Development of volatile composition and C₁₃-norisoprenoid precursors in Pinot noir grape

Graduation date: 2013This study first investigated the developmental changes in the volatile composition and carotenoids of Pinot noir grapes. Grape berries were sampled every week from pea size to harvest during the 2011 and 2012 season. Carotenoids and organic acids were analyzed by HPLC. Volatile compounds were extracted from crushed berries using headspace solid-phase microextraction (HS-SPME) and analyzed by gas chromatography-mass spectrometry (GC-MS), and C₁₃-norisoprenoids potentials were analyzed by HS-SPME-GC-MS after acid hydrolysis. Malic acid accumulated before véraison and decreased dramatically during ripening. Carotenoids and chlorophylls decreased during entire developmental period although some of carotenoids showed a short accumulation stage before véraison. Pinot noir grapes had a more complex volatile compound composition pre-véraison than post-véraison, which may due to the decreasing of monoterpenes during ripening. C6-aldehydes significantly increased in concentration after véraison. C6-alcohols accumulated around véraison and decreased during ripening. Benzyl and phenylethyl alcohols increased before véraison, reached the highest amount two weeks after véraison and slightly decreased towards harvest. The concentration of volatile phenols reached the highest amount at véraison, decreased in about one week, then stayed relatively stable through maturity. Free-form C₁₃-norisoprenoids was low, but higher after acid hydrolysis, indicating the dominance of C₁₃-norisoprenoids precursors. Total C₁₃-norisoprenoids increased after véraison, corresponding to carotenoid breaking down. The analysis of grape composition in this study demonstrated a quantitative means of assessing the relationships between vineyard management practices and grape-derived secondary metabolites, some of which are important wine aroma and flavor components. Effect of cluster zone leaf removal management on grape composition were further investigated. Three cluster zone leaf removal management, including 0% leaf removal (Control), 50% leaf removal and 100% leaf removal of the cluster zone were studied in commercial vineyards from 2010 to 2012. Grape samples were harvested every year and analyzed for total soluble solids (TSS), organic acids, phenolics and carotenoids. Leaf removal had no impact on grape TSS, citric and tartaric acids but lowered malic acid in year 2012. Leaf removal increased quercetin glycoside content in grape berry in three years, and increased anthocyanin content in year 2010 and 2012. For carotenoids, leaf removal decreased flavoxanthin content in the grape berry and decreased β-carotene in 2012. It is evident that more sun exposure as a result of leaf removal increases degradation of carotenoids, and could potentially increase concentration of norisoprenoids in grapes