Molecular structure and properties of kappa-carrageenan-gelatin gels

Rheological studies, FTIR spectroscopy and a molecular docking approach were used to explore the structural basis of the peculiar physicochemical properties of gelatin gels modified with a kappa-carrageenan admixture. Mixed gel properties are affected by the polysaccharide-to-gelatin ratio, Z, and can be divided into two categories. At low ratios, the strength of mixed gels varies insignificantly compared to gelatin due to the similar structures of the gels. Above the threshold content of kappa-carrageenan (Z > 0.1), the storage modulus and yield stress of mixed gels are significantly enhanced. The nonadditivity and threshold character of the rheological properties could be the result of conformational ordering of both gelatin and kappa-carrageenan, leading to the formation of additional junction zones in the gel network. According to molecular docking studies, the junctions could be formed as a result of complementary interactions between the gelatin triple helix and the kappa-carrageenan double helix. The stack formation increases the interaction energy, which explains the strengthening of the gel network.