Differential Influence of Microwave and Conventional Thermal Treatments on Digestibility and Molecular Structure of Buckwheat Protein Isolates

This study investigated the impact of heating and microwave treatment on the in vitro digestibility (using the INFOGEST method) of buckwheat protein isolates (BPIs) and explored the mechanism. The microwave treatment at level 4 (480 W) for 3 min (ML4T3) increased the BPI digestibility by 67.1% over that of the control, while heating for 20—40 min decreased the digestibility by 26.7% on average. Structural analysis showed that microwave treatment decreased the disulfide content, increased the sulfhydryl content, and distorted both the protein microstructure and surface morphology. Meanwhile, microwave treatment decreased the β-turn content and increased both the contents of the β-sheet structure by 35.6% and the random coil structure by 6.9%. In contrast, conventional heating increased the disulfide content and formation of aggregates, and decreased the contents of the random coil, α-helix and β-turn with concomitant increase in the β-sheet content. In conclusion, microwave treatment could be an effective approach to improve the digestibility of BPIs because of its multi-effects on the structure of proteins.