Phenolic acids, flavonoids and total antioxidant capacity of selected leafy vegetables

Phenolic compounds and total antioxidant capacity of eight leafy vegetables, namely Komatsuna, Mizuna, Pok choi, Mitsuba, Salad spinach, Lettuce, Red amaranth and Green amaranth were determined. The phenolic compounds were characterized as hydroxybenzoic acids, hydroxycinnamic acids and flavonoids. Salicylic acid was, by far, the most common hydroxybenzoic acid, ranging from 4.40 to 117.36 μg/g fresh frozen weight (ffw). Vanilic acid, gallic acid, caffeic acid, chlorogenic acid, p-coumaric acid, ferulic acid and m-coumaric acid were commonly found in all of these vegetables. Isoquercetin and rutin, the most common flavonoids, ranged from 3.70 to 19.26 and 1.60 to 7.89 μg/g ffw, respectively, and hyperoside was highest (38.72 μg/g ffw) in Mizuna. Total antioxidant capacity values varied widely between ABTS+ and DPPH assay methods, with values reported as equivalents to trolox, quercetin and ascorbic acid. Among these vegetables, total antioxidant capacity was found in the following order: Pok choi > Komatsuna > Mizuna > Mitsuba > Red amaranth > Lettuce > Green amaranth > Salad spinach.