Influence of molecular weight and degree of substitution of carboxymethylcellulose on the stability of acidified milk drinks

The influence of molecular weight (Mw, 250,000, 700,000) and degree of substitution (DS, 0.7, 0.9 and 1.2) of carboxymethylcellulose (CMC) on the diameter and ζ-potential of casein micelles during acidification in diluted dispersions and on the stability of acidified milk drinks was investigated. The experimental results suggested that CMC with high Mw or low DS would result in thick adsorbed layer onto casein micelles. The ζ-potential of CMC-coated casein micelle increased with increasing the Mw of CMC with the same DS while at a fixed Mw the ζ-potential for CMC with high DS (1.2) increased in comparison with those for CMC with low DS (0.7 and 0.9). Both Mw and DS of CMC influenced the stability of acidified milk drinks. CMC with high Mw increased the viscosity of acidified milk drinks significantly and therefore contributed to the stability. CMC with high DS resulted in high ζ-potential of CMC-coated casein micelles, increasing the electrostatic repulsion between casein particles, which prevented the phase separation in acidified milk drinks. It was also found that the amount of CMC needed for efficient coverage of casein micelles increased with increasing the Mw of CMC. Above the efficient coverage concentration, the long-term stability of acidified milk drinks with high Mw CMC was better than that with low Mw CMC.