Abstract: This study was performed in order to explore the antioxidant activity and structural characteristics of purple speckled kidney bean protein during simulated gastric digestion in vitro. Experimental results showed that as the digestion proceeded, the degree of hydrolysis (DH) and the solubility of the protein increased significantly due to enzymatic action, and more and more peptides with low molecular masses were produced resulting in increased antioxidant activity of the digestion product. At the end of digestion, the total antioxidant capacity and ferric ion reducing power increased by 296.97% and 54.01% as compared to the protein, respectively. Fourier transform infrared (FTIR) spectroscopy analysis showed that the secondary structure of the protein changed significantly after the digestion process. The relative contents of α-helix and β-turn increased and the relative content of β-sheet decreased with increasing digestion time. The contents of free sulfhydryl group and total sulfhydryl group of kidney bean protein decreased greatly after simulated gastric digestion, although they only slightly increased with the extension of digestion time. Under scanning electron microscopy (SEM), the digested protein exhibited granules that were arranged in a disorderly manner to form a dense reticular structure.

Key words: kidney bean protein; antioxidant activity; simulated digestion; secondary structure