The Role of Salivary Proteins in the Mechanism of Astringency

Understanding astringency has focused on the interaction of tannins with the salivary proline-rich proteins (PRPs), although it remains unclear if other astringents precipitate the PRPs or how this interaction relates to sensory perceptions of astringency. We used 2 approaches to compare how distinct classes of astringent compounds interacted with the salivary PRPs and mucins. Using sodium dodecyl sulfate polyacrylamide gel electrophoresis, we evaluated protein patterns and characterized the salivary proteins present in the supernatants and pellets of pooled saliva assayed with tannin, alum, and hydrochloric acid solutions. Tannins and alum precipitated many of the PRPs, but acid did not. Mucins were precipitated by both the acid and alum, but not by the tannins. From our research, it appears that the precipitation of salivary proteins may be involved in the mechanism of astringency, but the precipitation of PRPs is not requisite for the development of astringency. We also measured mucin and deoxyribonucleic acid content of expectorated solutions of astringents that panelists swished in their mouths to determine if astringency was associated with a loss of oral lubricating films.