Tribo-rheology characteristics and microstructure of a protein solution with varying casein to whey protein ratios and addition of hydrocolloids

In this study, the effect of four different hydrocolloids (gelatin, κ-carrageenan, low methoxy pectin and curdlan) on the rheology, tribology and microstructure of milk protein solutions with fixed protein content (3.4%) but varying casein to whey protein ratios were investigated. Replacing casein by whey protein isolate improved the protein stability, increased the viscosity and lubrication property of protein solution, whilst the milky white colour of the solution reduced. Gelling was observed with independent addition of 0.05% of κ-carrageenan and 0.25% of low methoxy pectin to the protein solution with high casein to whey protein ratio (≥50/50). The hydrocolloids addition increased the viscosity and lowered the friction coefficient of protein solutions to some extent, especially protein solution containing 0.25% curdlan showed the best lubrication property. The solutions with low casein content were more homogeneous, and adding hydrocolloids caused phase separation, especially in protein solutions with high casein fraction