Effect of pomace-contacting method on the concentration of cis- and trans-resveratrol and resveratrol glucoside isomers in wine

The effect of various pomace-contacting (maceration) methods on the concentrations of cis- and trans-resveratrol and resveratrol glucoside isomers were investigated in Vitis vinifera L. cv. Cabernet Sauvignon grape musts during alcoholic fermentation. Compared to a classical red wine vinification (control), carbonic maceration resulted in no detectable quantities of all four forms of resveratrol throughout fermentation and pressing. Prefermentation cold-soaking significantly increased (p < 0.01) both free isomers of resveratrol in free-run, press, and mix wine despite no significant differences with the control in trans-resveratrol glucoside concentration and slightly less extraction of cis-resveratrol glucoside. Free resveratrol was absent in the must heated prior to fermentation, while the level of resveratrol glucosides significantly increased (p < 0.001) relative to the control. In the final wines ready for bottling or aging, thermovinification proved most beneficial with respect to total resveratrol concentration, being 266% higher than that achieved in the control, while cold-soaking proved less beneficial, improving total resveratrol by 27%.