Interplay between soluble and insoluble protein/calcium/phytic acid complexes in dispersions of faba bean and pea protein concentrates around neutral pH

Abstract

Pulses are rich in proteins and a good source of calcium. However, antinutritional compounds such as phytic acid can bind to proteins and minerals to form complexes, reducing their digestibility and bioavailability, respectively. This study investigated interactions and potential complex formation between phytic acid, calcium, and proteins in pea and faba bean concentrate dispersions. The solubility of the 3 compounds was measured at pH 6.5, 7.0 and 7.5. Formation of complexes was investigated by chelating calcium upon EDTA addition or by removing proteins via ultrafiltration. Protein profiles were compared using Size Exclusion Chromatography (SEC). For both pea and faba bean, protein solubility increased with increasing pH. Phytic acid solubility was minimum at pH 7.0, while simultaneously calcium solubility was maximum. Protein solubility increased with EDTA addition compared to the control at pH 6.5 (pea and faba bean) and 7.0 (pea), supporting the presence of insoluble binary complexes between calcium and proteins. The concomitant rise in phytic acid solubility for pea (pH 6.5 and 7.0) highlighted the formation of either insoluble binary (phytic acid to calcium) or ternary complexes. Also, the formation of soluble protein complexes with phytic acid and, possibly, with calcium was highlighted. Small amounts of soluble ternary complexes were observed at pH 7.5. SEC results showed an increase in globulin's (especially legumin) solubility after calcium chelation; this demonstrated the formation of insoluble complexes mediated by calcium. This study highlighted that the different protein fractions from pulses must be considered separately in their ability to establish complexes with calcium and phytic acid.