Abstract:

Various methods including reducing power, Fe2+-chelating, 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic
acid) diammonium salt (ABTS) radical scavenging, 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging and liposome
oxidation inhibition capacity assays were used for evaluating the antioxidant activities of soybean peptide employing butyl
hydroxylanisole (BHA), VC and VE as controls, aiming to investigate the applicability of these assays for measuring the
antioxidant activities of polypeptide in vitro. The results showed that the reducing power of soybean peptide increased with
its concentration in the range of 0–30 mg/mL, attaining a maximum value of only 0.487, and BHA, VC, and VE similarly
exhibited reducing power in a concentration-dependent manner. The inhibitory activity of soybean peptide against liposome
oxidation was lower than that of BHA and VE, and this antioxidant activity exhibited a stable upward trend with increasing
concentration of soybean peptide, reaching maximum percentage inhibition of 20.6%. Fe2+-chelating capacity of soybean
peptide increased up to 38.7% with its concentration in the range of 0–15 mg/mL, whereas BHA, VE and VC had no such
activity. Soybean peptide in the concentration range of 0–3.0 mg/mL possessed ABTS radical scavenging activity very
similar to that of VC and higher than that of BHA and VE, and the maximum scavenging percentage was 61.2%. However,
the maximum DPPH radical scavenging percentage of soybean peptide was only 2.1%, which was much lower than that of
VC (45.0%), BHA (10.1%), and VE (10.7%). Therefore, Fe2+-chelating capacity, ABTS radical scavenging, and liposome
oxidation inhibition capacity assays can be used to investigate the antioxidant activity of soybean peptide in vitro.

Key words: polypeptide, antioxidant activity in vitro, assay, applicability