Vine Microclimate and Norisoprenoid Concentration in Cabernet Sauvignon Grapes and Wines

Abstract

Effects of light exposure and vine microclimate on C₁₃-norisoprenoid concentration in Cabernet Sauvignon grapes and wines were investigated by measuring the amounts of β-damascenone (megastigma-3,5,8-trien-7-one), TDN (1,1,6-trimethyl-1,2-dihydronaphthalene), and vitispirane (6,9-epoxy-3,5(13)-megastigmadiene) using gas chromatography-mass spectrometry. In grapes and wines, the most exposed treatment (all lateral and primary leaves removed) had the highest light intensity and temperature and showed the highest concentrations of TDN and vitispirane (p < 0.05). However, in the more shaded treatments, concentrations of all norisoprenoids were variable and dependent on the treatment conditions. When leaves were removed, C₁₃-norisoprenoid concentrations were linearly (r > 0.90; p < 0.1) and positively correlated with increasing sunlight exposure. In contrast, in the most shaded treatments with no leaf removal there were high concentrations of norisoprenoids. β-Damascenone concentrations in particular were highest when no leaves were removed. Grapes and corresponding wines from the south side of the vine had higher levels of measured norisoprenoids than those from the north side. However, the leaf layer number was also correlated (r > 0.89; p < 0.1) with norisoprenoid concentration. Norisoprenoid concentrations in grapes were significantly correlated (p = 0.025) with those in wines. These results suggest that in addition to sunlight exposure, leaf removal and cluster microclimate can significantly alter norisoprenoid concentrations in grapes and wines.