Improvement of emulsifying properties of soybean protein isolate by conjugation with carboxymethyl cellulose

Soybean protein isolate (SBPI) was mixed with sodium carboxymethyl cellulose (NaCMC) and dry-heated at 60C for a time period of up to 5 weeks. An improvement in emulsifying properties of the mixture, especially in oil droplet size reduction and emulsion stabilization against creaming was observed, depending on polysaccharide molecular weight, SBPI/NaCMC weight ratio and time of incubation. This is attributed to formation, upon heating, of a covalent protein–polysaccharide conjugate which, following adsorption through its protein moiety at the oil–water interface, may enhance repulsive steric forces between the oil droplets as a result of polysaccharide chain overlapping. The conjugate formation was confirmed by SDS-PAGE and the results are discussed in terms of protein solubility and surface adsorption behaviour.