Physiological factors contributing to the variability of sensory assessments: Relationship between salivary flow rate and temporal perception of gustatory stimuli☆

Abstract Stimulation by oral manipulation or ingestion of stimuli causes the salivary flow rate to increase. Not only do gustatory stimuli affect salivary response, but saliva in turn can affect perception of taste by titration, dilution, or precipitation of stimuli. Average bitterness and astringency time-intensity (TI) curves and individual TI parameters generated in response to wines varying in ethanol, pH and phenolic composition revealed differences in temporal perception among the salivary flow groups. For both attributes, low-flow (LF) subjects took a longer time to reach maximum intensity and had a longer duration than high-flow (HF) subjects. For wines with tannic acid at pH 3·0 and pH 3·6, LF subjects recorded a higher intensity at maximum of bitterness and astringency than HF subjects. This perceptual difference was more pronounced at pH 3·6, where a greater difference in salivary flow rate was also elicited between flow groups. The log intensity decay curves for bitterness and astringency were linear, suggesting that a first-order decay process governed the perception function. Desorption is thus considered to be the primary phenomenon, rather than diffusion through a boundary layer. For all flow groups, the decay constants for bitterness were higher than those for astringency. However, the decay constants within one modality were similar for all flow groups, indicating similar desorption rates. Reciprocal plots of salivary flow rate were linear, suggesting that a second-order process governed salivary flow.