Structure and visco-elastic properties of set yoghurt with altered casein to whey protein ratios

Abstract

Abstract Set yoghurts with a consistent total protein content were manufactured from milks reconstituted from skim milk powder (SMP), or blends of SMP and whey protein concentrate (WPC) powders with crude protein concentrations between 25% and 80% (w/w) so that the casein to whey protein ratio varied from 4.7:1 to 0.5:1. As the casein to whey protein ratio was decreased the maximum gel strength of the yoghurt increased, the initial gradient of the force–distance curves generally decreased, whey drainage was reduced, and the gels were generally less viscous. Scanning electron microscopy indicated that gels with a lower proportion of casein had a finer structure with numerous small pores and a dense network of crosslinks. When the casein to whey protein ratio was maintained at a constant level, the physical properties of the gels were generally similar, regardless of the protein concentration of the WPC powder that was used. The relationship between the casein to whey protein ratio and the physical properties of the yoghurts is considered in terms of the microstructure of the protein network.