Network formation of canola protein–κ-carrageenan mixtures as affected by salts, urea and dithiothreitol

Rheological characterization of plant proteins can be improved by inclusion of low levels of polysaccharides. The gelling behavior of canola protein isolate (CPI)–κ-carrageenan (κ-CAR) mixtures were evaluated to determine the effects of sodium salts (sulfate, acetate, chloride, and thiocyanate), urea, and dithiothreitol (DTT) on network formation and structure. The G′ values for gels prepared from the CPI–κ-CAR mixtures in the presence of various 0.5 mol/l salts in the lyotropic series were ranked as follows: Cl−–SO42−–C2H3O2−>SCN−. tan δ values ranked as follows: SO42−>C2H3O2− >SCN−–Cl−. A CPI–κ-CAR gel prepared in the presence of 360 g/l urea had a weak elastic network, indicating that CPI has sufficient linkages to support a gel network; this was not the case when κ-CAR was not part of the system. DTT-treated CPI–κ-CAR gels had G′ values comparable to the untreated sample, suggesting that non-covalent forces play a major role in gel formation. Only weak interactions were seen for the CPI in DTT. Unlike gels formed with CPI alone, the gels from the CPI–κ-CAR mixtures provided enough covalent linkage to form a gel when non-covalent interactions are inhibited, and at the same time, did not require disulfide bonding to form strong elastic gel. This demonstrates that CPI–κ-CAR not only produces better networks than CPI alone, but these networks are less sensitive to environmental factors.