Effects of partial dehydration techniques on the metabolite composition in 'Refosk' grape berries and wine

Authors: MAJA MIKULIC PETKOVSEK, TJASA JUG, JAN RESCIC, DENIS RUSJAN

Abstract: The aim of the study was to investigate the impact of the on-vine double maturation raisonnée (DMR) and off-vine berry partial dehydration in the chamber (PDC) on the chemical characteristics of the grape and wine grapevine cultivar 'Refosk'. A liquid chromatography-mass spectrometry (LC-MS) system was used for the identification and quantification of phenolics and the HPLC for sugars and organic acids. Berries subjected to DMR partial dehydration reached technological maturity (18.5 °Brix) within 14 days of cane cutting and those under PDC in 22 days upon harvest. The greatest decline in berry weight was recorded in the PDC treatment (14%), followed by the DMR technique (approx. 8%). Both dehydrations significantly increased titratable and total acidity in berry and wine, while the pH level was significantly lower in DMR treated berries. Compared to PDC, DMR significantly increased the content of total flavonols and anthocyanins in berries and wine, as well as the total flavanols in berries and stilbenoids in wine. DMR treated berries contained 1.7-fold higher content of total anthocyanins, up to 2-fold higher content of total flavonols, and 1.6-fold higher total phenolic content in the skin compared to those from PDC treatment. Moreover, it increased the content of total anthocyanins, stilbenoids, and flavonol glycosides in wine. On the other hand, PDC treatment showed greater impact on phenolics in wine, especially with an increase of total hydroxycinnamic acids, flavanols, and total phenolics but with a decrease in anthocyanins contents. The study suggests that berries subjected to DMR respond differently to partial dehydration than those subjected to PDC, which was evident from the accumulation of secondary metabolites. Undoubtedly, DMR showed interesting results regarding berry and wine composition and therefore it could be introduced in the vineyard for production of dry wine as well.

Keywords: Dehydration, anthocyanins, organic acids, phenolics, 'Refosk', sugars

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