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Intensity of taste and astringency sensations elicited by red wines is associated with sensitivity to PROP (6-n-propylthiouracil)
Food Quality and Preference 15 (2004) 147–154 www.elsevier.com/locate/foodqual
Intensity of taste and astringency sensations elicited by red wines is associated with sensitivity to PROP (6-n-propylthiouracil) Gary J. Pickeringa,b,c,*, Katerina Simunkovaa, David DiBattistac a Department of Biological Sciences, Brock University, St. Catharines, Canada L2S 3A1 Cool Climate Oenology and Viticulture Institute, Brock University, St. Catharines, Canada L2S 3A1 c Department of Psychology; Brock University, St. Catharines, Canada L2S 3A1
b
Received 10 January 2003; received in revised form 10 March 2003; accepted 28 March 2003
Abstract The relationship between sensitivity to 6-n-propylthiouracil (PROP) and taste and astringency perception elicited by red wines was examined. Twenty-five subjects were classified into three PROP sensitivity groups (non-tasters, tasters and super-tasters) based on their bitterness ratings of a 0.32 mM PROP solution as measured on a Labeled Magnitude Scale (LMS). In a completely randomized block design, subjects used the LMS to rate the bitterness, astringency and acidity intensities of three commercial red wines. Contrary to the findings of previous studies with wine, bitterness, astringency and acidity intensities were all correlated with individual PROP taster status. PROP non-tasters gave significantly lower intensity ratings for the bitterness, astringency and acidity of the red wines than did PROP tasters and super-tasters. Individual differences among taster groups may be related to preference and consumption behavior of consumers of wine and other alcoholic beverages. # 2003 Elsevier Ltd. All rights reserved. Keywords: PROP; 6-n-Propylthiouracil; Wine; Astringency; Taste; Bitterness; Acidity
1. Introduction 1.1. Genetic variation in taste and its measurement The variation in the sensitivity of individuals to bitter compounds has been shown in numerous studies since the accidental discovery by Fox in the early 1930s that only some people can taste the bitter compound phenylthiocarbamide (PTC; Fox, 1931). 6-n-propylthiouracil (PROP) is now widely used for bitterness sensitivity tests as it lacks the sulfurous odor of PTC, and is generally regarded as a safer compound. The perceptual differences between people that can taste PTC/PROP (‘tasters’) and those that cannot (‘non-tasters’) extends to other compounds, including caffeine, saccharin, KCl, sodium and potassium benzoate, sucrose and neohesperidin dihydrochalcone (Bartoshuk, Duffy, Reed, & Williams, 1996). PROP tasters are also more sensitive than non-tasters to other tastes and oral sensations, including sweetness (Gent & Bartoshuk, 1983), saltiness * Corresponding author. Tel.: +1-905-688-5550; fax: +1-905-6883104. E-mail address: [email protected] (G.J. Pickering). 0950-3293/03/$ - see front matter # 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0950-3293(03)00053-3
(Bartoshuk, Duffy, Lucchina, Prutkin, & Fast, 1998), irritation (Karrer & Bartoshuk, 1991) and perception of the tactile properties of fats, such as creaminess, oiliness and smoothness (Tepper & Nurse, 1997). Early research used sensation threshold procedures to categorize individuals with respect to their ability to taste bitter substances. For example, Harris and Kalmus (1949) classified subjects as having either low, intermediate or high thresholds for the detection of PTC. However, more recent research has made it clear that thresholds do not reliably predict suprathreshold taste perception. Thus, individuals who are classified as tasters based on their PROP detection threshold may differ widely in their ratings of the bitterness of suprathreshold PROP solutions. For example, some tasters will rate the bitterness of a PROP solution as a medium taste sensation while others will give the same stimulus the highest bitterness rating (Bartoshuk, 1993). Recent studies suggest that the ability to taste bitter compounds such as PTC and PROP represents a trait with incomplete dominance (Guo & Reed, 2001). In addition, gender (Bartoshuk, Duffy, & Miller, 1994) and race (Guo, Shen, Zheng, & Wang, 1998; Parr, 1934) effects have been reported for PROP/PTC sensitivity,
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and sensitivity to PROP has been correlated with number of fungiform papillae and taste pores (Miller & Reedy, 1990; Reedy, Bartoshuk, Miller, Duffy, Lucchina, & Yanagisawa, 1993; Bartoshuk et al., 1994). A number of suprathreshold methods have been used to classify individuals into PROP taster groups (Bartoshuk et al., 1994; Bartoshuk, 2000; Drewnowski, Henderson, Shore, & Barratt-Fornell, 1997). There is now consensus that the Labeled Magnitude Scale (LMS; Green, Dalton, Cowart, Shaffer, Rankin, & Higgins, 1996; Green, Shaffer, & Gilmore, 1993) allows for superior separation of PROP taster groups. The LMS is a quasilogarithmic scale with verbal label descriptors that is anchored at the lower end with the phrase ‘barely detectable’ and at the upper end with ‘strongest imaginable.’ The LMS provides ratio-level data that are comparable to data yielded by the magnitude estimation procedure, and it is not affected by the ceiling effects that may reduce the usefulness of other scales, such as the Natick nine-point scale (Drewnowski et al., 1997; Prutkin et al., 2000; Tepper & Nurse, 1997). A trimodal distribution for PROP sensitivity has now been demonstrated (Bartoshuk et al., 1993, 1994). Based on their ratings of the bitter taste of PROP, individuals can be classified as being either non-tasters, tasters or supertasters, with the last group giving the highest ratings. This individual variability in the perception of intensity of a range of taste and oral sensations extends to food (Kaminski, Henderson, & Drewnowski, 2000) and beverages (Intranuovo & Powers, 1998), and has implications for food-related behaviors. For instance, PROP tasters tend to give lower acceptance ratings to foods high in fat content, such as cheese and whole milk (Tepper, Christensen, & Cao, 2001) and bitter foods, such as brussel sprouts, broccoli, and spinach (Kaminski et al., 2000). 1.2. Sensory properties of wine and relationship to PROP taster status Wine is a complex beverage containing numerous organic and inorganic constituents that contribute to its aroma and flavor. It can elicit sweet, sour, bitter and salt taste responses as well as numerous tactile sensations (Thorngate, 1997). Indeed, this complexity of sensation is part of the overall consumer appeal of the product. In red wine, the presence of relatively high concentrations of phenolic compounds results in the emergence of astringency and, to a lesser extent bitterness, as particularly important components of the flavor matrix. Both bitterness and astringency are primarily elicited by the flavan-3-ols (+)-catechin and ( )-epicatechin and their polymers, which are derived from seeds and skins of grapes and extracted into red wine during fermentation (Gawel, Iland, & Francis, 2001). The perception of astringency results from cross-linking and subsequent precipitation of these polyphenols with salivary proteins
and glycoproteins (Kielhorn & Thorngate, 1999). Following polyphenol–salivary protein interaction, the lubricating quality of saliva decreases, and the increased friction between the oral surfaces activates mechanoreceptors and leads to the sensation of astringency (Gawel et al., 2001). Ethanol has also been shown to contribute to bitterness perception in wine (Fischer, 1990). No relationship has yet been detected between PROP taster status and the sensations elicited either by red wine or its components. Ishikawa and Noble (1995) found no relationship between PROP taster status and the perception of astringency in Carnelian red wine, and Smith, June, and Noble (1996) found no relationship between PROP taster status and the perception of bitterness and astringency of grape seed tannin. However, in both of these studies, PROP taster status was based on subjects’ threshold sensitivity to PROP, and we speculate that the use of this technique may have contributed to the null results. Indeed, when the LMS was employed by Delwiche, Buletic and Breslin (2001), the data suggested differences between PROP taster status groups with respect to bitterness intensity ratings for a number of bitter compounds, including the important red wine phenolic ( )epicatechin (Figure 7, p 772). However, perhaps because of the low statistical power associated with having only four subjects in two of the PROP groups, the analysis failed to reveal significant differences between the groups for these bitter compounds (Delwiche et al., 2001). Accordingly, we investigated the relationship between PROP taster status and the perception of bitterness and astringency in red wine using the LMS both to classify subjects into PROP taster status categories and to rate the sensations elicited by red wines. The use of this more sensitive suprathreshold measurement scale may increase the likelihood of detecting differences in the sensations elicited by red wines in individuals differing in PROP taster status.
2. Materials and methods 2.1. Participants To ensure adequate representation of each of the three PROP taster status groups, 200 students and staff of Brock University, Ontario, Canada underwent an initial screening. Following the procedure of Tepper et al. (2001), these individuals used the LMS to rate the bitterness of a paper filter strip that had been impregnated with a 3.2 mM solution of PROP solution (ICN Biochemicals Inc., Aurora, Ohio). The only significant deviance from the screening procedure used by Tepper et al. (2001) was that NaCl standards were not employed here. The LMS used for screening, training and data collection was 102 mm long, and the top anchor term ‘strongest imaginable’ referred to all sensations.
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Based on the results from the paper filter strips, 30 people were invited to participate in the experiment. Twenty-five people (7 men, 18 women), ranging in age from 19 to 46 years, completed all training and data collection sessions, and their data are included in the analyses reported later. All were in good health, and were allergy and medication free, as determined by a questionnaire. Five had significant prior experience with wine tasting. 2.2. Stimuli The training stimuli consisted of aqueous solutions of quinine sulfate, alum sulfate, tartaric acid (all Fischer Chemicals Scientific, New Jersey, USA) and PROP, all prepared using distilled water. Solutions of quinine sulfate (0.1 g/l), alum sulfate (1 g/l), and tartaric acid (2 g/l) were used to train participants to recognize bitterness, astringency, and acidity, respectively. A 3.2 mM PROP solution was prepared by dissolving PROP in distilled water on a medium heat stirring plate. Less concentrated PROP solutions (0.32 and 0.032 mM) were prepared by dilution. Solutions were prepared one day before training and data collection sessions and stored at room temperature (23 C 2 C). Three commercial dry red table wines, believed likely to vary in bitterness and astringency characteristics, were selected for testing: 2000 Folonari Valpolicella Classico (Corby Distilleries Ltd., Italy, 12% alcohol v/v); 2000 Pinot Noir (Inniskillin Wines, Canada, 12.5% alcohol v/v); and non-vintage L’Epayrie (Armand Roux, France, 11.5% alcohol v/v). These wines were introduced during training sessions and were later used for all data collection sessions. 2.3. Classification and training of participants Four 45-min sessions were held over 2 weeks. During the first session, PROP status was reassessed by having participants rate the bitterness of three PROP solutions (0.032, 0.32, and 3.2 mM) that were presented in increasing order of concentration. Participants were given 20 ml of solution and instructed to move the sample from side to side in the mouth for 5–10 s and then to expectorate. After waiting for 10–15 s, they used the LMS to rate the bitterness of the sample. Participants rinsed thoroughly with water prior to each sample. This tasting procedure was used throughout the study. During the next three sessions, participants were trained to distinguish between bitter, astringent and acidic sensations. A simple written description of each sensation quality was provided in order to assist with identification and differentiation. Acidic was defined as sour, tart; bitter as caffeine (strong coffee); and astringent as dryness, cheek puckering. In each session, parti-
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cipants were given 20 ml of the bitter, astringent and acidic training solutions, and they tasted and rated the principal sensation for each solution. During the last session, discriminative ability was assessed using these three aqueous solutions. Twenty milliliters samples (labeled A, B or C) were presented in random order, and participants were instructed to identify the solutions as bitter, astringent or acidic. All participants correctly identified all solutions (data not shown). The final training session also served as a dry-run for the data collection procedure, with participants rating the bitterness, astringency and acidity of 20 ml samples of the three commercial wines. Discussion among participants was encouraged to identify and address any potential concerns. Participants confirmed that bitterness, astringency and acidity were the dominant oral sensations elicited by these wine samples. 2.4. Data collection and analysis Data collection took place during three 45-min sessions over a 2-week period. Nose clips were worn to avoid any olfactory biases. At the start of each session, participants were refamiliarized with the taste qualities to be evaluated. The written descriptions of bitterness, astringency and acidity were reviewed, and the first flight of samples consisted of the three training solutions of quinine sulfate, alum sulfate and tartaric acid, which were presented in plastic cups with identifying labels. The second flight consisted of the three wine samples, which were presented in 250-ml opaque plastic cups coded with three-digit random numbers. The order of presentation was randomized, and a 2–4 min break between samples was enforced to minimize palate fatigue and carry-over effects. Participants used the LMS to rate the intensity of bitterness, astringency and acidity of each wine. Acidity was rated first, followed by astringency and then bitterness, reflecting the typical time-course of these sensations. Acidity was included in this design to avoid potential dumping effects on the other attributes being rated (Clark & Lawless, 1994). After all three wines had been presented, an aqueous solution of 1 g/l alum sulfate was presented in a cup labeled astringency. Participants used the LMS to rate the astringency of this solution. Statistical analyses were conducted using SPSS 11.0 software for Windows (SPSS Inc., Chicago, IL). Mixeddesign analyses of variance (ANOVA) were used to analyze data. If Mauchly’s test of sphericity led to rejection of the null hypothesis, the Huynh–Feldt correction factor was used to adjust the degrees of freedom (Keppel, 1991). Fisher’s LSD procedure was used for post hoc comparisons. Only differences corresponding to P < 0.05 are reported as statistically significant.
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3. Results 3.1. PROP taster status response to PROP stimuli Participants were classified as non-tasters, tasters or super-tasters based on the bitterness rating they assigned to the 0.32 mM PROP solution using the LMS (nontaster: 415.5; taster: > 15.5 and < 51; super-taster: 551; Tepper et al., 2001). Ratings for PROP solutions were then analyzed using a 33 mixed-design ANOVA (between-subjects variable: taster status; within-subjects variable: PROP concentration). There were significant main effects of taster status, F(2, 22)=58.45, P=0.000, and PROP concentration, F(2, 44)=127.15, P=0.000. As expected, perceived bitterness intensities varied as a function of both taster status and PROP concentration. The Taster status PROP concentration interaction was also significant, F(4, 44)=21.87, P=0.000. These data are summarized in Table 1. Non-tasters gave low ratings to all three PROP solutions, although they gave a significantly higher rating to the 3.2 mM solution. In contrast, for both tasters and super-tasters, there were significant differences in perceived intensity across all three solutions, with super-tasters giving extremely high ratings to the 3.2 mM solution. Also, for the 0.032 mM PROP solution, there were no perceived differences in bitterness intensity as a function of taster status. However, for the two higher concentration solutions, tasters gave ratings that were significantly higher than those of non-tasters, but lower than those of super-tasters. 3.1.1. Bitterness intensity ratings of red wines A 333 mixed-design ANOVA was carried out on the bitterness ratings (between-subjects variable: taster status; within-subjects variables: wine type and session). There were significant main effects of taster status, F(2, 22)=11.73, P=0.000, and wine type, F(2, 44)=8.486, P=0.001. As Fig. 1 indicates, the overall bitterness ratings of non-tasters were low in absolute terms, and they were significantly lower than those of both tasters and Table 1 Bitterness ratings of PROP solutions using the Labeled Magnitude Scale PROP Solution (mM)
Non-tasters (n=10)
Tasters (n=7)
Super-tasters (n=8)
0.032 0.32 3.2
1.73 1.25a,x 2.50 0.56a,x 17.295.52a,y
6.87 4.02a,x 34.096.46b,y 67.768.91b,z
10.724.06a,x 64.806.38c,y 93.152.08c,z
Values shown are MeanSEM. Participants were classified as being either non-tasters, tasters or super-tasters based on the bitterness rating assigned to the 0.32 mM PROP solution (Tepper et al., 2001). For each concentration, means sharing the same indicator (a, b, c) do not differ significantly, and for each taster status group, means sharing the same indicator (x, y, z) do not differ significantly (P> 0.05, Fisher’s LSD procedure).
super-tasters. Furthermore, the mean bitterness rating of the Pinot Noir (mean SEM=18.06 2.04) was significantly lower than that of both the L’Epayrie (26.26 1.90) and the Valpolicella (23.44 2.75). Fig. 2 illustrates the only significant interaction effect, which was the Wine type Taster status interaction, F(4, 44)=3.38, P=0.017. Non-tasters did not report different levels of bitterness in the three wines. However, tasters gave significantly higher bitterness ratings to the L’Epayrie than to the other wines, and super-tasters gave significantly lower bitterness rating to the Pinot Noir than to the other wines. 3.1.2. Astringency intensity ratings of red wines A 33 mixed-design ANOVA of the astringency ratings revealed significant main effects of taster status, F(2, 22)=8.43, P=0.000, wine type F(2, 44)=3.60, P=0.035, and session, F(2, 44)=4.55, P=0.016. As Fig. 1 shows, tasters and super-tasters gave significantly higher astringency ratings than did non-tasters. Moreover, the astringency ratings for the Valpolicella (31.45 2.13) were significantly higher than those for the Pinot Noir (25.99 2.07), but they did not differ from the ratings for the L’Epayrie (29.01 2.69). Finally, ratings were significantly higher for tasting session 2 (32.56 2.82) than for session 3 (24.71 1.80), but they did not differ from the ratings for session 1 (29.19 2.75). The origins of the differences across sessions are not clear. 3.1.3. Acidity intensity ratings of red wines A 33 mixed-design ANOVA of the acidity ratings revealed only a significant main effects of taster status, F(2, 22)=11.23, P=0.000. As Fig. 1 indicates, the ratings of tasters and super-tasters did not differ from each other, but both were significantly higher than those of non-tasters. 3.2. Alum sulfate ratings The alum sulfate solution provided another measure of whether participants perceived a difference in astringency as a function of PROP taster status. A 33 mixed-design ANOVA (between-subjects variable: taster status; within-subjects variable: session) revealed no significant effects (Fig. 3). In particular, there was not a significant effect of taster status, F(2, 22)=2.003, P=0.159, with the overall mean rating of the alum sulfate solution being 47.46 4.28. Thus, the alum sulfate solution was given substantially higher astringency ratings than were any of the three wines that were used.
4. Discussion In contrast to previous studies (Ishikawa & Noble, 1995; Smith et al., 1996), significant differences in the bitterness, astringency and acidity elicited by red wine
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Fig. 1. Mean intensity ratings for bitterness, astringency and acidity elicited by red wines across the three taster groups; PROP non-tasters NT (n=10), tasters T (n=7) and super-tasters ST (n=8). Values shown are meansSE averaged across sessions (3), and wine types (3). For each attribute, means sharing the same letter do not differ significantly (LSD0.05).
Fig. 2. Mean bitterness intensity ratings for three wine types among PROP non-tasters NT (n=10), tasters T (n=7) and super-tasters ST (n=8). Values shown are meansSE . Wine 1 is 2000 Folonari, Valpolicella Classico, Italy; Wine 2 is 2000 Inniskillin Wines, Pinot Noir, Canada; and Wine 3 is (non-vintage) Armand Roux, L’Epayrie, France. For each wine type, means sharing the same letter do not differ significantly (LSD0.05).
were observed as a function of PROP taster status (Fig. 1). This effect was observed for all three red wines examined, with tasters and super-tasters perceiving higher bitterness, astringency and acidity intensities when compared to non-tasters. No difference was found between the PROP taster and super-taster groups. We speculate that we were able to show significant PROP taster status effects because we used the LMS both for PROP taster status classification and for rating the sensations elicited by red wines. In previous studies
(Ishikawa & Noble, 1995; Smith et al., 1996), some subjects may have been misclassified due to the use of threshold techniques for classification into PROP taster status groups. The use of the LMS here may have yielded more accurate differentiation of PROP-sensitive individuals, as well as allowing for a greater range of responses during data collection. Significant effects of wine type were observed in the analysis of the bitterness and astringency intensity ratings, indicating that the wines used here varied in their
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Fig. 3. Mean astringency ratings for an aqueous solution of 1 g/l alum sulfate among PROP non-tasters NT (n=10), tasters T (n=7) and supertasters ST (n=8). Values shown are meansSE averaged across three sessions. Means are not significantly different for PROP taster status [ANOVA, F(2, 22)=2.003, P=0.159].
bitter and astringent characteristics. Furthermore, a significant Wine type Taster status interaction was observed for bitterness ratings, indicating that there is a complex relationship between the bitterness of red wine and PROP taster status (Fig. 2). Contrary to expectations, no differences were observed between tasters and super-tasters for any attribute assessed. This may be related to some overlap in the classification of these two groups, or the relatively small sample size used. The sample size may not necessarily reflect accurately the differences that might exist between population groups. To the authors’ knowledge, the association between PROP taster status and the perception of acidity and astringency has not previously been reported in the literature. However, PROP taster status has previously been shown to be related to the perception of a variety of other oral sensations. For example, in addition to being less sensitive to bitter tastes, PROP nontasters are relatively insensitive to salty and sweet tastes (Bartoshuk et al., 1998; Gent & Bartoshuk, 1983), to the irritation produced by capsaicin (Karrer & Bartoshuk, 1991), and to the tactile properties of fats (Duffy, Bartoshuk, Lucchina, Snyder, & Tym, 1996; Prutkin, Fast, Lucchina, & Bartoshuk, 1999; Tepper & Nurse, 1997). Increased density of fungiform papillae, higher numbers of taste pores per papillae, and greater trigeminal innervation have been associated with these differences in sensitivity. It is possible that a similar mechanism may be responsible for the astringency effect observed here. The sensation of astringency starts with activation of mechanoreceptors in the oral cavity, which themselves are innervated by trigeminal fibers.
The intensity of the sensation of astringency elicited by the alum sulfate solution was not related to PROP taster status. However, averaged across all groups and samples, the overall mean astringency rating of the alum sulfate solution (47.5 4.3) was considerably higher than that of the red wines (28.8 2.0). Therefore, the relevance of this finding to the perception of astringency in the context of wine tasting is questionable. It is possible that context or carry-over effects may have contributed to this result because the alum sulfate solution was always presented after all of the red wines had been tasted. This research has shown that PROP super-tasters and tasters perceive higher intensities of bitterness, astringency and acidity in red wines than do non-tasters. Further research on the relationship between PROP taster status and the perception of oral sensations elicited by wines is clearly in order. This could include determining whether the perception of sweetness, irritation, and viscosity elicited by wine is associated with PROP taster status. In addition, it would be of interest to extend this study to a wider range of alcoholic beverages, including white wine. Individuals differing in sensitivity to PROP may also vary in their preference for and consumption of wine and other beverages. For instance, PROP super-tasters and tasters might avoid wine styles and other alcoholic beverages that are high in bitterants and/or astringents. Consistent with this proposition, DiCarlo and Powers (1998) indicate that alcohol consumption is linked to PROP status, with PROP tasters less prone to one form of alcoholism, perhaps because they find the bitter and/ or irritant properties of ethanol unpleasant (Bartoshuk et al., 1993, Bartoshuk, 2000).
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5. Conclusion Twenty-five subjects used the Labeled Magnitude Scale to rate the bitterness intensity of a 0.32 mM PROP solution, and based on their responses were classified as non-tasters (n=10), tasters (n=7) and super-tasters (n=8). After training for taste and astringency identification and discrimination, participants used the LMS to rate the intensity of bitterness, acidity and astringency elicited by three commercial red wines. PROP tasters and super-tasters gave higher intensity ratings for all three attributes than did non-tasters. The accurate measurement of differences between PROP non-tasters, tasters, and super-tasters in their taste and tactile responses to red wine is an important starting point in describing the preference and consumption patterns of wine consumers. Further research is now needed to take these findings outside of the laboratory and relate PROP taster status data to actual consumer behavior towards wine and other alcoholic beverages.
Acknowledgements The National Science and Engineering Research Council of Canada, the Wine Council of Ontario and the Grape Growers of Ontario are gratefully acknowledged for their financial support of this research.
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Drewnowski, A., Henderson, S. A., Shore, A. B., & Barratt-Fornell, A. (1997). Non-tasters, tasters, and super-tasters of 6-n-propylthiouracil (PROP) and hedonic response to sweet. Physiology and Behavior, 62(3), 649–655. Duffy, V. B., Bartoshuk, L. M., Lucchina, L. A., Snyder, D. J., & Tym, A. (1996). Supertasters of PROP (6-n-propylthouracil) rate the highest creaminess to high-fat milk products. Chemical Senses, 21, 598 [abstract].. Fischer, U. (1990). MSc thesis, University of California, Davis. Fox, A. L. (1931). Six in ten ‘tasteblind’ to bitter chemical. Scientific NewsLetter, 9, 249. Gawel, R., Iland, P. G., & Francis, I. L. (2001). Characterizing the astringency of red wine: a case study. Food Quality and Preference, 12, 83–94. Gent, J. F., & Bartoshuk, L. M. (1983). Sweetness of sucrose, neohesperidin dihydrochalcone and saccharin is related to genetic ability to taste the bitter substance 6-n-propylthiouracil. Chemical Senses, 7, 265–272. Green, B. G., Dalton, P., Cowart, B., Shaffer, G., Rankin, K., & Higgins, J. (1996). Evaluating the ‘Labeled Magnitude Scale’ for measuring sensations of taste and smell. Chemical Senses, 21, 323–334. Green, B. G., Shaffer, G. S., & Gilmore, M. M. (1993). A semantically labeled magnitude scale of oral sensation with apparent ratio properties. Chemical Senses, 18, 683–702. Guo, S-W., & Reed, D. R. (2001). The genetics of phenylthiocarbamide perception. Ann. Hum. Biol., 28(2), 111–142. Guo, S. W., Shen, F. M., Zheng, C. J., & Wang, Y. (1998). Threshold distributions of phenylthiocarbamide (PTC) in the Chinese population. In C. Murphy (Ed.), International Symposium on Olfaction and Taste XII (pp. 855). NY: NY Academy of Sciences. Harris, H., & Kalmus, H. (1949). The measurement of taste sensitivity to phenylthiourea (P.T.C.). Annals of Eugenics, 15, 24–31. Intranuovo, L. R., & Powers, A. S. (1998). The perceived bitterness of beer and 6-n-propylthiouracil (PROP) taste sensitivity. Olfaction and Taste XII, Annals of the New York Academy of Sciences, 855, 813–815. Ishikawa, T., & Noble, A. C. (1995). Temporal perception of astringency and sweetness in red wine. Food Quality and Preference, 6, 27–33. Kaminski, L. C., Henderson, S. A., & Drewnowski, A. (2000). Young women’s food preferences and taste responsiveness to 6-n-propylthiouracil (PROP). Physiology and Behaviour, 68, 691–697. Karrer, T., & Bartoshuk, L. (1991). Capsaicin desensitization and recovery on the human tongue. Physiology and Behavior, 49, 757– 764. Keppel, G. (1991). Design and analysis: a researcher’s handbook. Englewood Cliffs, NJ: Prentice Hall. Kielhorn, S., & Thorngate, J. H. III. (1999). Oral sensations associated with the flavan-3-ols (+)-catechin and ( )-epicatechin. Food Quality and Preference, 10, 109–116. Miller, I. J., & Reedy, F. E. (1990). Variations in human taste bud density and taste intensity perception. Physiology and Behavior, 47, 1213–1219. Parr, L. W. (1934). Taste blindness and race. J. Heredity, 25, 187–190. Prutkin, J. M., Fast, K., Lucchina, L. A., & Bartoshuk, L. M. (1999). Prop (6-n-propylthouracil) genetics and trigeminal innervation of fungiform papillae. Chemical Senses, 24, 243 [abstract]. Prutkin, J., Duffy, V. B., Etter, L., Fast, K., Gardner, E., Lucchina, L. A., Snyder, D. J., Tie, K., Weiffenbach, J., & Bartoshuk, L. M. (2000). Genetic variation and inferences about perceived taste intensity in mice and men. Physiology and Behavior, 69, 161–173. Reedy, F. E., Bartoshuk, L. M., Miller, I. J., Duffy, V. B., Lucchina, L., & Yanagisawa, K. (1993). Relationships among papillae, taste pores and 6-n-propylthouracil (PROP) suprathreshold taste sensitivity. Chemical Senses, 18, 618–619. Smith, A. K., June, H., & Noble, A. C. (1996). Effects of viscosity on the bitterness and astringency of grape seed tannin. Food Quality and Preference, 7(3/4), 161–166.
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Tepper, B. J., Christensen, C. M., & Cao, J. (2001). Development of brief methods to classify individuals by PROP taster status. Physiology and Behavior, 73, 571–577. Tepper, B. J., & Nurse, R. J. (1997). Fat perception is related to PROP taster status. Physiology and Behavior, 61(6), 949–954. Thorngate, J. H. III. (1997). The physiology of human sensory response to wine: a review. American Journal of Oenology and Viticulture, 48(3), 271–278.
Dr Gary Pickering is Associate Professor of Oenology with the Department of Biological Sciences at Brock University. He is also a member of the Department of Psychology and the Cool Climate Oenology and Viticulture Institute, also at Brock University. Katerina Simunkova is a graduate of the BSc Honors (Biological Sciences) program at Brock University. Dr David DiBattista is a Professor in the Department of Psychology at Brock University.
Intensity of taste and astringency sensations elicited by red wines is associated with sensitivity to PROP (6-n-propylthiouracil) Gary J. Pickeringa,b,c,*, Katerina Simunkovaa, David DiBattistac a Department of Biological Sciences, Brock University, St. Catharines, Canada L2S 3A1 Cool Climate Oenology and Viticulture Institute, Brock University, St. Catharines, Canada L2S 3A1 c Department of Psychology; Brock University, St. Catharines, Canada L2S 3A1
b
Received 10 January 2003; received in revised form 10 March 2003; accepted 28 March 2003
Abstract The relationship between sensitivity to 6-n-propylthiouracil (PROP) and taste and astringency perception elicited by red wines was examined. Twenty-five subjects were classified into three PROP sensitivity groups (non-tasters, tasters and super-tasters) based on their bitterness ratings of a 0.32 mM PROP solution as measured on a Labeled Magnitude Scale (LMS). In a completely randomized block design, subjects used the LMS to rate the bitterness, astringency and acidity intensities of three commercial red wines. Contrary to the findings of previous studies with wine, bitterness, astringency and acidity intensities were all correlated with individual PROP taster status. PROP non-tasters gave significantly lower intensity ratings for the bitterness, astringency and acidity of the red wines than did PROP tasters and super-tasters. Individual differences among taster groups may be related to preference and consumption behavior of consumers of wine and other alcoholic beverages. # 2003 Elsevier Ltd. All rights reserved. Keywords: PROP; 6-n-Propylthiouracil; Wine; Astringency; Taste; Bitterness; Acidity
1. Introduction 1.1. Genetic variation in taste and its measurement The variation in the sensitivity of individuals to bitter compounds has been shown in numerous studies since the accidental discovery by Fox in the early 1930s that only some people can taste the bitter compound phenylthiocarbamide (PTC; Fox, 1931). 6-n-propylthiouracil (PROP) is now widely used for bitterness sensitivity tests as it lacks the sulfurous odor of PTC, and is generally regarded as a safer compound. The perceptual differences between people that can taste PTC/PROP (‘tasters’) and those that cannot (‘non-tasters’) extends to other compounds, including caffeine, saccharin, KCl, sodium and potassium benzoate, sucrose and neohesperidin dihydrochalcone (Bartoshuk, Duffy, Reed, & Williams, 1996). PROP tasters are also more sensitive than non-tasters to other tastes and oral sensations, including sweetness (Gent & Bartoshuk, 1983), saltiness * Corresponding author. Tel.: +1-905-688-5550; fax: +1-905-6883104. E-mail address: [email protected] (G.J. Pickering). 0950-3293/03/$ - see front matter # 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0950-3293(03)00053-3
(Bartoshuk, Duffy, Lucchina, Prutkin, & Fast, 1998), irritation (Karrer & Bartoshuk, 1991) and perception of the tactile properties of fats, such as creaminess, oiliness and smoothness (Tepper & Nurse, 1997). Early research used sensation threshold procedures to categorize individuals with respect to their ability to taste bitter substances. For example, Harris and Kalmus (1949) classified subjects as having either low, intermediate or high thresholds for the detection of PTC. However, more recent research has made it clear that thresholds do not reliably predict suprathreshold taste perception. Thus, individuals who are classified as tasters based on their PROP detection threshold may differ widely in their ratings of the bitterness of suprathreshold PROP solutions. For example, some tasters will rate the bitterness of a PROP solution as a medium taste sensation while others will give the same stimulus the highest bitterness rating (Bartoshuk, 1993). Recent studies suggest that the ability to taste bitter compounds such as PTC and PROP represents a trait with incomplete dominance (Guo & Reed, 2001). In addition, gender (Bartoshuk, Duffy, & Miller, 1994) and race (Guo, Shen, Zheng, & Wang, 1998; Parr, 1934) effects have been reported for PROP/PTC sensitivity,
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and sensitivity to PROP has been correlated with number of fungiform papillae and taste pores (Miller & Reedy, 1990; Reedy, Bartoshuk, Miller, Duffy, Lucchina, & Yanagisawa, 1993; Bartoshuk et al., 1994). A number of suprathreshold methods have been used to classify individuals into PROP taster groups (Bartoshuk et al., 1994; Bartoshuk, 2000; Drewnowski, Henderson, Shore, & Barratt-Fornell, 1997). There is now consensus that the Labeled Magnitude Scale (LMS; Green, Dalton, Cowart, Shaffer, Rankin, & Higgins, 1996; Green, Shaffer, & Gilmore, 1993) allows for superior separation of PROP taster groups. The LMS is a quasilogarithmic scale with verbal label descriptors that is anchored at the lower end with the phrase ‘barely detectable’ and at the upper end with ‘strongest imaginable.’ The LMS provides ratio-level data that are comparable to data yielded by the magnitude estimation procedure, and it is not affected by the ceiling effects that may reduce the usefulness of other scales, such as the Natick nine-point scale (Drewnowski et al., 1997; Prutkin et al., 2000; Tepper & Nurse, 1997). A trimodal distribution for PROP sensitivity has now been demonstrated (Bartoshuk et al., 1993, 1994). Based on their ratings of the bitter taste of PROP, individuals can be classified as being either non-tasters, tasters or supertasters, with the last group giving the highest ratings. This individual variability in the perception of intensity of a range of taste and oral sensations extends to food (Kaminski, Henderson, & Drewnowski, 2000) and beverages (Intranuovo & Powers, 1998), and has implications for food-related behaviors. For instance, PROP tasters tend to give lower acceptance ratings to foods high in fat content, such as cheese and whole milk (Tepper, Christensen, & Cao, 2001) and bitter foods, such as brussel sprouts, broccoli, and spinach (Kaminski et al., 2000). 1.2. Sensory properties of wine and relationship to PROP taster status Wine is a complex beverage containing numerous organic and inorganic constituents that contribute to its aroma and flavor. It can elicit sweet, sour, bitter and salt taste responses as well as numerous tactile sensations (Thorngate, 1997). Indeed, this complexity of sensation is part of the overall consumer appeal of the product. In red wine, the presence of relatively high concentrations of phenolic compounds results in the emergence of astringency and, to a lesser extent bitterness, as particularly important components of the flavor matrix. Both bitterness and astringency are primarily elicited by the flavan-3-ols (+)-catechin and ( )-epicatechin and their polymers, which are derived from seeds and skins of grapes and extracted into red wine during fermentation (Gawel, Iland, & Francis, 2001). The perception of astringency results from cross-linking and subsequent precipitation of these polyphenols with salivary proteins
and glycoproteins (Kielhorn & Thorngate, 1999). Following polyphenol–salivary protein interaction, the lubricating quality of saliva decreases, and the increased friction between the oral surfaces activates mechanoreceptors and leads to the sensation of astringency (Gawel et al., 2001). Ethanol has also been shown to contribute to bitterness perception in wine (Fischer, 1990). No relationship has yet been detected between PROP taster status and the sensations elicited either by red wine or its components. Ishikawa and Noble (1995) found no relationship between PROP taster status and the perception of astringency in Carnelian red wine, and Smith, June, and Noble (1996) found no relationship between PROP taster status and the perception of bitterness and astringency of grape seed tannin. However, in both of these studies, PROP taster status was based on subjects’ threshold sensitivity to PROP, and we speculate that the use of this technique may have contributed to the null results. Indeed, when the LMS was employed by Delwiche, Buletic and Breslin (2001), the data suggested differences between PROP taster status groups with respect to bitterness intensity ratings for a number of bitter compounds, including the important red wine phenolic ( )epicatechin (Figure 7, p 772). However, perhaps because of the low statistical power associated with having only four subjects in two of the PROP groups, the analysis failed to reveal significant differences between the groups for these bitter compounds (Delwiche et al., 2001). Accordingly, we investigated the relationship between PROP taster status and the perception of bitterness and astringency in red wine using the LMS both to classify subjects into PROP taster status categories and to rate the sensations elicited by red wines. The use of this more sensitive suprathreshold measurement scale may increase the likelihood of detecting differences in the sensations elicited by red wines in individuals differing in PROP taster status.
2. Materials and methods 2.1. Participants To ensure adequate representation of each of the three PROP taster status groups, 200 students and staff of Brock University, Ontario, Canada underwent an initial screening. Following the procedure of Tepper et al. (2001), these individuals used the LMS to rate the bitterness of a paper filter strip that had been impregnated with a 3.2 mM solution of PROP solution (ICN Biochemicals Inc., Aurora, Ohio). The only significant deviance from the screening procedure used by Tepper et al. (2001) was that NaCl standards were not employed here. The LMS used for screening, training and data collection was 102 mm long, and the top anchor term ‘strongest imaginable’ referred to all sensations.
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Based on the results from the paper filter strips, 30 people were invited to participate in the experiment. Twenty-five people (7 men, 18 women), ranging in age from 19 to 46 years, completed all training and data collection sessions, and their data are included in the analyses reported later. All were in good health, and were allergy and medication free, as determined by a questionnaire. Five had significant prior experience with wine tasting. 2.2. Stimuli The training stimuli consisted of aqueous solutions of quinine sulfate, alum sulfate, tartaric acid (all Fischer Chemicals Scientific, New Jersey, USA) and PROP, all prepared using distilled water. Solutions of quinine sulfate (0.1 g/l), alum sulfate (1 g/l), and tartaric acid (2 g/l) were used to train participants to recognize bitterness, astringency, and acidity, respectively. A 3.2 mM PROP solution was prepared by dissolving PROP in distilled water on a medium heat stirring plate. Less concentrated PROP solutions (0.32 and 0.032 mM) were prepared by dilution. Solutions were prepared one day before training and data collection sessions and stored at room temperature (23 C 2 C). Three commercial dry red table wines, believed likely to vary in bitterness and astringency characteristics, were selected for testing: 2000 Folonari Valpolicella Classico (Corby Distilleries Ltd., Italy, 12% alcohol v/v); 2000 Pinot Noir (Inniskillin Wines, Canada, 12.5% alcohol v/v); and non-vintage L’Epayrie (Armand Roux, France, 11.5% alcohol v/v). These wines were introduced during training sessions and were later used for all data collection sessions. 2.3. Classification and training of participants Four 45-min sessions were held over 2 weeks. During the first session, PROP status was reassessed by having participants rate the bitterness of three PROP solutions (0.032, 0.32, and 3.2 mM) that were presented in increasing order of concentration. Participants were given 20 ml of solution and instructed to move the sample from side to side in the mouth for 5–10 s and then to expectorate. After waiting for 10–15 s, they used the LMS to rate the bitterness of the sample. Participants rinsed thoroughly with water prior to each sample. This tasting procedure was used throughout the study. During the next three sessions, participants were trained to distinguish between bitter, astringent and acidic sensations. A simple written description of each sensation quality was provided in order to assist with identification and differentiation. Acidic was defined as sour, tart; bitter as caffeine (strong coffee); and astringent as dryness, cheek puckering. In each session, parti-
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cipants were given 20 ml of the bitter, astringent and acidic training solutions, and they tasted and rated the principal sensation for each solution. During the last session, discriminative ability was assessed using these three aqueous solutions. Twenty milliliters samples (labeled A, B or C) were presented in random order, and participants were instructed to identify the solutions as bitter, astringent or acidic. All participants correctly identified all solutions (data not shown). The final training session also served as a dry-run for the data collection procedure, with participants rating the bitterness, astringency and acidity of 20 ml samples of the three commercial wines. Discussion among participants was encouraged to identify and address any potential concerns. Participants confirmed that bitterness, astringency and acidity were the dominant oral sensations elicited by these wine samples. 2.4. Data collection and analysis Data collection took place during three 45-min sessions over a 2-week period. Nose clips were worn to avoid any olfactory biases. At the start of each session, participants were refamiliarized with the taste qualities to be evaluated. The written descriptions of bitterness, astringency and acidity were reviewed, and the first flight of samples consisted of the three training solutions of quinine sulfate, alum sulfate and tartaric acid, which were presented in plastic cups with identifying labels. The second flight consisted of the three wine samples, which were presented in 250-ml opaque plastic cups coded with three-digit random numbers. The order of presentation was randomized, and a 2–4 min break between samples was enforced to minimize palate fatigue and carry-over effects. Participants used the LMS to rate the intensity of bitterness, astringency and acidity of each wine. Acidity was rated first, followed by astringency and then bitterness, reflecting the typical time-course of these sensations. Acidity was included in this design to avoid potential dumping effects on the other attributes being rated (Clark & Lawless, 1994). After all three wines had been presented, an aqueous solution of 1 g/l alum sulfate was presented in a cup labeled astringency. Participants used the LMS to rate the astringency of this solution. Statistical analyses were conducted using SPSS 11.0 software for Windows (SPSS Inc., Chicago, IL). Mixeddesign analyses of variance (ANOVA) were used to analyze data. If Mauchly’s test of sphericity led to rejection of the null hypothesis, the Huynh–Feldt correction factor was used to adjust the degrees of freedom (Keppel, 1991). Fisher’s LSD procedure was used for post hoc comparisons. Only differences corresponding to P < 0.05 are reported as statistically significant.
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3. Results 3.1. PROP taster status response to PROP stimuli Participants were classified as non-tasters, tasters or super-tasters based on the bitterness rating they assigned to the 0.32 mM PROP solution using the LMS (nontaster: 415.5; taster: > 15.5 and < 51; super-taster: 551; Tepper et al., 2001). Ratings for PROP solutions were then analyzed using a 33 mixed-design ANOVA (between-subjects variable: taster status; within-subjects variable: PROP concentration). There were significant main effects of taster status, F(2, 22)=58.45, P=0.000, and PROP concentration, F(2, 44)=127.15, P=0.000. As expected, perceived bitterness intensities varied as a function of both taster status and PROP concentration. The Taster status PROP concentration interaction was also significant, F(4, 44)=21.87, P=0.000. These data are summarized in Table 1. Non-tasters gave low ratings to all three PROP solutions, although they gave a significantly higher rating to the 3.2 mM solution. In contrast, for both tasters and super-tasters, there were significant differences in perceived intensity across all three solutions, with super-tasters giving extremely high ratings to the 3.2 mM solution. Also, for the 0.032 mM PROP solution, there were no perceived differences in bitterness intensity as a function of taster status. However, for the two higher concentration solutions, tasters gave ratings that were significantly higher than those of non-tasters, but lower than those of super-tasters. 3.1.1. Bitterness intensity ratings of red wines A 333 mixed-design ANOVA was carried out on the bitterness ratings (between-subjects variable: taster status; within-subjects variables: wine type and session). There were significant main effects of taster status, F(2, 22)=11.73, P=0.000, and wine type, F(2, 44)=8.486, P=0.001. As Fig. 1 indicates, the overall bitterness ratings of non-tasters were low in absolute terms, and they were significantly lower than those of both tasters and Table 1 Bitterness ratings of PROP solutions using the Labeled Magnitude Scale PROP Solution (mM)
Non-tasters (n=10)
Tasters (n=7)
Super-tasters (n=8)
0.032 0.32 3.2
1.73 1.25a,x 2.50 0.56a,x 17.295.52a,y
6.87 4.02a,x 34.096.46b,y 67.768.91b,z
10.724.06a,x 64.806.38c,y 93.152.08c,z
Values shown are MeanSEM. Participants were classified as being either non-tasters, tasters or super-tasters based on the bitterness rating assigned to the 0.32 mM PROP solution (Tepper et al., 2001). For each concentration, means sharing the same indicator (a, b, c) do not differ significantly, and for each taster status group, means sharing the same indicator (x, y, z) do not differ significantly (P> 0.05, Fisher’s LSD procedure).
super-tasters. Furthermore, the mean bitterness rating of the Pinot Noir (mean SEM=18.06 2.04) was significantly lower than that of both the L’Epayrie (26.26 1.90) and the Valpolicella (23.44 2.75). Fig. 2 illustrates the only significant interaction effect, which was the Wine type Taster status interaction, F(4, 44)=3.38, P=0.017. Non-tasters did not report different levels of bitterness in the three wines. However, tasters gave significantly higher bitterness ratings to the L’Epayrie than to the other wines, and super-tasters gave significantly lower bitterness rating to the Pinot Noir than to the other wines. 3.1.2. Astringency intensity ratings of red wines A 33 mixed-design ANOVA of the astringency ratings revealed significant main effects of taster status, F(2, 22)=8.43, P=0.000, wine type F(2, 44)=3.60, P=0.035, and session, F(2, 44)=4.55, P=0.016. As Fig. 1 shows, tasters and super-tasters gave significantly higher astringency ratings than did non-tasters. Moreover, the astringency ratings for the Valpolicella (31.45 2.13) were significantly higher than those for the Pinot Noir (25.99 2.07), but they did not differ from the ratings for the L’Epayrie (29.01 2.69). Finally, ratings were significantly higher for tasting session 2 (32.56 2.82) than for session 3 (24.71 1.80), but they did not differ from the ratings for session 1 (29.19 2.75). The origins of the differences across sessions are not clear. 3.1.3. Acidity intensity ratings of red wines A 33 mixed-design ANOVA of the acidity ratings revealed only a significant main effects of taster status, F(2, 22)=11.23, P=0.000. As Fig. 1 indicates, the ratings of tasters and super-tasters did not differ from each other, but both were significantly higher than those of non-tasters. 3.2. Alum sulfate ratings The alum sulfate solution provided another measure of whether participants perceived a difference in astringency as a function of PROP taster status. A 33 mixed-design ANOVA (between-subjects variable: taster status; within-subjects variable: session) revealed no significant effects (Fig. 3). In particular, there was not a significant effect of taster status, F(2, 22)=2.003, P=0.159, with the overall mean rating of the alum sulfate solution being 47.46 4.28. Thus, the alum sulfate solution was given substantially higher astringency ratings than were any of the three wines that were used.
4. Discussion In contrast to previous studies (Ishikawa & Noble, 1995; Smith et al., 1996), significant differences in the bitterness, astringency and acidity elicited by red wine
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Fig. 1. Mean intensity ratings for bitterness, astringency and acidity elicited by red wines across the three taster groups; PROP non-tasters NT (n=10), tasters T (n=7) and super-tasters ST (n=8). Values shown are meansSE averaged across sessions (3), and wine types (3). For each attribute, means sharing the same letter do not differ significantly (LSD0.05).
Fig. 2. Mean bitterness intensity ratings for three wine types among PROP non-tasters NT (n=10), tasters T (n=7) and super-tasters ST (n=8). Values shown are meansSE . Wine 1 is 2000 Folonari, Valpolicella Classico, Italy; Wine 2 is 2000 Inniskillin Wines, Pinot Noir, Canada; and Wine 3 is (non-vintage) Armand Roux, L’Epayrie, France. For each wine type, means sharing the same letter do not differ significantly (LSD0.05).
were observed as a function of PROP taster status (Fig. 1). This effect was observed for all three red wines examined, with tasters and super-tasters perceiving higher bitterness, astringency and acidity intensities when compared to non-tasters. No difference was found between the PROP taster and super-taster groups. We speculate that we were able to show significant PROP taster status effects because we used the LMS both for PROP taster status classification and for rating the sensations elicited by red wines. In previous studies
(Ishikawa & Noble, 1995; Smith et al., 1996), some subjects may have been misclassified due to the use of threshold techniques for classification into PROP taster status groups. The use of the LMS here may have yielded more accurate differentiation of PROP-sensitive individuals, as well as allowing for a greater range of responses during data collection. Significant effects of wine type were observed in the analysis of the bitterness and astringency intensity ratings, indicating that the wines used here varied in their
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Fig. 3. Mean astringency ratings for an aqueous solution of 1 g/l alum sulfate among PROP non-tasters NT (n=10), tasters T (n=7) and supertasters ST (n=8). Values shown are meansSE averaged across three sessions. Means are not significantly different for PROP taster status [ANOVA, F(2, 22)=2.003, P=0.159].
bitter and astringent characteristics. Furthermore, a significant Wine type Taster status interaction was observed for bitterness ratings, indicating that there is a complex relationship between the bitterness of red wine and PROP taster status (Fig. 2). Contrary to expectations, no differences were observed between tasters and super-tasters for any attribute assessed. This may be related to some overlap in the classification of these two groups, or the relatively small sample size used. The sample size may not necessarily reflect accurately the differences that might exist between population groups. To the authors’ knowledge, the association between PROP taster status and the perception of acidity and astringency has not previously been reported in the literature. However, PROP taster status has previously been shown to be related to the perception of a variety of other oral sensations. For example, in addition to being less sensitive to bitter tastes, PROP nontasters are relatively insensitive to salty and sweet tastes (Bartoshuk et al., 1998; Gent & Bartoshuk, 1983), to the irritation produced by capsaicin (Karrer & Bartoshuk, 1991), and to the tactile properties of fats (Duffy, Bartoshuk, Lucchina, Snyder, & Tym, 1996; Prutkin, Fast, Lucchina, & Bartoshuk, 1999; Tepper & Nurse, 1997). Increased density of fungiform papillae, higher numbers of taste pores per papillae, and greater trigeminal innervation have been associated with these differences in sensitivity. It is possible that a similar mechanism may be responsible for the astringency effect observed here. The sensation of astringency starts with activation of mechanoreceptors in the oral cavity, which themselves are innervated by trigeminal fibers.
The intensity of the sensation of astringency elicited by the alum sulfate solution was not related to PROP taster status. However, averaged across all groups and samples, the overall mean astringency rating of the alum sulfate solution (47.5 4.3) was considerably higher than that of the red wines (28.8 2.0). Therefore, the relevance of this finding to the perception of astringency in the context of wine tasting is questionable. It is possible that context or carry-over effects may have contributed to this result because the alum sulfate solution was always presented after all of the red wines had been tasted. This research has shown that PROP super-tasters and tasters perceive higher intensities of bitterness, astringency and acidity in red wines than do non-tasters. Further research on the relationship between PROP taster status and the perception of oral sensations elicited by wines is clearly in order. This could include determining whether the perception of sweetness, irritation, and viscosity elicited by wine is associated with PROP taster status. In addition, it would be of interest to extend this study to a wider range of alcoholic beverages, including white wine. Individuals differing in sensitivity to PROP may also vary in their preference for and consumption of wine and other beverages. For instance, PROP super-tasters and tasters might avoid wine styles and other alcoholic beverages that are high in bitterants and/or astringents. Consistent with this proposition, DiCarlo and Powers (1998) indicate that alcohol consumption is linked to PROP status, with PROP tasters less prone to one form of alcoholism, perhaps because they find the bitter and/ or irritant properties of ethanol unpleasant (Bartoshuk et al., 1993, Bartoshuk, 2000).
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5. Conclusion Twenty-five subjects used the Labeled Magnitude Scale to rate the bitterness intensity of a 0.32 mM PROP solution, and based on their responses were classified as non-tasters (n=10), tasters (n=7) and super-tasters (n=8). After training for taste and astringency identification and discrimination, participants used the LMS to rate the intensity of bitterness, acidity and astringency elicited by three commercial red wines. PROP tasters and super-tasters gave higher intensity ratings for all three attributes than did non-tasters. The accurate measurement of differences between PROP non-tasters, tasters, and super-tasters in their taste and tactile responses to red wine is an important starting point in describing the preference and consumption patterns of wine consumers. Further research is now needed to take these findings outside of the laboratory and relate PROP taster status data to actual consumer behavior towards wine and other alcoholic beverages.
Acknowledgements The National Science and Engineering Research Council of Canada, the Wine Council of Ontario and the Grape Growers of Ontario are gratefully acknowledged for their financial support of this research.
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Dr Gary Pickering is Associate Professor of Oenology with the Department of Biological Sciences at Brock University. He is also a member of the Department of Psychology and the Cool Climate Oenology and Viticulture Institute, also at Brock University. Katerina Simunkova is a graduate of the BSc Honors (Biological Sciences) program at Brock University. Dr David DiBattista is a Professor in the Department of Psychology at Brock University.