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Antioxidant activity is widely used as a parameter to characterize different plant materials for potential health benefits. This activity is related with compounds capable of protecting a biological system against the harmful effect of reactions that can cause excessive oxidation, involving reactive oxygen and nitrogen species (RONS). There has been growing interest in the beneficial health effects of consuming fruits and vegetables. Mainly, the presence of lycopene, ascorbic acid, and phenolic antioxidants is believed to have the protective mechanism. The free radical-scavenging activities of grapefruit extract of `Rio Red', `Marsh White', and commercial juice were extracted with different solvents, such as hexane, ethyl acetate, and chloroform. The dried extracts were screened for their radical scavenging activity using the α,α -diphenyl-β-picrylhydrazyl (DPPH) method. The ethyl acetate extracts of commercial juice and `Marsh White' were found to possess more radical scavenging activity compared with the other two extracts. However, chloroform extracts of `Rio Red' grapefruit were the most active, which may be ascribed to the presence of more lycopene. Furthermore, the antioxidant capacity of `Rio Red' and `Marsh White' extracts was assayed through the phosphomolybdenum method and expressed as equivalent to ascorbic acid (μmol·g^-1 of the extract). The order of antioxidant capacity for `Rio Red' extracts was found to be hexane > chloroform > ethyl acetate, while the order for `Marsh White' was chloroform > hexane > ethyl acetate. The results indicate that the extent of antioxidant activity of the extract is in accordance with the amount of lycopene/phenolics present in that extract; commercial juice and `Rio Red' may provide a good source of antioxidants.

Irradiation of fruit and vegetables can potentially be used by industry as a quarantine method to contain insect pests, microorganisms, and to extend shelf life. Gamma, electron beam, and ultraviolet radiation are the most frequently used radiation techniques. These radiation treatments have an effect on bioactive compounds. Grapefruit juice contains bioactive compounds such as limonoids, flavonoids, and furocoumarins. Bioactive furocoumarins in grapefruit juice have been found to increase the bioavailability of many drugs. Bergamottin, dihydroxybergamottin, and paradisin A are major furocoumarins that are shown to inhibit the activity of CYP P450 3A4 and P-gylcoprotein, which are involved in the first pass metabolism of drugs in the gut. This results in a dose-dependent increase of the drug beyond what is intended. Furocoumarins are photoreactive compounds and will readily react to ultraviolet radiation. The effect of various doses of ultraviolet radiation was investigated on `Rio Red' and `Marsh White' grapefruit. Grapefruit juice (50 mL) was irradiated with Ultraviolet A, B, and C radiation for either 5 or 10 min. Treated and control juice was extracted with 100, 50, and 50 mL of ethyl acetate. The extract was then dried and reconstituted with methanol and filtered through a 0.4-μm PTFE membrane filter. The methanol extracts were analyzed by HPLC and the concentrations of bergamottin, dihydroxybergamottin, and paradisin A were compared for UVA, UVB, UVC, and control. This project is based upon work supported by the USDA-CSREES under Agreement USDA IFAFS # 2001 52102 02294 and USDA # 2005-34402-14401 “Designing Foods for Health” through the Vegetable & Fruit Improvement Center.

Food and drug interaction has been under discussionm and specifically grapefruit and drug interaction has been under investigation, in recent years. Irradiation of food has multiple benefits in food preservation through several processes, such as sprout inhibition, disinfection, decontamination, delayed maturation, and sterilization. When ionizing radiation is passed through food, it may affect the functional components, including organoleptic characteristics. In addition to naringin, dihydroxybergamottin, paradisin A, and bergamottin, as well as their isomers, are considered putative bioactive furocoumarins present in the grapefruit juice, which interfere with the first pass metabolism of the drugs. These compounds inhibit the activity of CYP P450 3A4 and P-glycoprotein, which, in turn, will increase bioavailability of certain medications. In order to investigate the effect of pre-and postharvest practices on furocoumarins, `Rio Red' and `Marsh White' grapefruits were irradiated with 1, 5, and 10 kGys of e-beam. The irradiated fruit juice was analyzed for qualitative and quantitative changes in furocoumarins. Fifty milliliters of grapefruit juice was extracted with ethyl acetate three times and ethyl acetate extract was dried under vacuum and analyzed by HPLC. Irradiation at 1 kGys showed a decrease in the total content of dihydroxybergamottin, paradisin A, and bergamottin compared to 5 kGys, 10 kGys, and control. This project is based upon work supported by the USDA-CSREES under Agreement USDA IFAFS # 2001 52102 02294 and USDA # 2005-34402-14401 “Designing Foods for Health” through the Vegetable & Fruit Improvement Center.

Grapefruit juice contain furanocoumarin derivatives which are known to interact with various drugs such as felodipine, leading to the increased bioavailability. Due to very low concentrations of furocoumarin in grapefruit juice, isolation of these compounds has been a challenge to researchers. Five grapefruit (Citrus paradisi Macf.) varieties such as `Marsh White', `Duncan', `Rio Red', `Orange Flesh', and `Mexican Red' were harvested and analyzed. Samples were extracted successively three times with ethyl acetate until all furocoumarins were extracted. The dried extract was reconstituted in methanol and used for quantification using high-performance liquid chromatography. Furanocoumarins were quantified by gradient elution with methanol and water as mobile phase with a flow rate of 1.1 mL/min at 240 nm. The concentrations of bergamottin, dihydroxybergamotin (DHB) and dimer of DHB were shown to distinctly differ among varieties. Red colored grapefruit showed lower concentrations of the furocoumarins compared to white colored grapefruit. Among the five varieties, `Rio Red' grapefruit contain lower concentrations of bergamottin and DHB. Further studies are continued to quantify other dimers and commercial varieties. Knowledge of furocoumarin levels in grapefruit may eventually help the consumer to make decision about eating grapefruit and/or drinking juice while taking certain medications.