Abstract
A full understanding of the origin, formation and degradation of volatile compounds that contribute to wine aroma is required before wine style can be effectively managed. Fractionation of grapes represents a convenient and robust method to simplify the grape matrix to enhance our understanding of the grape contribution to volatile compound production during yeast fermentation. In this study, acetone extracts of both Riesling and Cabernet Sauvignon grape berries were fractionated and model wines produced by spiking aliquots of these grape fractions into model grape juice must and fermented. Non-targeted SPME-GCMS analyses of the wines showed that several medium chain fatty acid ethyl esters were more abundant in wines made by fermenting model musts spiked with certain fractions. Further fractionation of the non-polar fractions and fermentation of model must after addition of these fractions led to the identification of a mixture of polyunsaturated triacylglycerides that, when added to fermenting model must, increase the concentration of medium chain fatty acid ethyl esters in wines. Dosage-response fermentation studies with commercially-available trilinolein revealed that the concentration of medium chain fatty acid ethyl esters can be increased by the addition of this triacylglyceride to model musts. This work suggests that grape triacylglycerides can enhance the production of fermentation-derived ethyl esters and show that this fractionation method is effective in segregating precursors or factors involved in altering the concentration of fermentation volatiles.
Highlights
Volatile organic compounds in the wine matrix are responsible for determining the flavour and aroma of a wine and changes in concentrations of these volatile compounds will affect flavour and aroma attributes [1,2,3]
The PSDVB loading method offers a convenient, repeatable method to fractionate organic extracts of marine sponges [20] and has been used previously on plant extracts [21]. This method was applied to organic grape berry extracts to test its usefulness in fractionating grape samples
The influence of the different grape fractions on wine aroma and volatile compound production during yeast fermentation was tested in small-scale model fermentations
Summary
Volatile organic compounds in the wine matrix are responsible for determining the flavour and aroma of a wine and changes in concentrations of these volatile compounds will affect flavour and aroma attributes [1,2,3]. There is increasing evidence that grape components in a must can modulate the concentrations of varietal impact compounds [4,5,6], and yeast-derived non-varietal compounds [7,8,9] in wines. Molecules 2018, 23, 152 or degradation of wine volatile compounds provides the potential to produce wines with specific flavour properties for targeted consumer groups. This knowledge will inform novel grape growing, wine making and ageing techniques that could allow such opportunities. To improve the understanding of the origins of volatile compounds in wine, grape-derived precursors to wine aroma compounds or grape-derived compounds that alter yeast volatile compound production need to be identified. As grapes and wine contain a very complex mix of compounds, fractionation of samples is a good method for simplifying these matrices for compound discovery
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