Antioxidant activity, phenolic and anthocyanin contents of various rhubarb (Rheum spp.) varieties

Antioxidant activity (ABTS assay), total phenolics and total anthocyanins were determined in the petioles of twenty-nine rhubarb (Rheum spp.) varieties. Antioxidant activity ranged from 463 +/- 50 (Rheum officinale) to 1242 +/- 2 mu mol Trolox per g DW (Valentine). The phenolic content varied from 673 +/- 41 (Loher Blut) to 4173 +/- 23 mg GAE/100 g DW (Plum Hutt) and had a low correlation (r = 0.663) with antioxidant results. Seven of the varieties (Plum Hutt, Valentine, Minnesota No. 8, Cherry Red, Cawood Delight, Coulter McDonald and OR 23) had higher total phenolics than kale, a vegetable rich in phenolics. The concentration of anthocyanins ranged from 19.8 +/- 1.5 (Crimson Red) to 341.1 +/- 41.6 mg/100 g DW (Valentine). The percentages of two main anthocyanins in rhubarb, cyanidin 3-glucoside and cyanidin 3-rutinoside varied from 66.07:33.93, respectively, in Valentine to 9.36:90.64, respectively, in R. officinale.