Analyses of Free and Bound Phenolics in Rice

Abstract

Free and bound phenolics in 21 japonica cultivars (Oryza sativa) of rice bran and polished rice were analyzed using 3D-HPLC. Although we observed high content variations among cultivars, the major free phenolics were ferulic acid (1) and p-coumaric acid (2). Rice bran and polished rice contained 0.25-2.9 (mean, 0.56) mg/100 g and 0-277 (mean, 65) μg/100 g of 1 and 0.1-1.1 (mean, 0.43) mg/100 g and 0-159 (mean, 24) μg/100 g of 2, respectively. Contents of bound phenolics were much more than those of free phenolics and variations in contents of bound phenolics among cultivars were less than those of free phenolics. The major bound phenolics were 1, 2 and 5, 5'-diferulic acid ((E, E)-4, 4'-dihydroxy-5, 5'-dimethoxy-3'-bicinnamic acid, 3). Rice bran and polished rice contained 22-225 (mean, 155) mg/100 g and 1.7-13 (mean, 7.1) mg/100 g of bound 1, 51-243 (mean, 116) mg/100 g and 0.5-4.9 (mean, 1.8) mg/100 g of bound 2 and 3-22 (mean, 9.8) mg/100 g and 0.04-0.5 (mean, 0.26 mg/100 g) of bound 3, respectively. 5, 8'-Diferulic acid benzofuran form (trans-5-[(E)-2-carboxyvinyl]-2-(4-hydroxy-3-methoxyphenyl)-7-methoxy-2, 3-dihydrobenzofuran-3-carboxylic acid, 4) was first detected in cell wall of rice bran and the content of 4 was seven times higher than 3, showing that 4 is the major diferulic acid in this location.