Effects And Mechanisms Of Essential Oils On Quality Maintenance In Postharvest Starawberry And Chinese Bayberry Fruit

Strawberry and bayberry are all berries and they are very popular with consumers for their special moderate sweet and sour taste, rich in nutritions and bright and attractive color. Non-epicarp and high water content of flesh exposed to the atmosphere is susceptible to mechanical injury, physiological deterioration, water loss and microbiological decay. Botrytis cinerea is the major postharvest fungal disease on strawberries and Verticicladiella abietina (Peck) Hughes is the main postharvest fungal disease on Chinese bayberries. At present, refrigerated method combined with synthetic chemical fungicides are most commonly used method of storage for strawberries and Chinese bayberries, but the synthetic chemical fungicides have many problems such as food safety, resistance of chemicals and environmental pollution with long-term and heavy use. Therefore, the search for a safe and effective alternative to chemical fungicides or a part replacement is very important. In this paper, freshly harvested strawberries (Fragaria ananassa Duch. Cv. Fengxiang) and Chinese bayberries(Myrica rubra sieb.et Zucc. Cv. Wumei) were used to study the preservation effect of five essential oils, carvacrol, cinnamaldehyde, perillaldehyde, linalool and allyl isothiocyanate. Then, we investigated the mechanism from the anti-oxidation, fruit disease resistance and the effect of antifungal aspects to provide the theoretical basis for preservation of berries. The results were as follows:1 In the selected experiments, all five plant essential oils had significant effect on the storage of strawberries and Chinese bayberries. Decay index and weight loss rate were significantly inhibited by all five plant essential oils. High fruit firmness was maintained, The TSS, Vc content and other quality parameters were not adversely affected, the decrease of total sugar and reducing sugar content were also inhibited late in storage. However, high concentrations caused injury, injury emerged on strawberry fruit only with 5μL/L AITC and perillaldehyde treatments and 10μL/L in the other three kinds of essential oils treatments. Furthermore, the resistance of essential oils for Chinese bayberry fruits were higher than the strawberry fruits. The suitable experimental concentration on strawberry fruits were as follows:AITC-1μL/L, perillaldehyde-1μL/L, cinnamaldehyde-1μL/L, carvacrol-5μL/L and linalool-5μL/L; The suitable experimental concentration on Chinese bayberry fruits were as follows:AITC-20μL/L, carvacrol-1μL/L, cinnamaldehyde-0.5μL/L, linalool-1μL/L and perillaldehyde-1μL/L.2 Significant effects on antioxidant systems of postharvest strawberry and Chinese bayberry fruits were determined in other four kinds of essential oil treatments except AITC treatment, including an increase of antioxidant related substances total phenolics, total flavonoids, total anthocyanins, phenolic monomers content, and the activity of antioxidant-related enzymes SOD, POD, APX, CAT. The mechanism for these four essential oils to reduce fruit decay may be related to the improving of antioxidant activity to enhance free radical scavenging capacity and delay senescence. AITC treatment had the opposite effect in antioxidant capacity, the antioxidant capacity was significantly lower than control group, but O2- production was significantly higher. Therefore, the mechanism of AITC to inhibit fruit rot of strawberries and Chinese bayberries may be a kind of "pro-oxidant" effect to inhibit the growth of fungi directly.3 Carvacrol, cinnamaldehyde, perillaldehyde and linalool could significantly improve the activities of disease resistance related enzymes PAL, POD, chitinase andβ-1,3 glucanase in strawberry and Chinese bayberry fruits. The activity of PAL, POD, chitinase andβ-1,3 glucanase in AITC treatments were significantly lower than the control group. Most of the suitable concentration in vivo experiments had some kind of antifungal effect in vitro too. As the oil concentration increased, the inhibition rate increased, spore germination and germ tube length decreased, and the AITC treatment had the best antifungal activity. Therefore, combining the findings of the third chapter, carvacrol, cinnamaldehyde, perillaldehyde and linalool may through the synergy effect of enhancing fruit antioxidant capacity, improving fruit disease resistance and direct antifungal effect. AITC may through the pro-oxidant effect to inhibit the growth of fungi directly to reduce the decay of berries.