Valid across-group comparisons with labeled scales: the gLMS versus magnitude matching.

Labeled scales are commonly used for across-group comparisons. The labels consist of adjective/adverb intensity descriptors (e.g., "very strong"). The relative distances among descriptors are essentially constant but the absolute perceived intensities they denote vary with the domain to which they are applied (e.g., a "very strong" rose odor is weaker than a "very strong" headache), as if descriptors were printed on an elastic ruler that compresses or expands to fit the domain of interest. Variation in individual experience also causes the elastic ruler to compress or expand. Taste varies genetically: supertasters perceive the most intense tastes; nontasters, the weakest; and medium tasters, intermediate tastes. Taste intensity descriptors on conventional-labeled scales denote different absolute perceived intensities to the three groups making comparisons across the groups invalid. Magnitude matching provides valid comparisons by asking subjects to express tastes relative to a standard not related to taste (e.g., supertasters match tastes to louder sounds than do nontasters). Borrowing the logic of magnitude matching, we constructed a labeled scale using descriptors unrelated to taste. We reasoned that expressing tastes on a scale labeled in terms of all sensory experience might work. We generalized an existing scale, the Labeled Magnitude Scale (LMS), by placing the label "strongest imaginable sensation of any kind" at the top. One hundred subjects rated tastes and tones using the generalized LMS (gLMS) and magnitude matching. The two methods produced similar results suggesting that the gLMS is valid for taste comparisons across nontasters, medium tasters, and supertasters.

Genetic variation and inferences about perceived taste intensity in mice and men.

The study of genetic variation in taste produces parallels between mice and men. In mice, genetic variation across strains has been documented with psychophysical and anatomical measures as well as with recordings from whole nerves. In humans, the variation has been documented with psychophysical and anatomical measures. Whole-nerve recordings from animals and psychophysical ratings of perceived intensities from human subjects have a similar logical limitation: absolute comparisons across individuals require a standard stimulus that can be assumed equally intense to all. Comparisons across whole-nerve recordings are aided by single-fiber recordings. Comparisons across psychophysical ratings of perceived intensity have been aided by recent advances in methodology; these advances now reveal that the magnitude of genetic variation in human subjects is larger than previously suspected. In females, hormones further contribute to variation in taste. There is evidence that the ability to taste (particularly bitter) cycles with hormones in women of child-bearing age, rises to a maximum early in pregnancy and declines after menopause. Taste affects food preferences, which in turn affect dietary behavior and thus disease risks. Valid assessment of taste variation now permits measurement of the impact of taste variation on health. Advances in psychophysical methodology were essential to understanding genetic variation in taste. In turn, the association of perceived taste intensities with tongue anatomy now provides a new tool for psychophysics. The ability of a psychophysical scale to provide across-subject comparisons can be assessed through its ability to show the fungiform papillae density-taste association.

PROP (6-n-propylthiouracil) supertasters and the saltiness of NaCl.

Taste blindness to phenylthiocarbamide (PTC) and its chemical relative 6-n-propylthiouracil (PROP) was discovered in the 1930s. Family studies showed that those who could not taste PTC/PROP (nontasters) carried two recessive alleles. In recent years, we have classified tasters into two groups: medium (PROP is moderately bitter) and supertasters (PROP is intensely bitter). With our classification, approximately 25% of Americans are nontasters, 50%, medium tasters, and 25%, supertasters. Studies showed that supertasters form a cohesive group. Anatomical studies showed that supertasters have the most fungiform papillae. Psychophysical studies showed that supertasters perceive the most intense bitterness and sweetness from a variety of compounds, the most intense burn from oral irritants, and the most intense tactile sensations from viscous solutions. Oral burn and touch are presumably perceived to be the most intense to supertasters because taste buds in fungiform papillae are innervated by the trigeminal nerve (pain, touch) as well as the chorda tympani nerve (taste). The psychophysical scaling method used was magnitude matching with NaCl as the control modality. With this method, subjects rated the intensities of a series of NaCl and PROP solutions. The assumption that the taste of NaCl did not vary with PROP status allowed comparisons of the bitterness of PROP across subjects. Early magnitude matching studies, using sound as the control, had suggested that this assumption was reasonable. However, recent studies challenged that conclusion. Larger samples with more diverse populations, using sound as the control, showed that the taste of NaCl varied with PROP bitterness; supertasters perceived the strongest taste and nontasters, the weakest. Thus our earlier conclusions were conservative because differences between nontasters, medium tasters, and supertasters were concealed by using NaCl as a standard. Using magnitude matching with sound as the standard, or using the Green scale, which employs intensity labels, we found that the differences between PROP groups are larger. Note that the association between PROP status and salt taste is interesting in itself, since variability in salt taste may have important nutritional consequences.

Comparison of the Green scale versus magnitude estimation for taste perception.

The Green scale is a new psychophysical method that is simple for subjects to use, but its relation with magnitude estimation has yet to be fully characterized. In comparing the consistency between the Green scale and magnitude estimation, we found that the former seems to provide a psychological oral sensation measurement that is different from the latter method. A simple correction formula can be derived.

Psychophysical measurement of 6-n-propylthiouracil (PROP) taste perception.

The ability to taste 6-n-propylthiouracil (PROP) is genetically determined. PROP tastes moderately bitter to 'medium tasters' (MT), intensely bitter to 'supertasters' (ST), and tasteless to 'nontasters' (NT). The psychophysical method used to characterize PROP status should capture the entire range of perception, while minimizing context, ceiling and other effects. Magnitude estimation successfully captures the variability in PROP perception, but requires normalization and may be difficult to conduct in industrial settings. Two labeled scales were tested as part of three separate studies (S1, S2 and S3) to measure perceived intensity of PROP and sweeteners. All studies included reportedly healthy volunteers aged 21-62 years recruited at Cultor Food Science in Groton, CT. In S1 [n = 163 (55 males, 108 females)], subjects rated perceived intensity of PROP-saturated paper and sucrose (1.0 M) on the Labeled Magnitude (Green) Scale (LMS) [labeled line with descriptors (no taste--strongest imaginable)]. In S2 [n = 152 (49 males, 103 females)], subjects rated perceived intensity of sucrose (1.0 M) and PROP solutions (0.001 M, 0.0032 M) on the LMS. In S3 [n = 136 (48 males, 88 females)], subjects rated perceived intensity of sucrose (1.0 M) and PROP solutions (0.001 M, 0.0032 M) on a 9-point category scale (1 = not at all; 9 = extremely). In all experiments, water rinses were included between each tastant and PROP was the final stimulus. Statistical analyses included descriptive statistics, regression analysis, and ANOVA. In S1 and S2, those with higher PROP perception perceived sucrose more intensely [(S1: r = 0.32; p < 0.001); (S2: r = 0.25; p < 0.01)]. A higher frequency of females were ST than males. Also, the PROP effect on sweet perception was most evident in female ST. This apparent sex difference may be the result of hormonal variation associated with menstruation. As well, in S1 and S2 subjects aged 20-40 years, females had significantly greater variance among sucrose intensity ratings than males (F = 3.66; p < 0.01), which may be due to hormonal changes with menses. The S3 results failed to show either the positive correlation between PROP and sucrose perception or the sex difference. Thus of the two labeled scales, the LMS appears to be better for assessing PROP perception, as it is continuous and also minimizes ceiling effects. Future research will extend these studies by including sucrose and high intensity sweetener concentration series.

Effects of Maillard browned egg albumin on drug-metabolizing enzyme systems in the rat.

Adult male Sprague-Dawley rats were fed a purified diet containing 5% Maillard browned egg albumin (EA-B) or browned hydrolysed egg albumin (HEA-B) for 10 wk. Control animals were pair-fed a corresponding isocaloric, isonitrogenous non-browned egg albumin (EA-C) or hydrolysed egg albumin (HEA-C) diet. At the end of 10 wk, the rats were killed and hepatic, small intestinal and colonic microsomes and cytosol fractions were prepared by ultracentrifugation. Animals fed EA-B exhibited significantly (P less than 0.05) increased hepatic benzo[alpha]pyrene hydroxylase activity and significantly (P less than 0.05) decreased colonic aminopyrine N-demethylase activity compared to control (EA-C) animals. HEA-B-fed animals also exhibited a significant (P less than 0.05) decrease in colonic aminopyrine N-demethylase activity compared with HEA-C controls, but no significant differences were detected in hepatic or small intestinal enzyme activities in this group. These data suggest that Maillard browned protein products may modify hepatic and/or colonic drug-metabolizing enzyme system activities, and may thus contribute to alterations in the metabolism of endogenous substrates and of exogenous drugs, precarcinogens and other xenobiotics.