Gelation of whey protein concentrate in the presence of partially hydrolyzed waxy maize starch and urea at pH 7.5

The effect of urea (50 and 100 g/l) and of partially hydrolyzed waxy maize starch (HWS, 100 and 150 g/l) on the heat-induced gelation of whey protein concentrate (WPC) at 100 g/l and pH 7.5 was investigated by small amplitude oscillatory measurements under heating to 80 °C and cooling to 25 °C, both treatments being followed by a stabilization period. Addition of urea contributed to the reduction of the values of the storage and loss moduli all over the heating/cooling treatment. On the contrary, addition of HWS alone led to higher moduli values. At the same HWS concentration, the increase of the moduli values was less pronounced when urea was present at 50 g/l. The microstructure of the systems was visualized by light microscopy at 25 °C, after the heating/cooling treatment. Addition of HWS affected the protein network in such a way that at 100 g/l, WPC/HWS mixed gels were visualized as a thick network with large pores, and at 150 g/l, the mixed gels were composed of denser strands with a larger number of smaller pores. However, when urea was also added to these mixed systems, homogeneous gels were imaged. Although leading to weaker gels, addition of urea seems to promote the compatibility of the two macromolecules.