Development of polysaccharide-casein gel-like structures resistant to in vitro gastric digestion

Controlling protein digestion is a promising strategy to modulate hormonal responses involved in satiety and appetite regulation. In this context, polysaccharide-casein gel-like structures have been developed and subjected to in-vitro gastrointestinal digestions to evaluate their potential for delaying casein hydrolysis. The effect of the polysaccharide type (agar vs. κ-carrageenan), the polysaccharide:casein ratio and the physical state of the structures (hydrogels vs. aerogels) on the protection ability was investigated. The microstructure evolution of the materials upon the digestions was studied and the molecular weight distribution and peptidomic profile of the digestion products were also determined. During the gastric phase most of the developed structures exerted a protective effect and intact casein clusters were even detected in some of the formulations. In contrast, during the intestinal phase most of the casein was released and hydrolysed to a certain extent. In general, the hydrogels showed a greater protective effect than the aerogels, due to a limited diffusion of the protein towards the liquid medium. Moreover, a higher polysaccharide:protein ratio produced stronger gel networks which provided greater protection. In particular, agar-based and κ-carrageenan hydrogels with 25% polysaccharide and agar-based aerogels with 75% polysaccharide would be the most optimum for delaying casein digestion, since they were able to preserve intact casein after the gastric phase while promoting the release of peptides during the intestinal phase.