Genes Manage How People Taste Sweeteners

Penn State research looks at different consumer taste perceptions of ace-K and stevia.

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Genetics may play a role in how people's taste receptors send signals, leading to a wide spectrum of taste preferences, according to scientists at Pennsylvania State University (Penn State), University Park, Pa. These varied, genetically influenced responses may mean that food and beverage companies need a range of non-nutritive sweeteners to accommodate different consumer tastes.

"Genetic differences lead to differences in how people respond to tastes of foods," said John Hayes, assistant professor in food science and director of the sensory evaluation center.

Based on the participants' genetic profile, researchers were able to explain the reactions of subjects in a taste test when they sampled acesulfame potassium (ace-K) in the laboratory. Ace-K is a man-made non-nutritive sweetener commonly found in carbonated soft drinks and other products.

Non-nutritive sweeteners are sweeteners with minimal or no calories.

While some people find ace-K sweet, others find it both bitter and sweet.

The researchers, who reported their findings in a recent issue of the journal Chemical Senses, said that variants of two bitter taste receptor genes -- TAS2R9 and TAS2R31 -- explained some of the differences in ace-K's bitterness. These two taste receptor genes work independently, but they can combine to form a range of responses, said Alissa Allen, doctoral student in food science, who worked with Hayes.

Humans have 25 bitter-taste receptors and one sweet receptor that act like locks on gates. When molecules fit certain receptors like keys, a signal is sent to the brain, which interprets these signals as tastes -- some pleasant and some not so pleasant, Allen said.

Our work suggests ingredient suppliers may want to consider commercializing reb-D, as it provides similar sweetness to reb-A with much less bitterness

– John Hayes

In another study recently published in the journal Chemosensory Perception, Allen had 122 participants taste two stevia extracts, rebaudioside A (reb-A) and rebaudioside D (reb-D). Those are the two glycosides from the stevia plant that currently are most researched and used as sweeteners. Stevia is a native South American plant that has served as a sweetener for centuries, according to the researchers. While the plant is becoming more popular as a natural non-nutritive sweetener, consumers have reported off-tastes from stevia-based sweeteners, including bitterness.

The researchers found that reb-A and reb-D bitterness varies greatly across subjects, but this was not related to whether or not participants found ace-K bitter. Likewise, variation in the TAS2R9 and TAS2R31 genes did not predict reb-A and reb-D bitterness. They also found that of the stevia extracts, the participants considered reb-D to be much less bitter than reb-A.

Most initial research and product development work in stevia focused on reb-A, and that was the ingredient that received generally recognized as safe (GRAS) approval in 2008. Only recently has reb-D come to the fore.

"Our work suggests ingredient suppliers may want to consider commercializing reb-D, as it provides similar sweetness to reb-A with much less bitterness," said Hayes.

Hayes also said that researchers are just beginning to understand the molecular basis of taste perception.

"We've known for over 80 years that some people differ in their ability to taste bitterness, but we have only begun to tease apart the molecular basis of these differences in the last decade," Hayes said.

The National Institutes of Health supported the Penn State research.

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