Whey protein concentrate/pullulan gel as a novel microencapsulated wall material for astaxanthin with improving stability and bioaccessibility

Astaxanthin (AST) has various biological activities such as antioxidant, antitumor and anti-inflammatory, but poor water solubility, instability and low bioaccessibility greatly limit the development of its industrial appli-cation. In this study, whey protein concentrate (WPC) and pullulan (PUL) were used to prepare WPC/PUL gels under different conditions, the microstructure, drying activation energy and powder hygroscopicity were investigated. The WPC/PUL gel formed by heating 10% WPC and 8.0% PUL (pH 7.0) at 80 degrees C was selected as wall material to encapsulate AST by freeze-drying. The highest encapsulation efficiency achieved 93.14% when the volume ratio of AST solution to WPC/PUL gel was 1:2. Compared with free AST, the stability of AST encapsulated in WPC/PUL gel was significantly enhanced during simulated gastrointestinal digestion and the bioaccessibility was increased up to 5.1 times. AST retention was significantly improved after 26 weeks of storage at 4 degrees C and 25 degrees C, with half-lives of 822.38 d and 516.17 d, respectively. The results of X-ray diffraction and differential scanning calorimetry showed that AST was encapsulated in WPC/PUL gel in an amorphous state. The incorporation of AST caused a decrease in the surface hydrophobicity of WPC/PUL gel. It was confirmed by UV, Fourier transform infrared and fluorescence spectra that AST changed the protein conformation of WPC/PUL gel, and the formation of the WPC/PUL/AST complex was mainly due to hydrophobic interaction and hydrogen bond. This study provided a microcapsule based on WPC/PUL gel as a wall material to encapsulate AST, which has a promising future in food processing.