No abstract

The rice bran protein (RBP) was then hydrolyzed with various proteases (papain, flavorzyme, neutrase, protamex, and trypsin) to prepare antioxidant peptides. The rice bran protein hydrolysates (RBPH) were assessed using method of DPPH radical scavenging ability. Hydrolysate prepared with papain and flavorzyme (activity ratio 1:1) was found to have the highest antioxidant activity (IC50=6.778±0.21 mg/ml). This hydrolysate was purified using ultrafiltration, RBPH-III (Mw＜3KDa) had the highest DPPH and hydroxyl radical scavenging activity (IC50 value of 6.56±0.28, 5.43±0.22, respectively) and highest reducing power activity (1.02±0.18 at 4 mg/mL). Later, RBPH-III was fractionated by SP-SephadexC-25 cation-exchange column into six fractions (A–F), fraction F with the highest DPPH scavenging activity, was then separated by size exclusion chromatography on a SephadexG-25 into three major fractions (F1–F3). Fraction F2 exhibited the highest DPPH scavenging activity was choose to fractionate by reversed-phase high performance liquid chromatography (RP-HPLC), seven antioxidant peptides were isolated, The F2-5 peptide displayed the highest DPPH radical-scavenging activity (58.2±1.63%; at 250 μg/ml) among these peptides, the amino acids composition of F2-5 was determined, which might play an important role on its antioxidant activity. In addition, purified peptide did show remarkable inhibition rate on SGC-7901 cells proliferation, and it also revealed the dose-dependent relationship. The results of this study suggest that rice bran protein hydrolysates are good source of natural antioxidants.

The preparation, approximate composition, degree of hydrolysis (DH), lipase activity and antioxidant capacity (including the ability of scavenging DPPH and ABTS free radicals) were determined for various of aqueous enzymatic extract (AEE) obtained from rice bran (RB) using alcalase (A), trypsin (T), papain (Pn), neutrase (N) and protamex (Px). Peptides and γ-oryzanol are the major functional components of AEE. Generally, the protein yield varied with the type of enzyme used in the order of T>Pn>N>Px>A. Both trypsin and alcalase extracts exhibit a higher level of γ-oryzanol than other enzymes. Lipase activity was measured using the 4-Nitrophenyl Laurate (p-NPL) substrate method, and significantly different (P<0.05) lipase activity values ranging from 0.55 to 2.38 mU/mL were observed from five hydrolysates. Furthermore, two synthetic free radicals were used to evaluate the antioxidant activity of AEE. The alcalase extract (at 4.35±0.15mg protein/mL AEE) shows the greatest scavenging rate (28.42%) of DPPH, but trypsin extract has highest ABTS radical-scavenging activity of 94.05%. Data revealed trypsin was possible the most effective extractant under their optimal conditions. These results demonstrate that the product obtained from rice bran by different enzymatic digestions may contain bioactive components and might potentially be natural antioxidants. Meanwhile, the aqueous enzymatic extraction method can also improve the stability of the hydrolysates.