Rheology and microstructure of beta-lactoglobulin sodium polypectate gels

Thermally induced beta-lactoglobulin (beta-Lg) and sodium polypectate (SPP) composite gels or coagulum were formed at pH 6.5 and 3.5 and evaluated by dynamic rheological techniques and transmission electron microscopy(TEM). At pH 6.5, SPP-induced beta-Lg gelation, resulting in the formation of opaque beta-Lg/SPP and transluscent beta-Lg/SPP/CaCl2 gels. Co-gelation of beta-Lg and SPP increased the storage modulus (G') of beta-Lg/SPP/CaCl2 gels during cooling, whereas ungelled SPP prevented further increases in G' of beta-Lg/SPP gels. Irrespective of calcium cations, beta-Lg and SPP interacted at pH 3.5 to form a grainy white precipitate that coagulated on heating. At pH 6.5, TEM micrographs revealed a nonuniform distribution of beta-Lg aggregates in beta-Lg/SPP gels as opposed to a homogenuous beta-Lg/SPP/CaCl2 gel matrix. At pH 3.5, however, micrographs indicated the formation of a curd-like beta-Lg/SPP coagulum that did not form a cohesive network structure. Overall, there is a potential for using pectates or other anionic polysaccharides to modify the gelling properties of whey proteins and subsequently expand whey utilization in diverse food applications.