Circular Dichroism and Spectroscopic Studies of Vitis vinifera cv. Cabernet Sauvignon and Vitis rotundifolia cv. Noble Red Wine Liquid Chromatographic Fractions

Abstract

Red wines were made with Vitis vinifera cv. Cabernet Sauvignon and Vitis rotundifolia cv. Noble grapes with three different skin contact times and with added acetaldehyde to investigate monoglucoside and diglucoside anthocyanin polymerization. The anthocyanins were extracted from the wines by a low-pressure liquid chromatographic (LC) procedure using a silica/PVPP column, producing three to four chromatographic fractions from each wine. The UV/Vis and circular dichroism (CD) spectra of each fraction were then determined. The Noble wine polymers had CD spectra while the Cabernet Sauvignon wines did not. The chirality of the Noble wine polymers is theorized to be due to the polymer structure, which may be visualized as vertically stacked, as opposed to the apparent planar or net non-chiral structure of the Cabernet Sauvignon wine polymers. The intensity of the Cabernet Sauvignon fraction UV/Vis spectra increased with increasing skin contact, while those of the Noble wines did not. Acetaldehyde treatment of the wines resulted in nonuniform changes in the UV/Vis spectra of the Cabernet Sauvignon fractions. The Noble wine fraction UV/ Vis spectra were not significantly affected by acetaldehyde addition. The CD spectral evidence in combination with the UV/Vis spectra indicate that the Cabernet Sauvignon wines are composed of three or four polymer "class" structures while the Noble wines contain similar polymer structures in each of the four LC fractions.