Chemical and biochemical change of healthy phenolic fractions in wine grape by postharvest dehydratation

Clusters of Aleatico winegrape were picked at 18 °Brix and placed at 10, 20, or 30 °C, 45% relative humidity (RH) and 1.5 m/s of air flow to dehydrate the berries up to 40% of loss of initial fresh weight. Sampling was done at 0, 10, 20, 30, and 40% weight loss (wl). Selected polyphenols and sugar content (expressed as SSC = soluble solids content) both measured on dry weight basis, polyphenol oxidase (PPO), and phenylpropanoid pathway gene expression were analyzed. Phenolic acids increased significantly at 20% wl at 20 °C, while at 10 °C the increase was lower. Stilbenes (trans-resveratrol and trans-piceid) and catechins rose more than double to 100 mg/kg and more than 3-fold to 135 mg/kg at 20 °C and 10% wl. At 10 °C the increase of these compounds was less, but higher than initial values. At 30 °C, except for a significant rise at 10% wl for catechins and stilbenes, all the rest of the compounds diminished. Anthocyanins increased at 10 and 20 °C, but decreased at 30 _C. PPO rapidly increased at 20 and 30 °C at 10% wl and then declined, while at 10 °C the activity lasted longer. Relative gene expression of phenylalanine ammonia lyase (PAL), stilbene synthase (STS), chalcone isomerase (CHI), dihydroflavonol reductase (DFR) were upregulated at 10 °C more than at 20 °C, at 20% wl, while at 30 °C the gene expression was downregulated.