Gelation properties of three common pulse proteins: Lentil, faba bean and chickpea

Pulse proteins are promising candidates to replace animal proteins for sustainable food production, such as for gel-based food products. Although the gelation properties of pulse protein extracts have been widely studied, the results show a lot of variation, due to their complex protein composition and presence of impurities in the extracts. In this study, the gelation mechanisms of the whole protein extracts and globulin fractions from lentil, faba bean and chickpea were investigated. The whole protein extracts are rich in globulins but also contain albumins and impurities (e.g., digestible starch and fiber). The structural and mechanical properties of gels formed by those extracts and globulin fractions were studied by using multiphoton excitation and scanning electron microscopy imaging, and small and large oscillatory shear deformations (SAOS and LAOS), respectively. The type and extent of molecular interactions that stabilize the gel network structures were further evaluated. This study found that all protein samples formed disordered particulate gels consisting of primary protein aggregates with a size of 50-110 nm, which tends to be larger with a higher content of free-SH group in the pulse protein. All whole protein extracts have higher gelation abilities than the corresponding globulin fractions, and the formed gels tend to have higher stiffness, likely due to the existence of albumins that form disulfide bonds in the gel network structures, and the positive effects from impurities like digestible starch and fibers. But a high content of impurities seems to increase the structural heterogeneity of the gels. In contrast to albumins, pulse legumins tend to decrease the gel stiffness. In large shear deformation, all gels have complex and different nonlinear behavior, where lentil globulin gel was less disrupted at large strain amplitude, probably due to its highest content of vicilins (plus convicilins). This study provides insights on the gelation mechanisms of pulse proteins, which could guide the targeted purification of pulse proteins for producing gel-based food products with desired textual properties.