Together with sweet, bitter, salty and sour, umami makes up the five taste sensations detectable by humans. It is described as a “hearty, savoury” taste, and has a part to play in the profile of a number of foods, including meat, fish, vegetables and dairy products.
Finding ways to enhancing foods’ an umani flavour is a target for food developers – not least since it can help reduce the use of salt to enhance flavours, in line with healthier eating strategies.
Researchers from Senomyx and Biopredict say that the umami taste of L-glutamate, an amino acid, can be “drastically enhanced” by 5’ribonucleotides.
“The synergy is a hallmark of this taste quality,” they wrote in the Proceedings of the National Academy of Science (PNAS).
The ability to identify umami is said to be down to two taste receptors, T1R1 and T1R3. The study set out to elucidate the synergy between L-glutamate and 5’ribonucleotides, using chimeric TR1 receptors, site-directed mutagenesis, and molecular modeling.
Lead researcher Xiaodong Li and team propose that the T1R1 receptor is shaped like a Venus flytrap – the iconic carnivorous plant that traps flying insects for nourishment. The L-glutamate binds inside the receptor near to the ‘hinge’, they say, and the ‘flytrap’ closes around it.
The 5’ ribonucleotides bind on an adjacent side of the flytrap, near the opening, “to further stabilize the closed conformation” – that is, to allow the glutamate to stay in the ‘mouth’ of the receptor for longer.
The researchers say that the mechanism “may apply to other class C-G protein coupled receptors” – thus contributing to knowledge in other areas as well.
This may allow researchers to elucidate taste preferences and uncover the workings of other similar proteins, according to the researchers.
PNAS, December 30 2008, vol 105, no 52
"Molecular mechanism for the umami taste synergism"
Authors: Feng Zhang, Boris Klebansky, Richard M Fine, Hong Xu, Alexey Pronin, Haitian Liu, Catherine Tachdjian, and Xiaodong Li