Interactions in casein micelle – Pea protein system (part I): Heat-induced denaturation and aggregation

Abstract

The aim of this work was to investigate the heat-induced interactions between pea proteins (vicilin 7S or legumin 11S enriched-fractions) in admixture with suspended casein micelles (SCM), at weight protein ratio of 1:1 and pH 7.1. The single-protein samples and mixtures thereof were prepared at concentrations of 18 and 36 mgprotein/gsample, respectively, then heated from 40 to 85 °C and incubated for 0–60 min. As compared to single-protein samples, differential scanning calorimetry (DSC) data indicated that the denaturation temperature of pea proteins increased of about 4 °C in the presence of SCM. Heat-induced change in protein composition of the soluble (SP) and micellar (MP) phases from centrifuged SCM – pea protein mixture was assessed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and densitometry. Likewise SP was analyzed by size-exclusion chromatography (SEC-HPLC). While pea legumin 11S and vicilin 7S oligomers were markedly sedimentable in MP from their respective unheated mixture, thermal denaturation and protein aggregation (≥75 °C) resulted in increasing levels of dissolved pea proteins in SP. Heating of the SCM – legumin mixture (85 °C, 15–60 min incubation) resulted in the dissociation of the legumin subunits Lαβ into acidic Lα and basic Lβ polypeptides, yielding in comparable amounts soluble and insoluble disulfide-bonded aggregates, respectively. In contrast in the SCM – vicilin mixture, the heat-denatured vicilin polypeptides in a temperature range of 70–80 °C produced in majority soluble and non-covalent aggregates. Though the heat-induced interactions between pea proteins were altered in the presence of micelles, caseins would not be involved into pea proteins aggregation.