Preference of old world monkeys for amino acids and other gustatory stimuli: The influence of monosodium glutamate

Abstract

Monosodium glutamate (MSG) is widely considered to enhance the flavor of beef, chicken, fish, and vegetables. This effect may be due to the interaction of glutamate with free amino acids or other basic taste stimuli present in these foods. A single-bottle test was used in order to test the preference of Old World monkeys for an extended array of gustatory stimuli individually and in combination with MSG. Six male cynomolgus monkeys, maintained on an 18-h water deprivation schedule, were given 30 min access daily to a sapid stimulus or distilled water. The following stimuli (selected on the basis of prior experimentation) were tested alone and in combination with 0.03 M MSG: sucrose, fructose, glucose, maltose, polycose, sodium saccharin, glycine, sodium chloride, hydrochloric acid, tartaric acid, malic acid, citric acid, quinine hydrochloride, urea, and beef broth. The L-isomers of the following free amino acids also were tested: alanine, histidine, phenylalanine, proline, serine, valine. The addition of MSG to the stimuli listed above had no significant effect upon the monkeys' preference or aversion thresholds. Most suprathreshold stimuli that the monkeys neither preferred nor avoided were unaffected by the addition of MSG. The monkeys' preference for sugars was adversely affected in mixtures containing MSG, but other stimuli that humans report to be sweet tasting (alanine, glycine, polycose) were unaffected. The data from the present experiment demonstrate that MSG was capable of altering the monkeys' preference for some but not all of the gustatory stimuli tested. Because MSG did not enhance the monkeys' preference for the basic taste stimuli or free amino acids, the mechanism by which MSG enhances the taste of beef, chicken, and fish in humans remains unclear.