Is there a generalized sweetness sensitivity for an individual? A psychophysical investigation of inter-individual differences in detectability and discriminability for sucrose and fructose

- Individual's detection thresholds to sucrose and fructose are not correlated.
- The slope parameter of an individual's psychometric function is sugar-specific.
- Individuals may vary in discriminability between sucrose and fructose above thresholds.
- Inter-individual perceptual differences are important for relative sweetness ratios.

Despite the historical interest in the taste of sweetness, a seemingly fundamental question has not been properly addressed. That is, whether an individual's sensitivity can be generalized across different sugars. An answer to this question has a close relevance to illuminating the sensory physiology of the gustatory system, as well as to practical research of sucrose substitution. A cross-disciplinary review highlights two weak links with the psychophysical methods that have been employed in the literature. The present paper describes an empirical investigation of inter-individual differences in detectability and discriminability for two types of common sugars - sucrose and fructose, using psychometric functions (PF) and a controlled sensory discrimination test. The study found six of the 12 judges had significantly different thresholds for sucrose and fructose (p < 0.05), with no consistent pattern in the direction of differences. This observation challenges the conventional belief that people hold the same perception of relative difference in sweetness across substances. For seven judges, the individually-fitted PFs exhibited different shapes for the tested sugars, implying the detection processing might be substance-specific. Also, inter-individual differences were observed in the controlled discrimination task for sucrose and fructose at a supra-threshold level. These findings are discussed in relation to their theoretical, practical and methodological values. While this study uses sucrose and fructose as exemplars, the findings may provide important insights into sweetness perception in general.