Release characteristics and bioaccessibility of lutein from calcium alginate hydrogels during simulated digestion in vitro

In this study, the release of lutein from calcium alginate hydrogels during simulated digestion in vitro was investigated. The results showed that the cross-linked hydrogel with Ca2+ concentration >7.5 mM had a large amount of lutein retained on the surface, and digestive enzymes caused rapid degradation of the hydrogel structure, resulting in a high initial release rate. The particle size of the digestate was the largest in the simulated small intestinal digestion stage, with the gradual degradation of the outer wall proteins of lutein nanoparticles, showing a decreasing trend in the colonic digestion stage. The hydrogel cross-linked with high concentration of Ca2+ mainly released lutein nanoparticles with small particle size. In the later stage, the probability of agglomeration between lutein nanoparticles increased. The cumulative release rate of lutein in the hydrogel with Ca2+ concentration <7.5 mM was higher after digestion, but lutein retention was <80%. The formation of lutein mixed micelles was hindered by the hydrogel with a Ca2+ content more than 7.5 mM, and lutein bioaccessibility was reduced. As a result, appropriate concentration of Ca2+ cross-linked hydrogel carrier improved lutein bioavailability while also extending the residence period.