Psychophysical, Physiological, and Semantic Characterization of Oral Astringents

Open Access
Fleming, Erin Elizabeth
Graduate Program:
Food Science
Master of Science
Document Type:
Master Thesis
Date of Defense:
March 25, 2015
Committee Members:
  • John E Hayes, Thesis Advisor
  • astringency
  • individual differences
  • sub-qualities
  • side tastes
  • organic acids
  • polyphenols
  • salivary proteins
  • Isobole approach
The American Society for Testing and Materials defines astringency as ‘the complex of sensations due to shrinking, drawing, or puckering of the epithelium as a result of exposure to substances such as alums or tannins.’ While a salient attribute in a wide range of food products, such as tea, coffee, red wine, and a variety of berries, nuts, and fruits, this percept remains poorly understood. The present studies aim to address and provide insight into the semantic, psychophysical, physiological issues related to oral astringency. Regarding physiological aspects of the percept, salivary precipitation index (SPI), an in vitro method for estimating individual differences oral astringency, generalized to both a polyphenol and multivalent salt. However, a non-significant relationship was observed for solid chocolate, indicating this measure may not generalize to complex food, especially those which are high in fat. In terms of psychophysical response, antagonism was observed for 1:1 mixtures of astringent compounds for the attribute ‘astringency,’ whereas varied interactions (synergy or antagonism) were observed for the sub-qualities ‘drying,’ ‘roughing,’ and ‘puckering,’ depending on the specific stimuli present in the mixture. These varied effects, as determined by the isobole method, may be due to chemical modifications affecting binding of astringents with oral proteins rather than to cognitive differences (e.g. mixture suppression). Finally, in order to address the semantic ambiguity of the percept, intensity ratings for astringent sub-qualities as well as side tastes across three classes of astringent compounds were analyzed via hierarchical clustering and multiple factor analysis. For sub-qualities, these analyses indicate the terms ‘drying’ and ‘roughing’ are somewhat redundant, while ‘puckering’ is related to, but not synonymous with ‘sourness.’ For side tastes, ‘sourness’ and ‘bitterness’ are salient attributes in organic acids and polyphenols, respectively, while mean ‘sweetness’ ratings are not. Taken together, these findings contribute to the psychophysical, physiological, and semantic understanding of astringency perception.