Perceptions and acceptance of grapefruit-like model beverages that vary in taste colour and aroma sensory properties : effects of sensitivity to bitter taste and TAS2R38 and TAS2R19 bitter receptor genes

Abstract

Grapefruit juice is an excellent source of many nutrients and phytochemicals that contribute to a healthy diet. Currently, there is an increasing interest in grapefruit products because consumption appears to be associated with a reduced risk of certain chronic diseases, such as obesity, diabetes, cancers and cardiovascular disease. The consumption of grapefruit (Citrus paradisi Macfadyen) however remains low in South Africa as some individuals like grapefruit and others do not and the reason/s for this variation is not clear. Taste, aroma and colour are important fruit product quality factors that influence consumer preferences. Perception of grapefruit flavour does not depend on only one individual sense, but is the result of multisensory integration of unimodal signals. Where there is a mixture of appearance, taste and aroma signals, cross-modal sensory interaction occurs which may potentially change the intensity and character of flavour perception. Sensory perception is interpreted differently across individuals. The main objective of the study was to determine the effect of varying the bitterness, sweetness, colour and aroma intensities of a grapefruit-like model beverage on the perception of sensory properties and consumer liking of the beverages with the aim of giving guidance to breeders on selection and improvement of grapefruit traits to optimize hedonic value. The second objective of this study was to determine the effects of sensitivity to bitter taste [as determined through 6-propylthiouracil (PROP) taster classification] and genetic variation in TAS2R38 and TAS2R19 SNP genotypes on hedonic rating of the flavour of grapefruit-like beverages differing in bitter/sweet taste intensity. A factorial design was used to formulate 36 grapefruit-like beverages with deflavoured clarified apple juice as base and modification of bitter taste (3 levels), sweet taste (3 levels), aroma intensity (2 levels) and colour (red or yellow). Descriptive analysis was used to describe the sensory profiles of the 36 beverages. Hedonic rating of colour, aroma and flavour of the 12 most diverse beverages from the design was measured with a consumer panel. Sensitivity to bitter taste of 96 young African females (18-24 years) was measure and the respondents classified into PROP taster groups. DNA was extracted from the saliva of the participants for genotyping of TAS2R38 and TAS2R19 bitter receptor genes. The subjects also rated the flavour of grapefruit-like beverages differing in bitter taste intensity for hedonic value. The results showed that varying the bitterness, sweetness, colour and aroma intensity of the grapefruit-like model beverage have an effect on the sensory properties and consumer liking of the beverages. The concentration of naringin in the grapefruit-like beverage increased the bitter taste, aftertaste and grapefruit flavour intensity of the drink. Consumers preferred grapefruit-like beverages with a red colour and low bitterness. Sensitivity to the bitterness of grapefruit beverages and whether there is an association between genetics of bitter taste perception and liking of grapefruit were further explored. The results then showed that respondents’ sensitivity to bitter taste, as well as genetic variation in TAS2R38 and TAS2R19 (single SNP genotypes) are partly responsible for the lower liking of grapefruit model beverages with higher naringin (more bitterness) concentration. In this study, sensitivity of respondents to bitter taste (PROP status) has been linked to preference for red coloured grapefruit beverages, grapefruit beverages with low bitterness/high sweetness and grapefruit-like beverages with low intensity of grapefruit aroma. This is the first study to report on consumers’ perception and acceptance of grapefruit-like model beverages that vary in taste, colour and aroma sensory properties. People differ genetically in bitter taste sensitivity and this research demonstrated the role of some genetic variables (notably rs10772420 of the TAS2R19 SNP genotype and both rs713598 and rs1726866 of the TAS2R38 SNP genotypes). It is the first study showing the effect of TAS2R38 SNP genotypes on grapefruit liking. It is also the first study to determine the effect of PROP taster status, perception of grapefruit beverage characteristics (e.g. bitterness level, colour type and aroma level) and variation in TAS2R38 and TAS2R19 SNP genotypes on hedonic ratings for colour, aroma and flavour of grapefruit-like beverages in a group of South African females. So far populations from Africa have been under represented in similar studies. Most studies where a link between rs10772420 and lower bitterness perception and greater liking for unsweetened grapefruit juice was established, included only Caucasians. Studying the role of genetic differences in sensitivity to PROP bitterness (e.g. in taster status) in modulating multisensory grapefruit flavour perception is needed to determine why the liking for grapefruit varies between individuals. The findings of this study can help researchers and breeders to change properties and traits in grapefruit varieties, can assist product formulators and quality assurance staff to optimize the flavour of grapefruit products for consumer acceptance and to make the generic product more acceptable to a larger portion of the South African population. However, the sample of respondents used in this research represents only a small portion of the South African population and therefore cannot be extrapolated to represent the population. The insights gained from this subgroup may be used to enhance the acceptance of grapefruit products for the larger population.