Postharvest UV-A and UV-B treatments may cause a transient decrease in grape berry skin flavonol-glycoside contents and total antioxidant capacities

Csepregi, Kristóf and Kőrösi, László and Teszlák, Péter and Hideg, Éva (2019) Postharvest UV-A and UV-B treatments may cause a transient decrease in grape berry skin flavonol-glycoside contents and total antioxidant capacities. Phytochemistry Letters, 31. pp. 63-68. ISSN 1874-3900

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Abstract

Controlled postharvest abiotic stresses have already been shown to affect the secondary metabolism of freshproduce.Weappliedbroadbandultraviolet(either312nmcentredUV-Bor355nmcentredUV-A)radiationonharvested berry clusters of the red table grapeEmperor, and measured berry skin antioxidant capacities andphenolicprofiles2,24and48hafterthesetreatments.Therewasnosignificantchangeintheamountofcaftaricacid,thedominantphenolicacidcomponentfeaturinghigherUV-BthanUV-Aabsorbingcapacity.Ontheotherhand, but both types of UV treatment decreased the amounts of the two major quercetin-glycosides 2h afterirradiation. This effect was temporal, and concentration recovered during berry storage at 20°C under lowintensitylight.BerryskinUV-AandUV-Babsorbingcapacitiesshowedthesame,transitionaldecreaseregardlessof the wavelength of the irradiation. In the whole data set, antioxidant capacities and quercetin-glycosidecontent data showed strong and positive correlations. Berry skin peroxidase activity, as visualized with diami-nobenzidine-staining showed a transitional increase after 2h in response to both UV treatments. These datasuggestthattheobservedUV-inducedpostharvestchangesinphenolicmetabolitesarerelatedtotheoxidationofflavonols as peroxidase substrates rather than to direct UV photo-effects.

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