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.

Chez la banane dessert, les saveurs sucrée et acide, caractéristiques importantes pour les consommateurs, sont pilotées par les teneurs en acides citrique et malique. Ce travail a donc porté sur l’étude des processus physiologiques qui pilotent l’accumulation de ces acides dans la pulpe de banane (Musa sp. AA) en combinant analyse expérimentale et modélisation écophysiologique. Nous nous sommes notamment intéressés à l’effet du génotype et des conditions de croissance du fruit en adoptant une approche intégrative liant les phases pré et post récolte.Les effets de la charge en fruit, de la fertilisation potassique, et du stade de récolte sur l’accumulation du citrate et du malate dans la pulpe ont été étudiés expérimentalement. La variabilité génotypique a été prise en compte en choisissant trois génotypes présentant des acidités contrastées à maturité. Des différences d’évolution des teneurs en acides, dues à des modifications métaboliques, ont été observées entre les génotypes pendant les phases pré et post récolte. Le stade de récolte a eu un effet significatif sur les teneurs en acides des fruits pendant la maturation post récolte. La charge en fruit et la fertilisation potassique n’en ont eu aucun. Des modèles écophysiologiques ont été développés pour prédire différents critères d’acidité de la banane en pré et post récolte. Le pH et l’acidité titrable ont été prédits par un modèle d’équilibres acido-basiques, la teneur en malate par un modèle de stockage vacuolaire, et la teneur en citrate par un modèle du cycle de Krebs. Ces modèles ont permis d’identifier les processus physiologiques clés qui pilotent l’acidité de la banane. Des paramètres génotypiques ont été identifiés liés à l’activité de l’enzyme malique mitochondriale et à celle des transporteurs mitochondriaux du malate pour le modèle citrate, et à l’activité des pompes à protons vacuolaire ATPases pour le modèle malate. Ces modèles ont également permis de disséquer l’effet des conditions de croissance du fruit sur l’acidité de la banane. L’intégration des modèles développés dans un modèle d’élaboration de l’acidité et son utilisation potentielle pour l’amélioration variétale sont discutées. / Citric and malic acids determine the sourness and sweetness of banana pulp, which are the two main determinants of consumer preferences. The present work focused on the physiological processes controlling the accumulation of citric and malic acids in banana pulp (Musa sp. AA) using experimental analysis and ecophysiological modeling. We chose an integrative approach linking the pre and post-harvest stages, and focused on the effect of genotype and fruit growing conditions. Experiments were conducted to study the effect of fruit load, potassium fertilization and fruit age at harvest on the accumulation of citrate and malate in banana pulp. To account for genotypic variability, three genotypes with contrasting acidity at the eating stage were studied. Major differences in the pattern of citrate and malate accumulation were found in the three cultivars both during growth and post-harvest ripening and were shown to be the result of metabolic changes. The harvest stage had a significant effect on the concentrations of acids during post-harvest ripening. Fruit load and potassium fertilization had no effect.Ecophysiological models were developed to predict several banana acidity criteria during the pre and post harvest stages. pH and titratable acidity were predicted by a model of acid-base reactions; malate content by a model of vacuolar storage; and citrate content by a model of the TCA cycle. These models led to the identification of the key physiological processes that control banana acidity. Genotypic parameters were identified, which were related to the activity of the mitochondrial malic enzyme and of the malate mitochondrial carriers in the citrate model, as well as to the activity of the vacuolar proton pump, ATPase, in the malate model. The two models were also used to analyze the effects of fruit growth conditions on banana acidity.Combining the three models in a global model of banana acidity, and the possible use of this model for varietal improvement are discussed.