Effect of Temperature on Human Sensitivity to Sweetness. Keiko Yoshida**

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1 日本調理科学会誌 Effect of Temperature Vol. 47,No. on Human 2,97~102(2014) Sensitivity to Sweetness Report Effect of Temperature on Human Sensitivity to Sweetness Yoko Okamoto* Keiko Yoshida** To investigate the effect of the temperature of the substance on how taste is experienced, sweetness intensity was measured by a sensory evaluation method for sweeteners and commercially available sweetened beverages. Sucrose, D-glucose, D-fructose, D-maltose, erythritol, xylitol, D-sorbitol and maltitol (eight types)were used as sweeteners in the present study. The number of commercial sweetened beverages tested was 11. The solution temperatures tested were 7, 25 (as standard), and 43. The participants were 27 healthy female students. Of the eight sweeteners, differences in sweetness intensity by temperature were found in D-fructose and xylitol but not in other sweeteners. On the other hand, among the commercial sweetened beverages tested, sweetness intensity was weaker at 7 than at 25 and stronger at 43 than at 25 in many of the beverages. Also, significance in the main effect of temperature on sweetness intensity was not found in the sweeteners group but was found in the commercial sweetened beverages group. The commercial sweetened beverages contain components other than sweeteners, and our results indicated the need to investigate the effects of the components on perceived sweetness. Keyword: human sensitivity to sweetness, sensory evaluation, temperature, sweet compound solution, commercial beverage containing sweet compound INTRODUCTION It is generally considered that the taste of chemical substances and beverages experienced by humans is influenced by the temperature of the chemical substance or beverage. Many classic studies have reported alterations in human sensitivity to chemical substances caused by a temperature change (Pangborn et al., 1970; McBurney et al., 1973; Moskowitz, 1973; Bartoshuk et al., 1982; Cardello and Maller, 1982; Green and Frankmann, 1987); however, few such studies have been reported recently (Cruz and Green, 2000; The Chemical Society of Japan (Ed.), 2000). Many of the reported results are mutually exclusive, failing to yield conclusive trends. Therefore, to investigate the effect of the temperature of the substance on how taste is experienced, here sweetness intensity was measured by a sensory evaluation method for sweeteners and commercially available sweetened beverages. MATERIALS AND METHODS Samples The samples used in the two experiments are shown in Table 1. The sample solutions in Experiment 1 were prepared by mixing each of the 8 sweeteners (special-grade chemicals purchased from Mitsubishi-Kagaku Foods, Nacalai Tesque, Tokyo Chemical Industry, and Sigma- * Suzugamine Women s College ** Tsukuba International University Inquiry Suzugamine Women s College 6-18, Inokuchi, 4-chome, Nishi-ku, Hiroshima , Japan TEL 082(278)1103 FAX 082(277)0301 Aldrich)in pure water (Table 1). The concentrations of the sweetened solutions were selected in accordance with the method of Yamaguchi et al. (1970)so that the solutions had a sweetness equivalent to that of 10.0% sucrose solution, which is the sweetness level of sweetened beverage products that individuals sense as tasty (Yamazaki et al., 2003). The concentrations of the sweetened solutions were prepared as percentage weight (%, W/V). The 11 sweetened beverages used in Experiment 2 were products that do not have an acidic flavor. Of the 11 commercial sweetened beverages (A K)tested, A, B, H, I, and J contained coffee, C, D, and, G contained tea, K contained cocoa, and A, C, D, E, F, G, and K contained flavorings as ingredients. Their carbohydrate concentrations ranged from 4.0 to 17.1 g per 100 ml. Their sugar content ranged from 0.0% to 15.0%. A hand-held refractometer (Atago, Tokyo, Japan)was used to measure the sugar content. Each solution was tested at the following temperatures: 7, 25 (as standard), and 43. The temperature of the sweetened solution was first reduced to 7 by placing a cup containing the solution in ice. The temperature of the sweetened solution was increased to 25 and then to 43 by placing a cup containing the solution in a thermostat bath (Taitek Co. Ltd., Water Bath Shaker Personal 11, Saitama, Japan). The solutions were dispensed into 15-ml plastic containers. The solutions were tested within one minute of being removed from the thermostat bath. Sensory evaluation The participants were 27 healthy female students aged between 18 and 20 years who attended our junior college. (97) 39

2 J. Cookery Sci. Jpn. Vol. 47 No. 2(2014) Table 1. Samples 10.0% Sucrose 17.0% D-Glucose 8.0% D-Fructose 25.0% D-Maltose Experiment 1 Sweet compound solution 12.5% Erythritol 17.0% Xylitol 17.0% D-Sorbitol 12.5% Maltitol Experiment 2 Commercial beverage containing sweet compound Eleven types: A K Concentrations of sweet compounds are expressed as percentage weight (%, W/V). Commercial beverages containing sweet compounds are represented by the characters A K. Erythritol, xylitol, and maltitol were purchased from Mitsubishi-Kagaku Foods Inc., Nacalai Tesque Inc., and Tokyo Chemical Industry Inc., respectively. Other compounds were purchased from Sigma-Aldrich Japan Inc. The participants underwent a preliminary experiment and a training session before participating in the two experiments. In both Experiments 1 and 2, sensory evaluations were conducted in an air-conditioned, quiet room according to the method described below. The room contained a desk for testing, as well as a water supply and a sink for gargling. The sensory evaluation experiments were conducted between 2 p.m. and 4 p.m., more than one hour after the last meal had been consumed by the participants. The participants first gargled with pure water, and then drank and retained approximately 15 ml of the standard solution (i.e., the solution at 25 )in their mouth for tasting. Then, they drank and retained approximately 15 ml of the test solution (i.e., the solution at 7 or 43 )in their mouth for tasting. The participants were instructed to expectorate within five seconds because the standard and test solutions would be quickly warmed to body temperature. They gargled with pure water again and proceeded to the next solution. In both Experiments 1 and 2, nose clips were not used. The participants first tasted the standard solution (25 )and then the 7 or 43 test solution of the same solution to compare their sweetness intensities. The sweetness of the standard solution was set at 0, and the participants were asked to rate the sweetness of the test solution in comparison with the standard solution according to a seven-point scale ranging from -3 to +3 (Yamano et al., 2003)as follows: +1, slightly sweeter ; +2, moderately sweeter ; +3, much sweeter ; -1, slightly less sweet, -2, moderately less sweet ; -3, much less sweet ; and 0, same sweetness intensity. These measures of sweetness were set at regular intervals. Before conducting this study, approval of the Research Ethics Review Committee of Suzugamine Women s College was obtained. Informed consent was obtained from all participants. Data Analysis The evaluation score for each solution or beverage was expressed as the mean±standard deviation. Each variable was tested by the Shapiro-Wilk test for normality. To compare the perceived sweetness (evaluation score) of the same sample, a test of the difference between the average value under one condition and a constant was used (one-sample t-test)(mori and Yoshida, 1998). In addition, analysis of variance was performed by considering the evaluation score data of the sensory evaluation as a quantitative variable (interval scale)(mori and Yoshida, 1998). The changes in the sweetness evaluation score were tested for statistical significance by a two-way analysis of variance using sample type (Factor 1)and testing temperature (Factor 2)as intra-participant factors (repeated measurement, dependent/dependent). Assuming sphericity, the Mauchly s sphericity test was used to test intra-participant effects (main effect of sample, main effect of temperature, and interaction between sample and temperature). IBM SPSS Statistics 19.0 for Windows (IBM Company, Tokyo, Japan)was used for statistical analysis. RESULTS Sensory evaluation of the sweetened sample solutions (Experiment 1) Perceived sweetness (evaluation score)was expressed by the mean±standard deviation for each sweetened sample solution and temperature (Table 2). Perceived sweetness was compared among the sweetened sample solutions and temperatures (Table 3). At 7, D-fructose and xylitol were experienced to be significantly sweeter than the respective standard solution. At 43, D-fructose and xylitol were experienced to be significantly less sweet than the respective standard solution. Analysis of variance on the perception changes of sweetness using sweetened sample solution (eight types) and temperature (7 and 25 )as independent variables 40 (98)

3 Effect of Temperature on Human Sensitivity to Sweetness Table 2. Perceived sweetness (evaluation score)of eight sweetened solutions Sweet compound solution Sucrose D-Glucose D-Fructose D-Maltose Erythritol Xylitol D-Sorbitol Maltitol Mean score of test solution (n=27) 7 43 Mean SD Mean SD Mean SD Mean SD Mean SD Mean SD Mean SD Mean SD Test solutions with a mean score lower than 0 are less sweet than the respective standard solution at 25, whereas those with a mean score higher than 0 are sweeter than the respective standard solution at 25. (factors)showed significance in the main effect of sweeteners [F(7,182)=2.90, MSe=0.64, p<0.01] and the interaction between sweetened sample solution and temperature [F(7,182)=2.90, MSe =0.64, p<0.01]. Analysis of variance did not show significance in the main effect of temperature [F(1,26)=2.23, MSe=0.65 (ns)]. Analysis of variance using sweetened sample solution (eight types)and temperature (25 and 43 )as factors showed significance in the main effect of sweetener [F(7,182)=3.20, MSe=0.38, p<0.01] and in the interaction between sweetened sample solution and temperature [F(7,182)=3.20, MSe=0.38, p<0.01]. Analysis of variance did not show significance in the main effect of temperature [F(1,26)=1.02, MSe=0.82 (ns)]. In summary, the perception of sweetness was significantly different depending on the type of sweetened sample solution. By contrast, there were no differences in the perception of sweetness between 7 and 25, or between 25 and 43. Table 3. Comparison of difference in sweetness between the standard (25 )and test (7 and 43 )solutions for each sweet compound Sweet compound solution Sucrose D-Glucose D-Fructose D-Maltose Erythritol Xylitol D-Sorbitol Maltitol t-value for solution at ** * t-value for solution at ** * A one-sample t-test was performed between the standard solution and the test solution at each test temperature. **p<0.01, *p<0.05. Table 4. Perceived sweetness (evaluation score)of 11 commercial sweetened beverages Commercial beverage containing sweet compound Mean score of test beverage (n=27) 7 43 A (Ingredients: milk, sugar, coffee, flavors, etc.) Mean SD B (Ingredients: milk, sugar, coffee, etc.) Mean SD C (Ingredients: milk, sugar, tea, flavors, etc.) Mean SD D (Ingredients: high fructose corn syrup, sugar, tea, flavors, etc.) Mean SD E (Ingredients: sugar, high fructose corn syrup, flavors, etc.) Mean SD F (Ingredients: high fructose corn syrup, flavors, sucralose, etc.) Mean SD G (Ingredients: milk, sugar, tea, flavors, etc.) Mean SD H (Ingredients: durable milk, sugar, coffee, etc.) Mean SD I (Ingredients: sugar, coffee, flavors, etc.) Mean SD J (Ingredients: jersey milk, coffee, sugar, etc.) Mean SD K (Ingredients: sugar, skim milk, cocoa, flavors, etc.) Mean SD Test beverages with a mean score lower than 0 are less sweet than the respective standard beverage at 25, whereas those with a mean score higher than 0 are sweeter than the respective standard beverage at 25. (99) 41

4 Table 5. J. Cookery Sci. Jpn. Vol. 47 No. 2(2014) Comparison of difference in sweetness between the standard (25 )and test (7 and 43 )beverages containing different sweet compounds Commercial beverage containing sweet compound A B C D E F G H I J K t-value for test beverage at ** 2.37* -4.33** -2.08* ** t-value for test beverage at * 6.48** 3.50** ** 2.25* 5.05** 6.48** 1.95 A one-sample t-test was performed between the standard beverage and the test beverage at each test temperature. **p<0.01, *p<0.05. Sensory evaluation of commercial sweetened beverages (Experiment 2) Perceived sweetness (evaluation score)was expressed as the mean±standard deviation for each commercial sweetened beverage and temperature (Table 4). Perceived sweetness was compared among the different commercial sweetened beverages and temperatures (Table 5). Among the 11 sweetened beverages, perceived sweetness was significantly weaker at 7 compared with the respective standard in five beverages, and perceived sweetness was significantly stronger at 43 compared with the respective standard in seven beverages. Analysis of variance on the perception changes of sweetness using sweetened beverage (11 types)and temperature (7 and 25 )as factors showed significance in the main effect of sweetened beverages [F(10,260)=6.28, MSe=0.30, p<0.01], the main effect of temperature [F(1,26)=4.94, MSe=2.41, p<0.05)] and the interaction between sweetened beverage and temperature [F(10,260)=6.28, MSe=0.30, p<0.01)]. Analysis of variance using sweet beverage (11 types) and temperature (25 and 43 )as factors showed significance (p<0.01)in the main effect of sweetened beverage [F(10,260)=4.76, MSe=0.66, p<0.01], the main effect of temperature [F(1,26)=72.63, MSe=0.80, p< 0.01] and the interaction between sweetened beverage and temperature [F(10,260)=4.76, MSe=0.66, p<0.01]. It was therefore shown that the perception of sweetness differed significantly depending on the type of sweetened beverage. Moreover, the perception of sweetness differed significantly both between 7 and 25 and between 25 and 43. DISCUSSION Among the eight sweetened solutions, at the low temperature (7 )D-fructose and xylitol were experienced to be significantly sweeter than the respective standard solution, and at 43, D-fructose and xylitol were experienced to be significantly less sweet than the respective standard solution (Experiment 1). For the sweetened solutions, no significant differences were found in the perception of sweetness between 7 and 25 and between 25 and 43 on two-way ANOVA (Experiment 1). In other words, there was no significance in the main effect of temperature on perceived sweetness. Classical studies that investigated the relationship between sweetness intensity and temperature (McBurney et al., 1973 [dulcin, ], Moskowitz, 1973 [glucose, ] and Bartoshuk et al., 1982 [sucrose, 4 44 ]) reported that sweetness intensity was highest at Using a device that they developed that can locally cool or warm the tongue, Cruz and Green (2000)investigated the tastes experienced by participants when the local temperature of their tongue was changed. It was shown that, when the temperature of the tongue of the participants was maintained at 20 and then increased to 35, the participants experienced a sweet taste even though no taste stimuli were given. By contrast, when the temperature of the tongue was reduced from 20 to below 10, the participants experienced a salty taste. Those results are not consistent with our results because, in Experiment 1, no significance was found in the main effect of temperature on the sweetness perception of the sweeteners on two-way ANOVA. In Experiment 1 of our study, the solutions were tested within one minute of being warmed or cooled to the test temperatures and the participants were instructed to expectorate within five seconds; therefore, this experiment did not change the temperature of the participants tongues. However, Cruz and Green (2000)changed the local temperatures of the subjects tongues and concluded that taste intensities changed as a result. It is suggested that this marked difference in conclusion between our study and the study of Cruz and Green (2000)or aforementioned classic studies was due to these different approaches of controlling tongue temperature. Regarding the commercial sweetened beverages, the perception of sweetness differed significantly both between 7 and 25 and between 25 and (100)

5 Effect of Temperature on Human Sensitivity to Sweetness (Experiment 2). In other words, in the commercial sweetened beverages, significance was found in the main effect of temperature on sweetness intensity on two-way ANOVA. These results show conflicting trends compared with the studies of McBurney et al. (1973), Moskowitz (1973), Bartoshuk et al. (1982)and Cruz and Green (2000). Commercial sweetened beverages contain ingredients other than sweeteners, such as flavor components, and it is possible that such substances have an influence on the taste of the beverages. Kawaguchi et al. (1998)reported that flavor components increased the taste intensity of bitterness and astringency. Generally, flavor components have low volatility at low temperature and become more volatile as their temperature increases and this property might have markedly influenced the sweetness intensities of the commercial sweetened beverages in our study. Another example of non-sweetener substances that influence sweetness intensity is milk. Matsui et al. (2006) reported a positive correlation between the sweetness intensity and thickness of milk. Sakai and Yamamoto (2001)showed in rats that the addition of sweet flavors to sucrose solution enhanced its perceived sweetness, and that this was a learned association between taste information and olfactory information and the learning occurred in the frontal region of the brain, not in the processing pathways of taste and smell. Therefore, in our study the learning that had been formed through daily ingestive experience (flavors enhance taste) might have influenced the participants sensory evaluations. Further investigation on beverage ingredients is necessary in the future. Also, the integrated sense of taste and smell is a future issue. CONCLUSION To investigate the effect of the temperature of the substance on how taste is experienced, sweetness intensity was measured by a sensory evaluation method for sweeteners and commercially available sweetened beverages. Sucrose, D-glucose, D-fructose, D-maltose, erythritol, xylitol, D-sorbitol and maltitol (eight types)were used as sweeteners in the present study. The number of commercial sweetened beverages tested was 11. The solution temperatures tested were 7, 25 (as standard), and 43. The participants were 27 healthy female students aged between 18 and 20 years who attended our junior college. The sensory evaluation data were analyzed by one-sample t-test to investigate within-sample differences and by two-way analysis of variance to investigate the main effect of sample, main effect of temperature, and interaction between sample and temperature. Of the eight sweeteners, differences in sweetness intensity by temperature were found in D-fructose and xylitol but not in other sweeteners. On the other hand, among the commercial sweetened beverages tested, sweetness intensity was weaker at 7 than at 25 and stronger at 43 than at 25 in many of the beverages. Also, significance in the main effect of temperature on sweetness intensity was not found in the sweeteners group but was found in the commercial sweetened beverages group. The commercial sweetened beverages contain components other than sweeteners, and our results indicated the need to investigate the effects of the components on perceived sweetness. We thank Toshiaki Mori, professor at Hiroshima University, for his advice on statistical analysis. References Bartoshuk, L. M., Rennert, K., Rodin, J. and Stevevs, J. C. (1982), Effects of Temperature on the Perceived Sweetness of Sucrose, Physiol. Behav., 28, Cruz, A. and Green, B. G. (2000), Thermal stimulation of taste, Nature, 403, Green, B. G. and Frankmann, S. P. (1987), The effect of cooling the tongue on the perceived intensity of taste, Chem. Sens., 12, Kawaguchi, Y., Kubota, K., Kobayashi, A. and Hara, Y. (1998), The effect of tea aroma on bitterness and astringency in tea infusion, Jpn. J. Taste Smell Res., 5, Nippon Kagakukai Hen (2000), Aji to Nioi no Bunshi Ninshiki (in Japanese), Gakkai Syupan Senta, Tokyo, p. 52 Matsui,H., Mizota, Y., Sumi, M., Ikeda, M. and Iwatsuki, K. (2006), Sensory Characteristics of Membrane Treated- Milk, Journal of the Japanese Society for Food Science and Technology, 53, McBurney, D. H., Collings, V. B. and Glanz, L. M. (1973), Temperature Dependence of Human Taste Responses, Physiol. Behav., 11, Moskowitz, H. R. (1973), Effects of Solution Temperature on Taste Intensity in Humans, Physiol. Behav., 10, Mori, T. and Yoshida, H. (1998), Shinrigaku notameno Deta Kaiseki Tekunikalbukku (in Japanese), Kitaojisyobo, Kyoto, pp Pangborn, R. M., Chrisp, R. B. and Bertolero, L. L. (1970), Gustatory, salivary, and oral thermal responses to solutions of sodium chloride at four temperatures. Percept, Psychophysics, 8, Sakai, N. and Yamamoto, T. (2001), Effects of excitotoxic brain lesions on taste-mediated odor learning in the rat, Neurobiol. Learn. Mem., 75, (101) 43

6 J. Cookery Sci. Jpn. Vol. 47 No. 2(2014) Yamaguchi S., Yoshikawa T. and Ikeda S. (1970), Studies on the Taste of Some Sweet Substances Part II. Interrelationships among them, Agr. Biol. Chem., 34, Yamano, Y. (2003), Oishisa No Kagaku Jiten (in Japanese), Asakurasyoten, Tokyo, pp , pp Yamazaki, K., Shimada, K., Shibukawa, S. and Shimomura, M. (2003), Cookery and its Theory (in Japanese), Dobunsyoin, Tokyo, pp (Received Sep, 25, 2013 Accepted Jan, 16, 2014) 甘味感受性に及ぼす温度の影響 岡本洋子 * 吉田惠子 ** 和文抄録味の感じ方に及ぼす温度の影響を調べることを目的に, 甘味料および市販甘味飲料を用いて官能評価法によって甘味強度を測定した 甘味料として, スクロース,D-グルコース,D-フルクトース,D-マルトース, エリスリトール, キシリトール,D-ソルビトール, マルチトールの 8 種類, 市販甘味飲料としては 11 種類を用いた 実験参加者は年齢 18~20 歳の健康な女子学生 27 名である 検査の液温は,7,25 ( 基準 ),43 とした 8 種甘味料のうち D-フルクトースおよびキシリトールについては, 温度による甘味強度の変化がみられたが, それ以外の甘味料は温度による呈味性の変化はみられなかった 一方, 市販甘味飲料については,7 では 25 に比べ甘味強度が弱く,43 では 25 に比べ甘味強度が強い飲料が多かった また, 甘味料群では, 甘味強度について温度要因の統計的な主効果に有意性はなかったが, 市販甘味飲料群では, その効果に有意性がみられた 市販飲料に含まれる甘味料以外の成分について, 呈味性に及ぼす影響を検討する必要が示唆された キーワード : 甘味感受性, 官能評価, 温度, 甘味溶液, 市販甘味飲料 * 鈴峯女子短期大学 ** つくば国際大学 連絡先 鈴峯女子短期大学 広島市西区井口 4 丁目 6-18 TEL 082(278)1103 FAX 082(277) (102)