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The Pennsylvania State University The Graduate School Department of Food Science BITTER RECEPTOR POLYMORPHISMS INFLUENCE BITTERNESS OF NON- NUTRITIVE SWEETENERS AND ALCOHOLIC BEVERAGE LIKING A Thesis in Food Science by Alissa Allen © 2013 Alissa Allen Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science May 2013 The thesis of Alissa Allen was reviewed and approved* by the following: John E. Hayes Assistant Professor of Food Science Thesis Advisor Kathleen Keller Assistant Professor of Health and Nutritional Sciences and Food Science Joshua Lambert Assistant Professor of Food Science Robert Roberts Professor of Food Science Head of the Department of Food Science *Signatures are on file in the Graduate School iii ABSTRACT Bitterness is largely aversive and commonly associated with lower liking and intake. However, the ability to perceive bitterness differs across individuals due to genetic variation within bitter receptor genes (TAS2Rs). The goal of the present thesis is to investigate effects of bitter receptor polymorphisms on liking and perception, of reported bitterness and sweetness of non-nutritive and the remembered liking of different alcoholic beverages. The work presented here compares genotypes for putatively functional polymorphisms in bitter receptor genes in attempt to explain individual differences. Major experimental findings include: Study 1- Polymorphisms (SNPs) in bitter receptors TAS2R9 and TAS2R31 explains 13.4% of the variation in the perceived bitterness from Acesulfame K (AceK). Study 2 - The non-nutritive sweetener rebaudioside A (RebA) elicited greater perceived bitterness than rebaudioside D (RebD), with no difference in sweetness intensity. SNPs that were previously reported in Study 1 to explain AceK bitterness were not associated with perceived bitterness of RebA or RebD. Study 3 - Liking ratings for non-sweet alcoholic beverages were associated with TAS2R38 diplotype. However, the diplotype failed to predict liking for sweet alcoholic beverages. This latter finding was as anticipated, as we would not expect TAS2R38 to meditate liking or intake for foods or beverages where mixture suppression removes bitterness. Together these findings expand the understanding of individual differences in taste perception with the respect to polymorphisms within taste receptor genes. With this knowledge, researchers and product developers may be better positioned to explore consequences of genetic variations, to further expand the relationship associated with intensity, liking and intake, and to develop tailored products. iv TABLE OF CONTENTS LIST OF FIGURES ................................................................................................................. v ACKNOWLEDGEMENTS ..................................................................................................... vii Chapter 1 Literature Review ................................................................................................... 1 Introduction ...................................................................................................................... 1 Importance of tase perception .......................................................................................... 4 Individual differences in perception ................................................................................ 15 Taste Receptors ................................................................................................................ 21 Bitterness in beverages .................................................................................................... 26 Sensations from alcoholic beverages ............................................................................... 38 Conclusions ..................................................................................................................... 41 Aims and Hypothesis ....................................................................................................... 45 Chapter 2 Bitterness of the non-nutritive sweetener Acesulfame Potassium vaires with polymorphisms in TAS2R9 and TAS2R3 ......................................................................... 46 Introduction ...................................................................................................................... 47 Materials and Methods ..................................................................................................... 49 Results .............................................................................................................................. 55 Discussion ........................................................................................................................ 63 Chapter 3 Rebaudioside A and Rebaudioside D bitterness do not covary with acesulfame-K or polymorphisms in TAS2R9 and TAS2R31 ............................................ 70 Introduction ...................................................................................................................... 71 Materials and Methods ..................................................................................................... 74 Results .............................................................................................................................. 78 Discussion ........................................................................................................................ 86 Chapter 4 Bitter receptor alleles differentially influence alcoholic beverage liking .............. 89 Introduction ...................................................................................................................... 90 Materials and Methods ..................................................................................................... 92 Results .............................................................................................................................. 95 Discussion ........................................................................................................................ 100 Chapter 5 Conclusions and further steps ................................................................................ 105 References ............................................................................................................................... 108 Appendix A: Chapter 2 Supplemental figure .......................................................................... 120 v LIST OF FIGURES Figure 1-1: Green’s Labeled Magnitude Scale, with ‘strongest imaginable’ located at 100. For the gLMS, the top anchor is changed to ‘strongest imaginable sensation of any kind’. The gVAS only includes the ‘no sensation’ and ‘strongest imaginable sensation of any kind’. Values are not including in the participant’s scale. Figure taken from [(Green 1993)] ............................................................................................... 14 Figure 1-2: Amino acid sequence and orientation of the bitter taste receptor TAS2R38. Figure is from [(Wiener 2011)] ....................................................................................... 23 Figure 1-3: Sweetness and bitterness response curves for sucrose, acesulfame-K, aspartame and rebaudioside A. These figures are taken from [(DuBois, Walters et al. 1991)] ............................................................................................................................... 32 Figure 2-1: Effect of the TAS2R9 Val187Ala polymorphism on the bitterness and sweetness of AceK and the bitterness of PROP. The bitterness of AceK was significantly different across genotype; no effect was observed for AceK bitterness or PROP bitterness (p-values provided in text). Adjectives refer to semantic labels on a general Labeled Magnitude Scale (gLMS; see text). BD refers to ‘barely detectable’... ..................................................................................................................... 56 Figure 2-2: LD Plot for TAS2R SNPs on chromosomes 7 (top) and 12 (bottom). Numbers indicate rounded R-squared values and shading indicates exact R-squared values generated via Haploview ................................................................................................. 57 Figure 2-3: Effect of the TAS2R31 Val240Ile allele on the bitterness and sweetness of AceK and the bitterness of PROP. The bitterness of AceK was significantly different across genotype; no effect was observed for AceK bitterness or PROP bitterness (p- values provided in text). Adjectives refer to semantic labels on a general Labeled Magnitude Scale (gLMS; see text). BD refers to ‘barely detectable’ .............................. 59 Figure 2-4: Effect of AV/PA TAS2R38 diplotype. PROP bitterness differed by diplotype; differences in AceK bitterness or sweetness across diplotype were not significant (p- values provided in text). ................................................................................................... 61 Figure 3-1: Mean (±Std Error) gLMS ratings for bitterness and sweetness of AceK (collected previously: indicated by the grey 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; see text). BD refers to ‘barely detectable’. .. 80 vi Figure 3-2 Scatter plots showing (top) sweetness