Fabrication of W/O/W Emulsions Encapsulating Mango Peel Extract Using Soy Protein Isolate–Sodium Alginate Complexes: Enhancing the Oxidative Stability of Soybean Oil

A water-in-oil-in-water (W/O/W) emulsion was constructed for encapsulating mango peel extract (MPE). This study investigated the effect of soy protein isolate (SPI) concentration on the microstructure and stability of MPE W/O/W emulsions with sodium alginate (SA) in the outer aqueous phase. The optimal SPI concentration was found to be 4% (w/v), which yielded a stable W/O/W emulsion with the smallest droplet size (7.14 ± 0.14 µm), higher ζ-potential (-38.61 ± 0.33 mV), highest encapsulation efficiency (85.3 ± 0.5%), favorable rheological properties, and superior storage stability. Subsequently, MPE encapsulated by SA (2% w/v), SPI (4% w/v), or an SPI/SA composite was incorporated into soybean oil at concentrations of 100, 200, and 300 ppm. The oxidative stability of the oil during storage was evaluated and compared with samples containing unencapsulated MPE and the synthetic antioxidant butylated hydroxytoluene (BHT). From the results, the SPI/SA-encapsulated MPE most effectively enhanced the oxidative stability of soybean oil during storage, outperforming both the singly-encapsulated (SA or SPI alone) and unencapsulated forms. PRACTICAL APPLICATIONS: Mango peel extract can lose activity during processing and storage, which limits its direct use in edible oils. This study shows that a SPI sodium alginate based W/O/W emulsion can carry mango peel antioxidants into soybean oil at 100-300 ppm and lower oxidation indices under accelerated storage compared with adding the extract directly, providing an option alongside existing antioxidant strategies.