Differences in a taste receptor gene influences the taste sensitivity of humans, accounting for individual differences in taste preferences and food selection.
In addition to genes, age and culture also contribute to taste preferences, at times overriding the influence of genetics.
It may be that childhood represents a time of heightened bitter taste sensitivity in some children, which lessens with age, say scientists at the US-based Monell Chemical Senses Center.
"Such a scenario would account for the increase of vegetable consumption that often occurs as children mature into adulthood," they add.
In the study, published in the February 2005 issue of Pediatrics (115 (2), e216-e222), researchers compared taste sensitivity and food-related behaviours across three genotypes of the TAS2R38 gene, which encodes a taste receptor responsive to bitter taste.
The scientists classified 143 children and their mothers into three groups based on their TAS2R38 genotype: Type AA had two bitter-insensitive sites (alleles), type PP had two bitter-sensitive alleles, and type AP had one of each.
To provide a behavioural measure of sensitivity to bitter taste, children - who were between 5 and 10 years of age - and mothers categorised three concentrations of a bitter-tasting compound (propylthiouracil; PROP) as tasting either "like water" or "bitter or yucky."
Having a bitter-sensitive allele (P) on the TAS2R38 receptor gene predicted sensitivity to the bitter taste of PROP in both children and mothers. While 70 per cent of children and 50 per cent of mothers with either AP or PP alleles detected bitterness in the weakest PROP solution, the same solution tasted bitter to only a few individuals with two bitter-insensitive alleles (AA).
Children and adults with two bitter-sensitive alleles (PP) were more sensitive to bitter taste than those with just one (AP).
Genetic influences on bitter taste sensitivity were in some cases modified by age. In individuals with the mixed AP genotype, children were more sensitive to bitter than adults, with 64 per cent of children but only 43 per cent of adults able to detect bitterness in the weakest PROP solution.
The researchers conclude:"It may be that childhood represents a time of heightened bitter taste sensitivity in some children, which lessens with age.
Such a scenario would account for the increase of vegetable consumption that often occurs as children mature into adulthood."
The bitter receptor genotype also predicted children's sweet preference, along with their preference for sweet-tasting beverages and foods. Children with a bitter-sensitive allele (PP or AP) preferred higher concentrations of sucrose solutions than did bitter-insensitive (AA) children, and were more likely to identify carbonated drinks as a preferred beverage.
They also were less likely to name milk or water as one of their two favourite beverages. Favourite cereals and beverages of PP children had higher sugar content than corresponding selections of AA children.
According to study co-author, geneticist Danielle Reed: "The children most sensitive to PROP liked sweet more, but the reason for this relationship is not known." She claims the difference could be due to taste receptor biology or it could be because those who are most bitter sensitive use more sugar to mask unpleasant tastes in food, and therefore come to prefer it more.
"Whatever the explanation, this is an important puzzle to solve,"she adds.
Unlike children, bitter receptor genotype did not influence sweet preference in adults. Instead, effects of race/ethnicity were the strongest determinants.
"What I find most interesting is that you do not see the relationship between bitter taste receptor genotype and sweet preference in adults. The forces of experience and culture appear to have overridden the genetic effect," comments co-author Julie Mennella.
The scientist at Monell will continue to examine how experience and genetics interact to determine why consumers - both adults and children - like the foods they do.