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Dunyaporn Trachootham, Shizuko Satoh-Kuriwada, Aroonwan Lam-ubol, Chadamas Promkam, Nattida Chotechuang, Takashi Sasano, Noriaki Shoji, Differences in Taste Perception and Spicy Preference: A Thai–Japanese Cross-cultural Study, Chemical Senses, Volume 43, Issue 1, January 2018, Pages 65–74, https://doi.org/10.1093/chemse/bjx071
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Abstract
Taste perception is influenced by several factors. However, the relation between taste perception and food culture is unclear. This study compared taste thresholds between populations with different food culture, i.e. Thai and Japanese. A matched case–control study was conducted in 168 adults (84 for each; aged between 50 and 90 years). The age, sex, systemic disease, medication, smoking, xerostomia, and oral hygiene of both groups were not different. Recognition thresholds (RTs) of sweet, salty, sour, bitter, and umami were measured using filter paper disc (FPD). Detection taste thresholds were measured using electrogustometry. Spicy preference was measured by calibrated questionnaires. Higher RTs of all tastes and higher detection taste thresholds were found in Thai as compared to those of Japanese (P < 0.0001). Separate analyses of healthy and unhealthy persons confirmed the significant differences between 2 countries. The average thresholds for sweet, salty, sour, and bitter in Thai and Japanese were 4 and 2, respectively. The average threshold for umami in Thai and Japanese was 5 and 3, respectively. Moreover, Thai population had stronger preference for spicy food (P < 0.0001) with 70% mild- or moderate and 10% strong lovers, compared to over 90% non- or mild-spicy lovers in Japanese. In addition, 70% of Thai consumed spicy food weekly, whilst 80% of Japanese consumed it monthly. Our findings suggested that population with stronger spicy preference such as Thai had much poorer taste sensitivity and perception than that with milder preference like Japanese. Extensive international survey is needed to conclude the influence of food culture on taste perception.
Introduction
Enjoying taste is a great pleasure for older persons; however, taste alteration is a common worldwide complaint in those people (Schiffman 1997). Deteriorated taste sensitivity does lead to poor appetite, decreased food intake, weight loss, malnutrition, and consequently poor quality of life (Murphy 2008). Furthermore, decreased taste perception can lead to unhealthy food choices (Rolls 1999; Lau 2008). For example, high threshold of salty or sweet taste increases more consumption of sodium or sugar, resulting in increased risk of heart disease, hypertension, and/or diabetes mellitus (Rolls 1999). Thus, a new strategy to improve taste threshold should have global impact on food intake, nutrition, and health for the older people.
Previous studies demonstrated that several factors can influence taste thresholds including older age (Methven et al. 2012), systemic diseases (cancer, stroke), decreased salivary flow, side effects of radiation, medications, nutritional deficiency (Yoshinaka et al. 2007; Imoscopi et al. 2012), and oral hygiene (Solemdal et al. 2012). Besides those health-related factors, dietary intake and preference may also affect taste thresholds (Duffy 2007). Interestingly, a large-scale study in European children demonstrated that country of residence with different dietary habit was the strongest factor related to preferences for sweet, salty, bitter, and umami (Ahrens 2015). Consistently, a study in various regions of Malaysia showed that habitat location influences the individual taste sensitivity and preference for sweet and sour tastes (Baharuddin and Sharifudin 2015). Both studies suggested that food culture may play a key role in food preference and taste perception. Nevertheless, it is still unclear how food culture affects taste thresholds of older persons.
Thai food culture is well-known because of its flavorfulness and spiciness. Thai cuisine involves balanced mixture of multiple tastes. It is a complex interaction of at least 3 and up to 5 taste qualities in each dish or the overall meal (Svasti 2010). A spicy Thai dish usually contains not only hot chilies but also seasonings of sweet, sour, salty, bitter, and umami. In contrast to Thai cuisine, Japanese does not like different flavored dishes touching each other on a single plate (Shimbo 2000). Therefore, each Japanese dish is served in individual plate and only one prominent taste is provided at a time. In addition, Japanese people rarely use hot chilies in their cuisine. Despites the remarkable difference between Thai and Japanese food culture, the difference in taste thresholds between these countries has yet to be conclusively reported. Our previous reports showed that filter paper disc (FPD) method can be used to measure the taste thresholds in both Japanese and Thai older persons (Satoh-Kuriwada et al. 2014; Madiloggovit et al. 2016). This background prompted us to study the difference in detection (electrogustometer) thresholds and recognition thresholds (RTs) of 5 basic tastes i.e., sweet, salty, sour, bitter, and umami, in Thai and matched Japanese older persons. Spicy preference of participants from both nations was also compared.
Materials and methods
Materials
A commercially available FPD taste kits, Taste Discs® were purchased from Sanwa Chemical. Laboratory Inc., Nagoya, Japan. The commercial FPD kit is composed of taste solutions (5 concentrations of each): sucrose, sodium chloride, tartaric acid and quinine hydrochloride for sweet, salty, sour, and bitter taste, respectively. For umami taste, 6 concentrations of monosodium glutamate (MSG) solution were prepared by dissolving MSG in distilled water and filtered through 0.2 μm pore prior to use. MSG was purchased from Ajinomoto Co, Inc., Japan. The concentrations of each taste solution as % (g/100 mL) and mM were depicted in Table 1a and b, respectively.
a) %, g/100 mL . | |||||
---|---|---|---|---|---|
Taste . | Sweet . | Salty . | Sour . | Bitter . | Umami . |
Level . | Sucrose . | Sodium chloride . | Tartaric acid . | Quinine hydrochloride . | Monosodium glutamate . |
1 | 0.3 | 0.3 | 0.02 | 0.001 | 0.0187 |
2 | 2.5 | 1.25 | 0.2 | 0.02 | 0.0935 |
3 | 10 | 5 | 2 | 0.1 | 0.187 |
4 | 20 | 10 | 4 | 0.5 | 0.935 |
5 | 80 | 20 | 8 | 4 | 1.87 |
6 | 3.74 | ||||
b) mM | |||||
Taste | Sweet | Salty | Sour | Bitter | Umami |
level | Sucrose | Sodium chloride | Tartaric acid | Quinine hydrochloride | Monosodium glutamate |
1 | 9 | 51 | 1 | 0.03 | 1 |
2 | 73 | 214 | 13 | 0.55 | 5 |
3 | 292 | 856 | 133 | 3 | 10 |
4 | 584 | 1711 | 267 | 14 | 50 |
5 | 2337 | 3422 | 533 | 111 | 100 |
6 | 200 |
a) %, g/100 mL . | |||||
---|---|---|---|---|---|
Taste . | Sweet . | Salty . | Sour . | Bitter . | Umami . |
Level . | Sucrose . | Sodium chloride . | Tartaric acid . | Quinine hydrochloride . | Monosodium glutamate . |
1 | 0.3 | 0.3 | 0.02 | 0.001 | 0.0187 |
2 | 2.5 | 1.25 | 0.2 | 0.02 | 0.0935 |
3 | 10 | 5 | 2 | 0.1 | 0.187 |
4 | 20 | 10 | 4 | 0.5 | 0.935 |
5 | 80 | 20 | 8 | 4 | 1.87 |
6 | 3.74 | ||||
b) mM | |||||
Taste | Sweet | Salty | Sour | Bitter | Umami |
level | Sucrose | Sodium chloride | Tartaric acid | Quinine hydrochloride | Monosodium glutamate |
1 | 9 | 51 | 1 | 0.03 | 1 |
2 | 73 | 214 | 13 | 0.55 | 5 |
3 | 292 | 856 | 133 | 3 | 10 |
4 | 584 | 1711 | 267 | 14 | 50 |
5 | 2337 | 3422 | 533 | 111 | 100 |
6 | 200 |
a) %, g/100 mL . | |||||
---|---|---|---|---|---|
Taste . | Sweet . | Salty . | Sour . | Bitter . | Umami . |
Level . | Sucrose . | Sodium chloride . | Tartaric acid . | Quinine hydrochloride . | Monosodium glutamate . |
1 | 0.3 | 0.3 | 0.02 | 0.001 | 0.0187 |
2 | 2.5 | 1.25 | 0.2 | 0.02 | 0.0935 |
3 | 10 | 5 | 2 | 0.1 | 0.187 |
4 | 20 | 10 | 4 | 0.5 | 0.935 |
5 | 80 | 20 | 8 | 4 | 1.87 |
6 | 3.74 | ||||
b) mM | |||||
Taste | Sweet | Salty | Sour | Bitter | Umami |
level | Sucrose | Sodium chloride | Tartaric acid | Quinine hydrochloride | Monosodium glutamate |
1 | 9 | 51 | 1 | 0.03 | 1 |
2 | 73 | 214 | 13 | 0.55 | 5 |
3 | 292 | 856 | 133 | 3 | 10 |
4 | 584 | 1711 | 267 | 14 | 50 |
5 | 2337 | 3422 | 533 | 111 | 100 |
6 | 200 |
a) %, g/100 mL . | |||||
---|---|---|---|---|---|
Taste . | Sweet . | Salty . | Sour . | Bitter . | Umami . |
Level . | Sucrose . | Sodium chloride . | Tartaric acid . | Quinine hydrochloride . | Monosodium glutamate . |
1 | 0.3 | 0.3 | 0.02 | 0.001 | 0.0187 |
2 | 2.5 | 1.25 | 0.2 | 0.02 | 0.0935 |
3 | 10 | 5 | 2 | 0.1 | 0.187 |
4 | 20 | 10 | 4 | 0.5 | 0.935 |
5 | 80 | 20 | 8 | 4 | 1.87 |
6 | 3.74 | ||||
b) mM | |||||
Taste | Sweet | Salty | Sour | Bitter | Umami |
level | Sucrose | Sodium chloride | Tartaric acid | Quinine hydrochloride | Monosodium glutamate |
1 | 9 | 51 | 1 | 0.03 | 1 |
2 | 73 | 214 | 13 | 0.55 | 5 |
3 | 292 | 856 | 133 | 3 | 10 |
4 | 584 | 1711 | 267 | 14 | 50 |
5 | 2337 | 3422 | 533 | 111 | 100 |
6 | 200 |
Participants
Thai participants were recruited from the dental clinic of Maha Chakri Sirindhorn Dental Hospital, Mahidol University. Japanese participants were recruited from the dental clinic of Tohoku University Hospital. Prior to the recruitment, all the participants were screened based on the following inclusion criteria: being 50–90 years old; born and resided either in Thailand or Japan for at least 5 continuous years; having no history of systemic diseases or having well-controlled systemic diseases. Exclusion criteria were as follows: having tongue cancer or history of tongue surgery; complete loss of all taste sensation; being critically ill or unconscious; disability to communicate; intolerance with FPD or electrogustometer test. All the participants signed their written informed consent prior to data collection. Their identities have been protected, following International Conference on Harmonization-Good Clinical Practice (ICH-GCP). In this study, we defined the participants aged 50 years old or above as older persons, according to a World Health Organization’s statement (WHO 2002).
Sample size calculation
Sample size was calculated based on the ability to match participants in both groups. First, we enroll a small number of participants from each country. Thereafter, we calculated sample size required to match those parameters of age, sex, smoking, systemic disease, dry mouth, and oral hygiene. Final data from 84 participants in each group were matched. Post hoc power of this sample was calculated using G Power 3.1. Post-hoc power of 0.99 was achieved for Mann–Whitney test to compare taste threshold data of both groups at 5% significance level.
Study procedures
This study was approved by Mahidol University Central Institutional Review Board (MU-CIRB) with the approval number 2015/040.2703 and the institutional ethic committee for research in human of Tohoku University Hospital with approval number 2016-3-7. The study was performed according to Declaration of Helsinki.
This was a cross-sectional study. The data were collected in parallel in both Thailand and Japan. At the beginning, all the participants who passed the inclusion criteria and signed the written informed consent were interviewed for spicy food preference. Then, they received history taking and oral examination for oral hygiene and signs of dry mouth. Finally, a trained dentist measured the RTs using FPD method and detection thresholds using electrogustometry.
Outcome
The primary outcome was spicy food preference and the RTs of sweet, salty, sour, bitter, and umami tastes. The secondary outcome was detection taste thresholds.
Spicy preference
Participants from both countries were interviewed for their spicy preference by scoring the degree of spiciness they prefer (non-, mild, moderate, strong lover of spicy). Scoring of both countries was calibrated by comparing the degree of spiciness in a curry prepared at similar restaurant branches located in Japan and Thailand (CoCoichibanya 2016). The selection of curry as a calibrated menu was based on the fact that curry is the most common spicy food in Japan. Frequency of spicy food intake (weekly or monthly) by each participant was also interviewed.
Taste sensitivity and perception
Taste thresholds can be divided into detection thresholds and RTs. Detection (sensitivity) taste thresholds are the minimum level of taste substances which can stimulate the taste receptors to convert and transmit the signals to higher centers. Recognition taste thresholds are the minimum level of taste substances which can be perceived and recognized the identity by the brain (Adams and Taylor 2012). In this study, we measured taste perception using FPD as RTs of sweet, salty, sour, bitter, and umami, and measured taste sensitivity using electrogustometry as detection threshold. While higher recognition taste threshold suggests poorer taste perception, higher detection threshold suggest poorer taste sensitivity.
RT of each taste determined by FPD
The threshold of each taste was measured by Taste Discs®. Briefly, sucrose, sodium chloride, tartaric acid and quinine hydrochloride were used as tastant (taste solution) for sweet, salty, sour, and bitter taste, respectively (Berling et al. 2011). For umami tastant, MSG was used as a newly developed FPD method, as reported recently (Satoh-Kuriwada et al. 2014). The round FPD (0.5 cm in diameter) soaked in each taste solution was placed for 3 s on the special area of the tongue innervated by different taste nerve fibers, i.e. right anterior (near the tongue tip) or left posterior (near the circumvallate papillae) parts. Then, the paper disc was removed and subjects were asked to swallow their saliva once to distribute the taste substance. Finally, the subjects answered whether they had felt any taste and the name of taste (taste quality). The RT was identified as the lowest level which the subjects could correctly recognize the taste quality. This threshold reflects ability of the brain to perceive and interpret the taste (Wise and Breslin 2013). The procedure of the RT measurement was started from the lowest concentration of each taste to the higher levels of concentration (level 1–5 for sweet, salty, sour, and bitter taste and level 1–6 for umami: Table 1) until the thresholds were identified. To avoid interference between tastes, the subjects rinsed their mouth with water several times until no previous taste remained. The order of the taste test was random except for bitter taste which was performed in the end to avoid unpleasantness. In this study, we used 2-point stimulation (right anterior and left posterior tongue) except soft palate, because the older persons could not tolerate soft palate stimulation although they could tolerate anterior and posterior tongue stimulation (Madiloggovit et al. 2016). The total time of test in each subject for the 5 basic tastes was approximately 8 min.
Detection threshold determined by electrogustometry
Electrogustrometry was performed as described (Grant et al. 1987; Tomita and Ikeda 2002) using commercially available equipment (TR-06®, Rion Co., Ltd). In brief, a cathode cuff was wrapped around the wrist of the participant and an anode rod was placed on the right anterior or left posterior side of the tongue (same area as in FPD method). The electrical stimuli were pulse from the lowest power (−6 dB) and gradually increased. The smallest stimulus that the subjects noticed was regarded as the detection threshold (Stillman et al. 2000). The highest limit of the stimuli was 34 dB. The test was performed by the same person throughout the study.
Statistical analysis
Sample size and power were calculated by G Power 3.1. Data from 168 participants yield post hoc power of 0.99 for Mann–Whitney test. Graphing and statistical analysis were performed by GraphPad Prism 7.0. The following statistical tests were used to compare characteristics between groups; Mann–Whitney test for age; Chi-square test for systemic disease and medication; Fisher’s exact test for sex, smoking, oral hygiene, and xerostomia. Two-way ANOVA was used to compare or RTs of each taste between Thai and Japanese. Mann–Whitney test was used to compare electrogustometer thresholds between groups. All tests were performed with 2-tailed, α = 0.05. P-value < 0.05 was considered statistically significant.
Results
Matched characteristics between Thai and Japanese older persons
In order to compare the taste data from both groups, we matched the data of all factors including the age, sex, systemic disease, medication, smoking, xerostomia, and oral hygiene. As shown in Table 2, there were no significant differences noted in those factors between Thai and Japanese groups. The mean age of both countries was similar (67.8 ± 6.1 in Thai and 69.4 ± 10.5 in Japan). Most participants from both countries were female, having controlled systemic diseases (metabolic syndrome) and poly-medications, non-smokers, having no symptoms of dry mouth, and having good or fair oral hygiene.
Characteristics . | Thai group (n = 84) . | Japanese group (n = 84) . | P-value . | |
---|---|---|---|---|
Age | Range | 59–83 | 50–85 | |
Mean ± SD | 67.82 ± 6.14 | 69.39 ± 10.46 | 0.164a | |
N (%) | N (%) | |||
Sex | Female | 62 (74) | 63 (75) | >0.99b |
Male | 22 (26) | 21 (25) | ||
History of systemic diseases | No diseases | 22 (26) | 16 (19) | 0.187c |
Metabolic syndrome (HT, DLP, DM, CVD, kidney) | 50 (60) | 61 (73) | ||
Other diseases (bone, GI, neurological) | 12 (14) | 7 (8) | ||
Medication | None | 20 (24) | 19 (23) | 0.797c |
Single medication | 19 (22) | 16 (19) | ||
Poly medications | 45 (54) | 49 (58) | ||
Smoking | No smoking | 75 (89) | 73 (87) | 0.812b |
Smoking | 9 (11) | 11 (13) | ||
Symptoms of xerostomia | No symptoms of dry mouth | 54 (64) | 50 (60) | 0.634b |
Having symptoms of dry mouth | 30 (36) | 34 (40) | ||
Oral hygiene | Good or fair | 67 (80) | 67 (80) | >0.99b |
Poor | 17 (20) | 17 (20) |
Characteristics . | Thai group (n = 84) . | Japanese group (n = 84) . | P-value . | |
---|---|---|---|---|
Age | Range | 59–83 | 50–85 | |
Mean ± SD | 67.82 ± 6.14 | 69.39 ± 10.46 | 0.164a | |
N (%) | N (%) | |||
Sex | Female | 62 (74) | 63 (75) | >0.99b |
Male | 22 (26) | 21 (25) | ||
History of systemic diseases | No diseases | 22 (26) | 16 (19) | 0.187c |
Metabolic syndrome (HT, DLP, DM, CVD, kidney) | 50 (60) | 61 (73) | ||
Other diseases (bone, GI, neurological) | 12 (14) | 7 (8) | ||
Medication | None | 20 (24) | 19 (23) | 0.797c |
Single medication | 19 (22) | 16 (19) | ||
Poly medications | 45 (54) | 49 (58) | ||
Smoking | No smoking | 75 (89) | 73 (87) | 0.812b |
Smoking | 9 (11) | 11 (13) | ||
Symptoms of xerostomia | No symptoms of dry mouth | 54 (64) | 50 (60) | 0.634b |
Having symptoms of dry mouth | 30 (36) | 34 (40) | ||
Oral hygiene | Good or fair | 67 (80) | 67 (80) | >0.99b |
Poor | 17 (20) | 17 (20) |
CVD, cardiovascular disease; DLP, dyslipidemia; DM, diabetes mellitus; GI, gastrointestinal; HT, hypertension.
P-value from aMann–Whitney test, bFisher’s exact test, cChi-square test.
Characteristics . | Thai group (n = 84) . | Japanese group (n = 84) . | P-value . | |
---|---|---|---|---|
Age | Range | 59–83 | 50–85 | |
Mean ± SD | 67.82 ± 6.14 | 69.39 ± 10.46 | 0.164a | |
N (%) | N (%) | |||
Sex | Female | 62 (74) | 63 (75) | >0.99b |
Male | 22 (26) | 21 (25) | ||
History of systemic diseases | No diseases | 22 (26) | 16 (19) | 0.187c |
Metabolic syndrome (HT, DLP, DM, CVD, kidney) | 50 (60) | 61 (73) | ||
Other diseases (bone, GI, neurological) | 12 (14) | 7 (8) | ||
Medication | None | 20 (24) | 19 (23) | 0.797c |
Single medication | 19 (22) | 16 (19) | ||
Poly medications | 45 (54) | 49 (58) | ||
Smoking | No smoking | 75 (89) | 73 (87) | 0.812b |
Smoking | 9 (11) | 11 (13) | ||
Symptoms of xerostomia | No symptoms of dry mouth | 54 (64) | 50 (60) | 0.634b |
Having symptoms of dry mouth | 30 (36) | 34 (40) | ||
Oral hygiene | Good or fair | 67 (80) | 67 (80) | >0.99b |
Poor | 17 (20) | 17 (20) |
Characteristics . | Thai group (n = 84) . | Japanese group (n = 84) . | P-value . | |
---|---|---|---|---|
Age | Range | 59–83 | 50–85 | |
Mean ± SD | 67.82 ± 6.14 | 69.39 ± 10.46 | 0.164a | |
N (%) | N (%) | |||
Sex | Female | 62 (74) | 63 (75) | >0.99b |
Male | 22 (26) | 21 (25) | ||
History of systemic diseases | No diseases | 22 (26) | 16 (19) | 0.187c |
Metabolic syndrome (HT, DLP, DM, CVD, kidney) | 50 (60) | 61 (73) | ||
Other diseases (bone, GI, neurological) | 12 (14) | 7 (8) | ||
Medication | None | 20 (24) | 19 (23) | 0.797c |
Single medication | 19 (22) | 16 (19) | ||
Poly medications | 45 (54) | 49 (58) | ||
Smoking | No smoking | 75 (89) | 73 (87) | 0.812b |
Smoking | 9 (11) | 11 (13) | ||
Symptoms of xerostomia | No symptoms of dry mouth | 54 (64) | 50 (60) | 0.634b |
Having symptoms of dry mouth | 30 (36) | 34 (40) | ||
Oral hygiene | Good or fair | 67 (80) | 67 (80) | >0.99b |
Poor | 17 (20) | 17 (20) |
CVD, cardiovascular disease; DLP, dyslipidemia; DM, diabetes mellitus; GI, gastrointestinal; HT, hypertension.
P-value from aMann–Whitney test, bFisher’s exact test, cChi-square test.
Spicy preference
As shown in Figure 1a, almost 60% of Japanese were non-spicy lovers, whilst 70% of Thai older persons were mild or moderate lovers for spicy foods. The distribution of the spicy preference between Thai and Japanese was statistically significant (P < 0.001). Interestingly, 10% of Thai older persons were strong spicy lovers, whilst no Japanese had strong spicy preference. Figure 2a demonstrated that 85% of Japanese older persons eat spicy food only once a month. In contrast, 70% of Thai older persons eat spicy food once a week. This difference was statistically significant (P < 0.001). As shown in Figures 1b,c and 2b,c, separate analyses for healthy and unhealthy participants consistently showed significant difference toward stronger preference on spicy food and higher frequency of spicy consumption in Thai than those of Japanese adults.
RTs of each taste determined by FPD
Figures 3a and 4a showed each taste threshold of the Thai and Japanese subjects at anterior tongue and posterior tongue, respectively. The mean RTs (RTs) for sweet, salty, sour, and bitter in Thai were 3–4 whilst that of Japanese was around 2, except umami because the setting of the RT point was different from other 4 taste (see Materials and Methods). The mean RTs for umami in Thai and Japanese were 5 and 3, respectively. As shown, the results were consistent in both test area of the anterior and the posterior tongue. Consequently, the RTs in Thai were statistically higher than those of Japanese older persons for all the 5 basic tastes (P < 0.0001). As shown in Figures 3b,c and 4b,c, separate analyses for healthy and unhealthy participants consistently showed significantly higher thresholds of all taste at anterior and posterior tongue in Thai than those of Japanese adults.
Table 3 shows the number of subjects with thresholds beyond the highest concentration of all the 5 tastes. As shown, there were some Thai with thresholds beyond the highest concentration of the FPD kit, whereas Japanese could recognize all of the tastes within the set concentration. In particularly on umami taste, over 20% of Thai participants recognized no umami sensation even after stimulated with the highest concentration of MSG (level 6). Besides umami taste, some Thai older persons could not recognize sweet, salty, and sour tastes either, even at the highest concentration of each taste substance. Sixty percent of the participants with excessive thresholds were moderate to strong spicy lovers and 70% had weekly consumption of spicy food.
Area of taste stimulation . | Taste . | Thai . | Japan . |
---|---|---|---|
Number (% total) . | Number (% total) . | ||
Anterior tongue | Sweet | 2 (2.4) | 0 (0) |
Salty | 6 (7.1) | 0 (0) | |
Sour | 13 (15.5) | 0 (0) | |
Umami | 21 (25) | 0 (0) | |
Bitter | 5 (6) | 0 (0) | |
Posterior tongue | Sweet | 10 (11.9) | 0 (0) |
Salty | 10 (11.9) | 0 (0) | |
Sour | 11 (13.1) | 0 (0) | |
Umami | 18 (21.4) | 0 (0) | |
Bitter | 1 (1.2) | 0 (0) |
Area of taste stimulation . | Taste . | Thai . | Japan . |
---|---|---|---|
Number (% total) . | Number (% total) . | ||
Anterior tongue | Sweet | 2 (2.4) | 0 (0) |
Salty | 6 (7.1) | 0 (0) | |
Sour | 13 (15.5) | 0 (0) | |
Umami | 21 (25) | 0 (0) | |
Bitter | 5 (6) | 0 (0) | |
Posterior tongue | Sweet | 10 (11.9) | 0 (0) |
Salty | 10 (11.9) | 0 (0) | |
Sour | 11 (13.1) | 0 (0) | |
Umami | 18 (21.4) | 0 (0) | |
Bitter | 1 (1.2) | 0 (0) |
Area of taste stimulation . | Taste . | Thai . | Japan . |
---|---|---|---|
Number (% total) . | Number (% total) . | ||
Anterior tongue | Sweet | 2 (2.4) | 0 (0) |
Salty | 6 (7.1) | 0 (0) | |
Sour | 13 (15.5) | 0 (0) | |
Umami | 21 (25) | 0 (0) | |
Bitter | 5 (6) | 0 (0) | |
Posterior tongue | Sweet | 10 (11.9) | 0 (0) |
Salty | 10 (11.9) | 0 (0) | |
Sour | 11 (13.1) | 0 (0) | |
Umami | 18 (21.4) | 0 (0) | |
Bitter | 1 (1.2) | 0 (0) |
Area of taste stimulation . | Taste . | Thai . | Japan . |
---|---|---|---|
Number (% total) . | Number (% total) . | ||
Anterior tongue | Sweet | 2 (2.4) | 0 (0) |
Salty | 6 (7.1) | 0 (0) | |
Sour | 13 (15.5) | 0 (0) | |
Umami | 21 (25) | 0 (0) | |
Bitter | 5 (6) | 0 (0) | |
Posterior tongue | Sweet | 10 (11.9) | 0 (0) |
Salty | 10 (11.9) | 0 (0) | |
Sour | 11 (13.1) | 0 (0) | |
Umami | 18 (21.4) | 0 (0) | |
Bitter | 1 (1.2) | 0 (0) |
Detection (electrogustometer) thresholds of each taste determined by electrogustometry
Figures 5a and 6a showed taste threshold of the Thai and Japanese subjects at anterior tongue and posterior tongue, respectively. The mean electrogustometer thresholds of anterior tongue in Thai were about 24 whilst that of Japanese was around 2. The mean electrogustometer thresholds of posterior tongue in Thai were about 26 whilst that of Japanese was around 7. Consequently, the thresholds in Thai were statistically higher than those of Japanese older persons (P < 0.0001). As shown in Figures 5b,c and 6b,c, separate analyses for healthy and unhealthy participants consistently showed significantly higher thresholds at anterior and posterior tongue in Thai than those of Japanese adults (P < 0.0001). Consistent with the data determined by FPD method, 15% of Thai participants had thresholds beyond the highest level of electrogustometer, whereas Japanese thresholds were all within the machine’s limit.
Discussion
Food culture may have impact on food preference, which could affect the taste perception (Krueger et al. 2006; Ahren 2015). Nevertheless, how food culture influences the taste sensitivity of the older persons has yet to be known whereas the taste sensation is well known to be important for overall health particularly for the aged people (Sasano et al. 2015). The relation between taste perception and food culture will become clearer once we understand how different cultural cuisine affects ability to recognize taste. Such research insight could be achieved only when we ruled out other contributing factors. In this study, we compared the taste thresholds between populations with distinctive food culture; i.e. Thai and Japanese. To rule out the influence from other factors, we obtained data from participants with matched age, sex, systemic diseases, oral hygiene and smoking. Therefore, any differences in taste thresholds among 2 countries are likely to result from cultural or ethnical difference. Here we investigated the difference in RTs of 5 basic tastes i.e., sweet, salty, sour, bitter, and umami measured by FPD and detection thresholds measured by electrogustometry, in Thai and matched Japanese older adults with different food culture. Our current study demonstrated that Thai older persons have higher detection thresholds and higher recognition taste thresholds of the all 5 basic tastes, i.e. umami, sweet, sour, salty, and bitter than those of Japanese older persons. The data suggests that Thai population had much poorer taste sensitivity and perception than Japanese. Since all characters relevant to taste perception (age, sex, systemic disease, medication, smoking, xerostomia, and oral hygiene) have been matched between groups, the striking difference in taste perception likely resulted from different food culture; i.e. stronger spicy preference in Thai, as evidenced by higher preference and more frequent consumption of spicy food.
Our result also showed the difference of spicy preference between Thai and Japanese older person as demonstrated that Thai people showed much more spicy preference and spicy food consumption than Japanese. Considering the distinct food preference in Thai and Japanese people, spicy food is robust in Thai cuisine while it is rare in Japanese cuisine (Svasti 2010; Shimbo 2000). The preference in spicy food of Thai people might be associated with hotter climates in Thailand, in comparison with Japan. Some scientists suggested a link between a nation’s ambient temperature and the spiciness of its foods (Thornton 2016). Several reasons were proposed including stimulation of perspiration and cooling down of body temperature, bacteria killing and protection from food poisoning (Thornton 2016). On the other hand, previous studies showed no significant differences in taste sensitivity and hedonic response for sweet, salty, sour, and bitter between Japanese and Australian adults (Prescott et al. 1992; Laing et al. 1993) suggesting that the result means a similar food culture between Japanese and Australian people who are not familiar with spicy foods.
Previous in vitro study showed that capsaicin in chili pepper may affect threshold of sweet, bitter and sour taste receptors (Moon et al. 2010; Ishii et al. 2012). However, no clinical/population studies had performed to determine the association between spicy food consumption and taste thresholds in human. The finding from this clinical study suggested a link between stronger preference on spicy food and higher thresholds of all tastes. There are 2 possible explanations for the finding, i.e. 1) direct effect of spice on sensitivity of taste receptors, 2) indirect effect from high amount of seasoning use in spicy food.
For the first hypothesis, spicy preference may lead to increase frequency of spice consumption. And consumption of spicy food since juvenile period may directly modulate the sensitivity of other tastes and result in high taste thresholds in older adults. In fact, previous in vitro studies suggest a direct interaction between capsaicin and taste receptors (Moon et al. 2010; Ishii et al. 2012). And spicy preference or liking of spicy food was shown to be strongly associated with frequency of chili consumption (Byrnes and Hayes 2013). Consistently, our study observed higher spicy preference along with more frequent consumption of spicy food in Thai adults, compared to that of Japanese adults. However, the study by Byrnes and Hayes found no associations between frequency of chili consumption and the spicy thresholds for burn/sting perception of sampled capsaicin. The study suggests that spicy thresholds may not necessarily be associated with spicy preference. Since the study was conducted in American, population with non-spicy cuisine, future studies to investigate the correlation between spicy food consumption, spicy thresholds and spicy preference in Thai population may be worthwhile.
For the second hypothesis, spicy Thai food usually comes with high amount of seasonings, i.e. fish sauce, sugar, lime juice, and aromatic herbs (lemon grass, kaffir lime leaf, basil) (Seubsman et al. 2009; Svasti 2010). Those seasonings contain taste substances for salty, umami, sweet, sour, and bitter, respectively (Chotechuang 2012). Therefore, people who usually eat more spicy food likely consume those taste substances in higher amount. Since Thai people get accustomed to spicy food since childhood, routine (weekly) consumption of spicy food for several decades may eventually increase taste thresholds of all tastes in Thai people till they became older persons. In fact, a recent study showed that preference for spicy foods was more predicted by past experience of consuming spicy food, rather than physiological or personality differences (Ludy and Mattes 2012). The study also found that regular spicy food lovers admitted the consumption of spicy foods since childhood and rated spicy foods as more palatable (Ludy and Mattes 2012). Thus, adaptation to the food resources may develop a unique flavor principle (Rozin 1976). Future cohort studies monitoring taste thresholds and spicy food consumption of Thai people from childhood to adulthood is warranted to confirm the latter hypothesis. Furthermore, cross-sectional studies comparing thresholds between several age groups of Thai people with matched culture may be worthwhile to elucidate whether high thresholds in Thai elderly was due to aging or dietary behavior.
This research is a cross-national study. Besides spicy preference, some genetic variations in different ethnic backgrounds may also influence the taste thresholds (Kim et al. 2006). Polymorphisms of bitter taste receptors such as TAS2R38 were shown to affect differential taste perception. Interestingly, a recent global genomic study found that the proportion of “taster” PAV (Proline, Alanine, Valine) and “non-taster” AVI (Alanine, Valine, Isoleucine) haplotypes for the bitter receptor TAS2R38 in Japanese and Thai populations were relatively similar, i.e. more taster than non-taster variants (Risso et al. 2016). Polymorphism of TAS1R3 was found at highest frequencies in East Asian populations (including Japan), compared to other ethnic population and associated with the degree of sweet taste perception (Fushan et al. 2009). However, such polymorphism in Thai population has not been studied. Future researches for comparing genetic variations in taste receptors between Thai and Japanese are required to elucidate if the observed difference in taste thresholds was due to spicy food preference or genetic background. It is also possible that both genetic and environmental factors are involved.
It is worth noting that there are some limitations in this study. Regarding spicy preference, questionnaire survey is simple and non-invasive but somewhat subjective. Future studies should include more objective measurements such as dietary record of spice consumption and spice thresholds using stepwise concentration of capsaicin sample.
Japanese cuisine is well-known for one flavor per dish concept (Shimbo 2000). Furthermore, common Japanese dishes contain natural umami from combu seaweed and katsuo fish flake (Shimbo 2000). Umami taste usually stimulates appetite. Therefore, Japanese dishes generally needs very small amount of seasonings. In contrast, the signature of Thai cuisine is the complex balance between 3 and 5 taste qualities in each dish (Svasti 2010). Common Thai dishes such as Tom-yam soup and spicy papaya salad usually contains high amount of seasonings including sugar, fish sauce, lime juice, and MSG. A previous study showed that median intake of MSG in rural Thai population was 3.6 g/day (Insawang et al. 2012). In contrast, the estimated average MSG intake in the 1990s of Japanese was 1.2–1.7 g/day (Beyreuther et al. 2007). The higher intake of MSG in Thai population may be responsible for the higher umami thresholds in Thai, compared to that of Japanese. Although the role of MSG as risk factors of chronic diseases is inconclusive, a recent longitudinal study found association between MSG consumption and overweight development in Chinese people (He et al. 2011). Future studies regarding MSG intake in correlation with taste threshold will be beneficial.
Funding
This work was supported by Grants-in-Aid for Exploratory Research (grant numbers # 25305039) from the Japan Society for the Promotion of Science (JSPS).
Conflicts of interest
All authors have no conflicts of interest.
Acknowledgements
The authors are thankful to all subjects. Ms. Pakkaorn Tiabrat and Ms. Pisamai Ting for research assistance; Dr. Mehraj Ahmad, an English native speaker for professional editing of the manuscript; dental staffs of Maha Chakri Sirindhorn Dental Hospital and Tohoku University Hospital for facilitating data collection.