The health maintaining properties of citrus consumption are attributed to the wide assortment of bioactive compounds. Consumption of grapefruit along with certain medications, however, is posing a risk of drug toxicity and side reactions. The first study involved isolation of bioactive furocoumarins with a combination of chromatographic techniques and synthesis. Five furocoumarins namely, dihydroxybergamottin, paradisin A, bergamottin, bergaptol and geranylcoumarin were isolated from grapefruit and series of furocoumarin monomers and paradisin A were synthesized. The second study involved influence of pre- and post-harvest factors on the levels of furocoumarins in grapefruit juice. Considerable differences were observed in the levels of these compounds in different grapefruit cultivars. Ray Red showed the lowest levels of all three furocoumarins and Duncan contains the highest amount of DHB and bergamottin, where as the highest levels of paradisin A was observed in Star Ruby. The highest levels of DHB and bergamottin were found in Flame cultivar grown in California. The changes in the levels of these furocoumarins during the season in Rio Red and Marsh White grapefruit cultivars were evaluated. The third study investigated biological activities of grapefruit juices and furocoumarins. Grapefruit and Pummelo juices were found to be potent inhibitors of cytochrome CYP3A4 and CYP2C9 isoenzymes at 5% concentration while CYP2D6 was less affected. Among the five furocoumarins tested, the inhibitory potency was in the order of paradisin A>dihydroxybergamottin>bergamottin>bergaptol>geranylcoumarin at 0.1 µM to 0.1 mM concentrations. A fourth study investigated the effect of furocoumarins on bacterial auto-inducer signaling, and found that furocoumarins are potent inhibitors of AI-1 and AI-2 activities at 0.01% concentration. In a fifth study, involving synthesized furocoumarin monomers and dimer on anti-proliferative activities on normal and cancer cell lines, furocoumarins found to be non-toxic to normal cells. However, bergamottin showed a significant anti-proliferative activity in HT-29 and MCF-7 cell lines. This dissertation indicates that furocoumarins are bioactive compounds from grapefruit juice with potent inhibitory property of major drug metabolizing cytochrome P450 isoenzymes. Furocoumarins show a considerable variation between varieties, location and season. These results corroborate the involvement of furocoumarins in grapefruit drug interaction.

Peppers are a rich source of diverse bioactive compounds with potential health-promoting properties. The levels of bioactive compounds and antioxidant activity can be affected by analytical methods, pre-harvest factors, and the quality of peppers. In order to understand the nutrient composition and antioxidant activity in peppers, determination of factors influencing the contents of bioactive compounds is important. The overall objectives were to determine the efficient conditions of sample preparation and the impact of pre-harvest factors affecting bioactive compounds and antioxidant activity. Optimal extraction procedures were developed, and HPLC methods were validated for bioactive compounds in peppers. The highest flavonoids were extracted in ethanol, while myricetin was extracted using N-N-dimethylformamide. Optimized conditions for flavonoids were obtained during 3 h of extraction time and hydrolysis in M HCl for 60 min at 95 degrees C. Capsaicinoids and ascorbic acid were simultaneously separated and extracted using a solvent mixture consisting of 3% metaphosphoric acid: ethanol (2:8) after 30 min of sonication. To determine the relationship between bioactive compounds and antioxidant activities in pepper extracts from different solvent properties, bioactive compounds were analyzed, and the antioxidant activities were assayed by 2,2,-Diphenyl-1-picryl hydrazyl (DPPH), reducing power, and degradation of deoxyribose. Hexane extracts had the highest levels of capsaicinoids and carotenoids, while methanol extracts had the highest levels of flavonoids. Strong DPPH scavenging activity and reducing power were found in lipophilic extracts, while hydrophilic extracts were appropriate for inhibition of deoxyribose degradation. Variation in content of ascorbic acid, capsaicinoids, and flavonoids was evaluated at immature and mature stages of pepper cultivars in different locations over two years. Mature peppers contained the highest levels of capsaicinoids and ascorbic acid. Flavonoids were variable at different maturity stages. Interactions between pre-harvest factors and bioactive compounds were highly significant. This study demonstrated the efficient sample preparation methods and simultaneous separation of bioactive compounds, which reduces analysis time and leads to reduced cost. The antioxidant properties were strongly associated with the concentration of bioactive compounds based on selective pepper extracts. The pepper quality can be improved by using appropriate pre-harvest conditions that increase the levels of bioactive compounds in peppers.