Submitted to: American Journal of Enology and Viticulture
Publication Type: Abstract Only
Publication Acceptance Date: 3/18/2008
Publication Date: 9/3/2008
Citation: Tarara, J.M., Lee, J., Spayd, S.E., Scagel, C.F. 2008. Field temperature and anthocyanins in Merlot grape berries. American Journal of Enology and Viticulture. 59(3).
Technical Abstract: On field-grown vines, temperatures of 'Merlot' grape clusters were monitored and controlled from pre-veraison until harvest to produce a dynamic range of berry temperatures in both sun-exposed and shaded fruit. Ten combinations of temperature and solar radiation exposure were applied, and resulting phenolic profiles and total concentrations of skin anthocyanin (TSA) in the fruit were quantified at commercial maturity. Concentrations of flavonol-glycosides increased with exposure to solar radiation. Low light and high berry temperatures in concert decreased TSA rather than low incident solar radiation alone, which appeared not to compromise total anthocyanin accumulation. At higher berry temperatures, malvidin-based anthocyanins were at higher concentrations and comprised a larger proportion of TSA, regardless of the clusters' exposure to solar radiation. Acylated anthocyanins were a larger proportion of TSA than non-acylated anthocyanins under high temperature extremes in sunlit and shaded fruit, and under shade alone. When berry temperature was held equal to that of shaded fruit, exposure to solar radiation decreased the proportion of TSA in acylated derivatives of all five base anthocyanins and increased the proportion of TSA comprised by dihydroxylated anthocyanins. There appears to be a complex combined effect of solar radiation and berry temperature on anthocyanin composition in the field that is synergistic at moderate berry temperatures and potentially antagonistic at high temperature extremes. Exposure of berries to high temperature extremes for relatively short periods during ripening appears to alter the partitioning of anthocyanins between acylated and non-acylated forms, and between dihydroxylated and trihydroxylated branches of the anthocyanin biosynthetic pathway.