Fractionation by microfiltration: Effect of casein micelle size on composition and rheology of high protein, low fat set yoghurt

The effects of casein micelle size on rheological properties of high protein (5.6% crude protein), low fat (≤0.2%) set yoghurt were investigated. Microfiltration with 0.20 μm membranes was used to fractionate skim milk with an average casein micelle size of ∼174 nm into a retentate and a permeate containing “large” (∼183 nm) and “small” (∼129 nm) casein micelles, respectively. The permeate containing the small casein micelles was further concentrated with 0.10 μm membranes. Yoghurt milk bases with large or small casein micelles were subjected to heat treatment at two different temperatures; 95 °C or 75 °C for 5 min. Yoghurt milk base with small casein micelles gave set yoghurts with higher storage modulus (G′) and higher firmness than yoghurt milk base with large casein micelles. Increased gelation capacity can be attributed to an increased amount of κ-casein in the yoghurt milk base containing small casein micelles.