Rheological characterization of set yoghurt produced with additives of native whey proteins

The influence of native whey protein isolate (WPI) addition on the consistency and microstructure of set yoghurt was studied. Native WPI with nutraceutical properties was added (3–12%) to the yoghurt milk immediately before fermentation. The consistency of the yoghurts was analysed and compared using two rheological methods: the penetration resistance of a cylinder and an oscillation method for which a vane was used. The effects of the WPI on the rheologically determined values were quantified whereby a remarkably good correlation between the two methods was achieved. With both methods the texture characteristics of the different set yoghurts could be well characterized and enabled good comparisons. The addition of WPI gave rise to a weaker texture of the set yoghurt. Microstructure was observed by confocal laser scanning microscopy. The addition of WPI led to a less-coherent microstructure, which was in agreement with the rheological observations.