Rheological, thermal and microstructural properties of whey protein-cassava starch gels

Mixed gels of cassava starch (CS) and a whey protein isolate (WPI), obtained by heating solutions of 10% total solids, pH 5.75 to 85 degrees C, were characterized as a function of the starch fraction, U-s by axial compression, small-amplitude oscillatory rheometry, differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Gelation did not occur for U-s>0.7. In the range 0<U-s<0.4 mixed gels showed higher mechanical (E, elastic modulus) and rheological (G', storage modulus) properties than pure gels, with maximum values for U-s=0.2-0.3. Viscoelastic mesurements as a function of time showed that gels containing higher levels of WPI developed a larger G'. Blends of both biopolymers showed independent thermal transitions in DSC mesurements, related to gelatinization and denaturation. Microstructure of a mixed gel formed at U-s=0.2 showed a continuous matrix formed by strands of WPI particle aggregates and an independent CS phase.