Development of volatile compounds in Pinot noir grapes and their contributions to wine aroma.

摘要

It is often perceived that late maturity of grape gives a more complex aroma profile to Pinot noir wine, however, there is little understanding of the basic flavor chemistry of grape maturity on wine aroma. The aroma contributing compounds in Pinot noir were first identified by aroma extract dilution analysis (AEDA). Based on the AEDA results, the most important aroma compounds for Pinot noir include acids, alcohols, ethyl esters as well as beta-damascenone, vanillin, eugenol, nonalactone, whiskey lactone, trans-geraniol. Those important aroma compounds were investigated in wines made from early, middle and late maturity grapes by the stir bar sorptive extraction- gas chromatography/mass spectrometry (SBSE-GC/MS) method. Quantitative analysis showed that the Pinot noir wine made from late harvest grapes contained more monoterpenes, more C13-norisoprenoids, more gamma-nonalactone, guaiacol, and 4-ethylguaiacol, which contributed to more cherry, berry, more complex aroma characters; while wine produced with early harvest grapes have more short chain esters. The development of those aroma compounds in grapes was further investigated. The free aroma compounds were directed extracted from grape juice with the stir bar sorptive extraction and analyzed with gas chromatography-mass spectrometry, the glycoside bound aroma precursors were isolated with a reversed phase C18 column and hydrolyzed with glycosidic enzymes. The released aglycones were analyzed with SBSE-GC-MS. It was found that free monoterpenes and C13-norisoprenoids decreased during grape development, while free benzenoid alcohols increased. However, the bound C13-norisoprenoids dramatically increased during grape maturation. Since the glycoside bound aroma precursors had much higher concentrations than the free form, these precursors will be hydrolyzed during wine making process, and contribute to more cherry, berry, and more complex aroma to the finished wine.