Saliva and sensory perception : interplay between the person and the food stimuli

The perception of food is influenced by various parameters, many of them being different from individual to individual. What we perceive is not the same because each individual is different. Saliva volume and composition vary widely among people and will influence the chemical and structural composition of the food. Thus, the dilution and mixing of the food with saliva determines the extent of food-saliva interactions and connected to that also how the food item is perceived. It is clear from literature that saliva affects our perception and it is also clear that the rate and composition of salivation is dependent on what we perceive. However, it has not been clear to what extent. Since saliva can be measured objectively for each individual and it can be manipulated in a controlled fashion, more can be learned from the relationship between oral processing and perception. And with that various questions can be addressed, such as: Can the individual differences in sensory assessment be accounted for by their individual salivary composition? Is it possible to affect the sensory perception of an individual by modifying their salivary flow and composition? Different tastes stimulate different amounts of saliva but do they also affect the saliva composition? Or are the differences in saliva composition caused by the differences in salivary flow rate? Can different amounts of saliva, and thus also different dilution factors, affect the taste perception? Furthermore, can taste-taste interactions be explained by an increase in salivary flow rate? Is it possible that the increased salivation, induced by the increased thickness, will dilute the tastant and hence decrease the perceived intensity? Or are taste-texture interactions caused by cross-modal interactions? Or is the increased viscosity of the texture decreasing the concentration of taste molecules? The aim of this thesis is to show how and to what extent saliva influences, and is influenced by, taste and texture. The addition of amylase inhibitor reduces saliva α-amylase activity and increases perceived thickness and creaminess. However, alpha-amylase activity varies widely among subjects and therefore a decreased oral α-amylase activity will not guarantee an increase in perceived thickness and creaminess of starch-based foods. Comparisons of the different tastants show that the pH of stimulated parotid saliva increases linearly, irrespective of the nature of the tastant. Protein concentration decrease and protein amount increase with increase in flow rate for all tastants. After correcting for the effect of flow rate, the protein amount is affected by the nature of the tastant with the greatest secretion after stimulation by citric acid. Flow rate is largely responsible for pH but tastant appears to play an additional role in affecting protein secretion. Significant decreases in perception with increasing salivary flow rates are observed for citric acid and sodium chloride. This can partially be explained by a dilution effect which is in line with previous studies on detectable concentration differences. However, since the bitterness and sweetness remain unaffected by the salivary flow conditions and the dilution effect is comparable to that of saltiness, further explanations are still needed. Suppression of taste intensity in binary mixtures is not affected by the rate of salivation. This is more likely explained by psychophysics. When the taste is separated from the texture, no texture-taste effects are observed. Dilution with saliva did occur and the tastant availability was unaffected in this set-up. The conclusion is therefore that texture-taste interactions are not caused by dilution effects or cross-modal interactions but can best be explained by the release of tastants. The work described in this thesis shows how the individual perception can be affected by the salivary flow and composition and how the individual salivary flow and composition can be affected by the sensory stimuli taste and texture.