Preparation and characterization of walnut oil microcapsules by complex coacervation with sodium alginate and chitosan

Walnuts, with high oil content and various nutrients, are the ideal raw materials for oil production. However, walnut oil (WO) is highly prone to oxidative rancidity, which will decline product quality. To improve WO’s stability, this study utilized sodium alginate (SA) and chitosan (CS) as wall materials to create WO microcapsules. The impact of wall material concentration, core-to-wall ratio, SA-to-CS ratio, pH and other factors on encapsulation efficiency (EE) were assessed by complex coacervation. Physicochemical properties, release kinetics, oxidative stability, and in vitro digestion were analyzed. It was observed that the EE of WO microcapsules reached 91.18% under the following process conditions: 1:1 ratio of SA-to-CS, 3:2 ratio of core-to-wall, total wall concentration of 1.5%, and pH of 4. SEM, FTIR, and XRD results confirmed successful microencapsulation. Compared with single-layer WO microcapsules, double-layer microcapsules exhibited lower moisture content and hygroscopicity, higher in vitro gastrointestinal digestibility and oxidation stability. This study provides theoretical support for expanding the application of WO in the food industry. • Sodium alginate and chitosan could encapsulate walnut oil well with an encapsulation efficiency of 91.8%. • Microcapsules obtained from composite walls are more resistant to harsh environments than those obtained from single walls. • Encapsulated walnut oil has higher antioxidant capacity and longer shelf life than unencapsulated walnut oil. • Walnut oil is more digestible in the gastrointestinal tract after encapsulation.