Friction measurements of model saliva-wine solutions between polydimethylsiloxane surfaces

Abstract

Wine can have a complex sensory profile and one important characteristic of the mouth feel in red wines is astringency, or a drying sensation felt when drinking. Evaluation of wine astringency or mouth feel has typically been done qualitatively by trained sensory panels. In this work, the friction of model saliva and wine mixtures was directly measured using the surface force apparatus (SFA). To mimic the tongue/palate, thin films of roughened polydimethylsiloxane (PDMS) were the sliding surfaces. The studies used well-defined model solutions of saliva and wine with low and high tannin concentrations to focus specifically on the effect of tannin/proline-rich protein complexes on friction. Turbidity increased with tannin concentration, and higher friction forces were measured with increasing tannin concentration, also connecting turbidity to friction. Importantly, higher friction was shown to directly correlate with the amount of saliva-wine complexes confined between the sliding surfaces, increasing by about 50% from low tannin (0.2 g/L) to high tannin (1 g/L) model wine. These measurements demonstrate that adsorption of tannin/proline-rich protein complexes on model tongue/palate surfaces reduce lubricity, increase friction, and should correlate with astringency perception.