Increased acids with Susan
taste thresholds age1’2
S. Schffman,
Ph.D.,
Karen
were
were
extensive,
thresholds taste and Amino lowest
the
detection
elderly
were
2’4 times
higher
found. sweet
acids
of
Amino tastes
found amino
sulfur, Am.
Nutr.
as those 32:
Detection thresholds for two groups of subjects, young and elderly, were found. The young subjects were college student volunteers ranging in age from 17 to 27 years (mean 20.8). The elderly subjects were residents of the Methodist Retirement Home in Durham, NC., and ranged in age from 75 to 87 years (mean 78.4). The elderly subjects were healthy volunteers from a group preselected for their excellent medical status by the nursing staff of the retirement home. The young group consisted of 49% males and 51% females. The elderly group consisted of 17% males and 83% females. The sex ratios used are representative of the sex distributions for healthy persons without serious diseases for the two age
The American
elderly women included insure that any changes due to normal aging and shown in the “Results”
Journal
of Clinical
Downloaded from https://academic.oup.com/ajcn/article-abstract/32/8/1622/4692317 by Boston University user on 09 July 2018
and
Nutrition
with
those
tended
acidic
1622-1627,
of the
and
or basic
the
average,
between
the
suprathreshold
containing
to have
thresholds
On
Relationships
structures,
chains
monohydrochloride
ranges
sensitivity.
subjects.
chemical
four the
diminished
in young
side
and
Although
concentrations
Subjects
1622
their
aliphatic
Amino acids such as lysine, threonine, and methionine, as well as their derivatives, have been added to foods to improve the quality of protein as well as to improve the flavor (1-9). Amino acids have also been used to create diets for allergic patients (10). Most amino acids have taste qualities (1 1, 12) which could modify the flavor of foods depending on the concentrations at which they are added. The purpose of this study was to determine the taste detection thresholds for amino acids in two populations, young and elderly. Detection thresholds for some amino acids have been reported by Yoshida et al. (13), but age effects and range over individuals were not determined. Most taste studies indicate that there is a decrease in taste sensitivity with advancing age (14-24).
groups. The high percentage of in this study was necessary to found in taste thresholds were not disease state. (It will be
acids
subjects.
than
acids,
as well
J. Clin.
19 L-amino
significantly
elderly
with
Reilly
elderly
to have
in the
acids
for
and
at suprathreshold
containing
thresholds.
Debra
thresholds
for young
thresholds
were
having
and
detection
determined
were
qualities
Hornack,
Taste
ABSTRACT derivatives
of amino
the
groups,
taste
hydroxyl highest tended
groups thresholds.
to have
the
1979.
section hat no significant differences for taste thresholds were found to exist between males and females for either age group.) The two groups were approximately equal with regard to socioeconomic status and intelligence as determined from unpublished data gathered by the Center for the Study of Aging and Human Development at Duke Medical Center. Threshold measurements for each stimulus were determined for a minimum of 10 and a maximum of 15 individuals. All subjects were nonsmokers and were tested at least I hr after eating. None of the subjects wore dentures. The participants varied over stimuli, i.e., subjects were different for each of the amino acids.
Stimuli The stimuli hydrochloride HC1, L-histidine deionized water. cluded 16 serial other by a factor for amino acids been reported increased by a value and eight
were 19 L-amino acids and four monoderivatives: L-arginine HC1, L-cysteine HC1, and L-lysine HCI, dissolved in The initial concentration ranges indilutions which differed from one anof 2. The initial stimulus range chosen for which thresholds have previously (13) included eight concentrations that factor of 2 above the reported threshold concentrations that decreased by a factor
of 2 below the reported threshold value. The initial stimulus range for those amino acids for which thresholds have not been reported were determined by pretesting and included a maximum of 16 serial dilutions that differed by a factor of 2. In practice, it was found that From the Department of Psychiatry, Duke Center, Durham, North Carolina 27710. 2 Supported in part by Grant NIA-AG00443
and Grant
NSF-GB33464 3Ajinomoto Co., Ltd. anese Patent 40 26 1/70. Lilly and Co. 851. Matsuda, M. Patent 20 382/72.
Artificial
Medical to S.S.S.
to Dr. R. P. Erickson. Cake flour improvement. sweeteners.
British
JapPatent
269
32: AUGUST
Coffee
flavor
improvement.
1979, pp. 1622-1627.
Printed
Japanese
in U.S.A.
1
INCREASED eight
to
12 dilutions
that
varied
TASTE by
THRESHOLDS
a factor
of
2 ade-
quately covered the threshold ranges for each of the amino acids. Concentrations intermediate between two successive dilutions were included for some stimuli: Lalanine, L-argrnine HC1, L-asparagine, L-cysteine, L-cysteine HC1, L-glUtamic acid, L-histidtne HCI, L-leucine, L-lysine, L-methionine, L-phenylalanine, and L-threonine to further refine threshold determination. The amino acid solutions, prepared before testing, were presented to the subjects in S-ounce plastic cups at room temperature (72 F). Nineteen of the 23 stimuli were obtained from K and K (ICN Pharmaceutical, Inc., Plainview, N.Y.). L-lysifle HC1, L-phenylalanine, and L-serine were obtained from Sigma Chemical Co., St. Louis, Mo., and L-prohne was obtained from P-L Biochemicals, Inc., Milwaukee, Wis.
Procedure Thresholds for a given amino acid were determined as follows. Trials began with the weakest concentration and proceeded to progressively stronger concentrations. At each trial, subjects, seated at individual or partitioned tables, were presented with a tray on which three unmarked cups were placed. One cup contained an amino acid (or monohydrochloride derivative) dissolved in deionized water, the other two cups contained only deionized water. The cup position on the tray was randomized over trials; the randomness of the cup position was generated by the experimenters. The subjects, wearing noseplugs to reduce olfactory input, tasted approximately 10 ml from each of the three cups, letting the liquid swirl around in their mouths for approximately 4 sec. The liquid was ejected into a separate cup used as a spittoon. Subjects rinsed their mouths with deionized water before tasting the liquid in each cup. An interval of approximately 10 sec took place between sampling from successive cups. After tasting the liquid in each of the three cups, the subjects noted on a score sheet which cup, in their opinion, contained the amino acid solution. lf they were unable to determine which cup contained the amino acid, they were instructed to make a guess (forced choice procedure). Only one trial was given at each concentration level as the trials proceeded from weaker to increasingly stronger concentrations. A taste threshold for a given stimulus was considered to be established when a subject correctly distinguished the amino acid solution from the deionized water on three consecutive trials (i.e., at three consecutive increasing concentrations). The most dilute amino acid concentration that was correctly identified on these three consecutive trials was taken as the taste threshold for an individual subject. An interval of 3 mm was allowed between trials (i.e., each set of triads) to minimize the possibility of adaptation. Testing took place between 9:30 AM and 5:00 PM, excluding the 12:00 noon to 2:00 PM interval. Subjects were asked to abstain from eating and drinking for 1 hr before testing.
Results An examination of the thresholds for individual amino acids revealed that they were not normally distributed. For this reason, the
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OF
AMINO
ACIDS
WITH
AGE
1623
individual thresholds were converted to log units and a geometric mean and SD for young and elderly groups were computed for each amino acid. The geometric means for the amino acids for the young and elderly groups expressed in terms of molarity are given in columns 1 and 2 of Table 1. The ratio of the threshold in molarity for elderly subjects compared with young subjects for each amino acid is given in column 3. The ranges of thresholds in terms of molarity for young and elderly subjects are given in columns 4 and 5. The geometric means and standard deviations in log units from which columns 1 and 2 were determined are shown in columns 6 and 7 in Table 1. Mann-Whitney U tests (25) were used to determine whether the thresholds for the young and elderly populations differed significantly. If the difference was significant, this was indicated in column 8. Mann-Whitney U tests were used because multivariate models were considered mappropriate since subject participation varied over stimuli and because threshold distributions were not normal. Yoshida’s threshold values (13) are reported in column 9 as well. Twenty of the 23 mean thresholds given in columns 1 and 2 in Table 1 were lower for young subjects when compared with elderly subjects. The average ratio given in column 3 for the thresholds for elderly subjects cornpared with thresholds for young subjects is 2.49. Eleven of the amino acid thresholds differed significantly for the young and elderly groups as determined by Mann-Whitney U tests. A Poisson distribution (27, 28) was used to determine the probability of fmding statistical significance at the 0.05 level for 11 or more of the amino acids: P
=
I
k’x k-.0
where: N = total number of amino acids (i.e., 23); p, = probability level (i.e., 0.05); and k = 10 or the number of thresholds minus I found to be statistically significant. The results indicate that the decreased sensitivity in the elderly was extremely significant, P =
0.0000000041. No significant ues were found for either young ber of times the (and below) the
differences in threshold valbetween males and females or elderly subjects. The numthreshold values fell above mean for males and females
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INCREASED
TASTE
THRESHOLDS
OF
was examined for both the young and elderly groups. x2 values of 1.28 (df= 1) and 0.32 (df = 1) for the young and elderly groups, respectively, indicated that no significant sex differences in taste thresholds were found here for amino acids. The threshold values for the young subjects were arranged in descending order from highest (i.e., glycine) to lowest (i.e., cysteine HC1). The rank order of the threshold values for young subjects was very similar to that for elderly subjects (Spearman’s p = 0.97). Because the rank order of the thresholds was so similar for the two groups, the threshold values were related to chemical structure, taste quality, and solubility for the young subjects only. In column 1 of Table 2, the threshold values for young subjects are arranged in descending order, i.e., from highest to lowest. The chemical classification is given in column 2. The taste quality for each amino acid, as described by Schiffman and Dackis (11) and TABLE
AMINO
ACIDS
WITH
1625
AGE
Schiffman and Engeihard (12), is shown in column 3. Tanford’s (26) free energy per side chain in cal./mole for amino acids, which is related to solubility, is given in column 4. No relationship between the level ofthe detection threshold (i.e., whether it was high or low), chemical structure, taste quality, or solubility was found to be related to whether or not there was a significant difference between the young or elderly groups. Discussion The highly significant increase in detection thresholds for amino acids with age found in this experiment is consistent with increased taste thresholds found in other studies (14.24). The threshold values obtained here are also consistent with those reported by Yoshida et al. (13). The values of Yoshida et al. fell within the threshold ranges for either young or elderly subjects.
2
Glycmne0 L-threoflifle
lb II
L-serine L-alanine
II
L-proline
VII
L-glutamine
IV
L-isoleucine L-phenylalanine L-leucine L-valifle
VI
L-methionine
Ill
L-tryptophan L-asparagine L-histidine L-arginine HCI L-argiflifle L-lysifle L-lysine HCI L-aSpartic acid L-histidine HCI L-glutamic acid
VI IV V V V V V IV V IV
L-cysteine L-Cystemfle
HC1
III III
Sweet Flat to sweet; “fatty” Flat to sweet; Sweet; possibly
possibly possibly complex
bitter,
sour,
or
sour, complex with bitter
af-
440 40
tertaste Sweet; possibly complex with salty or sour components Flat, sweet, meaty, somewhat unpleasant Flat to bitter Bitter; possibly complex and strangling Flat to bitter Flat Flat
to bitter, slightly sweet to bitter, possibly sulphurous, meaty, or sweet Flat to bitter Flat to bitter Flat to bitter, minerally
730 2600
2970 2650 2420 1690 1300
300
730 Flat to bitter, alkaline, complex Flat, complex, minerally Bitter, complex, salty, sweet Flat, sour, slightly bitter Unique, sour, Sulphurous,
possibly
meaty,
salty,
isc 540 bitter,
550
complex obnoxious
Amino acids listed in order of the threshold values for young subjects from highest to lowest. It Chemical group: I, with aliphatic side chains; II, with side chains containing hydroxylic groups; Ill, with side chains containing sulfur atoms; IV, with side chains containing acidic groups or their amides; V. with side chains containing basic groups; VI, containing aromatic rings; VII, imino acid. Brief taste description from Schiffman and Engelhard (12). d Free energy per side chain in calorie/mole for amino acids (26) which is related to solubility. ‘Description was not given. “Value was not given. (C
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1626
SCHIFFMAN
Amino acids with correspondingly close thresholds tended to have similar chemical and taste properties. Amino acids with allphatic side chains and those containing hydroxyl groups, which have sweet tastes at suprathreshold concentrations, tended to have the highest detection thresholds, e.g., glycine, L-threOnine, L-seflne, and L-alanrne. These tended to be followed by flat and bitter amino acids: L-isoleucine, L-phenylalamne, L-leucine, L-valine, L-methionine, L-tryptophan, and L-asparagine. Succeeding this group tended to be a sequence of basic amino acids: L-arginine, L-histidrne, and L-lysine and their monohydrochloride derivatives. Amino acids with acidic groups, as well as L-cysteine and L-cysteine HC1, had the lowest detection thresholds. No relationship between threshold and solubility was found. No sex differences for taste thresholds of amino acids were found in this study. There are some studies, however, which suggest that taste thresholds for other kinds of stimuli are lower for women than for men, i.e., women show greater sensitivity (29). This could be partially explained by the fact that women have more experience with taste because they are the preparers of food in most cultures. Pangborn (30) noted that thresholds can be lowered by training. Heavier smoking habits in males could also explain a sex difference in thresholds ifone does exist for some stimuli other than amino acids. Kaplan et al. (31) found that taste sensitivity showed greater deterioration for smokers than for nonsmokers. If women had been found to be more sensitive in this study, the high percentage of elderly females used in this experiment would have tended to minimize the differences between the two groups. Thus, if such a sex difference had been found, inclusion of more elderly males in further testing would only have served to increase further the already highly statistically significant difference already found between the young and elderly groups. The diminished taste sensitivity among the elderly is most likely due to decline in the gustatory apparatus with age. Moses et al. (32) found that the number of fungiform papillae, which are elevated structures located on the dorsal surface of the front twothirds of the tongue on which taste buds are located, decreases with age. Arey et al. (33),
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ET
AL.
as well as Mochizuki (34), reported that the mean number of taste buds found on circumvallate papillae, which are sunken structures surrounded by “moats” located on the posterior tongue, decline with age. In addition, Mochizuki (35) found that the number of taste buds per foliate papilla, which take the form of folds on the lateral ridge at the root of the tongue, also decrease with age. Another factor relevant to the age-related decline found for taste acuity may be the decreased levels of estrogen and testosterone found in the elderly (see Reference 36). Animal data (37, 38) indicate that estrogen and testosterone can increase mitotic activity. Beidler and Smallman (39) have shown that receptor cells in taste buds are constantly dividing and turn over on the average of 10 to l0’/2 days. Thus, decreased hormone levels may reduce turnover and hence the number of receptors. In summary, taste thresholds for amino acids were 2/2 times higher on the average for elderly subjects than for young subjects. This decline in sensitivity is most likely due to decreased numbers of papillae and taste buds per papilla associated with aging. In addition, age-related decreases in hormone levels may reduce the proliferation rate and hence the number of taste cells. References 1. ALBANESE, A. A., L. A. ORTO AND E. H. WEIN. Evaluation of L-tryptophan supplemented gelatin in healthy normal females. Nutr. Rept. Internat. 9: 277, 1974. 2. DAMICO, R. An investigation of N-substituted methionine derivatives for food supplementation. J. Agric. Food Chem. 23: 30, 1975. 3. DUNLAP, C. 3., D. 0. GUADAGNI, J. C. MIERS AND 3. R. WAGNER. Methionine supplement alters flavor, PER of pinto beans canned in tomato sauce. Food Prod. Develop. 8: 88, 1974. 4. MAZUR, R. H., AND T. CRAIG. A new sugar substitute. Am. Soft Drink J. 125: 94, 1971. S. MIYOSHI, H. Utilization ofnatural sweete ng agents after prohibition of saccharin. Up to date food processing. Shokuhin Kaihatso 8: 26, 1973. 6. NOFRE, C., J. SABADIE AND D. BAL. Sweetening properties of L-alanine tert-butyl ester. Naturwiss. 61: 404, 1974. 7. NOGUCHI, M., M. YAMASHITA, S. ARAI AND M. FUJIMAKI.
On
the
bitter-masking
activity
of
a glu-
tamic acid-rich oligopeptide fraction. J. Food Sci. 40: 367, 1975. 8. PRENDERGAST, K. Protein hydrolysate-a review. Food Trade Rev. 44: 14, 1974. 9. YAMADA, S., M. YAMAMOTO, C. HONGO AND I.
INCREASED
TASTE
THRESHOLDS
CHIBATA. tryptophan 23: 653,
Preparation of optically active 6-chloroand tryptophan. 3. Agric. Food Chem. 1975. 10. BUCKLEY, C. E. Anergy, dysimmunoglobulinemia, and unexplained inflammation. A new therapeutic approach with a chemically defined diet. J. Allerg. 44: 355, 1969. I 1. SCHIFFMAN, S. S., AND C. DACKIS. Taste of nutrients: amino acids, vitamins, and fatty acids. Percept. Psychophys. 17: 140, 1975. 12. SCHIFFMAN, S. S., AND H. H. ENGELHARD. Taste of dipeptides. Physiol. Behav. 17: 523, 1976. 13. Y0SHIDA, M., T. NINOMIYA, S. IKEDA, S. YAMAGUCHI, T. YOSHIKAWA AND M. OHARA. Taste of amino acids. I. Determination ofthreshold values of various amino acids. Nippon Nogeikagaku Kaishi 40: 295, 1966. 14. BALOGH, K., AND K. LELKES. The tongue in old age. Gerontol. Clin. 3: 38, 1961. 15. BOULIERE, F., H. CENDRON AND A. RAPAPORT. Modification avec l’age des seuils gustatifs de perception et de reconnaissance aux saveurs sal#{235}e et sucr#{233}e,chez l’homme. Gerontologia 2: 104, 1958. 16. COPPER, R. M., I. BILASH AND J. P. ZUBEK. The effect of age on taste sensitivity. J. Gerontol. 14: 56, 1959. 17. H. HARRIS, AND H. KALMUS. The measurement of taste sensitivity to phenylthiourea (PTC). Ann. Eugen. 15: 24, 1949. 18. HERMEL, J., S. SCHONWETrER AND S. SAMUELOFF. Taste sensation and age in man. J. Oral Med. 25: 39, 1970. 19. HINCHCLIFF, R. Clinical quantitative gustometry. Acta Oto-Laryngol. 49: 453, 1958. 20. HINCHCLIFF, R. Aging and sensory thresholds. J. Gerontol. 17: 45, 1962. 21. MURPHY, C. Gustatory absolute thresholds as a function of age: An investigation into the mechanism for coding bitter. Dissertation, University of Massachusetts, 1975. 22. MURPHY, C. The effect of age on taste sensitivity. In: Proceedings of the Symposium on Biology of Special Senses in Aging, 1977. 23. RICHTER, C. P., AND K. H. CAMPBELL. Sucrose taste thresholds of rats and humans. Am. 3. Physiol. 128: 291, 1940. 24. SCHIFFMAN, S. Food recognition by the elderly. 3. Gerontol. 32: 586, 1977. 25. SPATZ, C., AND 3. 0. JOHNSON. Basic Statistics: Tales
Downloaded from https://academic.oup.com/ajcn/article-abstract/32/8/1622/4692317 by Boston University user on 09 July 2018
OF
AMINO of Distributions.
26.
ACIDS
WITH Monterey:
1627
AGE Brooks/Cole,
1976.
C. Contribution of hydrophobic interactionS to the stability of globular conformation of proteins. J. Am. Chem. Soc. 84: 4240, 1962. 27. BROWNLEE, K. A. Statistical Theory and Methodology in Science and Engineering. New York: John Wiley, 1960, p. 135. 28. DIxoN, W. J., AND F. 3. MASSEY. Introduction to Statistical Analysis. New York: McGraw-Hill, 1951, pp. 194-195. 29. DOTY, R. L. Gender and reproductive state correlates of taste perception in humans. In: Sex and Behavior: Status and Prospectus, edited by T. McGill, D. A. Dewsbury, and B. Sacks. New York: Plenum Press, 1977. 30. PANGBORN, R. M. Influence of hunger on sweetness preferences and taste thresholds. Am. J. Clin. Nutr. 7: 280, 1959. 3 1 . KAPLAN, A., E. GLANVILLE AND R. FISCHER. Cumulative effect of age and smoking on taste sensitivity in males and females. J. Gerontol. 20: 334, 1965. 32. MOSES, S. W., Y. ROTEM, N. JAGODA, N. TALMOR, F. EICHHORN AND S. LEVIN. A clinical, genetic and biochemical study of familial dysautonomia in Israel. Israel 3. Med. Sci. 3: 358, 1967. 33. AREY, L. B., M. J. TREMAINE AND F. L. M0NzING0. The numerical and topographical relations of taste buds to human circumvallate papillae throughout the life span. Anat. Rec. 64: 9, 1935. 34. M0cHIzUKI, Y. An observation on the numerical and topographical relations of the taste buds to circumvallate papillae of Japanese. Okajimas Folia Anat. Japan. 15: 595, 1937. 35. MOCHIZUKI, Y. Studies on the papillae foliata of Japanese. II. The number of taste buds. Okajimas Folia Anat. Japan. 18: 355, 1939. 36. TALBERT, G. B. Aging of the reproductive system. In: Handbook of the Biology of Aging, edited by C. E. Finch and L. Hayflick. New York: Van Nostrand Reinhold Co., 1977. 37. BULLOUGH, H. F. Cyclical changes in the skin of the mouse during the oestrous cycle. J. Endocrinol. 3: 280, 1942. 38. EARTLY, H., B. GRAD AND C. P. LEBLOND. The antagonistic relationship between testosterone and thyroxine in maintaining the epidermis of the male rat. Endocrinology 49: 667, 1951. 39. BEIDLER, L. M., AND R. L. SMALLMAN. Renewal of cells within taste buds. 3. Cell. Biol. 27: 263, 1965. TANFORD,
taste thresholds age1’2
S. Schffman,
Ph.D.,
Karen
were
were
extensive,
thresholds taste and Amino lowest
the
detection
elderly
were
2’4 times
higher
found. sweet
acids
of
Amino tastes
found amino
sulfur, Am.
Nutr.
as those 32:
Detection thresholds for two groups of subjects, young and elderly, were found. The young subjects were college student volunteers ranging in age from 17 to 27 years (mean 20.8). The elderly subjects were residents of the Methodist Retirement Home in Durham, NC., and ranged in age from 75 to 87 years (mean 78.4). The elderly subjects were healthy volunteers from a group preselected for their excellent medical status by the nursing staff of the retirement home. The young group consisted of 49% males and 51% females. The elderly group consisted of 17% males and 83% females. The sex ratios used are representative of the sex distributions for healthy persons without serious diseases for the two age
The American
elderly women included insure that any changes due to normal aging and shown in the “Results”
Journal
of Clinical
Downloaded from https://academic.oup.com/ajcn/article-abstract/32/8/1622/4692317 by Boston University user on 09 July 2018
and
Nutrition
with
those
tended
acidic
1622-1627,
of the
and
or basic
the
average,
between
the
suprathreshold
containing
to have
thresholds
On
Relationships
structures,
chains
monohydrochloride
ranges
sensitivity.
subjects.
chemical
four the
diminished
in young
side
and
Although
concentrations
Subjects
1622
their
aliphatic
Amino acids such as lysine, threonine, and methionine, as well as their derivatives, have been added to foods to improve the quality of protein as well as to improve the flavor (1-9). Amino acids have also been used to create diets for allergic patients (10). Most amino acids have taste qualities (1 1, 12) which could modify the flavor of foods depending on the concentrations at which they are added. The purpose of this study was to determine the taste detection thresholds for amino acids in two populations, young and elderly. Detection thresholds for some amino acids have been reported by Yoshida et al. (13), but age effects and range over individuals were not determined. Most taste studies indicate that there is a decrease in taste sensitivity with advancing age (14-24).
groups. The high percentage of in this study was necessary to found in taste thresholds were not disease state. (It will be
acids
subjects.
than
acids,
as well
J. Clin.
19 L-amino
significantly
elderly
with
Reilly
elderly
to have
in the
acids
for
and
at suprathreshold
containing
thresholds.
Debra
thresholds
for young
thresholds
were
having
and
detection
determined
were
qualities
Hornack,
Taste
ABSTRACT derivatives
of amino
the
groups,
taste
hydroxyl highest tended
groups thresholds.
to have
the
1979.
section hat no significant differences for taste thresholds were found to exist between males and females for either age group.) The two groups were approximately equal with regard to socioeconomic status and intelligence as determined from unpublished data gathered by the Center for the Study of Aging and Human Development at Duke Medical Center. Threshold measurements for each stimulus were determined for a minimum of 10 and a maximum of 15 individuals. All subjects were nonsmokers and were tested at least I hr after eating. None of the subjects wore dentures. The participants varied over stimuli, i.e., subjects were different for each of the amino acids.
Stimuli The stimuli hydrochloride HC1, L-histidine deionized water. cluded 16 serial other by a factor for amino acids been reported increased by a value and eight
were 19 L-amino acids and four monoderivatives: L-arginine HC1, L-cysteine HC1, and L-lysine HCI, dissolved in The initial concentration ranges indilutions which differed from one anof 2. The initial stimulus range chosen for which thresholds have previously (13) included eight concentrations that factor of 2 above the reported threshold concentrations that decreased by a factor
of 2 below the reported threshold value. The initial stimulus range for those amino acids for which thresholds have not been reported were determined by pretesting and included a maximum of 16 serial dilutions that differed by a factor of 2. In practice, it was found that From the Department of Psychiatry, Duke Center, Durham, North Carolina 27710. 2 Supported in part by Grant NIA-AG00443
and Grant
NSF-GB33464 3Ajinomoto Co., Ltd. anese Patent 40 26 1/70. Lilly and Co. 851. Matsuda, M. Patent 20 382/72.
Artificial
Medical to S.S.S.
to Dr. R. P. Erickson. Cake flour improvement. sweeteners.
British
JapPatent
269
32: AUGUST
Coffee
flavor
improvement.
1979, pp. 1622-1627.
Printed
Japanese
in U.S.A.
1
INCREASED eight
to
12 dilutions
that
varied
TASTE by
THRESHOLDS
a factor
of
2 ade-
quately covered the threshold ranges for each of the amino acids. Concentrations intermediate between two successive dilutions were included for some stimuli: Lalanine, L-argrnine HC1, L-asparagine, L-cysteine, L-cysteine HC1, L-glUtamic acid, L-histidtne HCI, L-leucine, L-lysine, L-methionine, L-phenylalanine, and L-threonine to further refine threshold determination. The amino acid solutions, prepared before testing, were presented to the subjects in S-ounce plastic cups at room temperature (72 F). Nineteen of the 23 stimuli were obtained from K and K (ICN Pharmaceutical, Inc., Plainview, N.Y.). L-lysifle HC1, L-phenylalanine, and L-serine were obtained from Sigma Chemical Co., St. Louis, Mo., and L-prohne was obtained from P-L Biochemicals, Inc., Milwaukee, Wis.
Procedure Thresholds for a given amino acid were determined as follows. Trials began with the weakest concentration and proceeded to progressively stronger concentrations. At each trial, subjects, seated at individual or partitioned tables, were presented with a tray on which three unmarked cups were placed. One cup contained an amino acid (or monohydrochloride derivative) dissolved in deionized water, the other two cups contained only deionized water. The cup position on the tray was randomized over trials; the randomness of the cup position was generated by the experimenters. The subjects, wearing noseplugs to reduce olfactory input, tasted approximately 10 ml from each of the three cups, letting the liquid swirl around in their mouths for approximately 4 sec. The liquid was ejected into a separate cup used as a spittoon. Subjects rinsed their mouths with deionized water before tasting the liquid in each cup. An interval of approximately 10 sec took place between sampling from successive cups. After tasting the liquid in each of the three cups, the subjects noted on a score sheet which cup, in their opinion, contained the amino acid solution. lf they were unable to determine which cup contained the amino acid, they were instructed to make a guess (forced choice procedure). Only one trial was given at each concentration level as the trials proceeded from weaker to increasingly stronger concentrations. A taste threshold for a given stimulus was considered to be established when a subject correctly distinguished the amino acid solution from the deionized water on three consecutive trials (i.e., at three consecutive increasing concentrations). The most dilute amino acid concentration that was correctly identified on these three consecutive trials was taken as the taste threshold for an individual subject. An interval of 3 mm was allowed between trials (i.e., each set of triads) to minimize the possibility of adaptation. Testing took place between 9:30 AM and 5:00 PM, excluding the 12:00 noon to 2:00 PM interval. Subjects were asked to abstain from eating and drinking for 1 hr before testing.
Results An examination of the thresholds for individual amino acids revealed that they were not normally distributed. For this reason, the
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OF
AMINO
ACIDS
WITH
AGE
1623
individual thresholds were converted to log units and a geometric mean and SD for young and elderly groups were computed for each amino acid. The geometric means for the amino acids for the young and elderly groups expressed in terms of molarity are given in columns 1 and 2 of Table 1. The ratio of the threshold in molarity for elderly subjects compared with young subjects for each amino acid is given in column 3. The ranges of thresholds in terms of molarity for young and elderly subjects are given in columns 4 and 5. The geometric means and standard deviations in log units from which columns 1 and 2 were determined are shown in columns 6 and 7 in Table 1. Mann-Whitney U tests (25) were used to determine whether the thresholds for the young and elderly populations differed significantly. If the difference was significant, this was indicated in column 8. Mann-Whitney U tests were used because multivariate models were considered mappropriate since subject participation varied over stimuli and because threshold distributions were not normal. Yoshida’s threshold values (13) are reported in column 9 as well. Twenty of the 23 mean thresholds given in columns 1 and 2 in Table 1 were lower for young subjects when compared with elderly subjects. The average ratio given in column 3 for the thresholds for elderly subjects cornpared with thresholds for young subjects is 2.49. Eleven of the amino acid thresholds differed significantly for the young and elderly groups as determined by Mann-Whitney U tests. A Poisson distribution (27, 28) was used to determine the probability of fmding statistical significance at the 0.05 level for 11 or more of the amino acids: P
=
I
k’x k-.0
where: N = total number of amino acids (i.e., 23); p, = probability level (i.e., 0.05); and k = 10 or the number of thresholds minus I found to be statistically significant. The results indicate that the decreased sensitivity in the elderly was extremely significant, P =
0.0000000041. No significant ues were found for either young ber of times the (and below) the
differences in threshold valbetween males and females or elderly subjects. The numthreshold values fell above mean for males and females
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INCREASED
TASTE
THRESHOLDS
OF
was examined for both the young and elderly groups. x2 values of 1.28 (df= 1) and 0.32 (df = 1) for the young and elderly groups, respectively, indicated that no significant sex differences in taste thresholds were found here for amino acids. The threshold values for the young subjects were arranged in descending order from highest (i.e., glycine) to lowest (i.e., cysteine HC1). The rank order of the threshold values for young subjects was very similar to that for elderly subjects (Spearman’s p = 0.97). Because the rank order of the thresholds was so similar for the two groups, the threshold values were related to chemical structure, taste quality, and solubility for the young subjects only. In column 1 of Table 2, the threshold values for young subjects are arranged in descending order, i.e., from highest to lowest. The chemical classification is given in column 2. The taste quality for each amino acid, as described by Schiffman and Dackis (11) and TABLE
AMINO
ACIDS
WITH
1625
AGE
Schiffman and Engeihard (12), is shown in column 3. Tanford’s (26) free energy per side chain in cal./mole for amino acids, which is related to solubility, is given in column 4. No relationship between the level ofthe detection threshold (i.e., whether it was high or low), chemical structure, taste quality, or solubility was found to be related to whether or not there was a significant difference between the young or elderly groups. Discussion The highly significant increase in detection thresholds for amino acids with age found in this experiment is consistent with increased taste thresholds found in other studies (14.24). The threshold values obtained here are also consistent with those reported by Yoshida et al. (13). The values of Yoshida et al. fell within the threshold ranges for either young or elderly subjects.
2
Glycmne0 L-threoflifle
lb II
L-serine L-alanine
II
L-proline
VII
L-glutamine
IV
L-isoleucine L-phenylalanine L-leucine L-valifle
VI
L-methionine
Ill
L-tryptophan L-asparagine L-histidine L-arginine HCI L-argiflifle L-lysifle L-lysine HCI L-aSpartic acid L-histidine HCI L-glutamic acid
VI IV V V V V V IV V IV
L-cysteine L-Cystemfle
HC1
III III
Sweet Flat to sweet; “fatty” Flat to sweet; Sweet; possibly
possibly possibly complex
bitter,
sour,
or
sour, complex with bitter
af-
440 40
tertaste Sweet; possibly complex with salty or sour components Flat, sweet, meaty, somewhat unpleasant Flat to bitter Bitter; possibly complex and strangling Flat to bitter Flat Flat
to bitter, slightly sweet to bitter, possibly sulphurous, meaty, or sweet Flat to bitter Flat to bitter Flat to bitter, minerally
730 2600
2970 2650 2420 1690 1300
300
730 Flat to bitter, alkaline, complex Flat, complex, minerally Bitter, complex, salty, sweet Flat, sour, slightly bitter Unique, sour, Sulphurous,
possibly
meaty,
salty,
isc 540 bitter,
550
complex obnoxious
Amino acids listed in order of the threshold values for young subjects from highest to lowest. It Chemical group: I, with aliphatic side chains; II, with side chains containing hydroxylic groups; Ill, with side chains containing sulfur atoms; IV, with side chains containing acidic groups or their amides; V. with side chains containing basic groups; VI, containing aromatic rings; VII, imino acid. Brief taste description from Schiffman and Engelhard (12). d Free energy per side chain in calorie/mole for amino acids (26) which is related to solubility. ‘Description was not given. “Value was not given. (C
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1626
SCHIFFMAN
Amino acids with correspondingly close thresholds tended to have similar chemical and taste properties. Amino acids with allphatic side chains and those containing hydroxyl groups, which have sweet tastes at suprathreshold concentrations, tended to have the highest detection thresholds, e.g., glycine, L-threOnine, L-seflne, and L-alanrne. These tended to be followed by flat and bitter amino acids: L-isoleucine, L-phenylalamne, L-leucine, L-valine, L-methionine, L-tryptophan, and L-asparagine. Succeeding this group tended to be a sequence of basic amino acids: L-arginine, L-histidrne, and L-lysine and their monohydrochloride derivatives. Amino acids with acidic groups, as well as L-cysteine and L-cysteine HC1, had the lowest detection thresholds. No relationship between threshold and solubility was found. No sex differences for taste thresholds of amino acids were found in this study. There are some studies, however, which suggest that taste thresholds for other kinds of stimuli are lower for women than for men, i.e., women show greater sensitivity (29). This could be partially explained by the fact that women have more experience with taste because they are the preparers of food in most cultures. Pangborn (30) noted that thresholds can be lowered by training. Heavier smoking habits in males could also explain a sex difference in thresholds ifone does exist for some stimuli other than amino acids. Kaplan et al. (31) found that taste sensitivity showed greater deterioration for smokers than for nonsmokers. If women had been found to be more sensitive in this study, the high percentage of elderly females used in this experiment would have tended to minimize the differences between the two groups. Thus, if such a sex difference had been found, inclusion of more elderly males in further testing would only have served to increase further the already highly statistically significant difference already found between the young and elderly groups. The diminished taste sensitivity among the elderly is most likely due to decline in the gustatory apparatus with age. Moses et al. (32) found that the number of fungiform papillae, which are elevated structures located on the dorsal surface of the front twothirds of the tongue on which taste buds are located, decreases with age. Arey et al. (33),
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ET
AL.
as well as Mochizuki (34), reported that the mean number of taste buds found on circumvallate papillae, which are sunken structures surrounded by “moats” located on the posterior tongue, decline with age. In addition, Mochizuki (35) found that the number of taste buds per foliate papilla, which take the form of folds on the lateral ridge at the root of the tongue, also decrease with age. Another factor relevant to the age-related decline found for taste acuity may be the decreased levels of estrogen and testosterone found in the elderly (see Reference 36). Animal data (37, 38) indicate that estrogen and testosterone can increase mitotic activity. Beidler and Smallman (39) have shown that receptor cells in taste buds are constantly dividing and turn over on the average of 10 to l0’/2 days. Thus, decreased hormone levels may reduce turnover and hence the number of receptors. In summary, taste thresholds for amino acids were 2/2 times higher on the average for elderly subjects than for young subjects. This decline in sensitivity is most likely due to decreased numbers of papillae and taste buds per papilla associated with aging. In addition, age-related decreases in hormone levels may reduce the proliferation rate and hence the number of taste cells. References 1. ALBANESE, A. A., L. A. ORTO AND E. H. WEIN. Evaluation of L-tryptophan supplemented gelatin in healthy normal females. Nutr. Rept. Internat. 9: 277, 1974. 2. DAMICO, R. An investigation of N-substituted methionine derivatives for food supplementation. J. Agric. Food Chem. 23: 30, 1975. 3. DUNLAP, C. 3., D. 0. GUADAGNI, J. C. MIERS AND 3. R. WAGNER. Methionine supplement alters flavor, PER of pinto beans canned in tomato sauce. Food Prod. Develop. 8: 88, 1974. 4. MAZUR, R. H., AND T. CRAIG. A new sugar substitute. Am. Soft Drink J. 125: 94, 1971. S. MIYOSHI, H. Utilization ofnatural sweete ng agents after prohibition of saccharin. Up to date food processing. Shokuhin Kaihatso 8: 26, 1973. 6. NOFRE, C., J. SABADIE AND D. BAL. Sweetening properties of L-alanine tert-butyl ester. Naturwiss. 61: 404, 1974. 7. NOGUCHI, M., M. YAMASHITA, S. ARAI AND M. FUJIMAKI.
On
the
bitter-masking
activity
of
a glu-
tamic acid-rich oligopeptide fraction. J. Food Sci. 40: 367, 1975. 8. PRENDERGAST, K. Protein hydrolysate-a review. Food Trade Rev. 44: 14, 1974. 9. YAMADA, S., M. YAMAMOTO, C. HONGO AND I.
INCREASED
TASTE
THRESHOLDS
CHIBATA. tryptophan 23: 653,
Preparation of optically active 6-chloroand tryptophan. 3. Agric. Food Chem. 1975. 10. BUCKLEY, C. E. Anergy, dysimmunoglobulinemia, and unexplained inflammation. A new therapeutic approach with a chemically defined diet. J. Allerg. 44: 355, 1969. I 1. SCHIFFMAN, S. S., AND C. DACKIS. Taste of nutrients: amino acids, vitamins, and fatty acids. Percept. Psychophys. 17: 140, 1975. 12. SCHIFFMAN, S. S., AND H. H. ENGELHARD. Taste of dipeptides. Physiol. Behav. 17: 523, 1976. 13. Y0SHIDA, M., T. NINOMIYA, S. IKEDA, S. YAMAGUCHI, T. YOSHIKAWA AND M. OHARA. Taste of amino acids. I. Determination ofthreshold values of various amino acids. Nippon Nogeikagaku Kaishi 40: 295, 1966. 14. BALOGH, K., AND K. LELKES. The tongue in old age. Gerontol. Clin. 3: 38, 1961. 15. BOULIERE, F., H. CENDRON AND A. RAPAPORT. Modification avec l’age des seuils gustatifs de perception et de reconnaissance aux saveurs sal#{235}e et sucr#{233}e,chez l’homme. Gerontologia 2: 104, 1958. 16. COPPER, R. M., I. BILASH AND J. P. ZUBEK. The effect of age on taste sensitivity. J. Gerontol. 14: 56, 1959. 17. H. HARRIS, AND H. KALMUS. The measurement of taste sensitivity to phenylthiourea (PTC). Ann. Eugen. 15: 24, 1949. 18. HERMEL, J., S. SCHONWETrER AND S. SAMUELOFF. Taste sensation and age in man. J. Oral Med. 25: 39, 1970. 19. HINCHCLIFF, R. Clinical quantitative gustometry. Acta Oto-Laryngol. 49: 453, 1958. 20. HINCHCLIFF, R. Aging and sensory thresholds. J. Gerontol. 17: 45, 1962. 21. MURPHY, C. Gustatory absolute thresholds as a function of age: An investigation into the mechanism for coding bitter. Dissertation, University of Massachusetts, 1975. 22. MURPHY, C. The effect of age on taste sensitivity. In: Proceedings of the Symposium on Biology of Special Senses in Aging, 1977. 23. RICHTER, C. P., AND K. H. CAMPBELL. Sucrose taste thresholds of rats and humans. Am. 3. Physiol. 128: 291, 1940. 24. SCHIFFMAN, S. Food recognition by the elderly. 3. Gerontol. 32: 586, 1977. 25. SPATZ, C., AND 3. 0. JOHNSON. Basic Statistics: Tales
Downloaded from https://academic.oup.com/ajcn/article-abstract/32/8/1622/4692317 by Boston University user on 09 July 2018
OF
AMINO of Distributions.
26.
ACIDS
WITH Monterey:
1627
AGE Brooks/Cole,
1976.
C. Contribution of hydrophobic interactionS to the stability of globular conformation of proteins. J. Am. Chem. Soc. 84: 4240, 1962. 27. BROWNLEE, K. A. Statistical Theory and Methodology in Science and Engineering. New York: John Wiley, 1960, p. 135. 28. DIxoN, W. J., AND F. 3. MASSEY. Introduction to Statistical Analysis. New York: McGraw-Hill, 1951, pp. 194-195. 29. DOTY, R. L. Gender and reproductive state correlates of taste perception in humans. In: Sex and Behavior: Status and Prospectus, edited by T. McGill, D. A. Dewsbury, and B. Sacks. New York: Plenum Press, 1977. 30. PANGBORN, R. M. Influence of hunger on sweetness preferences and taste thresholds. Am. J. Clin. Nutr. 7: 280, 1959. 3 1 . KAPLAN, A., E. GLANVILLE AND R. FISCHER. Cumulative effect of age and smoking on taste sensitivity in males and females. J. Gerontol. 20: 334, 1965. 32. MOSES, S. W., Y. ROTEM, N. JAGODA, N. TALMOR, F. EICHHORN AND S. LEVIN. A clinical, genetic and biochemical study of familial dysautonomia in Israel. Israel 3. Med. Sci. 3: 358, 1967. 33. AREY, L. B., M. J. TREMAINE AND F. L. M0NzING0. The numerical and topographical relations of taste buds to human circumvallate papillae throughout the life span. Anat. Rec. 64: 9, 1935. 34. M0cHIzUKI, Y. An observation on the numerical and topographical relations of the taste buds to circumvallate papillae of Japanese. Okajimas Folia Anat. Japan. 15: 595, 1937. 35. MOCHIZUKI, Y. Studies on the papillae foliata of Japanese. II. The number of taste buds. Okajimas Folia Anat. Japan. 18: 355, 1939. 36. TALBERT, G. B. Aging of the reproductive system. In: Handbook of the Biology of Aging, edited by C. E. Finch and L. Hayflick. New York: Van Nostrand Reinhold Co., 1977. 37. BULLOUGH, H. F. Cyclical changes in the skin of the mouse during the oestrous cycle. J. Endocrinol. 3: 280, 1942. 38. EARTLY, H., B. GRAD AND C. P. LEBLOND. The antagonistic relationship between testosterone and thyroxine in maintaining the epidermis of the male rat. Endocrinology 49: 667, 1951. 39. BEIDLER, L. M., AND R. L. SMALLMAN. Renewal of cells within taste buds. 3. Cell. Biol. 27: 263, 1965. TANFORD,
