Microencapsulation efficiency, oxidative stability, and in vitro digestibility of walnut oil microcapsules: Effects of process conditions and antioxidants

Walnut oil (WO), rich in essential polyunsaturated fatty acids but highly oxidation-prone, was stabilized via spray-drying microencapsulation using octenyl succinic anhydride (OSA) starch-maltodextrin (MD) wall materials. Optimization yielded critical parameters: 4:1 OSA:MD ratio, 10% solids, 40% oil loading, 180°C inlet temperature, and 2.5 mL/min feed rate, achieving 88% encapsulation efficiency with only 4.8% surface oil. An antioxidant blend (tea polyphenol palmitate, ascorbyl palmitate, rosemary extract) significantly enhanced oxidative stability during accelerated storage (52°C, 15 days), limiting the increase in peroxide value (PV) to 2.89-fold and thiobarbituric acid reactive substances (TBARS) to 2.6-fold. Microcapsules exhibited favorable physical properties (solubility, angle of repose, bulk/tapped density, flowability, cohesiveness, moisture content) and negligible color change. Structural integrity and molecular stability were confirmed via microscopy (scanning electron microscopy SEM and confocal laser scanning microscopy CLSM) and spectroscopy (Fourier-transform infrared spectroscopy FTIR and X-ray diffraction XRD), while Thermogravimetric (TG/DTG) analysis indicated delayed decomposition. Oxidation followed first-order kinetic model, with shelf-life tests predicting extended shelf-life (349 days). In vitro digestion demonstrated effective gastric protection (10% oil release) and sustained intestinal liberation (83% oil release, 38% free fatty acids). This work establishes a non-protein-based microencapsulation platform with controlled release, effectively mitigating oxidation for highly unsaturated oils in food. • Optimal microencapsulation extended walnut oil shelf-life 349 d (10.6×) via antioxidants + encapsulation. • Structure-function integrity was confirmed by post-oxidation. • Microcapsules showed controlled-release functionality.