Paolo Pietromarchi

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

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 trans-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.