Résumé
Infancy period is marked by digestive immaturity characterized by limited secretory capacity and enzymatic activity, thus affecting the bioaccessibility of nutrients. Despite WHO recommendations for exclusive breastfeeding for 6 months followed by mixed breastfeeding, only 34% of 6-month-olds are breastfed. To ensure adequate intake during the dietary diversification, follow-on infant formulas (IFF) and infant flours (IF) are formulated specifically to meet the nutritional needs of infants from 6 months onward. Their formulation is linked to major challenges of nutritional optimization including the introduction of omega 3 fatty acids especially long chain ones like DHA which has become mandatory in Europe since 2020 in IFF. Such introduction raises issue in terms of oxidation and nutrients bioaccessibility. This study therefore had two objectives: i) optimize oxidative stability and the nutritional composition of IFF and IF, and ii) assess the bioaccessibility of lipids and proteins in these optimized products (n=3) compared with commercial products (n=2) using an in vitro digestion process adapted to the digestive conditions of 6-month-old infants. Optimized IFF (IFF_OP) and IF (IF_OP) were formulated according to overviews of products currently on the market (91 IFF and 96 IF) and by introducing ingredients of interest for infant nutrition, such as milk lipids and sources rich in omega 3 and carotenoids. They were subjected to a static in vitro digestion protocol whose conditions were established according to the literature in comparison with commercial products (IFF_REF or IF_REF). The in vitro static digestion process included two steps: i) a gastric phase (60 minutes, 37°C, pH=3) with a meal/digestive fluid ratio of 50:50 v/v and an enzyme activity of 295 and 22 U/mL for pepsin and lipase, respectively and ii) an intestinal phase (120 minutes, 37°C, pH=7) with a ratio of 25:75 v/v and an enzyme activity of 90 U/mL for lipase and 3.1 mM for bovine bile. For both types of products, the results showed reduced gastric lipids hydrolysis with the onset of DHA release in this compartment. A high lipolysis degree was observed at the end of the intestinal time with a released fatty acids profile reflecting the lipid composition of the source with the presence of short to medium chain in IFF_OP due to the introduction of dairy lipids. The bioaccessibility of omega 3 fatty acids was good and not matrix-dependent, although IF were less rich in lipids than IFF. Vitamin E bioaccessibility was low (7.1-20.7%) and intestinal proteolysis rates moderate (less than 30% released NH2 out of total) possibly influenced by large droplet size (0.8 µm) in IFF_OP and the presence of anti-nutritional factors in IF_OPTI. When optimized these two types of products are good nutritional carriers but the digestive fate of hydrophilic vitamins (A and E) and their oxidation products needs to be investigated further in the near future.