Abstract: In this study, a protein-polysaccharide-polyphenol complex was prepared from soybean protein isolate (SPI), high methoxyl citrus pectin (HMCP) and gallic acid (GA). The preparation conditions were optimized by using one-factor-at-a-time method and orthogonal array design. Furthermore, a Pickering emulsion was prepared with this complex and characterized for rheological properties, particle size and distribution, zeta potential and emulsion stability. The results showed that the maximum absorbance of 3.082 was observed for the emulsion containing the complex prepared at pH 4.5 and 35 ℃ using 40 mg of gallic acid. Under these conditions, SPI, HMCP and GA were most tightly bound. The Pickering emulsion with an oil volume fraction (φ) of 0.7 had the best elasticity and viscosity, and formed a dense gel network structure. Its zeta potential and average droplet size were (?54.08 ± 2.74) mV and (220.36 ± 7.13) nm, respectively. The Pickering emulsion showed weaker creaming and smaller droplet size at 4 ℃ than 25 ℃, which was more conducive to maintaining the emulsion stability. With the increase of heat treatment temperature, the creaming degree of the emulsion increased gradually. At φ values of 0.7 and 0.8, the droplet size was not affected by temperature. Freezing destroyed the interface of the emulsion. With increasing either φ value or freezing time, the creaming phenomenon became more obvious, greatly reducing the stability of the emulsion. With the increase of pH, the creaming phenomenon became more obvious. When the emulsion system pH was close to 4, the droplet size was the smallest and the droplet size distribution was relatively uniform. High concentration of salt ions destroyed the degree of binding of the complex, caused droplet aggregation and obvious creaming, and reduced the stability of the emulsion.

Key words: soy protein isolate-high methoxyl pectin-gallic acid complex; Pickering emulsion; rheological properties; stability