The effects of sodium alginate and calcium levels on pea proteins cold-set gelation

Abstract

A multi-scale investigation of pea proteins – alginate cold-set gels was proposed in this study. The gel preparation followed a two-steps procedure. Globular pea proteins were first denatured and aggregated by a pre-heating step. Sodium alginate was then added at different concentrations. Thereafter the in situ gelation process was induced at 20 °C using glucono-δ-lactone (GDL) and two calcium carbonate (CC) levels; calcium cations were released as the pH decreased. Small-amplitude rheology measurements (storage modulus G′) showed that stronger mixed gels were obtained than single-biopolymer solutions. Confocal laser scanning microscopy (CLSM) revealed phase-separating microstructures of mixed gels, foremost owing to biopolymers incompatibility. Phase separation was kinetically entrapped by gelation at different evolution stages. According to the co-occurrence method and microstructure classification, image texture analysis disclosed that a continuous protein network dispersing small gelled alginate microdomains corresponded to the strongest mixed gels. Transmission electron microscopy (TEM) evidenced that during gelation, the pre-aggregated proteins were mainly associated into large agglomerates with no peculiar pattern. Higher cohesiveness between both networks was hypothesized, since protein agglomerates could expose “anchoring points” for alginate chains. Depending on both protein – alginate initial composition and calcium availability, non-specific inter-biopolymer cross-links via calcium were assumed to be the key factor of synergism within mixed gels.