Paul A. S. Breslin

Phytochemistry: Ibuprofen-like activity in extra-virgin olive oil

Newly pressed extra-virgin olive oil contains oleocanthal — a compound whose pungency induces a strong stinging sensation in the throat, not unlike that caused by solutions of the non-steroidal anti-inflammatory drug ibuprofen. We show here that this similar perception seems to be an indicator of a shared pharmacological activity, with oleocanthal acting as a natural anti-inflammatory compound that has a potency and profile strikingly similar to that of ibuprofen. Although structurally dissimilar, both these molecules inhibit the same cyclooxygenase enzymes in the prostaglandin-biosynthesis pathway.

An overview of binary taste-taste interactions

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 chemical 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 compressive phase of the curve) predicts important interactions when reporting enhancement or suppression of taste mixtures.

The merging of the senses: integration of subthreshold taste and smell

Central neural integration of sensory input from different modalities is a prerequisite for many types of perception and behavior. One of the best examples of such an integrative process may be flavor perception, whereby activation in two peripherally distinct neural systems, olfaction and gustation, combines to give rise to a unified oral sensation. Here we used a psychophysical method to show cross-modal summation of subthreshold concentrations of selected gustatory and olfactory stimuli, thus demonstrating that central neural integration of taste and smell inputs generates a representation of flavor perception.

Salt enhances flavour by suppressing bitterness

Salts are used as flavouring agents in the cuisines of many cultures, the most commonly used being NaCl. They impart their own salty taste and enhance other flavours. The apparent ability to increase the intensity of other desirable flavours is puzzling as virtually all published psychophysical studies show that NaCl either suppresses or has no effect on other flavours. To reconcile this contradiction we have proposed that salts selectively filter flavours, such that unpleasant tastes (such as bitterness) are more suppressed than palatable ones (such as sweetness) thereby increasing the salience and/or intensity of the latter. We now present evidence to support this idea.

Gender-specific induction of enhanced sensitivity to odors.

Induction of olfactory sensitivity in humans was first illustrated when men and women who were initially unable to smell the volatile steroid androstenone (5α-androst-16-en-3-one) developed that ability after repeated, brief exposures. Because this finding has not been replicated with other compounds in humans, it has been assumed that olfactory induction is a narrowly constrained phenomenon, occurring only in individuals with specific anosmias, perhaps only to androstenone (compare ref. 2). Here we show that induction of enhanced olfactory sensitivity seems to be a more general phenomenon, with marked changes in olfactory acuity occurring during repeated test exposures to several odorants among people with average baseline sensitivity to these compounds. This increased sensitivity (averaging five orders of magnitude) was observed only among females of reproductive age. These observations provide convincing evidence that female olfactory acuity to a variety of odorants can vastly improve with repeated test exposures. They also suggest a sensory basis for the anecdotal observation of greater olfactory sensitivities among females and raise the possibility that the olfactory-induction process may be associated with female reproductive behaviors such as pair bonding and kin recognition.

Variability in a taste-receptor gene determines whether we taste toxins in food

Document S1. Supplemental Experimental ProceduresxDownload (.49 MB ) Document S1. Supplemental Experimental Procedures

Covariation in individuals' sensitivities to bitter compounds: evidence supporting multiple receptor/transduction mechanisms.

People vary widely in their sensitivities to bitter compounds, but the intercorrelation of these sensitivities is unknown. Our goal was to investigate correlations as a function of individual sensitivities to several bitter compounds representative of different chemical classes and, from these correlations, infer the number and variety of potential bitterness transduction systems for these compounds. Twenty-six subjects rated and ranked quinine HCl, caffeine, (−)-epicatechin, tetralone, L-phenylalanine, L-tryptophan, magnesium sulfate, urea, sucrose octaacetate (SOA), denatonium benzoate, andn-propylthiouracil (PROP) for bitterness. By examining individual differences, ratings and rankings could be grouped into two general clusters—urea/phenylalanine/tryptophan/epicatechin, and quinine/caffeine/SOA/denatonium benzoate/tetralone/magnesium sulfate—none of which contained PROP. When subjects were grouped into the extremes of sensitivity to PROP, a significant difference was found in the bitterness ratings, but not in the rankings. Therefore, there are also subjects who possess diminished absolute sensitivity to bitter stimuli but do not differ from other subjects in their relative sensitivities to these compounds.

Genetics of Human Taste Perception

Genetic approaches are rapidly yielding new information about our sense of taste. This information comes from both molecular studies of genes encoding taste receptors and other taste-signaling components, and from studies of inherited variation in taste abilities. Our understanding of bitter taste has advanced by combined information from discovery and study of the TAS2R family of taste receptor genes, hand in hand with genetic linkage and positional cloning studies, notably on the ability to taste phenylthiocarbamide (PTC). Sweet and umami tastes, mediated by TAS1R receptors, are becoming well-characterized at the molecular genetic level, and these taste classes are now targets for linkage, positional cloning, and genetic association strategies. Salty and sour tastes are still poorly characterized in genetic terms, and represent opportunities for the future.

Taste reactivity as a dependent measure of the rapid formation of conditioned taste aversion: a tool for the neural analysis of taste-visceral associations.

Several explanations may account for deficits in the ability of animals to form taste aversions following neural manipulations. These encompass impairments in conditioned stimulus (CS) and unconditioned stimulus (US) processing, conditioned response (CR) measurement, and expression, memory, and taste-visceral integration. A behavioral procedure that aids in the distinction between some of these possibilities is presented. In Experiment 1, 10 rats received seven intraoral (IO) infusions of sucrose (30 s, 0.55 ml) spaced every 5 min starting immediately after the injection of 3.0 mEq/kg of lithium chloride (LiCl). Control rats (n = 12) were treated identically except that they were injected with sodium chloride (NaCl). Oromotor and somatic taste reactivity behaviors were videotaped and analyzed. Lithium-injected rats systematically decreased their ingestive taste reactivity behavior over time, whereas aversive behavior increased. Control rats maintained high and stable levels of ingestive responding and demonstrated virtually no aversive behavior over the 30-min period following sodium injection. Rats were tested several days later for the presence of a conditioned taste aversion (CTA). Rats previously injected with lithium during sucrose infusions demonstrated significantly more aversive behavior than the control group, which demonstrated none. There were no differences in the level of ingestive behavior displayed by the two groups on the CTA test. Experiment 3 revealed that when similarly treated rats were tested for a CTA while in a lithium-induced state, a difference in the ingestive behavior between the two groups was observed. In Experiment 2, naive rats were injected with either NaCl or LiCl but did not receive their first sucrose infusion until 20 min later. These rats also received sucrose infusions at 25 and 30 min postinjection. There were no differences in the taste reactivity behavior displayed by lithium- or sodium-injected rats during any of the sucrose infusions. Collectively, these findings indicate that rats dramatically change their oromotor responses to sucrose during the period following LiCl administration, provided that the infusions start immediately after injection. Furthermore, this time-related behavioral change is predominantly attributable to associative processes. This paradigm can be useful in distinguishing between neural manipulations that affect the establishment of taste-visceral associations from others that affect the animals ability to retain such associations over the commonly employed 24-hr conditioning-test interval.

Interactions among salty, sour and bitter compounds

Abstract The human gustatory system is capable of responding to and processing the taste of solitary compounds in water. However, the taste system rarely contacts solitary compounds outside the laboratory and has surely evolved to process complex mixtures of sapid chemicals, such as occur in virtually all foods. This review will focus primarily on the lesser-studied interactions between pairs of salty, sour and bitter compounds. Pair-wise interactions among these three taste qualities should be of interest because they constitute a significant proportion (∼30–50%) of possible binary taste interactions. In general, salts and acids enhance each other at moderate concentrations but suppress each other at higher concentrations. Bitter compounds and acids can either enhance or suppress each other depending on the concentrations, the food stimuli and the experimental methods involved. Sodium salts and bitter compounds generally interact so that bitterness is suppressed to some variable degree and the saltiness is unaffected. As will be described below, there are exceptions to all of these generalities.