Abstract
Bioactive peptides represent an important source of health promoting food. Therefore, the objective of this study was to identify the in vitro antioxidant and ACE inhibitory peptides derived from bovine serum albumin (BSA) and to characterise them after further purification. To achieve this objective, BSA was hydrolyzed with pepsin enzyme, fractionated by ultrafiltration using a 10 kDa molecular weight cut off membrane, and purified by gel filtration chromatography prior to characterisation. The total antioxidant activity was evaluated in a linoleic acid model system using the ferric thiocyanate (FTC) and thiobarbituric acid reactive species (TBARS) methods. The results indicated that gel filtration fraction number 18 exhibited the highest FTC antioxidant activity (65.4 %) compared to the (< 10 kDa) ultrafiltration fraction (44.8 %) and BSA hydrolysate (34.9 %) using a concentration of 1mg peptide/ml. However, the peptide activities were lower than those of 0.01 % butylated hydroxyanisole (69.9 %) and 0.01 % trolox (78.5 %) (P ≤ 0.05). Likewise, TBARS inhibition values were 42.8, 54.8, 76.7 and 84.4 % for BSA hydrolysate, < 10 kDa, BHA and trolox, respectively. The antioxidant activity of the (Mw < 10 kDa) peptide was demonstrated by strong free radical scavenging using the 1, 1-diphenyl-2-picrylhydrazyl (DPPH•), hydroxyl (OH•) and superoxide anion (O2-•); ferric (Fe3+) reducing and ferrous (Fe2+) metal ion chelating capacity and reducing power activity. A second gel filtration fraction number 22 exhibited the highest ACE inhibitory activity (79.5%) compared to the (10 kDa) ultrafiltration fraction (44.7%) and BSA hydrolysate (33.2 %) at a concentration of 10 mg/ml, with corresponding low IC50 values of 0.32, 0.56 and 0.75 mg/ml respectively compared to captopril (88.5%, P ≤ 0.05). The peptide (GF 18) at 1 mg/ml had no cytotoxic effect in epithelial caco-2 cells. Moreover, the presence of the peptide showed high cell viability (99.7%) and reduced malondialdehyde formation (27.7 µg/ml) compared with cells treated with 3mM t-BHP alone, which showed low cell viability (54.6%) and high MDA (30.3 µg/ml) (P < 0.01). BSA peptides protected t-BHP treated cells from caspase-dependent apoptosis; inhibited intracellular ROS production and increased glutathione level and SOD activity. Similarly, the GF 22 peptides (1 mg/ml) protected the endothelial EA.hy 926 against 3mM t-BHP damage and showed reduced mROS production by both lucigenin-enhanced chemiluminescence and the DHE fluorescence techniques. Additionally, the peptides reduced nitrite concentration and inhibited the activity of angiotensin converting enzyme in a dose dependent manner. This study reports novel findings showing that BSA peptides have antioxidant and ACE inhibitory activities that could potentially be used as food supplements and pharmaceutical agents.