Absorption, excretion, and distribution of dietary antioxidant betalains in LDLs: potential health effects of betalains in humans.

BACKGROUND Betalains were recently identified as natural antioxidants. However, little is known about their bioavailability from dietary sources. OBJECTIVE The objective was to evaluate the bioavailability of betalains from dietary sources. DESIGN The plasma kinetics and urinary excretion of betalains were studied in healthy volunteers (n = 8) after a single ingestion of 500 g cactus pear fruit pulp, which provided 28 and 16 mg indicaxanthin and betanin, respectively. The incorporation of betalains in LDL and the resistance of the particles to ex vivo-induced oxidation was also researched. RESULTS Betanin and indicaxanthin reached their maximum plasma concentrations 3 h after the fruit meal and declined according to first-order kinetics. The half-life of betanin (0.94 +/- 0.07 h) was shorter than that of indicaxanthin (2.36 +/- 0.17 h). Both compounds had disappeared from plasma by 12 h after intake. The urinary excretion of indicaxanthin and betanin over 12 h represented 76 +/- 3.0% and 3.7 +/- 0.2%, respectively, of the ingested compounds. LDL isolated 3 and 5 h after the fruit meal incorporated betalains at concentrations of 100.5 +/- 11 and 50 +/- 7.2 pmol/mg LDL protein, respectively. In addition, the particles appeared more resistant to ex vivo-induced oxidative injury than did the samples isolated before fruit ingestion (P < 0.05)-the higher the amount of betalains incorporated, the higher the resistance. The concentrations of vitamin E and beta-carotene in LDL did not change significantly after fruit ingestion. CONCLUSION Our results show that cactus pear fruit is a source of bioavailable betalains and suggest that indicaxanthin and betanin may be involved in the observed protection of LDL against ex vivo-induced oxidative modifications.