Two dimensional gas chromatography: a powerful tool to unravel wine volatiles

A temporal and spatial investigation of Shiraz wine volatile composition from four vineyards located in warm to hot climates in New South Wales Australia was conducted. Shiraz wines were made from grapes harvested at two different berry maturity levels based upon a sugar accumulation model. Grape harvests were conducted between 10 to 12 days apart (H1 and H2, respectively) and wines made in triplicate using controlled fermentations. Wine volatile compounds were analysed by head space-solid phase micro extraction coupled to comprehensive two dimensional gas chromatography quadrupole time of flight mass spectrometry (HS-SPME-GCxGC-TOFMS). Acquired data were deconvoluted and aligned with LECO ChromaTOF Version 4.22 software at a signal to noise ratio 100. A total of 1240 putative compounds were detected, of which 240 were significantly different in at least one of the harvest dates among four vineyards. Compound identity was confirmed by authentic standards, Kovats retention index and or by comparing spectra of compounds to the NIST 2.0, Wiley 8 and the FFNSC 2 (Chromaleont, Messina, Italy) mass spectral libraries. A clear separation of samples based on the harvest date is evident in Principal Component 1 which accounted for 40% of data variation. Derivates of lipoxygenase pathway, i.e. C5, C6 and C9 compounds were typically found in higher levels in wines from the first harvest (H1) compared to wines from the second harvest (H2), irrespective of vineyard site. However, this trend was less pronounced for C6 esters such as E-hexenyl acetate and Z-3-hexenyl acetate. Several monoterpenes, norisoprenoids and sesquiterpenes were also identified in wines, however no clear trend according to harvest date is evident for these compounds. Preliminary results indicate significant and coherent modulations of wine volatiles in relation to harvest date, irrespective of vineyard location with similar climatic parameters. HS-SPME GCxGC-TOFMS was proven to be fast, reliable and a powerful technique to unravel wine volatile composition.