Influence of two polyphenols on the structure and lubrication of salivary pellicle: An in vitro study on astringency mechanism

This study investigated the influence of two polyphenols on the structure and lubrication of the salivary pellicle, aiming to extend the understanding of astringency mechanisms. The salivary pellicle was prepared by the adsorption of human whole saliva on the enamel substrate. Low-astringency catechin and high-astringency tannic acid were used as astringents. The changes induced by the two polyphenols in the structure and lubrication of the salivary pellicle were examined using quartz crystal microbalance with dissipation (QCM-D) and nano- indentation/scratch technique. The salivary pellicle suffers from changes in structure and physical properties owing to protein dehydration and protein-polyphenol complexation when encountering polyphenolic molecules, causing increases in the roughness and contact angle but a decrease in the load-bearing capacity. Therefore, the lubrication performance of the salivary pellicle is impaired, leading to an increase and fluctuation of the friction coefficient. The intensity of astringency has a strong positive correlation with the water contact angle, surface roughness, and friction coefficient of the salivary pellicle. In summary, astringency is a tactile perception driven by the roughness and wettability of the salivary pellicle rather than oral lubrication, and increased intraoral friction is an inevitable consequence of astringency. The findings of this study will help promote and assist the objective evaluation of astringency.