Cold-set whey protein-flaxseed gum gels induced by mono or divalent salt addition

摘要

Mixed cold-set whey protein isolate (WPI)-flaxseed gum (FG) gels, induced by the addition of CaCl_2 or NaCl at fixed ionic strength (150 mM), were evaluated with respect to their mechanical properties, water-holding capacity (WHC) and SEM microscopy. They were prepared by mixing FG and thermally denatured (90 ℃/30 min) WPI solutions at room temperature, but the gels were formed at 10 ℃ using two methods of salt incorporation: diffusion through dialysis membranes and direct addition. The mixed systems formed using dialysis membranes showed phase separation with the development of two (axial) layers, and the CaCl_2-induced gels presented radial phase separation. In general the CaCl_2-induced gels were less discontinuous, stronger, and showing lower WHC and deformability than the NaCl-induced gels. An increase in the FG concentration reduced the gel strength and WHC for both systems, which was associated with a prevailing phase separation between the biopolymers over the gelation process. Using direct salt addition, apparently none of the mixed gels showed macroscopic phase separation, but the NaCl-induced gels showed much higher hardness and elasticity than the CaCl_2-induced gels. Since the gelation process occurred more quickly by direct salt addition, and more effectively for the divalent salts, the more fragile structure of the CaCl_2-induced gels was a consequence of disruption of the cross-link interactions of the aggregates during the agitation used to homogenize the salt added.