The ability to taste bitter thiourea compounds and related chemicals is a well-known human trait. The majority of individuals perceive these compounds, typified by the bitterness of 6-n-propylthiouracil (PROP) and phenylthiocarbamide (PTC), as moderately-to-extremely bitter. Approximately 30\% of the population is taste blind to these substances. It has been hypothesized that PROP/PTC tasters are more sensitive to other bitter tastes, sweet taste, the pungency of chili peppers, the astringency of alcohol, and the texture of fats. Tasters may also show lower preferences for foods with these taste qualities than nontasters who show the opposite set of responses (i.e., lower taste sensitivities and higher preferences for these sensory qualities). This pathway is illustrated in the following model: PROP Sensitivity --> Food Perception -->Preference --> Selection. Robust associations between PROP status and taste perceptions have been well documented. However, subsequent links to food preferences and diet selection have been more difficult to demonstrate. This is not surprising given the complexity of human ingestive behavior that is influenced by numerous factors including health attitudes, personality traits, and cultural norms. Our laboratory has been using PROP screening to investigate individual differences in the selection of bitter foods, especially bitter tasting vegetables and fruits that may have long-term health implications. This chapter will discuss new and recent findings addressing the following issues: 1) whether PROP-related differences in perception of bitter compounds predict the perception and liking of bitter foods; 2) the role of bitter taste modifiers; and 3) the influence of personal characteristics such as food attitudes and cultural background on PROP-related food preferences.
