Determination of ortho- and retronasal detection and recognition thresholds for off-favours in wine

Mestrado em Viticultura e Enologia - Instituto Superior de Agronomia - UL / Faculdade de Ciências - Universidade do PortoThe research performed in this thesis had as overall objective to fill the gap in the current literature about flavour thresholds and sensitivity to suprathreshold concentrations. Two groups of tasters were used, one comprised by 15 novices (student panel) and the other by 16 wine experts (professional panel). Detection (DT) and recognition (RT) thresholds were established in wine for six common off-flavour compounds when present in high concentration: acetaldehyde, acetic acid, ethyl acetate, hexanol, hydrogen sulfide and volatile phenols. Thresholds were evaluated orthonasally (ON) and retronasally (RN) by each participant, using the standardized procedures based on the ascending forced-choice (3-AFC) triangular tests. The suprathreshold intensity was obtained ON and RN after testing three measures of individual responsiveness: geometric mean (GM), area-under-curve (AUC) and slope of the response regression line. DT and RT thresholds yielded overall results within the range reported in literature. Interestingly, in both threshold and suprathreshold tests, contrary to predictions based on reports of an association between expertise and improvement of the olfactory and gustatory sensitivity, the thresholds for the same molecules were similar between tasting panels, indicating that sensitivities were practically not affected by expertise. The relationship between threshold and suprathreshold intensities was also studied. In most cases there was not a relationship, implying that a low threshold does not necessarily lead to greater sensations elicited by suprathreshold concentrations. On the other hand, the results suggested that some subjects perceived the molecules differently on both orthonasal and retronasal pathways, presenting higher variability on the orthonasal evaluation comparing with the retronasal one. Overall, results highlighted the high variability of individual olfactory responses and the importance of the retronasal pathway on the assessment of off-flavours in winesN/