Derek J. Snyder

Bitter receptor gene (TAS2R38), 6-n-propylthiouracil (PROP) bitterness and alcohol intake

BACKGROUND Phenylthiocarbamide (PTC) and 6-n-propylthiouracil (PROP), chemically related compounds, are probes for genetic variation in bitter taste, although PROP is safer with less sulfurous odor. Threshold for PROP distinguishes nontasters (increased threshold) from tasters (lower threshold); perceived intensity subdivides tasters into medium tasters (PROP is bitter) and supertasters (PROP is very bitter). Compared with supertasters, nontasters have fewer taste papillae on the anterior tongue (fungiform papillae) and experience less negative (e.g., bitterness) and more positive (eg, sweetness) sensations from alcohol. We determined whether the TAS2R38 gene at 7q36 predicted PROP bitterness, alcohol sensation and use. METHODS Healthy adults (53 women, 31 men; mean age 36 years)--primarily light and moderate drinkers--reported the bitterness of five PROP concentrations (0.032-3.2 mM) and intensity of 50% ethanol on the general Labeled Magnitude Scale. PROP threshold and density of fungiform papillae were also measured. Subjects had common TAS2R38 gene haplotypes [alanine-valine-isoleucine (AVI) and proline-alanine-valine (PAV)]. RESULTS PROP bitterness varied significantly across genotypes with repeated measures ANOVA: 26 AVI/AVI homozygotes tasted less bitterness than either 37 PAV/AVI heterozygotes or 21 PAV/PAV homozygotes. The PAV/PAV group exceeded the PAV/AVI group for bitterness only for the top PROP concentrations. The elevated bitterness was musch less than if we defined the groups using psychophysical criteria. With multiple regression analyses, greater bitterness from 3.2 mM PROP was a significant predictor of greater ethanol intensity and less alcohol intake--effects separate from age and sex. Genotype was a significant predictor of alcohol intake, but not ethanol intensity. With ANOVA, AVI/AVI homozygotes reported higher alcohol use than either PAV/AVI heterozygotes or PAV/PAV homozygotes. When age effects were minimized, PROP bitterness explained more variance in alcohol intake than did the TAS2R38 genotype. CONCLUSIONS These results support taste genetic effects on alcohol intake. PROP bitterness serves as a marker of these effects.

Psychophysics of sweet and fat perception in obesity: problems, solutions and new perspectives

Psychophysical comparisons seem to show that obese individuals experience normal sweet and fat sensations, they like sweetness the same or less, but like fat more than the non-obese do. These psychophysical comparisons have been made using scales (visual analogue or category) that assume intensity labels (e.g. extremely) which denote the same absolute perceived intensity to all. In reality, the perceived intensities denoted by labels vary because they depend on experiences with the substances to be judged. This variation makes comparisons invalid. Valid comparisons can be made by asking the subjects to rate their sensory/hedonic experiences in contexts that are not related to the specific experiences of interest. Using this methodology, we present the evidence that the sensory and hedonic properties of sweet and fat vary with body mass index. The obese live in different orosensory and orohedonic worlds than do the non-obese; the obese experience reduced sweetness, which probably intensifies fat sensations, and the obese like both sweet and fat more than the non-obese do. Genetic variation as well as taste pathology contribute to these results. These psychophysical advances will impact experimental as well as clinical studies of obesity and other eating disorders.

Labeled scales (e.g., category, Likert, VAS) and invalid across-group comparisons: what we have learned from genetic variation in taste

Direct comparisons of sensory or hedonic perceived intensities across individuals are impossible since we cannot share experiences. However, experiences can be compared indirectly if we can identify a standard assumed to be equal, on average, to groups compared. Sensory standards (i.e., magnitude matching) have proved very useful. Intensity adjectives/adverbs have also been used as standards (e.g., This tastes very strong to me; is it very strong to you?). We argue these labels often refer to experiences of different absolute intensity to the groups of interest making the comparisons invalid. An early solution rested on the assumption that the maximum intensity perceivable was equal for all sensory domains and individuals. Comparisons were then possible because all judgments could be made on a zero to maximum scale. We present data showing this assumption is not true.

The chemical interactions underlying tomato flavor preferences.

Although human perception of food flavors involves integration of multiple sensory inputs, the most salient sensations are taste and olfaction. Ortho- and retronasal olfaction are particularly crucial to flavor because they provide the qualitative diversity so important to identify safe versus dangerous foods. Historically, flavor research has prioritized aroma volatiles present at levels exceeding the orthonasally measured odor threshold, ignoring the variation in the rate at which odor intensities grow above threshold. Furthermore, the chemical composition of a food in itself tells us very little about whether or not that food will be liked. Clearly, alternative approaches are needed to elucidate flavor chemistry. Here we use targeted metabolomics and natural variation in flavor-associated sugars, acids, and aroma volatiles to evaluate the chemistry of tomato fruits, creating a predictive and testable model of liking. This nontraditional approach provides novel insights into flavor chemistry, the interactions between taste and retronasal olfaction, and a paradigm for enhancing liking of natural products. Some of the most abundant volatiles do not contribute to consumer liking, whereas other less abundant ones do. Aroma volatiles make contributions to perceived sweetness independent of sugar concentration, suggesting a novel way to increase perception of sweetness without adding sugar.

Differences in Our Sensory Worlds Invalid Comparisons With Labeled Scales

People use intensity descriptors to compare sensory differences: “This tastes strong to me; is it strong to you?” These comparisons are deceptive because they assume that intensity descriptors like strong denote the same absolute perceived intensities to everyone. This assumption is false. Visual-analogue and category scales are labeled with intensity descriptors, and whenever there are systematic differences across groups in the absolute perceived intensity denoted by these descriptors, across-group comparisons will be invalid. We have explored this problem using studies of taste perception. When intensity descriptors are falsely assumed to have universal meaning, real differences can be blunted, abolished, or reversed. One solution to this problem is to express sensations of interest relative to an unrelated standard; any variation in this standard will be equivalent across groups, allowing valid group comparisons. The importance of detecting and correcting these measurement errors is not limited to sensory comparisons, but applies to hedonic comparisons as well.

Modern Psychophysics and the Assessment of Human Oral Sensation

Psychophysical measures attempt to capture and compare subjective experiences objectively. In the chemical senses, these techniques have been instrumental in describing relationships between oral sensation and health risk, but they are often used incorrectly to make group comparisons. This chapter reviews contemporary methods of oral sensory assessment, with particular emphasis on suprathreshold scaling. We believe that these scales presently offer the most realistic picture of oral sensory function, but only when they are used correctly. Using converging methods from psychophysics, anatomy, and genetics, we demonstrate valid uses of modern chemosensory testing in clinical diagnosis and intervention.

Taste intensity in the Beaver Dam Offspring Study.

To determine the distribution of the perceived intensity of salt, sweet, sour, and bitter in a large population and to investigate factors associated with perceived taste intensity.

Measuring Taste Impairment in Epidemiologic Studies The Beaver Dam Offspring Study

Taste or gustatory function may play an important role in determining diet and nutritional status and therefore indirectly impact health. Yet there have been few attempts to study the spectrum of taste function and dysfunction in human populations. Epidemiologic studies are needed to understand the impact of taste function and dysfunction on public health, to identify modifiable risk factors, and to develop and test strategies to prevent clinically significant dysfunction. However, measuring taste function in epidemiologic studies is challenging and requires repeatable, efficient methods that can measure change over time. Insights gained from translating laboratory‐based methods to a population‐based study, the Beaver Dam Offspring Study (BOSS) will be shared. In this study, a generalized labeled magnitude scale (gLMS) method was used to measure taste intensity of filter paper disks saturated with salt, sucrose, citric acid, quinine, or 6‐n‐propylthiouracil, and a gLMS measure of taste preferences was administered. In addition, a portable, inexpensive camera system to capture digital images of fungiform papillae and a masked grading system to measure the density of fungiform papillae were developed. Adult children of participants in the population‐based Epidemiology of Hearing Loss Study in Beaver Dam, Wisconsin, are eligible for this ongoing study. The parents were residents of Beaver Dam and 43–84 years of age in 1987–1988; offspring ranged in age from 21–84 years in 2005–2008. Methods will be described in detail and preliminary results about the distributions of taste function in the BOSS cohort will be presented.

Epidemiological Studies of Taste Function: Discussion and Perspectives

Efforts to quantify the public health impact of chemosensation present significant challenges, including a strong need for testing methods suitable for field assessment. This discussion highlights several promising approaches to the population‐based study of taste function; it also identifies key principles that should be considered when adapting laboratory‐based taste tests for field use.

Taste: Vertebrate Psychophysics

Narrowly viewed, taste is limited to sweet, salt, sour, bitter, and umami (meaty, savory) sensations. Colloquially, taste refers to sensations from foods and beverages, where taste combines with other sensory inputs to produce complex sensations. Recent progress in psychophysics – the study of relationships between physical stimuli and the perceptions they induce – permits the characterization of normal variation and variation associated with aging or damage. Appropriate methods are needed to fully understand genetic, molecular, and neurochemical processes involved in taste sensation. Via psychophysics, we can measure how taste variation influences food preference and intake and ultimately our health and quality of life.