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S. GUNASEKARAN, Dept. of Biological Systems Engineering, Univ. of Wisconsin, Madison, 460 Henry Mall, 220 Agricultural Engineering Bldg., Madison, WI 53706-1533 Different functional properties and nutritional value of the whey proteins have made them an important dairy ingredient. Perhaps the chief among the many useful functional properties of the whey proteins is their ability to form stable gels. Gelation of whey proteins is affected by a number of factors such as concentration, pH, ionic strength, heating rate etc. These factors in turn allow us to control the structure and property of the whey protein gels to tailor the required end product quality. The effects of heating rate (0.1, 1, 5, 10 and 20 °C/min) and xanthan addition (0.1 %, 0.2%, 0.5 % and 1% w/w) on the gealtion of 15% w/w whey protein isolate (WPI) were studied at pH 7 in 0.1 M phosphate buffer solution. The WPI solutions were heated from 25 to 90 °C at different heating rates. Small amplitude oscillatory shear (SAOS) tests were performed to investigate gelation kinetics and small deformation rheological properties of the WPI gels during gelation. The 15% w/w WPI gels and 15% w/w WPI plus xanthan mixed gels were prepared using a controlled heating system. Cylindrical specimens of these gels were tested using a uniaxial compression system to determine their large deformation failure properties at 25 °C. The gelation temperature (Tgel) of WPI decreased with decreasing heating rate and with xanthan addition of xanthan. The fracture stress of the gel was higher when they were prepared at lower heating rates. At low xanthan contents (no more than 0.2 % w/w), the WPI gels exhibited brittle characteristics; when the xanthan content was increased up to 0.5 % w/w, the WPI gels were ductile.
Session 109, The rheology of dairy foods
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