| Abstract
| - Antioxidant nutrients from fruits and vegetables are believed to be a class of compounds that exerttheir effects in humans by preventing oxidative processes which contribute to the onset of severaldegenerative diseases. This study found a new class of dietary cationized antioxidants in red beets(Beta vulgaris L.). These antioxidants are betalains, and the major one, betanin, is a betanidin5-O-β-glucoside. Linoleate peroxidation by cytochrome c was inhibited by betanin, betanidin, catechin,and α-tocopherol with IC50 values of 0.4, 0.8, 1.2, and 5 μM, respectively. In addition, a relativelylow concentration of betanin was found to inhibit lipid peroxidation of membranes or linoleateemulsion catalyzed by the “free iron” redox cycle, H2O2-activated metmyoglobin, or lipoxygenase.The IC50 inhibition of H2O2-activated metmyoglobin catalysis of low-density lipoprotein oxidationby betanin was <2.5 μM and better than that of catechin. Betanin and betanidin at very smallconcentrations were found to inhibit lipid peroxidation and heme decomposition. During this reaction,betanidin was bleached completely, but betanin remained unchanged in its absorption. Thisdifference seems to derive from differing mechanisms of protection by these two compounds. Thehigh affinity of betanin and betanidin for membranes was demonstrated by determining the rate ofmigration of the compounds through a dialysis tube. Betanin bioavailability in humans wasdemonstrated with four volunteers who consumed 300 mL of red beet juice, containing 120 mg ofthe antioxidant. The betacyanins were absorbed from the gut and identified in urine after 2−4 h.The calculated amount of betacyanins found in the urine was 0.5−0.9% of that ingested. Red beetproducts used regularly in the diet may provide protection against certain oxidative stress-relateddisorders in humans. Keywords: Antioxidants; betalains; cationized; red beet; bioavailability; human
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