Development of product for elderly people: impact of the type of protein and matrix structures on the protein hydrolysis

In 2030, 1/3 of the European population will be over 60 years old. Elderly people exhibit specific nutritional needs, in particular they require higher protein intake. For this purpose, three dairy products were developed to provide a large amount of whey protein, known to be quickly digested and rich in leucine. Whey proteins allow a peak of leucine stimulating the muscle protein synthesis. This study aimed to understand the influence of protein nature (whey or caseins), heat-induced protein denaturation and structure of the food matrix on the kinetics of proteolysis and the bioaccessibility of amino acids during a simulated gastrointestinal digestion. Three whey protein-based dairy products were designed with exactly the same composition (24% whey proteins, 20% fat) but different textures (more or less firm gels) were obtained by modulating the manufacturing process. The liquid and native whey protein emulsion was also studied as a control. Mozzarella cheese was studied as the casein gel control. A multiscale characterization of the matrices was conducted including texture analysis, microstructure by confocal microscopy, and extent of heat induced whey protein denaturation. Protein digestion rates and amino acid liberation kinetics during the in vitro gastro-intestinal digestion (based on the INFOGEST protocol) were evaluated using biochemical analyses of digesta. Results showed that both the degree of hydrolysis and the amino acid liberation were significantly higher in the casein-based gel than in whey protein matrices. The extent of protein hydrolysis was higher in the whey protein gels compared to the liquid control sample, due to a facilitated hydrolysis of the heat-denatured proteins compared to native proteins. Peptide release and amino acid bioaccessibility were however not significantly influenced by the matrix structure. Further studies, using an in vivo digestion model (in dynamic condition with gastric emptying) will allow to assess the amino acids bioavailability of these matrices.