Effect of the pH of skim milk at heating on milk concentrate viscosity

Abstract Concentrates from skim milk heated at pH 6.5 to 7.1 had viscosities that followed power law behaviour and could be described by consistency coefficients ( K ) and flow behaviour indices ( n ). On evaporation to 40% total solids, milk heated at pH 6.5 produced concentrates with higher K than those from unheated milk. Milk samples heated at pH 7.1 produced concentrates with lower K than those from unheated milk. Above 40% totals solids, the K values of concentrates from heated milk were similar regardless of the pH at heating, and were higher than those from unheated milk. It is proposed that denatured whey proteins associated with the casein micelles increase the voluminosity of the micelles leading to an increased viscosity and K at all milk concentrations. In contrast, denatured whey proteins and κ-casein in the serum only make a small contribution to the viscosity and K until the milk is at high concentrations.