Ca²⁺-mediated pea protein isolate and low-methoxyl pectin systems for structuring peach kernel oil into reduced-oil...

Structuring unsaturated liquid oils into reduced-oil semi-solid emulsions requires simultaneous droplet stabilization and continuous-phase matrix formation. This study examined how pea protein isolate (PPI), low-methoxyl pectin (LM), and Ca²⁺ regulate these structural contributions, using peach kernel oil at a water-to-oil ratio of 5:1. Water distribution, water-holding capacity, storage stability, molecular environments, rheology, thermal degradation, and microstructure were evaluated. PPI-rich systems lacked sufficient matrix support, whereas LM-rich systems improved water retention and continuous-phase structuring but showed less uniform droplet distribution. PPI-LM blending balanced droplet stabilization with bulk matrix formation. Moderate Ca²⁺ promoted semi-solid structuring. Spectroscopic analysis of corresponding model systems revealed changes in carboxylate-associated and Trp environments, supporting Ca²⁺-dependent biopolymer association. The 5:5 PPI:LM emulsion containing 25 mM Ca²⁺ combined restricted water mobility, refrigerated storage stability, solid-like viscoelasticity, shear-thinning behavior, and relatively uniform droplet distribution. Its dominant T2 decreased from 135.1 ± 0.0 to 54.9 ± 3.8 ms after Ca²⁺ addition. Increasing Ca²⁺ to 50 mM produced only a small further decrease in dominant T2, while rheological properties showed no consistent improvement. A model involving pectin junctions, protein-associated Ca²⁺ interactions, and possible protein-pectin bridging was proposed to explain the composition-dependent structuring. These findings link biopolymer composition and ionic regulation to the storage and flow properties of reduced-oil semi-solid emulsions, informing the development of spreadable food bases.