The role of congruency in taste–odor interactions

• The role that congruency plays in taste–odor interactions was investigated.
• Taste–odor congruency is a key requirement for retronasal odor referral to the mouth to occur.
• Congruency is a necessary but not sufficient condition for retronasal odor enhancement by taste.

The present study investigated the role that congruency between tastes and odors plays in two types of taste–odor interactions: retronasal odor enhancement by taste and retronasal odor referral to the mouth. In the first experiment, subjects rated (1) the intensities of sweetness, sourness, bitterness, and specific odor of aqueous samples of 3 tastants (sucrose, citric acid, caffeine) and 2 odorants (citral, coffee odor), both alone and in taste–odor mixtures, and (2) the degree of congruency of all possible taste–odor pairs. The results showed that only sucrose significantly enhanced the perceived intensities of citrus and coffee odors (Tukey’s test, p < 0.05), while citric acid and caffeine failed to enhance or even suppressed the odors. In the second experiment, the returning subjects were asked (1) to report the perceived locations of the odors after inhaling 3 odorants (citral, “sweet” and “bitter” coffee odors) through the mouth alone or in the presence of either water or various tastes in the mouth, and (2) to rate the degree of congruency between tastes and odors. The data showed that a highly congruent taste or taste mixture significantly increased localization of odors to the mouth (χ2, p < 0.05). These findings suggest that taste–odor congruency is a necessary but not sufficient condition for retronasal odor enhancement. In contrast, taste–odor congruency is a critical component for retronasal odor referral, and the degree of congruency modulates the degree of odor referral to the mouth. The results and implications of the study findings are discussed in terms of cognitive and perceptual factors of flavor perception.