To establish a method combining size exclusion chromatography (SEC) with an optimized Infogest in vitro static digestion model for determining the relative molecular mass distribution of short-peptide-based enteral nutrition before and after digestion. To evaluate and assess the quality of three different products, to explore product quality characteristics and digestive stability, and to provide guidance for quality control and clinical individualized application of short-peptide-based enteral nutrition.

The SEC method was performed using two ECOSIL SEC G 2000 columns (300 mm×7.8 mm, 5 μm) in series, with acetonitrile-water-trifluoroacetic acid(15：8 5：0 .1) as the mobile phase, a flow rate of 0.7 mL·min^-1, the column temperature 30 ℃, the detection wavelength 215 nm, and the sample volume 20 μL. The in vitro simulated digestion process referred to and optimized the Infogest in vitro static digestion model, divided into simulated gastric digestion, simulated intestinal digestion, and simulated gastro-intestinal total digestion stages. The established SEC method was used to compare changes in the relative molecular mass distribution before and after digestion to evaluate in vitro digestive stability.

Within the range of relative molecular mass from 165.19 to 12 327, the logarithms of the relative molecular mass of the 8 reference standards showed good linear relationships with retention time. Specificity tests indicated that blank solvent and the simulated gastric-intestinal digestion solution had minimal impact on the measurement of relative molecular mass distribution. The RSDs for precision, repeatability, and 24 h stability tests were all less than 1.0%. The relative molecular mass of various short peptide enteral nutrition products was mainly concentrated between 150 and 1 000, but there were significant differences in the distribution ratios of relative molecular mass among different products. The hydrolysis of peptide components primarily occurred during the production stage, and after in vitro simulated digestion, their relative molecular mass distribution characteristics remained largely unchanged, with the degree of change mainly related to the original hydrolysis level of the product.

The SEC method combined with the optimized Infogest model is suitable for studying the molecular mass distribution and digestive stability of short-peptide-based enteral nutrition. The method is straightforward and rapid, facilitating a comprehensive assessment of the products quality characteristics and nutritional value.