Abstract
Understanding the behavior of human milk in the newborn gastrointestinal tract is a key step in developing substitutes with optimized health benefits. However, ethical and technical reasons limit the possibility of in vivo trials. Consequently, it is important to develop relevant in vitro models. The aim of this work was to compare a dynamic in vitro digestion system developed by the French National Institute for Agricultural Research1 against in vivo data from raw or pasteurized human milk gastric digestion.Supported by an exhaustive literature review2, the dynamic digester parameters were set in terms of types and amounts of enzymes, secretions, pH decrease and emptying rate to mimic as closely as possible the gastric digestive conditions of preterm newborns. Raw or pasteurized (62.5°C, 30 min) pooled preterm human milks (n=5 donors) were digested in triplicate3. In parallel, in vivo study was conducted on hospitalized preterm newborns at Rennes Hospital (NCT02112331, n=12)4. Gastric digesta were sampled regularly. Structural changes were evaluated by confocal microscopy and laser light scattering. Lipolysis and proteolysis kinetics were monitored by SDS-Page, thin-layer and gas chromatography methods. Likewise, gastric volume, pH and emptying rates were compared. During both in vitro and in vivo gastric digestions, pasteurization did not affect the kinetics and final degree of lipolysis and proteolysis, but impacted on emulsion disintegration, protein aggregation and the persistence of native fat globule structure. Results showed the rapid hydrolysis of caseins and a resistance of alpha-lactalbumin in vitro and in vivo. The relatively limited extent of lipolysis by the gastric lipase was confirmed in vitro and in vivo, with a lipolysis degree ranging from 7 to 19% at 90 min.Although curves of pH decrease and emptying rates can be improved to adjust closer to in vivo data, kinetics of hydrolysis and disintegration of human milk showed that thedynamic system of in vitro newborn digestion proposed here is a relevant tool to study gastric digestive kinetics. Our model will be useful to the scientist community and food manufacturers who focus on neonatal gastric digestion and infant formulas optimization.