Comparative Study on Nutritional, Structural, Digestive Properties and Bioactivities of Tartary Buckwheat Protein Fractions

This study systematically compared the nutritional value, structural characteristics, digestive properties, and functional activities of proteins from whole tartary buckwheat flour, tartary buckwheat bran, and tartary buckwheat core flour. The results revealed significant differences in protein content and essential amino acid (EAA) composition among the three protein sources (P < 0.05). All three protein fractions showed high amino acid scores (AAS) and chemical scores (CS), indicating the characteristics of high-quality plant proteins. Among them, the bran protein exhibited the highest protein content and the most favorable nutritional profile. Moreover, methionine and cystine were identified as the first limiting amino acids in all three proteins. Significant variations in solubility were found among them across the pH range of 2.0–9.0, with improved solubility observed under alkaline conditions. Fourier transform infrared spectroscopy (FTIR) indicated that the secondary structure of the three proteins was predominantly composed of β-sheets and β-turns. In vitro simulated digestion experiments showed that the core flour protein exhibited the highest digestibility (73.63%), the smallest average particle size post-digestion, and the highest absolute zeta potential value, suggesting superior digestive stability. Ultraviolet and fluorescence spectroscopy revealed conformational changes in the three proteins during digestion and structural and compositional differences among them. Furthermore, all these proteins exhibited free radical scavenging capacity and reducing power, and digestion treatment significantly enhanced their antioxidant activities (P < 0.001). The digested core flour protein exhibited superior scavenging capacity against 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) radical, 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) cation radical, and hydroxyl radical at 68.66%, 63.49%, and 72.21%, respectively, while the digested bran protein exhibited stronger reducing power. All three proteins had inhibitory effects on α-glucosidase and α-amylase, which significantly increased after digestive treatment (P < 0.001), indicating their potential for application in blood glucose regulation. This study establishes a theoretical foundation for the deep processing and comprehensive utilization of tartary buckwheat protein.