| Melon is rich in nutrients and excellent taste,as one of the characteristics of Xinjiang,loved by the public.Due to the high sugar content and sufficient water content of melon fruit,sunken spots are easy to appear on the surface of harvested melon during summer ripening and high temperature,which affects the quality of melon.In addition,due to the geographical location of Xinjiang,the market of melon in Xinjiang is limited,and the long transportation time and improper treatment are easy to rot the melon,which seriously affects its economic value.At present,chemical and physical preservation techniques are often used by most researchers in the study of post harvest storage of melon,but there are few reports on biological preservation techniques.In this study,West State honey twenty-five melon was used as the research object to analyse the effects of Antagonistic Bacteria on storage quality and physiological characteristics of melon,in order to provide a new way for melon storage through biological preservation technology.The main research contents and conclusions are as follows:1.Twenty five soil samples were collected from Hami by five point sampling method,and 67 strains of antagonistic bacteria were isolated by soil dilution method.Among 40 strains of antagonistic bacteria with different bacteriostatic effects,BG-1,BG-2 and BG-3 had the strongest inhibitory effect.After re screening,the antagonistic bacteria BG-2 with a diameter of 23.67 mm was selected as the test strain.BG-2 was identified as Bacillus velezensis by physiological,biochemical,morphological characteristics and molecular biology(16S r DNA,gyr B,rpo B).A major pathogen CH-3 was isolated from postharvest melon by tissue block isolation.The pathogenicity of melon was determined,and it was proved that the pathogenic part of the strain was consistent with the inoculated strain.By morphological characteristics and homology comparison of molecular biology(ITS,β-tub,tef),it was identified as Fusarium oxysporum.When the concentration ratio of pathogen spore suspension to antagonistic fermentation broth was 1:2,the inhibition rate of BG-2 to CH-3 spore germination was 99.30%.The relative inhibition rate of BG-2 was 60.11%.These results indicate that Bacillus velezensis BG-2 has obvious antagonistic effect on Fusarium oxysporum CH-3.2.The antagonistic strain BG-2 could delay the decline of antioxidant enzyme activity,especially in low temperature storage.The changes of antioxidant enzyme activities(POD,CAT,APX,PPO,SOD and PAL)of melon under different storage temperatures were determined.The antioxidant enzyme activities of antagonistic bacteria BG-2 and antagonistic bacteria BG-2 and pathogen CH-3 treatments were higher than those of control and CH-3 treatments during the whole storage period.The POD activity of BG-2 and CH-3 treatment was 26.53% higher than that of control treatment at room temperature for 20 d,and 60.08% higher than that of control treatment at low temperature for 50 d.The CAT activity of the control treatment was3.79 times lower than that of the BG-2 and CH-3 treatment when stored at room temperature for 25 d and 3.91 times at low temperature for 50 d.The APX activity of BG-2 treatment was 0.88 times higher than that of the control treatment at room temperature for 20 d,and 1.26 times higher than that of the control treatment at low temperature for 40 d.Compared with CH-3 treatment,PPO activity of BG-2+CH-3treatment was 12.66% higher at room temperature for 25 d and 10.31% higher at low temperature for 50 d.The SOD activity of BG-2 and CH-3 treatment was 69.27%higher than that of CH-3 treatment at room temperature for 25 d,and it was 2.10 times higher than that of CH-3 treatment at low temperature for 40 d.Compared with the control treatment,the PAL activity of BG-2 and CH-3 treatment was 50.00% higher at room temperature for 20 d and 47.86% higher at low temperature for 40 d.The results showed that BG-2 could delay the decline of enzyme activity,and the effect was more obvious in combination with low temperature storage,and the storage time of melon was longer.3.Under different storage temperatures,BG-2 could reduce the weight loss rate,maintain good fruit firmness and peel color,inhibit the decrease of pH,TA,TSS and Vc content,and inhibit the increase of electrical conductivity.BG-2 maintained the sensory quality and nutritional value of melon fruit better under low temperature.When the melon was stored at room temperature for 25 d,the weight loss rate was8.82%,the peel color L value was 53.26,the color saturation C was 16.17,and the Vc content was 71.59 μg/g·FW;when the melon was stored at low temperature for 40 d,the weight loss rate was 8.33%,the peel color L value was 51.26,the color saturation C was 15.83,and the Vc content was 53.41 μg/g·FW.The TSS content of BG-2treatment was 1.08 times higher than that of control treatment at 25 d of room temperature storage,and 1.29 times higher than that of control treatment at 50 d of low temperature storage.The TA content of BG-2 treatment was 1.20 times higher than that of control treatment at 25 d of room temperature storage,and 1.18 times higher than that of control treatment at 50 d of low temperature storage.The relative conductivity of melon treated with BG-2 was 48.18% at 25 d of room temperature storage,and 41.26% at 50 d of low temperature storage.When the melon was stored at low temperature for 50 d,the pH value of BG-2 treatment was 6.53,which was1.05 times higher than that at 25 d of room temperature storage. |
