Effect of carrageenan on the formation of rennet-induced casein micelle gels

Casein micelles (CMs) and carrageenan (CG) mixtures were prepared in simulated milk ultrafiltrate. Rennet-induced gelation in the CM/CG mixtures was studied by accessing the kinetics of released caseinomacropeptide (CMP) and the rheological properties of CM/CG mixtures. Particle size distributions, ζ-potential and ionic strength measurements, and microstructure observations were performed to understand the underlying mechanisms. At low CG concentrations, κ-CG, which had a tail-adsorption to the CM surface, affected the second phase of renneting through repulsive interactions. In mixtures containing ι-CG and λ-CG, both the first and second phase of renneting were affected. Flat-adsorption and ring-adsorption of ι-CG and λ-CG to the CM surface, respectively, increased the negative charges and covered more enzymatic action sites, thereby decreasing the maximum concentration of released CMP, increasing coagulation time, and weakening gel strength. At high CG concentrations, free CG molecules contributed to rennet-induced gelation, especially in the presence of κ-CG and ι-CG, which significantly accelerated the second phase of renneting through the self-association of CG double helices. Our findings suggested that ι-CG and λ-CG lead to soft cheese curds and improved low-fat cheese quality.