Effects of pH on the emulsifying, gelation and curcumin delivery properties of myofibrillar protein and carboxymethyl cellulose emulsions

This study was designed to explore the curcumin delivery properties of emulsion gel fabricated by myofibrillar protein (MP)-carboxymethyl cellulose (CMC) complexes with different pHs. Firstly, the MP-CMC complexes under pH 2, 3, 4, 5, and 6 were prepared, then the properties of these complex-stabilized emulsions were tested, and the gel properties and curcumin delivery ability of these heat-induced emulsion gels were compared. Results indicated that MP-CMC complexes showed different viscosities and combined states under different pHs. The emulsions fabricated by pH 6 complexes showed the highest emulsion activity index and emulsion stability, and the lowest droplet size value. The emulsion gel of the pH 6 complex showed the highest hardness, chewiness, gumminess, and resilience, while the pH 4 sample presented the lowest water and oil holding capacity among all samples. The pH 4 samples showed 99% curcumin-encapsulating efficiency as well as 70% curcumin retention after 4 h gastrointestinal digestion. The pH 4 samples could protect and control the release of the curcumin by protecting some proteins from pepsin digestion and controlling the release of fatty acid. As for curcumin release rate and bioavailability at the intestinal stage, the pH 6 samples showed the highest values, followed by the pH 5 samples, and the pH 4 showed the lowest. The emulsion gel prepared by pH 4 MP-CMC complexes could best protect and control the release of curcumin, whilst the pH 6 samples showed a better gel quality and a higher release rate and curcumin bioavailability.