Parotid Salivation in Response to Sodium Chloride and Monosodium Glutamate in Water and in Broths

Appetite: Journal for Intake Research 1981, 2, 380-385

Parotid Salivation in Response to Sodium Chloride and Monosodium Glutamate in Water and in Broths

ROSE MARIE PANGBORN and CHI MINH CHUNG Department of Food Science and Technology, University of California, Davis

Preliminary experiments on unilateral parotid secretion in response to sodium chloride (NaCl), monosodium glutamate (MSG) and equimolar mixtures ofthe two established that: (a) there was no glandular fatigue as flow was sustained during oral rinsing with 24 samples at 30-sec intervals; (b) generally, NaCl> MSG > equimolar mixtures ofthe two; (c) testing of salts in three media at 500 e resulted in flow rates where beef broth > chicken broth> distilled water; (d) parotid flow was nearly linear with concentration (0, 0'05, 0'10, 0'20, 0'30, 0·50 M) of the salts, singly and in combination; and (e) large variability among subjects necessitated expansion of testing to a larger population.

The distinctive gustatory and physiological properties of monosodium glutamate (MSG) is considered of such scientific and commercial importance to warrant a recent international symposium with resultant proceedings. In that volume, Yamaguchi and Kimizuka (1979) reported that addition of MSG to beef and chicken consomme had no effect on aroma but increased saltiness and sweetness, and flavour characteristics described as "continuity, mouth fullness, impact, mildness, and thickness". The only reference to saliva was the conclusion by Kenney (1979) that irritation of the esophageal mucosa in subjects exhibiting "Chinese restaurant syndrome" would be more prevalent among those without good flow of saliva to dilute and wash away the MSG. Recently, Kawamura, Yamamoto, Fujiwara, Matsuo and Takashi (1980) measured unilateral parotid secretion in response to MSG, NaCI and other taste compounds dispersed in distilled water, noting that 0·1 M NaCI induced more flow than O'IM MSG.

The experiments reported herein were undertaken to determine whether NaC!, MSG and equimolar combinations of the two, in water and in beef and chicken broths, would have similar sustained secretion on prolonged stimulation, and to determine the shape of the parotid flow rate as a function of concentration.

MATERIALS AND METHODS

Unilateral parotid saliva was collected by placement of a modified, stainless steel Carlson-Crittenden vacuum cap (Shannon, Prigmore, & Chauncey, 1962) over Stenson's duct, as described previously (Pangborn, & Berggren, 1973; Pangborn,

Based on a portion of the M.S. thesis of the junior author. The research was supported in part by a grant from the Wm. Underwood Co., Westwood, Massachusetts. Requests for reprints should be sent to the senior author, Department of Food Science and Technology,

University of California, Davis, CA 95616, U.S.A.

0195-6663/81/040380 + 06 ~02'00/0 if', 1981 Academic Press Inc. (London) Limited

SAllY A nON TO SALTS IN WATER AND BROTHS 381

Witherly, & Jones, 1979). The secretion was collected via Tygon tubing into a small vessel attached to a sialometer (Pangborn, Eriksson, & Remi, 1971), where the weight of the saliva was detected by a linear displacement transducer, and the output voltage was monitored continuously by a strip chart recorder (capacity = 2 g; sensitivity = ± 10 mg).

Stimuli consisted of reagent-grade NaCl and MSG dispersed in three liquids: double-distilled water, unsalted chicken broth and unsalted beef broth (singlestrength, canned commercial products; Health Valley Natural Foods, Montebello, CA). Salt concentrations tested are given in Figures 1 and 2. A sample of unsalted liquid served as a control at each session. After an orientation session, the test samples were presented in randomized order, across media and across additives. Sessions were conducted daily in early and mid-afternoon within a four-week period for each experiment. Samples of lO-ml aliquots were presented in a waterbath maintained at 50°C. The entire contents were placed in the mouth, manipulated for 5 sec then expectorated, with the sequence repeated every 30 sec for 12 min in the first experiment and for 2 min in the second experiment.

Subjects were selected on the basis of availability and interest and ability to retain the cap during extended collection periods (up to 1 h). Two subjects participated in the first experiment wherein 24 samples were tested at 30-sec intervals to determine whether secretion to continuous stimulation would be sustained, or whether the gland would adapt or fatigue. Four subjects participated in the second experiment wherein four samples of each concentration were tested to establish the shape of the salivation function across a wide concentration range.

RESUL TS AND DISCUSSION

Experiment 1 Both subjects demonstrated sustained flow in response to all test stimuli, with no

suggestion of adaptation even after 24 stimuli (Figure 1). This indicates that although the subject may have been psychologically fatigued or satiated, the gland continued to secrete at the same rate. This agrees with Kerr's (1961) observation of no parotid salivary fatigue in two subjects who sucked acid-drop candies for 1 min at 5-min intervals for up to 3 h. Shannon, Suddick and Down (1974) also noted sustained high parotid flow (0' 5-0·6 ml/min) among nine subjects who sucked sour-grape drops for up to 3 h.

Figure 1 ~hows that 0·5 M NaCI was a significantly greater sialogog than 0·5 M MSG or the mixture of 0·25 M NaCI with 0·25 M MSG. Response to 0·25 M NaCI was equivalent to that for 0·5 M MSG indicating that NaCI was twice as effective as MSG. For all salts, flow was slightly greater when dispersed in beef broth than in the other two media. This might be related to the greater natural sodium content of the beef (35 mg/100 g) than of the chicken broth (5 mg/lOO g).

Experiment 2 Mean flow rates from four subjects in response to distilled water and to five

concentrations ofMSG, NaCl, and equimolar concentrations of the two are depicted in Figure 2. When dispersed in distilled water, MSG and NaCI elicited similar patterns of increased flow with concentration, with a flatter slope for the mixture of the two compounds. The response patterns in chicken broth resembled those for water. In beef

382 R. M. AND C. M. CHUNG

o LIC:::'----J_-'------'-----'----'-----'----'----'----'-----'-----

(c) (d)

3-0 r-----------~ Salivary flow: chicken broth

r;:;---;------,-;-.,-------,----,-;--;---:-;-;------, A dd it i ve : Salivary flow: beef broth 0·50 M Noel

2·5

2·0

1·5

1·0

0·5

Judge # 2

I 2 3 4 5 6 7 8 9 10 II 12

(e)

Additive: 0·50 M Noel

0·25 M Nael 0·50 M MSG 0·25 M Noel + 0·25 M MSG None

Time (min)

Judge # 2

I 2 3 4 5 6 7 8 9 10 II 12

(tl

0·25 M Noel

0·25 M Noel + 0·25 M MSG 0·50 M MSG

None

FIGURE 1. Tracings from sialometric recordings of the persistence of unilateral parotid flow in response to 24 consecutive oral rinsings with sodium chloride, monosodium glutamate, and an equimolar combination of the two dispersed in distilled water, and in unsalted chicken and beef broths. Subjects rinsed the mouth with to-ml samples administered at sooe at 30-sec intervals. Tracings (a}-(c) are for subject # 1 and tracings (d}-(f) for subject #2.

broth, NaCl clearly emerged as the greatest stimulator at the three higher concentrations. All response slopes were highly correlated with concentration, with NaCl the highest and MSG the lowest (Table 1).


o 1.I2::L-l.-.~!~----,----'----'----'-----'---'----'--~ (c) (d)

3-0 rl -----------~ Salivary flow: chicken broth

r-=---:-----,,-----,---::-:-:;-;:--:::u::-----:l Add it i ve : I Salivary flow: beef broth ./ 10'50 M Noel

Judge # 2 2·5

2·0

1·5

1·0

0·5

Additive: 0-50 M Noel


Judge # 2

0·25 M Noel

0·25 M Noel + 0·25 M MSG 0·50 M MSG

None

O~I II

I 2 3 4 5 6 7 8 9 10 II 12 I 2 3 4 5 6 7 8 9 10 II 12

Time (min)

(e) (tl




o 1.I2::L-l.-.~!~----,----'----'----'-----'---'----'--~ (c) (d)

3-0 rl -----------~ Salivary flow: chicken broth

r-=---:-----,,-----,---::-:-:;-;:--:::u::-----:l Add it i ve : I Salivary flow: beef broth ./ 10'50 M Noel

Judge # 2 2·5

2·0

1·5

1·0

0·5

Additive: 0-50 M Noel


Judge # 2

0·25 M Noel

0·25 M Noel + 0·25 M MSG 0·50 M MSG

None

O~I II

I 2 3 4 5 6 7 8 9 10 II 12 I 2 3 4 5 6 7 8 9 10 II 12

Time (min)

(e) (tl



SAllY A nON TO SALTS IN WATER AND BROTHS

Parotid flow (4 Ss, 2 Reps)

D,sti lied water Chicken broth Beef broth

0·400 c:

~ 0,350 0>

~ 0,300 o

~ 0·250 ~

~ 0-200 /1' /

c: / g 0'150 " /'"

::;;: ,/'

0'100 /7 .. o 0·10 0·30 00·10 0·30 00·10 0'30

Molarity

383

FIGURE 2. Plot of the mean unilateral parotid salivary flow rate of four subjects (two replications) in response to oral rinsing with lO-ml portions of 0,0'05,0'1,0'2,0'3, and 0·5 M

additions of sodium chloride, monosodium glutamate, and an equimolar combination of the two to distilled water, and to unsalted chicken and beef broths. All solutions were administered in lO-ml portions at 50°e. MSG (e-e); NaC!, (,6.---,6.); ~ MSG+} NaCI (0--0).

TABLE 1 Linear correlation coefficients (r) and slopes of the regression line (b)for parotidflow as a

function of concentration (Experiment 2)

Distilled Chicken Beef Additive water broth broth

MSG r 0'964** 0·941 ** 0·971 ** b 0·245 0·257 0·226

NaCI r 0'988*** 0·991 *** 0'989*** b 0·356 0·377 0·525

MSG+NaC! r 0'982*** 0'960** 0'971** b 0·211 0·272 0·341

**p<O'OI; ***p<O'OOI (ddj).

Analysis of variance of the invidivual data (Table 2) indicated large variability attributable to subjects, with subject 4 giving significantly higher responses than the other three. Wide individual variation also was obtained for the interaction of subjects with media: for example, for MSG, one subject gave the highest responses to water, one to chicken broth and two to beef broth. As expected, the compound concentrations contributed a great amount of variation in flow rates, followed by media, with significantly higher flow rates to broths than to water solutions. Although additives did not differ significantly, the single compounds elicited greater flow than did the combination of the two. Replications did not differ significantly, attesting to the reproducibility of the response. All interactions involving subjects were significant at p <0·001, as were all interactions involving additives.


TABLE 2 Sources of variation, degrees offreedom, F -ratios and meanflow ratesfrom analysis of variance of data

from Experiment 2

Sources of Degrees of Pooled Test variation freedom F-ratio source Mean flow (g/min)

3 1 2 4 Subjects (S) 3 98'82*** Error 0·166 0·169 0·180 0·234

0 0·05 0·10 '0·20 0·30 0'50M Concentrations (C) 5 27'03*** SxC 0·124 0·152 0·155 0'190 0·217 0·286

H 2O Chicken Beef Media (M) 2 26'33*** SxM 0·153 0·187 0·222

MSG+NaCl MSG NaCl Additives (A) 2 0·362 SxA 0·174 0·193 0·196

li g Replications (R) 1·187 SxR 0·182 0·193

Interactions" CxM 10 2.455 Error CxA 10 8·091 *** Error CxR 5 1·235 Error MxA 4 19'727*** Error MxR 2 3-727* Error AxR 2 29'182*** Error

"All interactions involving subjects were significant at p<O·OOl. *p<0'05; ***p<O·OOl.

To compare responses obtained from the two experiments, flow rates at the end of two minutes were contrasted for subjects 1 and 2 (Table 3). Student's t-test for dependent variates indicated higher flow rates in the first experiment, particularly for additives dispersed in water (p < 0'05). There is no immediate explanation for this

TABLE 3 Comparison of flow rates for subjects 1 and 2 after two min of stimulation (Experiments 1

and 2)

Experiment 1 ~ ________ ~A~ ________ ~

Additive Water" Chickenb

~ ,-A---, 1 2 1 2

None 0·13 0·07 0·15 0·10 0'5M NaCI 0'52 0·53 0-46 0·49 0'5M MSG 0·44 0·37 0-44 0·30 0'5MNaCl+MSG 0'24 0-47 0·36 0'22

"Experiment 1 >2; t (6)=2-454, p<0·05. bExperiment 1>2; t (6)=1'694, p<0·20. 'Experiment 1 >2; t (6)=2'039, p<0·1O.

BeeF

~ 1 2

0·17 0·15 0·71 0·66 0·48 0'41 0·29 0·37

Experiment 2 r-________ ~A~ ________ ~

Water"

0·13 0·15 0·24 0·36 0·19 0·32 0·21 0·16

Chickenb

~

1 2

0·18 0·16 0·28 0·39 0'18 0·27 0·29 0·24

BeeF

~ 1 2

0·19 0·23 0·39 0·52 0·21 0'24 0·27 0·36

SALlY A nON TO SALTS IN WATER AND BROTHS 385

systematic observation. Nonetheless, in both experiments it is evident that at the same concentration, NaCI is a greater stimulator than was MSG, with no synergism evident for the mixtures. This is consistent with findings reported by Kawamura et al. (1980), where 0·1 M NaCl gave higher average unilateral parotid flow for 32 subjects than did 0·1 M MSG (c. 0·53 vs. 0·50 mlj3 min).

The third experiment in this series, currently in progress, is concerned with the effect of the two salts, singly and in equimolar combinations, on three measures among 20 subjects: (a) parotid flow; (b) Na +, Ca 2 +, and K + content of the parotid saliva; and (c) simultaneous recording of perceived taste intensity on a moving graph~the timeintensity technique (Larson-Powers, & Pangborn, 1978). The foregoing is designed to test the relation between flow, composition and perceived stimulus intensity.

REFERENCES

Kawamura, Y., Yamamoto, T., Fujiwara, T., Matsuo, R., & Takahasi, T. Studies on the gustatory-salivary reflex elicited by chemical taste enhancers. Journal of Osaka University Dental Society, 1980,25,179-185. (In Japanese.)

Kenney, R. A. Placebo-controlled studies on human reaction to oral monosodium L-glutamate. In L. J. Filer Jr. et al. (Eds.), Glutamic acid: advances in biochemistry and physiology. Pp. 363-373. New York: Raven Press, 1979.

Kerr, A. C. The physiological regulation of salivary secretions in man. New York: Pergamon Press, 1961.

Larson-Powers, N., & Pangborn, R. M. Paired comparison and time-intensity measurements of the sensory properties of beverages and gelatins containing sucrose or synthetic sweeteners. Journal of Food Science, 1978,43,41-46.

Pangborn, J., Eriksson, F., & Remi, K. Simplified sialometer for continuous weight monitoring of salivary secretion. Journal of Dental Research, 1971,50, 1689.

Pangborn, R. M., Witherly, S. A., & Jones, F. Parotid and whole-mouth secretion in response to viewing, handling, and sniffing food. Perception, 1979,8, 339-346.

Pangborn, R. M., & Berggren, B. Human parotid secretion in response to pleasant and unpleasant odorants. Psychophysiology, 1973, 10, 231-237.

Shannon, I. L., Prigmore, J. R., & Chauncey, H. H. Modified Carlson-Crittenden device for the collection of parotid fluid. Journal of Dental Research, 1962,41,778-783.

Shannon, I. L., Suddick, R. P., & Down, Jr., F. 1. Saliva: composition and secretion. Monographs in Oral Science. (Vol. 2). Basel: S. Krager AG, 1974.

Yamaguchi, S., & Kimizuka, A. Psychometric studies on the taste of monosodium glutamate. In L. J. Filer et al. (Eds.), Glutamic acid: advances in biochemistry and physiology. Pp. 35-54. New York: Raven Press, 1979.

Received 6 June, 1981

Documents

Parotid Salivation in Response to Sodium Chloride and Monosodium Glutamate in Water and in Broths