Ellagitannins and flavano-ellagitannins: concentration ranges in different areas and sensory evaluation
Abstract
C-Glucosidic ellagitannins, which are the main polyphenolic compounds in oak heartwood, are extracted by wine during aging in oak barrels. Although such maturing of alcoholic beverages in oak barrels is a multi-centennial practice, very little is known on the impact of these ellagitannins on the organoleptic properties of red wine. The objectives of the present investigation were (i) to isolate oak ellagitannins and to hemisynthesize some made-in-wine flavano-ellagitannins, such as acutissimin A; (ii) to analyse their concentration ranges depending on the cultivar area and (iii) to evaluate their sensory impact on the basis of their human threshold concentrations and dose/response relationships in different types of solutions. The C-glucosidic ellagitannins, castalagin and vescalagin, were extracted and purified (>95% pure) from Quercus robur heartwood (Quideau, S., Varadinova, T., et al., 2004). The hemisynthesis of acutissimins A and B and epiacutissimins A and B (>95% pure) was performed in an acidic organic solution [1.5% (v/v) TFA/THF] at 60 °C (Quideau, S., Jourdes, M., et al, 2005). The concentrations in ellagitannins and flavano-ellagitannins of 85 samples from different zones of Bordeaux and 100 wines from La Rioja were analyse by HPLC-DAD-MS after their extraction by a solid phase extraction (SPE) methodology using a column with TSK HW 50F gel. The average concentration of the sum of ellagitannins from Bordeaux samples was practically the double, 5.357 mg/L comparing with La Rioja ellagitannins sum average in wines, 3.022 mg/L. A panel of eighteen judges, trained with aqueous solutions of quinine sulfate (0.25 g/L), aluminium sulfate (3 g/L) and sucrose (4 g/L) to set bitterness, astringency and sweetness, took part in this sensory study. This panel passed different triangular tests using castalagin, vescalagin and a mixture of 8 ellagitannins with increasing concentrations in order to determine the concentration thresholds at two different pH values, pH 4.5 and pH 3.5, as in wine model solution and in a Merlot red wine with scarcity on ellagitannins. As a result, the castalagin astringency threshold was determined to correspond to a concentration of 5.7 mg/L at pH 4.5, whereas the same compound in the same aqueous solution adjusted at pH 3.5 has its astringency threshold at 9.2 mg/L.
Issue: Macrowine 2016
Type: Article
Authors
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