Abstract: Objective: To prepare peanut-derived antioxidant peptides and analyze their amino acid composition and molecular weights. Methods: Defatted cold-pressed soybean cake was hydrolyzed by alcalase or flavourzyme and the hydrolysates were preliminarily separated to collect peptides having a molecular weight of less than 1 kD. The obtained peptides were further separated by sequential chromatographies on Sephadex G-25 and Sephadex G-15 columns to obtain two peptide fractions with higher hydroxyl free radical scavenging activity named as J22 (from alcalase hydrolysis) and F22 (from flavourzyme hydrolysis). The amino acid composition of the two fractions was analyzed using an amino acid analyzer. Meanwhile, Waters Acquity UPLC -LCT premier time-of-flight mass spectrometer (UPLC-TOF-MS) was used to analyze their molecular weight distribution. Results: Compared with peanut protein, Ile, Met, Tyr and His contents in the fraction J22 were increased to 13.34%, 5.18%, 45.84% from 3.75%, 0.79%, 3.44%, respectively; similarly, Ile, Met, Tyr and His contents in the fraction F22 were increased to 6.12%, 3.78%, 11.53% and 51.13% from 3.75%, 0.79%, 3.44%, respectively. Two short-chain peptides were found in each of the two fractions with respective molecular weights of 291.9 D and 391.3 D for the fraction J22 and of 205 D and 391.3 D for F22. Conclusion: J22 and F22 are both rich in tyrosine and histidine. Both fractions with small molecular weights are characteristics of fast absorption. A certain molecular weight and amino acid residues offer them with higher antioxidant activity.

Key words: peanut peptide, antioxidant activity, amino acid assay, liquid-chromatography-time of flight mass spectrometry(LC-TOF-MS)