Effects And Mechanism Of UV-C Treatment On Nutritional Quality And Antioxidant Activity In Postharvest Fruits

Short-wave ultraviolet light(UV-C) irradiation is considered as a simple,safe and no population method for post-harvest treatment of fruit.It has been proved that UV-C can help to improve fruit quality and induce the synthesis of phenolics and enhancement of the antioxidant activity during storage.Actinidia arguta fruit,hawthorn,sweet cherry are favored by consumers for their abundance of phenolics and great health value.The objective of this paper is to study the change of nutritional quality and antioxidant activity of the three fruits treated by UV-C irradiation with different dosage during storage,explore the feasibility of improving health function and optimize the best UV-C dosage and storage time. Besides, mechanisms of UV-C physiological effect on fruits were studied from the point of physiology and molecular.The main contents and results are as follows.(1)Actinidia arguta fruit were exposed to different dosage(1.05、2.1、4.2 kJ /m2)of shortwave ultraviolet light(UV-C) and then stored at 25 ℃ and 0±1 ℃. The results showed that total soluble solid and reducing sugar content in fruit treated with UV-C increased while titratable acid declined. Besides,UV-C treatment delayed the decreases of fruit firmness and significantly enhanced the accumulation of total phenolics, flavonoid, anthocyanin and antioxidant activity of fruit.When stored at 25 ℃, fruit treated with 4.2 kJ /m2 UV-C irradiation showed the highest content of phenolic compounds after storage for 5 days. During storage at 0±1 ℃, phenolis compounds in fruits treated with 1.05 kJ /m2UV-C irradiation and stored for 3 days reached the maximum. These results suggest that Actinidia arguta fruit has a promising prospect in synthesis and maintenance of higher content phenolics and can be the health-promoting fruit when treated with UV-C irradiation.(2) Hawthorn fruits were exposed to different dosage(1.05、2.1、4.2 kJ /m2) of shortwave ultraviolet light(UV-C) irradiation and then stored at 25 ℃.The change of titratable acid and reducing sugar indicated that the quality of fruit treated with UV-C was not damaged. Phenolics content and antioxidant capacity of fruit increased immediately exposed to UV-C illumination, while high dosage of UV-C(4.2kJ/m2) made greater contribution to the enhancement of total phenolics(increased by 15% after storage for 4 h) and antioxidant capacity when compared with the control and other levels.These results suggest that hawthorn fruit has a limited prospect in synthesis and maintenance of higher content phenolics by UV-C treatment,which need further research.(3) Sweet cherry fruits were exposed to different dosage(1.05、2.1、4.2 kJ /m2)of shortwave ultraviolet light(UV-C) and then stored at 25 ℃. The results showed that UV-C delayed the decrease of titratable acid and promoted the increase of reduing sugar, improving the fruit quality. Besides, the accumulation of total phenolics, flavonoid, anthocyanin and antioxidant activity of fruit were significantly enhanced by UV-C treatment. Fruits treated with 2.1 kJ /m2 UV-C irradiation showed the highest content of phenolics(increased by 35.7%) and flavonoid compounds(16.0%)after storage for 6 days. The content of anthocyanin in fruit treated with UV-C reaches the maximum(increased by 60.6%) after storage for 8days. Sweet cherry has a promising prospect in synthesis and maintenance of higher content phenolicswhen treated with UV-C irradiation.(4) Phenylalanine-ammonidalyase(PAL) 、 Cinnamate-4-hydroxylase(C4H) and 4-coumarate:CoA ligase(4CL) activity of sweet cherry fruit treated with UV-C(2.1 kJ /m2) showed a significant increase as compared with control fruits.The expression levels of genes related to synthesis of phenolics significantly increased during storage at 24h-192 h, which may be major reasons for phenolics accumulation and antioxidant activity enhancement of post-harvest fruit treated with UV-C irradiation.