| Loquat fruit(Eriobotrya japonica Lindl),tastes delicious and is also good for nutrition.The special local fruit which is native to subtropical southern in China has a thousand years of history,and its annual output is about 10 to 15 tons.At present,China is the most important producers of loquat in the world.Because China have occupied more than two thirds of the world's total cultivated area and total output.Storage at ambient temperature can effectively reduce lignifications and maintain quality of loquat fruit at the greatest degree.But ambient temperature will short storage time,and high rotting rate is a major drawback of ambient temperature storage.Loquat fruit(Eriobotrya japonica Lindl,Jiefangzhong)was used as the experimental material in this paper.The effect of ultrasonic treatment combined with peracetic acid on harvest quality of loquat fruit and the control effect of this method on C.acutatum were studied.Also possible mechanism why this method can inhibit the growth of pathogenic bacteria to reduce the occurrence of anthracnose was investigated.It will provide a theoretical basis for the application of ultrasonic treatment combined with peracetic acid in storage and transport of loquat fruit after harvested.The main results were listed as following:(1)The condition of ultrasonic treatment with peracetic acid on postharvest loquat storage was optimized in this study.The effect of ultrasonic treatment(300-500 w,2-8 min)combined with peracetic acid(26-78 mmol/L)on the storage quality of loquat fruit was studied by the response surface methodology(RSM),and a quadratic polynomial mathematical mode was established.It was found the model was significant after tested and has a better goodness of fit.Through analysising the model surface plot,effects of processing time,ultrasonic power and peracetic acid concentration on fruit rotton,core browning and juice yield were explicit.And on this basis to optimize and validate the combined treatment conditions:ultrasonic power was 400w,processing time was 6 min,peracetic acid concentration was 0.4%.(2)The combined treatment of Ultrasonic(400 W)and peracetic acid(0.4%)for 6 min can effectively inhibit the increase in firmness,fruit rot index and core browning index compared with ultrasonic or peracetic acid alone.The combined treatment had the positive effects on maintaining TSS and Vc contents,thus ensure the quality of postharvest loquat fruit.In addition,the combined treatment can also keep high total phenols and flavonoids content in loquat fruit,While improve the activities of APX,SOD,CAT and POD,reduce the accumulation of superoxide anion and increase DPPH radical scavenging in loquat fruit.So reactive oxygen metabolism in loquat fruit can be balanced.These results suggest that the combined treatment can maintain the quality of postharvest loquat effectively,improve the antioxidant system activity of loquat fruit,reduce the damage of the reactive oxygen species to fruit cells,thereby delaying senescence and maintaining fruit quality.(3)The combined treatment of Ultrasonic(400 W)and peracetic acid(0.4%)for 6 min can results in significantly lower natural incidence compared with ultrasonic or peracetic acid alone.The combined treatment effectively maintained the disease-related enzymes activity of chitinase,?-1,3-glucanase and PAL.Meanwhile the combined treatment can significantly inhibit the spore budding rate,the germ tube length of C.acutatum,and the hyphae extension.It was analyzed from the estracellular experiment that the combined treatment can effectively destroy the membrane structure integrity of C.acutatum and increase membrane permeability,thus the increase of extracellular PH,conductivity and the change of cell components lead to cell death.These results shows that the combined treatment of ultrasonic and peracetic acid can increase the disease-related enzyme activity and direct inhibitory effect in vitro,thereby increasing fruit resistance and reduce the incidence of decay. |
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