Total phenolic contents and antioxidant properties of commonly consumed vegetables grown in Colorado

A total of 38 commonly consumed vegetable samples, including 3 kale, 1 rhubarb, 3 spinach, 3 broccoli, 2 green bean, 5 carrot, 10 tomato, and 11 potato samples, were investigated for their total phenolic contents (TPC) and antioxidant properties. The measured antioxidant properties included free radical scavenging activities against DPPH, superoxide anion radical (O₂⁻), ABTS⁺ and peroxyl radical, and Fe²⁺ chelating capacity. The tested vegetables differed in their antioxidant properties and TPC, although all vegetables had significant antioxidant activities and contained significant levels of phenolics. The TPC and the measured antioxidant properties were correlated to each other. The Fe⁺² chelating capacity and the scavenging capacities against ABTS⁺, DPPH and O₂⁻ were reported for these commonly consumed vegetables for the first time. Results from this study suggest that kale, spinach, broccoli, and rhubarb are the better dietary sources of natural antioxidant activities and phenolic compounds. Furthermore, kale, broccoli and spinach produced in Colorado may have greater antioxidant contents than those grown at other locations.