Formation conditions of soy protein isolate-carrageenan complex particles and their stabilization effect on the relationship between structure and rheology of emulsions

This study investigated the formation conditions of the soy protein isolate (SPI)/κ-carrageenan (κCG) complex particles (SCP) and their stabilization effect on the structure and rheology of emulsions over the range of SCP concentration (Cp, 0.5%-2.5%, w/v) and oil phase content (φ, 10%-60%, v/v). By conducting turbidity titration of SPI/κCG mixtures with different ratios and ionic strengths, we observed the formation of soluble complexes in all samples at pH 6.0. The saturation complex ratio of SPI/κCG at pH 6.0 was 1:0.2 using isothermal titration calorimetry, and thermal complex with saturation ratio to form SCP as stabilizers could prepare emulsions with smaller droplet size in comparison of other ratios. Microstructure showed that SCP provided stabilization at the interface, and excess SCP formed network in the bulk phase to give solid-like emulsions. Furthermore, the power-law relationships of G' with particle concentration (G' ∼ Cpn) and oil content (G' ∼ φm) was established. The exponent n and m decreased with increase of Cp and φ, indicating structure of SCPEs depends on Cp and φ. The G'/G'' crossover strain (γco) is indicator of breakdown of emulsion structure. For φ≤20%, γco slightly decreased with increasing Cp; For 30%<φ<50%, γco increased with increasing Cp; For φ=60%, γco significantly decreased with increasing Cp. In summary, these findings indicate the structure and rheology of soy protein-based emulsion can be regulated by controlling the formation condition of SCP and altering the SCP concentration and oil content.