Effects of Sub-Threshold Levels of Tastants and Flavours on Perception

Effects of Sub-Threshold Levels of Tastants and Flavours on Perception

Effects of Sub-Threshold Levels of Tastants and Flavors on Perception

Introduction

Our chemical senses (taste and smell) work together and influence each other in very specific ways. Murphy et al. (1977) reported that fruity smelling ethyl butyrate and a sweet tastant sodium saccharin show almost perfect additivity when presented in mixtures. In a subsequent study, Murphy and Cain (1980) showed that congruency or 'harmony' of taste-smell mixtures does not determine the degree of additivity: both the congruent or harmonious mixtures (lemon-smelling citral and sucrose) and the incongruent or dissonant mixtures (citral and sodium chloride) showed the same pattern of results. However, a series of studies that followed demonstrated that certain odors enhance the intensity of particular tastes, and that these changes in taste perception are both odorant- and tastantspecific. Odors such as strawberry (Frank and Byram, 1988; Frank et al., 1989, 1993; Lawless and Clark, 1992; Clark and Lawless, 1994; Schifferstein and Verglegh, 1996; Stevenson et al., 1999; Frank, 2002), vanilla (Sakai et al., 2001), lemon (Schifferstein and Verglegh, 1996; Frank, 2002), almond (Frank et al., 1993), caramel, maracuja and lychee (Stevenson et al., 1999) enhanced the sweetness of sucrose (most quoted studies) or aspartame (Lawless and Clark, 1992; Clark and Lawless, 1994; Sakai et al., 2001; Frank, 2002), whereas other odors—such as peanut butter (Frank and Byram, 1988; Frank, 2002), ham (Schifferstein and Verglegh, 1996), chocolate, and wintergreen (Frank et al., 1993; Frank, 2002)—did not change perceived sweetness.

Odor-induced changes in taste perception (OICTP) are not limited to sweetness enhancement. For example, maltol, angelica oil, and damascone odors can suppress perceived sweetness of sucrose (Stevenson et al., 1999). Furthermore, the effects of odors on taste perception are not limited to sweetness, but have been shown with sourness as well: chocolate (Frank et al., 1993) and caramel (Stevenson et al., 1999) odors were shown to suppress sourness, whereas lemon and strawberry odor enhanced sourness of citric acid (Frank, 2002). Finally, almond, chocolate, lemon, peanut, strawberry and wintergreen were shown to suppress perceived saltiness (Shaffer and Frank, 1990), although the odor-induced effects on saltiness have not been replicated (Frank, 2002).

Besides the group of studies demonstrating OICTP, Dalton et al. (2000) showed that particular tastants can alter odor perception. Olfactory sensitivity to benzaldehyde (a cherry-almond odor) was increased by the presence of a sub-threshold concentration of saccharin in the mouth, whereas having water or another tastant in the mouth did not make any difference; simply repeating the benzaldehyde threshold test for a second time did not result in a change of sensitivity either. Algom et al. (1993) used taste-smell interactions to study odor imagery. Participants in their study were either presented tastant-odorant mixtures (sucrose and orange), or asked to construct these mixtures mentally (both groups were previously familiarized with mixture constituents). The task was to rate the intensity of presented or imagined mixtures. The striking finding was that both perceived and mentally constructed mixtures (of different concentrations of ...