Identification of the major drivers of 'phenolic' taste in ... - GWRDC

AWRI: Identification Of The Major Drivers Of ‘Phenolic’ Taste In White Wines
Two non flow-through fractions also contained quercetin-3-glucuronide as a significant proportion of the
phenolic compounds that absorb maximally at 370 nm. Various flavonol glycosides (of which quercetin-
3-glucuronide is a member) have been reported to elicit astringency at very low concentrations (Scharbert
et al. 2004; Brock and Hofmann 2008). However, of the two fractions that contained quercetin-3-
glucuronide (F1 Fiano and F1 Riesling), only one was perceived to be more astringent than the low
phenolic control, and only marginally so. Therefore quercetin-3-glucuronide does not seem to contribute
to the astringency of these fractions.
Adding phenolic fractions (regardless of source or type) resulted in a consistent reduction in perceived
burning sensation and acid aftertaste. At this stage of the project, tasters were trained to understand the
notion of hotness resulting from alcohol, but had not been introduced to the possibility that other forms of
back-palate hotness might exist. The base wine had been extensively stripped of its phenolics, so it could
be reasonably assumed that any hotness arising from the base wine was alcohol derived. In this context,
every phenolic fraction, regardless of its source or type reduced the perception of burning sensation
(presumably resulting from alcohol). Of all the fractions, the F3 fraction from the Gerwurztraminer was
the most effective in reducing the burning aftertaste (p=0.0074). It contained a higher proportion of
caffeic and coumaric ethyl esters that the other fractions amounting to 97% of the compounds active at
320 nm.
Phenolic addition generally resulted in a reduction in the perception of acid aftertaste. The three fractions
that resulted in the greatest reduction in acid aftertaste had a common feature in that they were all rich in
free hydroxycinnamic acids. However, F2 from the Gerwurztraminer was also abundant in these, but its
addition only marginally decreased the acid aftertaste.
For the first time we show that phenolic addition has little effect on acidity when perceived in mouth, but
significantly affects the intensity of acidity once the wine has been expectorated. The reason for this is
unclear, but due to its implications on style perception this result should be pursued.
The Fiano F2 fraction differed from the others in that it was rich in monomeric flavan-3-ols (epicatechin
gallate, catechin and epicatechin). It was also perceived to be more bitter than the control than any other
fraction. Epicatechin gallate has recently been shown to react most strongly amongst the common
monomeric flavanols found in wine with the human bitter taste receptor hTAS2R39 (Narukawa et al.
2011). It also was deemed to be bitter and astringent in human taste tests, and it elicited a taste that was
the least preferred amongst the common monomeric flavanols; epicatechin, epicatechin gallate,
epigallocatechin and epigallocatechin gallate (Narukawa et al. 2010). The other two flavanols found in
this fraction, catechin and epicatechin are also known to contribute to bitterness (Kielhorn and Thorngate
1999; Peleg et al. 1999). Interestingly, all the above-mentioned authors have reported that the monomeric
flavanols elicit astringency as well as bitterness. Hufnagel and Hofmann (2008) concluded that flavanols
did not contribute to astringency in red wine, a conclusion supported by the data here. The Fiano F2
fraction whilst being slightly more bitter than the control was not more astringent. Hufnagel and Hofmann
(2008) also suggested that the major bitter compounds in red wine were ethyl esters of caffeic, vanillic
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