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Recently, a static in vitro digestion (IVD) protocol was published by Minekus and coworkers (Minekus et al., 2014) within the COST INFOGEST network. The protocol, concentrating on physiological enzyme activities had the main goal to improve the comparability of experimental data between labs. The protocol was validated in several inter-laboratory studies using skim milk powder (SMP) and indeed demonstrated improved harmonization compared with previous experiments with individual IVD protocols (Egger et al., 2016). Although the enzyme activities and salt concentrations of the harmonized protocol are based on available human in vivo data, confirmation of the protocol's physiological relevance has been lacking until now. The main goal of the study was therefore to compare the harmonized IVD protocol with data from in vivo digestion. Towards this aim, an in vivo pig experiment with the same SMP as used for the validation of the IVD protocol was performed followed by a comparison of protein hydrolysis between in vivo and in vitro results. Protein hydrolysis at different levels was analyzed with gel electrophoresis, mass spectrometry, high performance liquid chromatography, and spectrophotometric o-phthaldialdehyde determination of free amino acids. Principle component analysis was used for graphical data comparison. Milk proteins detected after gastric IVD corresponded to gastric and duodenal in vivo samples and intestinal IVD samples corresponded to distal jejunal in vivo samples. Peptides identified after the gastric phase of IVD, correlated with in vivo gastric samples (r=0.8) and intestinal IVD peptides correlated best with in vivo samples collected from the median jejunum (r=0.57). Free amino acids were in both systems mainly released during the intestinal phase of digestion. Protein hydrolysis in the harmonized IVD was similar to in vivo protein hydrolysis in pigs at the gastric and intestinal endpoints. Therefore, the harmonized static in vitro protocol is suited to study protein hydrolysis at these endpoints.

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The data in this article are related to the research article entitled “Physiological comparability of the harmonized INFOGEST in vitro digestion method to in vivo pig digestion” (Egger et al., 2012). In this article, proteins identified in the different sections of pig skim milk powder (SMP) digestion are presented. In addition to the exemplary β-casein profiles of the paper, the peptide patterns of the other most abundant milk proteins during in vivo digestion in individual pigs are shown as heatmaps and line graphs. These data clearly reveal the digestion resistant protein regions and illustrate the variability between the pigs in the different sampling sections. Moreover, peptide patterns of the same SMP proteins comparing the harmonized in vitro digestion (IVD) with pig in vivo digestion show the physiological relevance of the IVD protocol. Finally, correlation coefficients were calculated to indicate similarities between pig sampling sections and gastric and intestinal IVD endpoints.