Oranges are a good source of polyphenols including glycosides of hesperetin and naringenin (mainly hesperetin-7-O-rutinoside (hesperidin) and naringenin-7-O-rutinoside (narirutin)). Consumption of oranges has been shown to be inversely associated with cardiovascular disease. The protective effects of oranges has been suggested to be due to the presence of flavonoids. If flavonoids are responsible for the health benefits of oranges it might be expected that they are bioavailable. In fact, evidence suggests that orange flavanones are highly bioavailable, and that extensive metabolism of these flavonoids occurs following absorption. Because of the possible nutritional effects, studies have investigated the absorption and metabolism of orange polyphenols in human subjects. In one such study1, healthy subjects were asked to consume a low polyphenol diet for 2 weeks before consuming 250 mL of pulp enriched orange juice. This juice contained 584 μmol of total polyphenols and 537 μmol of flavanones.
Analysis of the urine showed that hesperetin-O-glucuronides, naringenin-O-glucuronides and hesperetin-3’-O-sulphate were the main metabolites. The total urinary content of these polyphenols corresponded to ~16 % of the intake concentration. A number of catabolic metabolites of flavanones were also detected in the urine following orange juice consumption and these were likely breakdown products of flavanones formed by colonic microflora. These metabolites were aromatic acid derivatives of propionic and hippuric acid and accounted for around 88 % of the total polyphenol intake from the orange juice. The polyphenols from orange juice are therefore present in urine largely as aromatic acids formed by colonic microflora and to a lesser extent glucuronide and sulphate metabolites formed following enterocyte and first pass metabolism of flavanone glucosides. The metabolism of orange flavanones and other polyphenols is therefore highly complex and includes both colonic and intracellular pathways.
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