Sensory Guided Investigation of Cocoa Polyphenol Induced Astringency

Open Access
- Author:
- Loi, Cynthia
- Graduate Program:
- Food Science
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- April 05, 2024
- Committee Members:
- Helene Hopfer, Thesis Advisor/Co-Advisor
Misha T Kwasniewski, Committee Member
Robert Roberts, Program Head/Chair
John Hayes, Thesis Advisor/Co-Advisor - Keywords:
- cocoa
chocolate
astringency
saliva
salivary proteins
polyphenols - Abstract:
- Cocoa products are rich sources of dietary polyphenols, which are compounds studied for their potential health benefits. Polyphenols elicit astringency, a mouthfeel sensation that is a salient attribute of foods such as tea, coffee, red wine, and various berries, yet unpleasant at high intensities. Despite extensive research investigating astringency, the mechanism behind the percept is still debated. Astringency is defined by the American Society for Testing and Materials 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”, and many researchers incorporate the distinct subqualities of drying, roughing, and puckering in the definition. It is widely accepted that the complexation of polyphenols and proteins initiates the astringency mechanism, however, more research is necessary to elucidate the downstream processes after complexation, namely, the interactions between specific polyphenols and certain salivary proteins, as well as how these interactions relate to sensory perception. Additionally, most research on astringency is studied through the context of wine, tea, or model solutions with tannic acid or epigallocatechin gallate, so this research aims to add to the limited body of work regarding astringency elicited by cocoa polyphenols. This thesis investigates how individual differences in astringency perception patterns may be explained through differences in salivary flow rate, total protein amount, protein composition, and protein-polyphenol interactions. The questions that this thesis aims to answer are as follows: (1) how do individuals that differ in their astringency perception of cocoa polyphenols differ in their salivary characteristics? (2) how does the polyphenol profile of a cocoa product differ after exposure to saliva of different segments of consumers varying in their astringency perception? A sensory test with 72 regular (1+/month) milk and dark chocolate consumers was conducted. Participants provided stimulated saliva, expectorated cocoa beverage, and rated the astringency, bitterness, sourness, sweetness, and chocolate flavor of a cocoa beverage at four discrete time points over 90 seconds. Upon analysis of the temporal sensory data as well as salivary flow rates, participants clustered into four segments in a PCA. Along PC 1, participants separated based on differences in maximal astringency (Imax). and area-under-the-curve (AUC); along PC 2, participants separated based on differences in decay to half-Imax and salivary flow. In the PCA, salivary flow rate is associated with the decay and onset of astringency, but not intensity maximum, suggesting two separate facets of astringency perception. Saliva from each participant within a cluster was pooled and the pooled saliva was then combined with cocoa polyphenols in a 1:1 ratio and analyzed alongside untreated pooled saliva for total protein content and protein composition. Total salivary protein content did not differ between clusters, but salivary composition differs between clusters in native saliva and saliva mixed with cocoa polyphenols. Greater loss of cystatins after exposure to polyphenols associated with greater Imax and AUC. Greater loss of acidic proline-rich proteins (aPRPs) was related to decreased rate of decay. Greater maximum astringency intensity associated with higher amount of polyphenols in supernatant and pellet and greater loss of proteins. This research adds to a growing body of evidence that specific types of salivary proteins, not merely the amount, is predictive of individuals’ differences in astringent sensations. Future work investigating how polyphenols of different sizes and structures react with specific types of salivary proteins is needed to further elucidate the connection between salivary protein profile and sensory perception of astringency in different products.