An overview of binary taste–taste interactions Russell S.J. Keast*, Paul A.S. Breslin Monell Chemical Senses Center, 3500 Market Street, Philadelphia, PA 19104, USA Accepted 21 July 2002 Abstract The human gustatory system is capable of identifying five major taste qualities: sweet, sour, bitter, salty and savory (umami), and perhaps several sub-qualities. This is a relatively small number of qualities given the vast number and structural diversity of che- mical compounds that elicit taste. When we consume a food, our taste receptor cells are activated by numerous stimuli via several transduction pathways. An important food-related taste question which remains largely unanswered is: How do taste perceptions change when multiple taste stimuli are presented together in a food or beverage rather than when presented alone? The interactions among taste compounds is a large research area that has interested electrophysiologists, psychophysicists, biochemists, and food scientists alike. On a practical level, taste interactions are important in the development and modification of foods, beverages or oral care products. Is there enhancement or suppression of intensity when adding stimuli of the same or different qualities together? Relevant psychophysical literature on taste–taste interactions along with selected psychophysical theory is reviewed. We suggest that the position of the individual taste stimuli on the concentration-intensity psychophysical curve (expansive, linear, or com- pressive phase of the curve) predicts important interactions when reporting enhancement or suppression of taste mixtures. # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Taste psychophysics; Food; Sweet; Sour; Salty; Umami; Savory; Bitter; Suppression; Enhancement; Taste mixtures 1. Introduction Phylogenetic arguments for taste suggest that it evolved to identify nutritive foods and potential toxins, thereby increasing the likelihood of survival and repro- duction of individuals who have these gustatory cap- abilities (Glendinning, 1994). Throughout the evolution of animals, potential toxins had to be identified from within a complex matrix. Perhaps this is why mixing a toxic, bitter stimulus with a sweet stimulus often results in a bitter-sweet tasting solution. Surely, the taste sys- tem evolved under circumstances in which it had to encode and identify complex mixtures of taste stimuli. Yet, non-interaction of taste mixture components is far from the rule. To the contrary, most taste compounds interact perceptually and in a manner that follows an apparently complex set of rules. Decisions based on taste–taste interactions are part of everyday life: Will a wedge of lemon improve the taste of my wheat beer? Is one teaspoon of sugar enough to sweeten my coffee, and if I add two teaspoons will it double the sweetness? When compounds eliciting tastes are mixed many outcomes are possible, including per- ceptual enhancement and suppression, unmasking of a taste not initially observed, or possibly chemical synth- esis of a new taste. These outcomes and their potential implications for taste transduction and food production have interested physiologists, psychophysicists, and food scientists. 1.1. Outline and objectives Taste–taste interactions are not well understood, partly because of contradictions in the literature. The aim of this paper is to review the taste–taste interaction literature taking into account factors that could lead to contradictions (Section 6), and to draw general conclu- sions about how tastes interact with each other. This paper includes sections on attributes of taste, analysis of psychophysical taste functions, and assessment of 0950-3293/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0950-3293(02)00110-6 Food Quality and Preference 14 (2002) 111–124 www.elsevier.com/locate/foodqual * Corresponding author. Tel.: +1-215-898-0858; fax: +1-215-898- 2084. E-mail address: keast@monell.org (R.S.J. Keast).