Identification and Quantification of a Marker Compound for ‘Pepper' Aroma and Flavor in Shiraz Grape Berries by Combination of Chemometrics and Gas Chromatography−Mass Spectrometry

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Abstract
‘Black pepper' aroma and flavor is important to some Australian Shiraz red wine styles but the aroma compounds involved have yet to be identified, and no objective analytical method to assess ‘pepper' grape aromas is available to date. Samples of potentially ‘spicy'/‘peppery' grapes were obtained from vineyards in South Australia and Victoria over two vintages. The important sensory attributes of the grapes, including the aroma descriptor ‘pepper', were rated by a sensory panel. The sensory study revealed a strong correlation between the intensity of ‘pepper' aroma and the intensity of ‘pepper' flavor perceived on the palate. The grape homogenates were analyzed by static headspace GC-MS using a cool inlet system. Vectors obtained by analysis of over 13 000 individual mass spectra per grape sample were then subjected to multivariate analyses. Both principal component analysis and partial least-squares regression were used to develop multivariate models based on mass spectra and aroma descriptors to explain the intensity of the rating of the ‘pepper' character. Corresponding differences in mass spectra and aroma were observed among vineyards and from the same vineyards in different years. Additional optimization of the methodology enabled selection of a single region of the GC-MS chromatogram that allowed prediction of ‘pepper' aroma intensity with a correlation coefficient >0.98 and led to the identification of α-ylangene, a tricyclic sesquiterpene. To assess the potential of α-ylangene as a marker for this sensory characteristic, a method for α-ylangene analysis of grapes and wine using HS-SPME-GC-MS was developed. Although not a significant aroma compound by itself, α-ylangene was a satisfactory marker for the ‘pepper' aroma in grapes and wine, and its concentration showed similar discrimination between ‘peppery' vineyards and vintages as that obtained using the multivariate models. Despite its presence in grapes, we could not detect α-ylangene in wine. Keywords: GC-MS; SPME; grape; wine; aroma; multivariate analysis; α-ylangene; sesquiterpenes

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