<p>This study focused on the development of heat-stable jelly fillings based on low-methoxyl citrus pectin and exhibiting enhanced biological and technological properties through the incorporation of a complex food additive (CFA) containing iron oxide nanoparticles (Fe₃O₄) and brown algae (<i>Laminaria japonica</i>). The additive was introduced in the amounts of 0.1, 0.15, and 0.2% (w/w) relative to the total mass of the final mixture. Sensory analysis was conducted by a panel of 15 trained assessors to evaluate preference and overall acceptability. The introduction of CFA increased the appearance, consistency, and overall scores by 1.06–1.11 times compared with the control, while also providing a more intense and uniform color. Among the tested concentrations, 0.15% CFA was identified as the optimal level, ensuring a balance between structural, sensory, and nutritional benefits. The incorporation of 0.15% CFA reduced moisture loss by 1.6-fold, lowered total acidity by 1.08–1.18 times, increased the thermal stability index by 18.9% (in the “open” baking state) and by 11.4% (in the “closed” baking state), decreased syneresis (water loss) intensity by 2.8 times, and stabilized viscosity and structural integrity during baking. Furthermore, the jelly filling with 0.15% CFA was enriched with protein, dietary fiber, minerals, iodine, and iron.</p> Graphical abstract