A subset of subjects displays extremes of sensitivity, and a battery of different psychophysical tests validated this observation. Statistical analysis showed that the rare T allele of single nucleotide polymorphism (SNP) R757C in TAS1R3 led to a doubling of umami ratings of 25 mmol MPG/L. Other suggestive SNPs of TAS1R3 include the A allele of A5T and the A allele of R247H, which both resulted in an approximate doubling of umami ratings of 200 mmol MPG/L. We confirmed the potential role of the human TAS1R1-TAS1R3 heteromer receptor in umami taste by recording responses, specifically to L-glutamate and inosine 5'-monophosphate (IMP) mixtures in a heterologous expression assay in HEK (human embryonic kidney) T cells.
ScienceDaily has more details:
In the study, Breslin and his team first conducted sensory tests on 242 individuals, who were asked to discriminate the taste of weak L-glutamate from salt. Approximately 5% were unable to tell the two tastes apart, indicating that certain people are highly insensitive to umami and thus have difficulty detecting low levels of this taste quality.
An additional 87 individuals were asked to assess the intensity of glutamate's umami taste. The subjects tasted five concentrations of glutamate and rated the umami intensity of each on a scale that ranged from 'no sensation' to 'the strongest imaginable.'
The researchers next examined DNA from these 87 individuals to look for variations in the genes that code for T1R1 and T1R3, two protein subunits that combine to form the G-protein coupled receptor T1R1-T1R3. Comparing DNA structure to the glutamate taste responses of each individual, they found that variations (known as SNPs; single nucleotide polymorphisms) at three sites on the T1R3 gene were associated with increased sensitivity to glutamate taste.
A fourth set of studies used in vitro cell biology techniques to provide additional evidence that T1R1-T1R3 is a human amino acid taste receptor. When human T1R1-T1R3 receptors were expressed in a host cell line, these cells were able to respond specifically to L-glutamate.
Together, the findings demonstrate that the T1R1-T1R3 receptor significantly affects human sensitivity to umami taste from glutamate, and that individual differences in umami perception are due, at least in part, to coding variations in the T1R3 gene.
These are not the only genes implicated in variation in taste perception. It seems there is a fair amount of genetic variation in taste & smell perception, just as there is genetic variation in color perception. As variation in the ability to consume various foods is controlled partly by genetics, it is not unsurprising that senses which allow one to perceive those foods may also vary.
I'd swear that back in the eighties, when I was in primary school, we were taught that the five basic flavours were sweet, sour, bitter, salty, and savoury. Of course, "savoury" is a vague term, meaning something like "having flavours culturally associated with main courses as opposed to desserts", and applicable to anything from bread to meat to vegetables (though I'm told that this sense of the word is not as common in America as it is elsewhere).
Was it sensible to import this "umami" word into English, on the grounds that it's far more chemically precise than "savoury", or would it have been better to adopt the more familiar word, giving it a new and more precise meaning for technical contexts? Personally, I've always thought this "umami" thing is a bit silly.