Measuring astringency with artificial saliva by quartz crystal microbalance with dissipation monitoring (QCM-D) : A dissertation submitted in partial fulfilment of the requirements for the Degree of Master of Science in Food Innovation at Lincoln University

Abstract

Astringency is a complex oral sensation characterized by dryness and friction, primarily caused by the interaction of phenolics with salivary proteins, which disrupts lubrication in the mouth. Traditional methods to assess astringency rely on subjective sensory panels and chemical assays, both of which face limitations in accuracy and correlation with sensory perception. Quartz Crystal Microbalance with Dissipation Monitoring (QCM-D) offers a novel, sensitive approach to objectively measure molecular interactions and viscoelastic changes in saliva-like matrices, potentially providing deeper insights into the mechanisms underlying astringency. This study investigates the use of QCM-D to detect changes in the viscoelastic and lubricating properties of artificial saliva with varying mucin and phenolic concentrations. The QCM-D technique measures frequency shifts and dissipation changes to assess molecular interactions, such as mucin and phenolic binding, by analyzing stable phases before and after sample additions. In trials with Epigallocatechin Gallate (EGCG), significant changes in dissipation indicated alterations in viscosity and film softness, but with minimal changes to frequency and film thickness. This reflects that EGCG’s interaction with mucin can increase film rigidity. Conversely, tannin trials provided results which showed statistically significant differences to both changes in frequency, film thickness, dissipation, and viscoelasticity. Although, these results possessed great variation across replicates, and generated limitations during analysis and interpretation.