Aggregation of casein micelles and κ-carrageenan in reconstituted skim milk

A novel method to form casein/κ-carrageenan aggregates in skim milk, by mixing solutions of each at 60 °C and cooling to 25 °C while shearing, was investigated. The average particle size of casein/κ-carrageenan aggregates decreased with increasing shear rate (200, 400 and 800 s−1) but increased with κ-carrageenan concentration (0.025% 0.05% and 0.075%). Oscillatory rheology measurements demonstrated that skim milk containing 0.025% κ-carrageenan behaved as a dilute solution, while skim milk with 0.05% or 0.075% κ-carrageenan formed weak gels, although solutions remained fluid and were at a much lower modulus compared to similar solutions cooled with no shearing. The aggregates were quite stable to shear once formed. The initial mixing temperature of reconstituted skim milk and κ-carrageenan dispersions greatly affected the particle size distribution of the aggregates. Microstructural observations as well as studies in the presence of NaI demonstrated that at particular protein/polysaccharide ratios, casein/κ-carrageenan aggregates formed in reconstituted skim milk via adsorption of κ-carrageenan with casein micelles.