Understanding the structural differences in chickpea globulins and their relationship with in vitro protein digestibility

Abstract

The relationship between structural protein differences and changes in legumin, vicilin, and chickpea globulin during digestion and protein digestibility has not yet been fully explored. In this study, we characterized the conformational properties and the secondary structures of chickpea protein isolates (globulin), legumin, and vicilin before and after in vitro digestion to understand their roles in protein digestibility. The globulins were characterized by size, surface charge, hydrophobicity, sulfhydryl group content, and solubility. Protein hydrolysis was determined by the OPA method and electrophoresis. The structural changes were elucidated using FTIR spectroscopy. Vicilin had a bimodal particle size distribution and high polydispersity, indicating more heterogeneous particles with lower surface hydrophobicity, fewer free SH groups, and higher solubility (62%) than those of legumin and globulin. Turbidity was correlated with the aggregation index, with legumin exhibiting the highest value. During the gastric phase, in contrast to legumin (34.2%) and vicilin (31.4%), the protein hydrolysis was the highest in globulin fraction (42.2%). However, at the intestinal level, vicilin exhibited highly digested proteins (99%), as confirmed by SDS-PAGE. FTIR analysis demonstrated differences in secondary structure changes between vicilin with an increase in random coils (22%) and globulin and legumin, which displayed highly parallel β-sheet structures (28.7% and 26%, respectively). These results highlight the importance of conformational switching in the secondary structure of globulins for protein digestibility. Promoting unorganized secondary structures, high solubility, and low aggregation improves globulin protein digestibility. Examination of the structure and digestion of chickpea globulins provides valuable information for the development of plant-based products.