Calcium-aided fabrication of pea protein hydrogels with filler emulsion particles coated by pH₁₂-shifting and ultrasound treated protein

Pea protein is a functional ingredient as well as a structure builder in meat substitution products, and the addition of calcium and inclusion of emulsified oil may improve product textural properties. In the present study, O/W emulsions prepared with pH₁₂-shifting (pH₁₂) and high-intensity ultrasound (US) treated pea protein were imbedded into the pea protein isolate (PPI) gel matrix with or without CaCl₂, and the effects on rheological, textural, and water-binding properties of the composite hydrogels were investigated. The addition of 5–20 mM CaCl₂ significantly enhanced the elastic modulus and textural properties of the hydrogels (16% protein, w/v) especially with the presence of 10% emulsified oil (v/v) stabilized by pH₁₂ or US modified PPI (P < 0.05). The gel hardness increased with CaCl₂ addition, reaching a maximum at 15 mM CaCl₂. Gels filled with pH₁₂ and US protein emulsions had less cooking loss but increased hardness than gels filled with native protein emulsion, and CaCl₂ further improved water binding. Microstructural examination revealed ordered PPI gel structures when filled with pH₁₂ and US protein emulsions and in the presence of Ca²⁺. The NMR results suggest that water was tightly bound despite some shifting of immobilized water (T₂₁) to free water (T₂₂) in Ca²⁺ treated PPI gels.