Table 3.

Recent studies on infant protein digestion using in vitro models

Model	Food	Analytical techniques	Adaptations for infants	Reference
Static infant gastric digestion model (with porcine pepsin or human neonatal gastric juice)	Whey protein concentrate, infant formula	SDS-PAGE, HPLC, N-terminal sequencing, western blot	(1) Human neonatal gastric juice for in vitro digestion; (2) pH 6.5,5.0, 4.0, 3.5, 3.0 and 2.0; (3) 1hr incubation	[90]
Static infant gastrointestinal model	Human milk with and without pasteurization (62.5°C for 30min)	LC-MS/MS	(1) Gastric pH 4.0; (2) 15min for gastric digestion; (3) 5min for intestinal digestion.	[96]
Static infant gastrointestinal model	Human milk, infant formula	LC-MS/MS	(1) Gastric pH 3.5; (2) 30min for gastric digestion; (3) 60min for intestinal digestion.	[91]
Static infant gastrointestinal model	Human milk, infant formula	LC-MS/MS, ELISA	(1) Gastric pH 4.0; (2) 100U pepsin/mg protein; (3) 5mg pancreatin and 30mg bile salt extract/mL sample for duodenal digestion.	[110]
Static infant gastroduodenal model (with enzymes and surfactants)	Milk protein solutions, Maillard reaction products, food matrices (milk and yogurt) with different processing	SDS-PAGE, ELISA, immunoblotting, RP-HPLC, LC-MS/MS	(1) Gastric pH 3.0 instead of 2.5; (2) 22.75U pepsin/mg substrate (8-fold reduction compared to adult model); (3) 1mM duodenal bile salt (4-fold reduction), 3.45U trypsin/mg substrate (10-fold reduction), 0.04U chymotrypsin/mg substrate (10-fold reduction).	[29, 92, 93]
Semi-dynamic infant gastric model	Model formulas with different processing	Chemical characterization for lipids and proteins, structural characterization for emulsions	Three subsequent stages: 0–60min at pH 6, 60–120min at pH 5, 120–180min at pH 4.	[40]
pH static and dynamic gastric models for infants and adults	Milk protein solutions, protein emulsions	SDS-PAGE, light scattering and fluorescence microscopy	(1) gastric digestion time 240min (120min for adults); (2) pH gradients from 6.5 to 3.5 (4.5 to 1.5 for adults) in dynamic models, and pH 2.5 in static models; (3) 210U pepsin/mg protein (240U for adults).	[94]
Dynamic gastric model mimicking infants aged 9–12 months	Human milk	SDS-PAGE, LC-MS/MS, immunoblotting	(1) pH gradients from 7 to 2 over 60min; (2) enzymatic content; (3) contraction; (4) half gastric emptying at 48min.	[95]