Nanostructural changes in Polysaccharide-Casein Gel-Like structures upon in vitro gastrointestinal digestion

This work reports on the nanostructural changes taking place during the in vitro gastrointestinal digestion of polysaccharide-casein gel-like structures through the use of small angle X-ray scattering (SAXS). The results indicated that during the gastric phase, the hydrolysis of casein led to a swelling of the micellar structure, yielding peptide clusters. The presence of sulphated polysaccharides such as agar and kappa-carrageenan was seen to limit the hydrolysis of casein during the gastric phase, hence decreasing the size of the formed clusters. After the intestinal phase, the produced peptidic fragments appeared to interact with the bile salts present in the digestion medium, yielding a mixture of bile salt lamellae/micelles and vesicular structures. However, in the presence of polysaccharides, which can interact with bile salts, the formation of vesicular structures was limited. Interestingly, the inclusion of casein within hybrid gel-like structures led to the formation of strong polysaccharideprotein interactions, especially in the case of kappa-carrageenan. As a result, in some of the formulations, polysaccharide-peptide complexes were released towards the liquid medium, which formed larger vesicular structures. This was related to the greater protective effect of these particular gel-like structures. Furthermore, kappa-carrageenan hindered the formation of bile salt lamellae/micelles. These results are of high relevance to understand the intestinal transport mechanism of the digestion products from protein-based ingredients and will allow a rational design of novel products with optimum nutritional and functional properties.

Automated summary

This work investigated the nanostructural changes that occur during the in vitro gastrointestinal digestion of polysaccharide-casein gel-like structures. The study found that the hydrolysis of casein during the gastric phase leads to the swelling of micellar structures and the formation of peptide clusters. The presence of sulphated polysaccharides limits the hydrolysis of casein and decreases the size of the formed clusters. After the intestinal phase, the peptidic fragments interact with bile salts, resulting in the formation of bile salt lamellae/micelles and vesicular structures. However, the presence of polysaccharides restricts the formation of vesicular structures and hinders the formation of bile salt lamellae/micelles.