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

Abstract

Summary 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 °C. Mechanical spectra of isolate dispersions obtained at 80 °C indicated the formation of a ‘pseudogel’ whose cohesion increased during cooling to 10 °C. Subsequent heating to 90 °C encouraged extensive formation of disulphide bonds as it produced gels that were insoluble in sodium dodecyl sulphate and urea solutions. Dialysis produced isolates of lower gelling concentrations, which also formed networks of a stronger relative elastic character. The presence of NaCl at concentrations up to 0.5 m had a reinforcing effect on networks. Protein over‐aggregation caused the opposite effect at higher salt levels. Finally, a comparison with results in the literature on soybean protein gelation suggested similar denaturation temperatures and a common pattern of structure formation for the two legume proteins.

Functional and physicochemical properties of pulse proteins

“…As reported by Kiosseoglou et al (1999), NaCl addition at levels of up to 0.5 M may bring about an increase in storage modulus and a reduction in tand values of lupin protein isolate gels. At a higher salt concentration, gel elasticity and strength appeared to decrease again, indicating that electrostatic interactions between the denatured protein molecules determined to some extent the properties of the gel network structure.…”

“…Thus, protein contents close to 90% have been reported in a number of papers for powdered materials obtained from pulses such as chickpea, pea, lupin or faba bean, by applying the so-called isolate process (Fan and Sosulski, 1974;Chakraborty et al, 1979;Paredes-Lopez et al, 1991;Kiosseoglou et al, 1999;Papalamprou et al, 2008;Zhang et al, 2009). In other studies, the protein content of the materials obtained from a number of pulses was lower than 90% and in some cases even lower than 70% (Sanchez-Vioque et al, 1999;Makri and Doxastakis, 2006a;Boye et al, 2010b).…”

“…These workers also observed that the gelling properties of the protein concentrates were improved when the method of ultrafiltration was applied for their preparation, with the LGC, for instance, of the lentil concentrate dropping to 8%. This latter finding emphasizes the importance of the method of protein manufacture on molecular interaction and gel network formation, something that was more systematically investigated for isolates obtained from lupin (Kiosseoglou et al, 1999) or chickpea ( Papalamprou et al, 2008). These studies reported LGC values in the range of 4-8% for isolates obtained by ultrafiltration or dialysis.…”

“…The main interactions responsible for gel network formation by pulse proteins appear to be hydrophobic in nature. Covalent disulfide bridges may also contribute to some extent to gel structure development (Kiosseoglou et al, 1999). Papalamprou et al (2008) observed that 50% of protein in the structure of gels, based on chickpea protein isolate, was solubilized when treated with sodium dodecyl sulfate (SDS) or urea.…”

Sodium dodecyl sulfate treatment improves properties of cast films from soy protein isolate

“…Ionic surfactants, such as sodium dodecyl sulfate (SDS), are powerful denaturing and dissociating agents for proteins (Graveland et al, 1979;Cheftel et al, 1985). Strength reduction, and even re-solubilization, of protein gels in SDS buffers has been reported (Kitabatake and Doi, 1993;McClements et al, 1993;Kiosseoglou et al, 1999). Therefore, incorporation of SDS into protein-based film-forming solutions would be expected to affect the structure and properties of cast protein films.…”