Effect of Postharvest Dehydration on Content of Volatile Organic Compounds in the Epicarp of Cesanese Grape Berry

Abstract

Postharvest dehydration is a technique to help increase polyphenol concentration and to modify volatile organic compounds (VOCs) in grape berry. Cesanese winegrape was dehydrated off the vine at 10°C, 45% relative humidity, and an air flow of 1.5 m/sec. Sampling was performed every week for 6 weeks, until it reached 37% mass loss. Proanthocyanidins in seeds increased progressively on both fresh and dry weight basis during dehydration until 30% mass loss. Total polyphenols extracted from the epicarp measured on a fresh weight basis increased during dehydration. A similar pattern was shown by anthocyanins. For VOCs, a high prevalence of benzenoids followed by norisoprenoids, terpenols, and C₆ compounds was observed. Benzenoids were more localized in the mesocarp (7352 μg/kg DW) than in the epicarp (3312 μg/kg DW) as were norisoprenoids. In contrast, as expected, terpenols were more concentrated in the epicarp (1787 μg/kg DW) than in the mesocarp (1370 μg/kg DW). During dehydration, a significant decrease was observed in these compounds in the mesocarp and a parallel increase in the epicarp, especially concerning benzyl alcohol and 2-phenylethanol among the benzenoids and vomifoliol and 3-OH-β-damascone among the norisoprenoids. Diendiol1, geraniol, and <i>trans</i>-8-OH-linalool in the mesocarp decreased progressively during dehydration, while the same compounds increased in the epicarp. C₆ increased significantly in the epicarp. In addition to epicarp biosynthesis of VOCs during postharvest dehydration, a mass transfer of VOCs from the mesocarp to the epicarp might also occur.