Effect of Subcritical Water for the Enhanced Extraction Efficiency of Polyphenols and Flavonoids from Black Rice Bran

The extraction of polyphenol and flavonoid from black rice bran was performed by diverse extraction methods using the sugar solution, ethanol, hot water (80C), and by subcritical water extraction (SWE) method. By SWE under operating conditions of 190C, 1,300 psi, and 10 min, the maximum yields of total polyphenolic compounds (35.06±1.28 mg quercetin equivalent (QE)/g dried material and flavonoids (7.08±0.31 mg QE/g dried material) could be obtained. These results were over 11.77and 12.21-fold higher than those of the ethanol extraction, which showed the highest extraction efficiency among tested conventional methods in total polyphenols (2.98±0.74 mg QE/ g dried material) and flavonoids (0.58±0.21 mg QE/g dried material), respectively. Though the highest antioxidant activity (87.14±1.14%) was observed at the dried extract obtained from ethanol method, the relative antioxidant activity per 1 g dried black rice bran by SWE (190C, 10 min) was over 11.53-fold higher than that by the ethanol extraction.