| Freshly harvested strawberry fruits named HongYang were treated with 0.5,1.0,2.0 and 4.0 kJ/m2 UV-C in the external irradiation device to investigate the effects of UV-C on postharvest physiology and quality,fruit rot,antioxidant ability and disease resistant ability from these angles of active oxygen metabolism,phenylpropanoid metabolism and induced disease resistance during storage time.The results were as follows:1.When exploring the effects of different dose of UV-C treatment on decay and quality in strawberry fruits,we found that these doses of UV-C could suppress the occurrence of strawberry fruit rot,and in a certain dose range?0.5?2.0 kJ/m2?,the higher dose the UV-C was used,the more obvious inhibition effect on fruit decay it had,especially the treatment of 2.0 kJ/m2 UV-C,while the effect of 4.0 kJ/m2 UV-C irradiation on inhibition of fruit decay was so weaken.In addition,UV-C irradiation at 1.0 kJ/m2 and 2.0 kJ/m2 could effectively promote the increase of fruit total phenol and total anthocyanins,while UV-C treatment at 1.0?4.0 kJ/m2 could significantly inhibit the fruit firmness,Vc,reducing sugar and total sugar content decreasing.However,the four UV-C treatments had no effect on changes of soluble fruit solids content,titratable acid content and fruit color.These results suggest that UV-C treatment at 0.5?4.0 kJ/m2 may has a potential application prospect in the field of strawberry preservation.2.When inquiring the effect of UV-C treatment on active oxygen metabolism and caducity,we found that the UV-C treatment at 2.0 kJ/m2 could improve the activity of antioxidant enzymes with POD,SOD and CAT in fruit,inhibite the CX activity of cell wall hydrolases rising and O2-producing,as well as reduce fruit decay and the accumulation of MDA content,meanwhile,it could maintain higher Vc content and fruit firmness.Besides,UV-C treatment at 2.0 kJ/m2 effectively increased the H2O2 production of three days before storage,and inhibited the accumulation of H2O2 from the third day on in strawberry fruit.These results suggest that UV-C treatment at 2.0 kJ/m2 can delay fruit senescence and inhibit fruit decay through maintaining the balance of active oxygen metabolism in postharvest strawberry fruit.3.When studying the effect of UV-C treatment on phenylpropanoid metabolism and antioxidant ability,we discovered that UV-C treatment at 2.0 kJ/m2 significantly enhanced the activities of phenylalnine ammonialyase,cinnamate-4-hydroxylase,4-coumarate coenzyme A ligase,chalcone isomerase and dihydroflavonol-4-reductase,maintained higher total phenolics,anthocyanins and flavnoids content as well as the main individual phenolic and anthocyanin compounds contents than controls,and promoted the increase of DPPH free radical scavenging activity and reducing power and inhibited the decrease of hydroxyl radical scavenging activity.These results showed UV-C treatment at 2.0 kJ/m2 can promote the synthesis of phenolic compounds by inducing related enzyme activity of phenylpropanoid metabolism to improve the antioxidant capacity of strawberry fruit.4.During investigating the effect of UV-C treatment on resistance to B.cinerea in strawberry fruit,we found UV-C treatment at 2.0 kJ/m2could inhibite the extension of lesion diameter,enhance the activity of PAL,PPO,POD,?-1,3-glucanase and chitinase,and induce the massive accumulation of total phenol.Besides,the treatment could prevent spore germination and germ tube growth of B.cinerea on culture medium,but the inhibitory effect was not obvious.In the reverse transcription experiment,we also found neither untreatment nor UV-C treatment could motivate the massive expression of PAL,PPO,POD,CAT and CCR-1 allele genes of strawberry,and while both only stab inoculation of B.cinerea and UV-C treated combining with stab inoculation of B.cinerea could induce substantial expression of disease-resistant related genes,but the latter treated fruits were more obvious.These results indicate that UV-C treatment at 2.0 kJ/m2 can restrain fruit rot of postharvest strawberry by enhancing fruit disease resistance. |
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