper treated with antistaling agent decreased by 6.67% and 30.44%,respectively.Compared with CK1(sterile water)and CK2(inoculation of conidial suspension of Rhizopus spp.),treatment with antistaling agent consisting of Syzygium aromaticum,Cinnamomum cassia extracts,guar gum and Pullulan polysacCharide enhanced the activities of phenylalanine ammonia-lyase(PAL)43.56%,37.87%(P<0.05),respectively,besides,the activities of Peroxldase(POD)was promoted 22.15%(P<0.05),12.54%(P>0.05),respectively,and the activities of polyphenol oxidase(PPO)was enhanced 81.48%,28.95%(P<0.05),respectively.In addition,treatment with antistaling agent consisting of Syzygium aromaticum,CinnaMomum cassia extracts,guar gum and Pullulan polysaccharide promoted the content of total phenolics 60.00%,45.45%(P<0.05),respectively,and the content of flavonoids was enhanced 82.05%,61.36%(P<0.05).These results suggested that treatment with antistaling agent consisting of Syzygium aromaticum,Cinnamomum cassia extracts,guar gum and Pullulan polysaccharide may induce the resistance of pepper on controlling Rhizopus spp.decay.4.The effects of postharvest coating with antistaling agent consisting of Syzygium aromaticum,Cinnamomum cassia extracts,guar gum and Pullulan polysaccharide on the fresh-keeping of pepper were examined.Compared with CK1(water)and CK2(no-treatment group),the results suggested that after 20 d storage,the weight of loss and rot rate treated with the antistaling agent consisting of Syzygium aromaticum,Cinnamomum cassia extracts,guar gum and Pullulan polysaccharide decreased by 31.20%,30.64%(P<0.05)and 71.43%,68.07%(P<0.05),respectively.In addition,respiration intensity was decreased by 13.61%(P<0.05),7.00%(P>0.05),respectively,and electric conductivity treated with antistaling agent decreased by 22.64% and 14.68%(P<0.05),respectively,slow down the loss of content of ascorbic acid(Vc)10.87%,6.25%(P<0.05),respectively,promoted degradation of chlorophyll 13.67%,16.75%(P<0.05),reduced the formation of malondialdehyde(MDA)content 26.29%,27.12%(P<0.05),respectively,Compared with CK1(water)and CK2(no-treatment group),The activities of catalase(CAT)peroxidase(POD),polyphenol oxidase(PPO),phenylalamine ammonia lyase(PAL)treated with the antistaling agent consisting of Syzygium aromaticum,Cinnamomum cassia extracts,guar gum and Pullulan polysaccharide promoted by 55.01%,37.50%,32.74%,58.37%(P<0.05)and 44.69%,12.58%,20.11%,34.14%(P<0.05).the content of total phenolics and flavonoids treated with the antistaling agent enhanced by 45.00%,38.95% and 13.74%,11.86%(P<0.05). |
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