Comparison of chemically measured and sensorially perceived astringency in phytochemical phenolic compounds : A dissertation submitted in partial fulfilment of the requirements for the Degree of Master of Science in Food Innovation at Lincoln University

Abstract

Astringency had traditionally been considered to the interaction and precipitation between phenolic compounds and salivary proteins, leading to disruption of the oral lubricating film and increased friction. However, growing research indicated that protein precipitation mechanism alone is insufficient to fully explain the variations in human perception of astringency intensity. This study selected 6 phytochemical phenolic compounds as research subjects. The methylcellulose precipitation (MCP) method was employed to define “equivalent chemical astringency levels” by calibrating the phenolics’ precipitation capacity at 280 nm wavelength converting to total tannin (mg/L epicatechin equivalent). Equivalent concentrations for each phenolic compound were determined across high, medium, and low chemical astringency levels. A two-alternative forced choice (2-AFC) sensory test was conducted to compare the human sensory astringency of different phenolic compounds at the 3 equivalent chemical astringency levels. Despite exhibiting similar protein precipitation capabilities in the MCP assay, participants were able to distinguish differences in astringency intensity among various paired phenolic samples level during the 2-AFC test. 74% of participants perceived that EGCG was more astringent (p = 0.001) than ferulic acid at medium chemical astringency level. EC was perceived more astringent than EGCG (p=0.004) and caffeic acid (p<0.001) at low chemical astringency level. While the salivary protein precipitation–lubrication loss model cannot fully explain astringency perception, additional mechanisms are likely involved. A single chemical precipitation indicator is not enough to predict overall astringency, holding significance for predicting, regulating, and optimizing the mouthfeel characteristics of food products.