Phytochemicals and antioxidant capacity of natural food colorant prepared from black waxy rice bran

This study determined the phytochemicals in black colorant powder (BCP) prepared from black waxy rice bran, including phenolic compounds, carotenoids, total anthocyanins, and antioxidant activity. The moisture content (MC) of the rice bran was adjusted to 30% and 40% (% wet basis). Four levels of electric field strength (E) of ohmic heating were applied to assist solvent extraction (OHM-ASE) to prepare the BCP. The steaming-assisted solvent extraction (ST-ASE) and solvent extraction (RB-SE) served as controls. BCP extraction using OHM-ASE with 30% MC (E=100, 150, and 200 V/cm) and 40% MC (E=50, 100, 150, and 200 V/cm) showed higher concentrations of gallic acid (253.29–257.57 µg/g), caffeic acid (129.34–136.12 µg/g) ferulic acid (630.74–663.34 µg/g), total phenolics (187.18–201.61 µg GAE/g), lutein (70.6–72.4 µg/g), β-carotene (4.81–5.12 µg/g), and total anthocyanins (812.17–847.09 mg/100 g) than those obtained from either ST-ASE or RB-SE. The zeaxanthin and p-coumaric acid concentrations in the BCP obtained from all OHM-ASE extracts were comparable to those from ST-ASE. In addition, the BCP extracted with OHM-ASE showed the strongest antioxidant activity of all treatments. This study demonstrated that BCP prepared from OHM-ASE can be considered as a valuable source of phytochemicals with high antioxidant properties.