Phytochemicals and antioxidant capacities in rice brans of different color

Abstract

Rice bran, a byproduct of the rice milling process, contains most of the phytochemicals. This study aimed at determining the concentrations of lipophilic, solvent-extractable (free), and cell wall-bound (bound) phytochemicals and their antioxidant capacities from brans of white, light brown, brown, purple, and red colors, and broccoli and blueberry for comparison. The concentrations of lipophilic antioxidants of vitamin E (tocopherol and tocotrienols) and γ-oryzanols were 319.67 to 443.73 and 3861.93 to 5911.12 μg/g bran dry weight (DW), respectively, and were not associated with bran color. The total phenolic, total flavonoid, and antioxidant capacities of ORAC (oxygen radical absorbance capacity), DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging, and iron-chelating in the free fraction were correlated with the intensity of bran color, while variations of these in the bound fraction were less than those in the free fraction among brans. Compounds in the bound fraction had higher antioxidant capacity of ORAC than DPPH, relative to those in the free fraction. The bound fraction of light-color brans contributed as much to its total ORAC as the free fraction. Total proanthocyanidin concentration was the highest in red rice bran, while total anthocyanin was highest in purple brans. The predominant anthocyanin was cyanidin-3-glucoside. Red and purple brans had several fold higher total phenolics and flavonoids as well as ORAC and DPPH, from both free and bound fractions, than freeze-dried blueberry and broccoli. These results indicate that rice brans are natural sources of hydrophilic and lipophilic phytochemicals for use in quality control of various food systems as well as for nutraceutical and functional food application.