The Inhibition Effect Of Galla Chinensis Extract On Postharvest Disease Of Blueberry And Its Storage Quality

In this study,Chinese gallnut(Galla chinensis),which showed the relative higher antifungus effect,was selected from 23 differnt kinds of Chinese herbal medicines as the test materials for further reshearch.The antifungus substance extraction conditions for Chinese gallnut were optimized,and its stability was studied.Moreover,the antibacterial mechanism of gulla extract on Botrytis cinerea,and its influence on blueberry postharvest quality were also investigated in this study.The results are as following:(1)Screening of antifungus and antibacterial Chinese herbal medicines.Botrytis cinerea Pers.,Monilia albican,Staphylococcus aureus,and Escherichia coli were used as test strains.23 different kinds of Chinese medicinal materials were screened by agar well diffusion assay.The inhibition zone diameter was determined as the evaluation index.The results showed that: within the 23 kinds of Chinese herbal medicines,the gallnut showed the most prominent antifungus effect,especiall on B.cinerea,was selected for further research.(2)The optimization of the extraction conditions and the stability of the gallnut extracts.Taking the antifungus effect on B.cinerea as index,the material-liquid ratio(g/m L),the concentration of ethanol(V/V),extraction temperature and ultrasonic duration were investigated.Determine the optimal extraction conditions: material-liquid ratio 1:15,ethanol concentration 70%,extraction temperature 45 °C,and ultrasound duration 1 h.The stability of Chinese gallnut extracts: The inhibitory effect of p H,light,and temperature on the antibacterial activity of gallnut extract was investigated using inhibition effect of B.cinerea as an indicator.The results showed that the antifungus effect was more effectively under acidic conditions.When p H>7,the antifungus effect decreased significantly(P<0.05),even lost its antifungus activity.The antifungus stability of gallnut extract was reduced when exposed to sunlight,while the temperature gradient had no obvious effect on the stability of antifungus substance.Therefore,the gallnut extract should be stored without light and under acidic conditions.(3)Antifungus mechanism of gallnut extract.The gallnut extract was distilled,freeze-dried,and then subjected to fractional extraction.The antifungus effects of different extract phases(petroleum ether,chloroform,ethyl acetate,and n-butanol)were comparatively studied.The diameter of the inhibition zone of B.cinerea was used as an index.The antifungus effect ranked as following: ethyl acetate> chloroform> n-butanol> raffinate> petroleum ether.Ethyl acetate phase with the most effective antifungus activity was distilled,freeze-dried.After rehydration(1:15,m/v),the antifungus effect of gullnut extract on B.cinerea was studied in vitro.The morphology and ultrastructure of mycelium were observed by scanning electron microscope(SEM),while the internal structure changes of B.cinerea was investigated by transmission electron microscope(TEM).The results showed that the gullnut extract result to broken and distorted of the B.cinerea mycelial,additionally the cell wall and organelles had different degrees of rupture and deformation.(4)Effect of gallnut extract on the post-harvest quality of blueberry.The indexes of blueberry quality including: rotting rate,weight loss rate,titratable acid content(TA),total soluble solids(TSS),electrical conductivity,and vitamin C were analyzed.Moreover,the activities of enzyme involved in defense system such as malondialdehyde(MDA),catalase(CAT),oxidase(PPO),and peroxidase(POD)were also studied to reflect the antibacterial effect of gallnut extract on B.cinerea.Results showed that the quality of blueberry fruit and rotting rate increased significantly;while the water loss rate,TA and TSS all decreased significantly(P<0.05).The deterioration of the nutrition index of the blueberry in the B.cinerea inoculated group was much faster than that of the gallnut extract treatment group.The defense system of blueberry was activated due to the infection of B.cinerea,and the enzyme activities of PPO,POD,and CAT were increased to form a defense system that eliminates free radicals and diseases.However,due to serious diseases,the defense system of blueberry was disordered,and enzyme activities were declined in the later period.While gallnut extract treatment significantly improved the postharvest quality and boosted the defense system of blueberry against B.cinerea infection.The enzyme activities in gallnut extract treatment groups were always in a dynamic equilibrium system,with slight decline due to aging.These results indicated that gallnut extract can effectively inhibit the growth of B.cinerea,and could be used as a new approach to control the postharvest quality of blueberry.