Diets rich in vegetables and fruit lower the risk of cancer and other systemic diseases. Phytochemicals such as phenols, flavonoids, isoflavones, terpenes and glucosinolates have anti-oxidant and anti-carcinogenic properties and demonstrate a wide spectrum of tumor-blocking activities. Many of these phytochemicals have a bitter taste, which could lead to avoidance of the foods containing them. Taste also is the most important factor in food choice; it is more important than nutritional value, cost, convenience and weight control. The ability, however, to perceive some bitter substances is genetically mediated; about 25% of the population is unable to perceive the bitterness of 6-n-propylthiouracil (PROP), 50% can taste it, and 25% are considered supertasters. It has been shown that PROP tasters have a lower acceptance of bitter vegetables and salad greens. PROP tasters might therefore be less likely to adopt a diet for cancer prevention that emphasizes consumption of bitter vegetables. Very little is known about threshold and suprathreshold bitter perception of the phytochemicals naringin, limonin, quercetin, sinigrin and genistein. The purpose of this study is to determine how these bitter phytochemicals are perceived by (super) tasters and non-tasters of PROP. The knowledge gained through the proposed experiments will provide insight into the role genetic taste sensitivity plays in food preference and food choice. Detection thresholds for the five phytochemicals and sodium chloride and PROP will be determined with a maximum likelihood adaptive staircase method. Psychophysical functions for all seven substances will be measured with the Labeled Magnitude Scale. Subjects will also rate how much they like each of five concentrations of the seven substances. Furthermore, food preference data will be gathered. It is anticipated that this study will result in safe and usable ranges of stimulation for each of the phytochemicals, so that in the future data from children can be obtained. ? ?