Xiaoqing Xie, Benjamin Loseke, Stephen Gamet, Paul Read,* and Changmou Xu
*University of Nebraska, Lincoln, 377 Plant Science Hall Department of Agronomy and Horticulture, Lincoln, NE 68583-0724 (pread1@unl.edu)

The vineyard and winery industry in Nebraska has grown greatly in the past 20 years. Since 1998, studies on cultivar evaluation of climate effects have been established to choose appropriate cultivars for specific regions of Nebraska. Although many studies have been performed to determine the impact of environmental factors on flavonoid accumulation in grape, little information is available for cultivars grown in Nebraska. Therefore, this study monitored the polyphenol accumulation, especially those responsible for berry color and antioxidant activities, such as anthocyanins and flavonoids, under darkness, UV light, jasmonic acid, or abscisic acid treatments for major grape cultivars in Nebraska. Grape berries of Frontenac, Frontenac gris, Norton, and Edelweiss were collected at veraison, surface disinfested, and cultured on 0.7% agar without pedicels. After maturity, the berries were collected for characteristic analysis. Skins and seeds were then separated and used for polyphenol profile and antioxidant activity analysis. In general, berry weight, Brix, and pH were observed to increase after the veraison stage. The effects of the darkness, UV, jasmonic acid, and abscisic acid treatments on the polyphenol profile and antioxidant activity were cultivar-dependent. For each treatment, optimal conditions for polyphenol accumulation were identified. In general, the polyphenol compounds increased with UV light and jasmonic acid treatments, but decreased with darkness and abscisic acid treatments. However, skin polyphenols accumulated during berry development, which was different from that in seeds. Moreover, total anthocyanins in skins of red color cultivars increased during berry development. Anthocyanins in berries cultured in agar were less abundant than in berries collected from the field at veraison and ripeness. This study investigated several factors which influence the secondary metabolites of grapes. These findings would be useful for producing grapes rich in health-beneficial polyphenols.  

Funding Support: UNL-IANR funds