Large enhancements in thermogelation of whey protein isolate by incorporation of very low concentrations of guar gum

The effect of the non-gelling polysaccharide guar gum on thermal gelation of whey protein isolate (WPI) was investigated by compression testing. oscillatory rheology and differential scanning calorimetry (DSC). All samples were prepared in 100mM NaCl, with the concentration of WPI held constant at 3.0 wt%. Under these conditions, DSC heating scans (Setaram microcalorimeter; sample mass approximate to 850 mg: 1 degrees C/min) for WPI in the absence of guar gum showed an endothermic denaturation process with maximum heat flow at similar to 76 degrees C and an exothermic aggregation process at similar to 87 degrees C. On incorporation of increasing amounts of guar gum (0.0-0.5wt%) the exotherm moved to progressively lower temperature, until eventually, at 0.5wt% guar gum, it was obscured by the more intense denaturation endotherm. This is attributed to segregative interactions ("thermodynamic incompatibility") with guar gum promoting aggregation of thermally denatured whey protein. After heating to 80 degrees C and cooling to induce gelation of the whey protein, Young's modulus (L) at 20 degrees C rose to a maximum at similar to 0.05 wt% added guar gum and decreased at higher concentrations. until at 0.5 wt% guar gum the mixture was liquid-like. A similar initial increase and subsequent decrease with increasing concentration of guar guru was observed by oscillatory measurements (1 rad s(-1); 0.5% strain) of storage modulus (G), but the maximum occurred at similar to 0.1 wt% guar,Gum. The difference in optimum concentration is ascribed to use of a different time-temperature regime in preparing the samples for compression testing. The reduction in gel strength observed by both techniques at high concentrations of guar gum is attributed to excessive aggregation of WPI in response to segregative interactions, with consequent collapse of the crosslinked network. However, at the very low optimum concentration of similar to 0.1 wt% guar gum a large (similar to 12-fold) enhancement in gel strength (G) was evident in comparison to WPI alone. (c) 2007 Elsevier Ltd. All rights reserved.