Astringency is a complex sensation mainly caused by the precipitation of salivary proteins with polyphenols. In wine it can be enhanced or reduced depending on the composition of the medium.
In order to investigate the effect of ethanol, tartaric acid, fructose, and commercial mannoproteins (MPs) addition on the precipitation of salivary proteins, the saliva precipitation index (SPI) was determined by means of the sodium dodecyl sulphate polyacrylamide gel electrophoresis of human saliva after the reaction with Merlot wines and model solutions. Gelatin index, ethanol index, and Folin–Ciocalteu index were also determined.
As resulted by Pearson's correlation, data on SPI were well correlated with the sensory analysis performed on the same samples.
In a second experiment, increasing the ethanol (11%–13%–17%), MPs (0–2–8 g/L), fructose (0–2–6 g/L) level, and pH values (2.9–3.0–3.6), a decrease in the precipitation of salivary proteins was observed.
A difference in the SPI between model solution and red wine stated that an influence of wine matrix on the precipitation of salivary proteins occurred.
Results provide interesting suggestions for enologists, which could modulate the astringency of red wine by: (i) leaving some residual reducing sugars (such as fructose) in red wine during winemaking of grapes rich in tannins; (ii) avoiding the lowering of pH; (iii) adding commercial mannoproteins or promoting a “sur lie” aging; and (iv) harvesting grapes at high technological maturity in order to obtain wines with a satisfactory alcoholic content when possible.
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