Application of Soluble Whey Protein-Carboxymethylcellulose Complex in Emulsion and Acid-induced Gelation
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Soluble complex between whey protein isolate (WPI) and carboxymethylcellulose (CMC) can be formed at pH above the pI of the protein. In the first study, the influence of CMC concentration and molecular weight (Mw = 270k, 750k, and 2,500kDa) on the stability and properties of WPI/CMC-stabilized oil-in-water emulsions was investigated. Emulsions were prepared using soluble WPI-CMC complexes by homogenization 5% vegetable oil with 95% mixed WPI-CMC solution (0.5% WPI and 0-0.5% CMC, pH 7.0) at 12,000 rpm for 1 min, followed by sonication at 30% amplitude of total power for 5 min, and the pH was adjusted to 5.2. Emulsions were assessed by measuring ζ-potential, droplet size, creaming stability, rheological properties, and protein surface coverage. At proper concentration, emulsions containing high Mw CMC (2,500k) were the most stable and showed no separation even after 15-day storage. In the second study, acid-induced gelation of heated WPI and CMC soluble complex was investigated. Heated soluble complexes were prepared by mixing the biopolymers at pH 7 and heated at 85 oC for 30min. Gels were formed by the addition of GDL. Results showed that CMC molecular weight and biopolymer ratio were the major factors affecting gel properties. Overall, gels from heated WPI-CMC complex showed smoother structure and less porosity, indicating less phase separation. Furthermore, gels showed better mechanical properties when heated WPI-CMC complex at higher protein concentration.