Abstract: In this study, response surface methodology was used to optimize the enzymatic hydrolysis conditions for the preparation of antioxidant peptides from marrow seed meal for improved reducing power and scavenging capacity against hydroxyl and DPPH radicals. The changes in the free amino acid composition, molecular mass distribution and antioxidant activity of the antioxidant peptides after simulated gastrointestinal digestion in vitro were studied. The results showed that the optimal conditions were obtained as follows: substrate concentration 6%, alkaline protease 3%, and enzymatic hydrolysis at 55 ℃ for 90 min at pH 8.5. The scavenging percentages against hydroxyl and DPPH radicals and reducing power of the hydrolysate obtained under these conditions were (58.19 ± 0.80)%, (60.27 ± 1.73)% and 0.49 ± 0.01, respectively. The antioxidant peptides with a molecular mass of less than 3 kDa, 3-5 kDa and more than 5 kDa were separated from the hydrolysate. After simulated gastrointestinal digestion, these antioxidant peptides contained 41.72%, 36.94% and 33.93% free amino acids, respectively, and the digested peptides consisted mainly of peptide fragments with a molecular mass of less than 500 Da account for 73.50%, 60.15% and 53.30% of the total amount, respectively. The hydroxyl radical scavenging capacity increase by 26.04%, 29.06% and 34.43%, respectively, ,and the reducing power increased by 50.98%, 64.53% and 67.35%, respectively when compared with those before digestion. The results of this study provide useful data for the production and application of antioxidant peptides from marrow seeds as a functional antioxidant.

Key words: marrow seeds, antioxidant peptide, in vitro simulated digestion, free amino acid, molecular mass distribution, antioxidant activity