Physical characterization of thermally induced networks of lupin protein isolates prepared by isoelectric precipitation and dialysis

Protein isolates of Lupinus albus were obtained from full fat and defatted lupin flour using isoelectric precipitation or dialysis. Calorimetric tests demonstrated that the main protein fractions of the isolates denature well below 100 degrees C. Mechanical spectra of isolate dispersions obtained at 80 degrees C indicated the formation of a 'pseudogel' whose cohesion incre ased during cooling to 10 degrees C. Subsequent heating to 90 degrees C enc ouraged extensive formation of disulphide bonds as it produced gels that we re insoluble in sodium dodecyl sulphate and urea solutions. Dialysis produc ed isolates of lower gelling concentrations, which also formed networks of a stronger relative elastic character. The presence of NaCl at concentratio ns up to 0.5 M had a reinforcing effect on networks. Protein over-aggregati on caused thr: opposite effect at higher salt levels. Finally, a comparison with results in the literature on soybean protein gelation suggested simil ar denaturation temperatures and a common pattern of structure formation fo r the two legume proteins.