| Green mold and sour rot are the most economically important postharvest diseases of citrus fruit. Currently, both diseases are primarily controlled by applying synthetic fungicides. These methods can control the rot in some degree, but owing to its high and acute residual toxicity, environmental pollution as well as the development of fungicide resistance by pathogens, some synthetic have been prohibited in many countries. Therefore, there is a need for alternative approaches for effective management of sour rot and green mold of citrus fruit. Cinnamaldehyde(CA), a main component of cinnamon oil, can also be used to prevent food spoilage due to its strong antifungal activity. Sodium dehydroacetate(SD), a safe food preservative with a relatively broad spectrum of antibacterial activity against food-borne pathogens and spoilage organisms, has been widely used in special food production.The antifungal activity of CA and SD against postharvest citrus green mold and sour rot tested through in vitro and in vivo experiments. The effect of CA and SD on fruit quality parameters, such as weight loss rate, coloration index, firmness, pH, total soluble solid, and Vc content, were analyzed. The activities of catalase(CAT), superoxide dismutase(SOD), peroxidase(POD) and polyphenol oxidase(PPO), as well as total phenolic and flavonoid contents were further studied. The main results were as followed:In vitro test: CA and SD treatments have strong inhibition on Geotrichum citri-aurantii and Penicillium digitatum. In addition, CA and SD dose-dependently inhibited the mycelial growth of G. citri-aurantii and P. digitatum. The minimum inhibitory concentration(MIC) and the minimum fungicidal concentration(MFC) of CA to G. citri-aurantii and P. digitatum were both 0.50mL/L. In case of SD, the MIC and MFC against G. citri-aurantii were both 0.80 mg/mL, whereas thoese against P. digitatum were 0.20 and 0.40 mg/mL, respectively.In vivo test: Wax+CA(WCA) treatments have strong inhibition effect on sour rot and green mold during storage time. After 9 days of inoculation, the sour rot incidence rate in wax control was up to 100%, whereas that in WCA(1×, 2×and 4×MFC) treated samples was only 80%,77% and 50%, respectively. After 5 days of storage, green mold incidence rates in wax-treated and WCA(1×MFC)-treated fruits were up to 100.0% and 93.3%, respectively, whereas that in the WCA(10×MFC)-treated fruits was only 33.3%. Similar results were found in SD-treatment. After 8 days of inoculation, the sour rot incidence rate in control was up to 100%, whereas that in SD(1×, 2×and 4×MFC) treated samples was only 60%,30% and 10%. After 3 days of inoculation, the green incidence rate in control was up to 100%, whereas that in SD(2×, 4×and 8×MFC) treated samples was only 67%, 17% and 7%, respectively.Fruit quality: WCA treatment remarkably decreased weight loss rate but had minor effects on other fruit quality parameters(i.e., Vc content, TSS, pH, coloration index, and firmness) on the Satsuma mandarin but had no minor effect on Ponkan fruit quality. Similar results were found in SD treatments, but these treatments could exclusively decrease weight loss of Satsuma mandarin rather than Ponkan, and others fruit parameters were not affected.Enzyme test: WCA treatments enhanced the activities of CAT, SOD, POD, PAL, PPO, as well as the total phenols and flavonoids contents in both sour rot and green mold test, thereby might improve the fruit’s resistance to pathogens, delay senescence, and decrease the rot incidence. SD treatment induced an increase in the activities of SOD, POD, and PAL but not CAT in the sour rot test. For green mold test, SD induced the accumulation of reactive oxygen, and increase in activities of SOD and PAL indicating the antioxidant and disease resistance were improved in fruit.Taken together, our present research can provide theoretical foundation for CA and SD can be used in postharvest disease control of citrus fruit. |
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