Physicochemical Properties and Structural Characterization of Blended Walnut Oil Microcapsules Prepared by Complex Coacervation Method

In this study, blended walnut oil (BWO) microcapsules with wall materials consisting of walnut protein isolate (WPI) and gum arabic (GA), sodium alginate (SA) or carboxymethyl cellulose sodium (CMC) were prepared by complex coacervation and freeze drying to improve the oxidative stability of vegetable oils. The optimum ratio of protein to polysaccharide (WPI:GA = 4:1, WPI:SA = 6:1, and WPI:CMC = 6:1) and pH (4.3, 4.3 and 4.4 for WPI combinations with GA, SA, and CMC, respectively) for the preparation of different composite wall materials were determined based on zeta potential and turbidity. The differences in encapsulation efficiency, physicochemical properties, and microscopic morphology of the three types of microcapsules were compared. The microcapsules (WPIGA-BWO) with a WPI:GA ratio of 4:1 at pH 4.3 had the highest encapsulation efficiency (94.02%) and solubility (84.49%) with an average particle size of 226.70 μm. Infrared spectroscopy confirmed that WPI and polysaccharides formed coacervates through electrostatic interactions, which could be used as wall materials for encapsulating blended oils. X-ray diffraction (XRD) analysis showed that the WPIGA-BWO microcapsules had high relative crystallinity (40.27%). Thermogravimetric analysis (TGA) indicated that the microcapsules exhibited good thermal stability below 250 ℃. This study can provide a theoretical reference for the development of powdered walnut oil products and the effective protection of vegetable oils, broadening the application scope of walnut oil in the field of food processing.