A tribo-chemical view on astringency of plant-based food substances

Consumption of plant-based food products having high composition of polyphenols leads to the sensation of astringency. For sliding oral surfaces, friction is an essential property during the oral perception of roughness and dryness which are attributes associated with astringency. Different factors including the chemical composition of interacting layers, structure and operation of interfaces have an effect on the astringency development process. The manner of interactions occurring at oral interfaces suggest there is a system dependence of astringency and highlights the importance of adopting a tribosystems approach. Available measurement techniques have shown an existing relationship between salivary protein-polyphenol interaction and an astringent mouthfeel. Nevertheless, the tribo-chemistry involved in this multifaceted sensation remains largely unexplored in a comprehensive manner. In this review the underlying tribo-chemical processes useful in understanding the mechanism of astringency are highlighted and discussed considering current techniques employed to investigate astringency perception. Loss of lubrication on oral surfaces owing to the tribo-chemical interactions involving saliva and astringent plant proteins requires subsequent deformations of oral tissues which are significant enough to induce strains at mechanoreceptor locations, leading to the sensation of astringency. It is proposed that micro-scale contact modelling on the interaction of food particles/aggregates, boundary layers and oral surfaces shows potential in addressing the knowledge gap between tribo-chemical measurement techniques and panel tests, making it possible to attain a predictor for astringency.