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Soluble glycoproteins were isolated from Semillon wines made over a 5-y period, from 1990 to 1994, by precipitation with ammonium sulfate and fractionated by chromatography on Sephadex G-100. The total phenols were extracted with 50% aqueous ethanol from Semillon seeds, and the four seed phenol fractions (catechins, dimeric phenols, and oligomeric and polymeric tannins) were fractionated by diatomaceous earth partition chromatography of the total phenols. The proteins, catechin, and dimeric fraction alone appeared unchanged during storage in a wine-like model solution (aqueous 10% ethanol solution of pH 3.0) at 20 °C from 3 to 48 ch. However, the oligomeric and polymeric tannins, as well as the total phenols, gave rise to appreciable turbidity. The possible sensory effects of added proteins were investigated using paired comparisons between pure compounds (catechins and dimers) and the same compounds mixed with proteins. The hypothesis was that the proteins would decrease the taste of the catechins and dimers by decreasing their availability to interact with the taste receptors. Results corroborated the hypothesis when lower concentration of phenols and proteins were used. However, at higher concentrations, the reverse trend was observed. It is hypothesized that higher protein concentrations increased the total taste intensity by adding a taste of their own. |
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