Abstract:

Absolute molecular weight, amino acid composition and bioactivity in vitro of rice peptide were investigated in
this study. Rice protein was hydrolyzed using alcalase and trypsin to obtain rice peptide. Multi-angle laser light scattering
combined with gel permeation chromatography (GPC/MALLS) was used to determine the absolute molecular weight of rice
peptide. High performance liquid chromatography (HPLC) with post-column derivatization technique was used to analyze
rice peptide for amino acid composition. The antioxidant activity of rice peptide was evaluated based on oxygen radical
absorbance capacity (ORAC) assays and DPPH free radical-scavenging capacity and the angiotensin Ⅰ-converting enzyme
(ACE) inhibitory activity was determined by HPLC. The results showed that the absolute molecular weight of rice peptide
mainly distributed from 549 to 1158. Rice peptide contained a full range of amino acids , and essential amino acids and
hydrophobic amino acids accounted for 35.610% and 45.200% of the total amino acids, respectively. The most abundant
amino acid was glutamic acid, accounting for 16.100% of the total amino acids. Rice peptide could eliminate free radicals
effectively and the IC50 for DPPH free radical was 1.170 mg/mL with ORAC value of 1568.006 μmol Trolox/g. In addition,
it had strong ACE inhibitory activity with IC50 of 0.057 mg/mL. Therefore, rice peptide has excellent antioxidant activity and
ACE inhibitory activity and therefore deserves further comprehensive exploitation and application.

Key words: rice peptide, absolute molecular weight, amino acid compositions, antioxidant activity, ACE inhibitory activity