Optimization, Characterization, and Application of Soy Protein Isolate–Catechin Composite Microspheres in Emulsified Beef Balls

Although catechins are strong dietary antioxidants with proven health benefits, yet they are very sensitive and unstable under normal condition to be used in practical food applications. To address this, a food-grade delivery system was developed through pH-driven co-assembly of catechin (CAT) with soy protein isolate (SPI), forming composite microspheres without the addition of chemical solvents or crosslinkers. The final assembly pH was identified as the primary factor affecting encapsulation, achieving a loading of 62.01%. The resulting microspheres (~ 16.8 nm) were stable, with analyses confirming encapsulation via hydrogen bonding and hydrophobic interactions, alongside a crystalline-to-amorphous transition of catechin. This improved stability under heat, salt, and pH stress while preventing loss in antioxidant activity. When applied to emulsified beef balls, 1.0% SPI-CAT reduced cooking loss (27% to 21%), increased yield (78%), and improved texture without affecting sensory quality. By linking molecular-scale composite characterization directly to functional performance in a real meat matrix within a single study, these results highlight its potential as a plant-based ingredient for stabilizing bioactives in food systems. Graphical