Prediction of grape polyphenol astringency by means of a fluorimetric micro-plate assay

Previous works have demonstrated that astringency can be predicted on the basis of turbidity developed by polyphenol/mucin mixes. In the present study, a micro-plate assay, based on the ability of haze particles to screen the radiation emitted by a fluorescent compound (I%), is proposed for polyphenol/mucin reactivity estimation. Grape seed extract (GSE) solutions prepared in a range of physiochemical active concentrations (0.0–2.9 g/L) were reacted with mucin. A significant linear relationship (r = 0.99; p = 0.000) was found between turbidity (NTU) and I% values of GSE/mucin samples. Within the experimental range of phenolic samples, the CV value of I% determinations was always lower than 10%. The relationship between sensory and instrumental responses, as a function of phenolic solution characteristics, was investigated. Variations in phenol concentration and pH induce similar modifications of both the intensity of perceived astringency and I% values. A significant linear relationship (r = 0.98; p = 0.000) was found by relating sensory ratings to the relevant I% values.