Rebaudioside A and Rebaudioside D bitterness do not covary with Acesulfame K bitterness or polymorphisms in TAS2R9 and TAS2R31

Abstract

In order to reduce calories in foods and beverages, the food industry routinely uses non-nutritive sweeteners. Unfortunately, many are synthetically derived, and many consumers have a strong preference for natural sweeteners, irrespective of the safety data on synthetic non-nutritive sweeteners. Additionally, many non-nutritive sweeteners elicit aversive side tastes such as bitter and metallic in addition to sweetness. Bitterness thresholds of acesulfame-K (AceK) and saccharin are known to vary across bitter taste receptors polymorphisms in TAS2R31. RebA has shown to activate hTAS2R4 and hTAS2R14 in vitro. Here we examined bitterness and sweetness perception of natural and synthetic non-nutritive sweeteners. In a follow-up to a previous gene-association study, participants (n=122) who had been genotyped previously rated sweet, bitter and metallic sensations from rebaudioside A (RebA), rebaudioside D (RebD), aspartame, sucrose and gentiobiose in duplicate in a single session. For comparison, we also present sweet and bitter ratings of AceK collected in the original experiment for the same participants. At similar sweetness levels, aspartame elicited less bitterness than RebD, which was significantly less bitter than RebA. The bitterness of RebA and RebD showed wide variability across individuals, and bitterness ratings for these compounds were correlated. However, RebA and RebD bitterness did not covary with AceK bitterness. Likewise, single nucleotide polymorphisms (SNPs) shown previously to explain variation in the suprathreshold bitterness of AceK (rs3741845 in TAS2R9 and rs10772423 in TAS2R31) did not explain variation in RebA and RebD bitterness. Because RebA activates hT2R4 and hT2R14, a SNP in TAS2R4 previously associated with variation in bitterness perception was included here; there are no known functional SNPs for TAS2R14. In present data, a putatively functional SNP (rs2234001) in TAS2R4 did not explain variation in RebA or RebD bitterness. Collectively, these data indicate the bitterness of RebA and RebD cannot be predicted by AceK bitterness, reinforcing our view that bitterness is not a simple monolithic trait that is high or low in an individual. This also implies consumers who reject AceK may not find RebA and RebD aversive, and vice versa. Finally, RebD may be a superior natural non-nutritive sweetener to RebA, as it elicits significantly less bitterness at similar levels of sweetness.

Keywords: Project GIANT-CS; bitterness; genetics; non-nutritive sweetener; rebaudioside A; rebaudioside D; taste phenotype.

Figure 1

Scatter plots showing (a) sweetness and (b) bitterness intensities for RebA and RebD to illustrate covariation of these compounds within an individual, and histograms are shown along the axes to illustrate the substantial amount of variation found across individuals. Mean sweetness was not significantly different between RebA and RebD, although both show substantial individual differences. Mean bitterness differed, with RebD showing significantly less bitterness at the concentrations tested here. Again, substantial individual differences in bitterness were observed for these sweeteners.

Figure 1

Scatter plots showing (a) sweetness and (b) bitterness intensities for RebA and RebD to illustrate covariation of these compounds within an individual, and histograms are shown along the axes to illustrate the substantial amount of variation found across individuals. Mean sweetness was not significantly different between RebA and RebD, although both show substantial individual differences. Mean bitterness differed, with RebD showing significantly less bitterness at the concentrations tested here. Again, substantial individual differences in bitterness were observed for these sweeteners.

Figure 2

Mean (±Std Error) gLMS ratings for bitterness and sweetness of AceK (collected in a separate test session: indicated by the gray box), RebA, RebD, aspartame, sucrose and gentiobiose are reported here. The sweetness ratings for AceK, RebA and RebD were not statistically different while bitterness was significantly different across the four non-nutritive sweeteners (see text). Adjectives refer to semantic labels on a general Labeled Magnitude Scale (gLMS). BD refers to ‘barely detectable’.

Figure 3

Correlations of bitterness ratings between RebA and RebD, AceK and aspartame.

Figure 4

Effect of the TAS2R9 Val187Ala polymorphism on the bitterness of AceK, RebA and RebD. As expected, the bitterness of AceK (collected on a separate day) was significantly different across genotype for these individuals; conversely, no effect of genotype was observed for RebA or RebD (see text).

Figure 5

Same as Figure 4, except for the Val240Ile polymorphism in TAS2R31. AceK bitterness ratings were significantly different across genotype, as expected, while there was no evidence of a effect for RebA and RebD (see text).