Effect of Ca2+ cross-linking on the properties and structure of lutein-loaded sodium alginate hydrogels

In order to construct nano-lutein hydrogels with sustained release properties, the basic properties and structure of nano-lutein hydrogels cross-linked with different concentrations of Ca2+ were investigated. The results showed that the highest loading capacity for lutein reached 770.88 μg/g, while the encapsulation efficiency was as high as 99.39%. When Ca2+ concentration was lower than 7.5 mM, the filling of lutein nanoparticles reduced the hardness and gumminess of the hydrogel. The resilience and cohesiveness of the hydrogel decreased as the concentration of Ca2+ increased. Filling with lutein nanoparticles and increasing Ca2+ concentration both increased the G′ and G″. The hydrogel loaded with lutein showed different swelling properties in different pH environments, the filling of lutein nanoparticles inhibited the swelling of the hydrogel. When Ca2+ concentration was greater than 7.5 mM, the cut-off amount of lutein on the surface of the Ca2+ cross-linked hydrogel was larger. The digestive enzymes quickly degraded the hydrogel structure, resulting in a high initial release of lutein. DSC and FTIR results showed that lutein nanoparticles were mainly physically trapped in the hydrogel network structure. Lutein nanoparticles and excessive Ca2+ affected the stability of cross-linked ionic bonds in the hydrogel, thereby reducing its thermodynamic stability.