Calcium-induced pea protein gels: Effect of structure on in-vitro protein digestibility and calcium bioaccessibility

The importance of plant protein gelation on the nutritional properties of foods is gaining considerable interest. In this study, we hypothesized that differences in the structural properties of calcium-induced pea protein gels would influence the in vitro protein digestibility and calcium bioaccessibility. These gels were created under different heating conditions (45 °C, 1000 min or 95 °C,10 min) and calcium concentrations (20 mM or 100 mM). The structural characteristics of gels showed that, within the testing range of this study, the influence of calcium concentration is more pronounced than that of the heating conditions. Gels with 20 mM calcium concentration had higher storage modulus Gʹ and also a finer, uniform gel network. Contrarily, the microstructure of gels formed at higher calcium concentration (100 mM) exhibited concentrated protein aggregates that shared fragile bonds. During the in vitro gastrointestinal digestion process, the heterogeneous gel network and compact aggregates in 100 mM gels seemed to limit the enzyme action, slowing the hydrolysis rate and resulting in a lower degree of protein hydrolysis. However, higher amounts of calcium in 100 mM gels resulted in higher levels of ionic calcium and soluble calcium, leading to higher calcium bioaccessibility. Interestingly, the bioaccessibility of calcium can be affected by protein hydrolysis due to the interaction between calcium ions and the released peptides. Thus, in the range of 20–100 mM calcium concentration, G′ correlates positively with the degree of proteolysis and negatively with calcium bioaccessibility.