Findings published by Monell Center scientists in the American Journal of Clinical Nutrition also indicate that variations in the genes that code for the proteins T1R1 and T1R3 correspond to individual variation in sensitivity to the perceived intensity of umami taste.
The two proteins combine to form the G-protein coupled receptor T1R1-T1R3.
"These findings bolster our understanding of human taste variation and individual differences in tastes for essential nutrients," said senior author Paul Breslin PhD, a sensory geneticist at Monell.
Together with sweet, bitter, salty and sour, umami makes up the five taste sensations detectable by humans. It is the taste quality associated with several amino acids, especially the amino acid L-glutamate, and is described as a “hearty, savoury” taste, playing a part in the profile of a number of foods, including meat, fish, vegetables and dairy products.
Commenting on clinical implications of the work, Breslin said: "Protein-energy malnutrition is one of the leading causes of death in children worldwide. Increased understanding of amino acid taste receptors may help nutritionists target the appetites of protein-malnourished children to provide good-tasting dietary supplements that kids will readily accept."
Breslin and his co-workers recruited 242 people and asked them to discriminate between the taste of weak L-glutamate and salt. About 5 per cent could not differentiate between the two tastes, indicating that certain people are highly insensitive to umami.
A second study with 87 people analysed the subjects’ sensitivity to five different concentrations of glutamate. DNA from these 87 individuals was examined in order to identify variations in their genes that code for T1R1 and T1R3.
By comparing the subjects’ glutamate taste responses and their DNA coding, Breslin and his co-workers found that variations at three sites on the T1R3 gene were associated with increased sensitivity to glutamate taste.
An additional in vitro study used human cells (human embryonic kidney T cells) expressing the T1R1-T1R3 receptors, and found that these cells did indeed respond specifically to L-glutamate.
“There is a reliable and valid variation in human umami taste of L-glutamate,” wrote the researchers in the AJCN. “Variations in perception of umami taste correlated with variations in the human TAS1R3 gene.
“Thus, [the putative human taste receptor TAS1R1-TAS1R3] likely contributes to human umami taste perception,” they concluded.
Breslin added that the researchers wanted to deepen their understanding of genetic influences on umami taste perception.
"This will in turn help in the discovery of other taste receptors that may play a role in umami taste and aid in our understanding of protein appetites,” he said.
The other researchers involved in the study were affiliated with Philadelphia-based Integral Molecular Inc, and Rutgers University.
Source: American Journal of Clinical Nutrition
Published online ahead of print, doi: 10.3945/ajcn.2009.27462N
“Perceptual variation in umami taste and polymorphisms in TAS1R taste receptor genes”
Authors: Q.-Y. Chen, S. Alarcon, A. Tharp, O.M. Ahmed, N.L. Estrella, T.A. Greene, J. Rucker, P.A.S. Breslin