Isolation and characterisation of antioxidative peptides from bromelain-hydrolysed brown rice protein by proteomic technique

In this study, proteins from Thai brown rice (Khao Dawk Mali 105) were separated into albumin (2.18%), globulin (3.98%), glutelin (84.23%), and prolamin (9.61%) fractions, and were hydrolysed with various bromelain concentrations and hydrolysis times. Liquid chromatography-electrospray ionization/mass spectrometry (LC-ESI-MS/MS) was conducted to assess the composition, molecular weight (MW) distribution, and sequence of the resulting peptides, and showed that most peptides have a MW below 2000 Da (60-70%). Glutelin fraction hydrolysates exhibited the highest 2,2'-azino-bis 3-ethylbenzthiazoline-6-sulfonic (ABTS center dot(+)) radical-scavenging (0.69 +/- 0.04 mM trolox) and copper chelating (4.12 +/- 0.01 mg ethylenediaminetetraacetic acid; EDTA) activities, which was further fractionated into six fractions using reversed-phase high-performance liquid chromatography. The fourth fraction showed the highest ABTS center dot(+) scavenging (1.08 +/- 0.03 mM trolox) and copper chelating (5.00 +/- 0.02 mg EDTA) activity. LC-MS/MS analysis revealed that the peptides with MW less than 1500 Da and hydrophobic or aromatic N-terminal residues, such as SPFWNINAHS, MPVDVIANAYR, VVYFDQ-TQAQA, AVYVYDVNNNANQ, YNILSGFDTEL and EFFDVSNELFQ, possibly contributed to the highest antioxidant activity in fourth fraction.