Oral bio-interfaces: Properties and functional roles of salivary multilayer in food oral processing

Background: A bio-interface is a thin fluid boundary layer that separates and protects biological surfaces by of-fering multi-functionalities. Saliva forms a typical bio-interface inside oral cavity and plays a critically important role in food oral processing. During oral processing of food, wetting and mixing of food particles, formation of food bolus, colloidal and enzymatic interactions of food components, oral lubrication, and diffusion of flavor compounds are all closely related to properties of the saliva bio-interface. A saliva bio-interface consists of a multi-layered microstructure with each layer for different functional roles.Scope and approach: This review presents information about the formations and structures of saliva films, and the underlying mechanisms of interactions occurring at interface. The review aims to provide solutions to following questions: how flavor compounds transport across, and how physical and chemical interactions are regulated at the saliva bio-interfaces. Important implications of saliva interfaces and their possible applications are also highlighted.Key findings and conclusions: Saliva film as an oral bio-interface can be seen as an indispensable component of food oral processing. It functions as an independent phase with its unique properties and behavior. For the point of view of either food oral manipulation or sensory perception, a proper understanding of functionalities of saliva film is essential. By analyzing saliva functions using five-layered model and at molecular level, it is hoped that this review can help to stimulate very different thinking and very different approaches to eating and sensory perception research.