Isolation and identification of bound compounds from corn bran and their antioxidant and angiotensin I-converting enzyme inhibitory activities

A large amount of bound compounds, especially phenolics, present in corn bran has been underestimated because of difficulties in extracting them directly by organic solvents under mild conditions. Based on alkaline digestion, the bound compounds in corn bran were released and extracted with ethyl acetate. An investigation of the chemical constituents of the ethyl acetate (EtOAc) extract led to the isolation of ten compounds: trans-ferulic acid (1), trans-ferulic acid methyl ester (2), cis-ferulic acid (3), cis-ferulic acid methyl ester (4), vanillin (5), para-hydroxybenzaldehyde (6), 2-(1-oxo-2-hydroxyethyl) furan (7), graminones B (8), beta-sitosterol glucoside (9), and sucrose (10). The chemical structures of these compounds were elucidated mainly by nuclear magnetic resonance and electrospray ionization mass spectrometry analysis. Graminones B was identified for the first time and showed potent angiotensin I-converting enzyme inhibitory activity, and compounds 1, 2, 3, and 4 displayed strong DPPH and ABTS(+) radical-scavenging activity. This work represents the first recorded example of the isolation of compounds 3, 4, 8, and 9 from corn bran in the bound form.