Gelation of whey proteins by microwave heating

The objective was to obtain whey protein isolate (WPI) gels by a conventional water bath method and by microwave heating. Protein suspensions (10% protein) were prepared by hydrating WPI in 0.05, 0.1, 0.2, 0.3 and 0.5M NaCl. The pH of WPI suspensions obtained at 0.1 NaCl was adjusted to 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0 and 10,0. Texture profile analysis of the gels was performed with a TA-XT2i Texture Analyser. Microstructure of WPI gel samples was observed by scanning electron microscopy. WPI gels obtained at pH 3 and 10 by microwave heating (MHI), which had fine-stranded structure were stronger than WPI gels obtained by conventional heating (CHI). In case of gels with particulate and mixed structure the opposite effect was observed. CHI gels obtained at pH range from 4 to 9 were stronger than MHI gels. Similarly, when concentration of Na+ increased, the microstructure changed from fine-stranded to mixed, the hardness of fast heated (MHI) gels dramatically decreased, and was observed especially at pH 3 and 10.