Simulated gastro-intestinal digestion is widely employed in many fields of food and nutritional sciences, as conducting human trials are often costly, resource intensive, and ethically disputable. As a consequence, in vitro alternatives that determine endpoints such as the bioaccessibility of nutrients and non-nutrients or the digestibility of macronutrients (e.g. lipids, proteins and carbohydrates) are used for screening and building new hypotheses. Various digestion models have been proposed, often impeding the possibility to compare results across research teams. For example, a large variety of enzymes from different sources such as of porcine, rabbit or human origin have been used, differing in their activity and characterization. Differences in pH, mineral type, ionic strength and digestion time, which alter enzyme activity and other phenomena, may also considerably alter results. Other parameters such as the presence of phospholipids, individual enzymes such as gastric lipase and digestive emulsifiers vs. their mixtures (e.g. pancreatin and bile salts), and the ratio of food bolus to digestive fluids, have also been discussed at length. In the present consensus paper, within the COST Infogest network, we propose a general standardised and practical static digestion method based on physiologically relevant conditions that can be applied for various endpoints, which may be amended to accommodate further specific requirements. A frameset of parameters including the oral, gastric and small intestinal digestion are outlined and their relevance discussed in relation to available in vivo data and enzymes. This consensus paper will give a detailed protocol and a line-by-line, guidance, recommendations and justifications but also limitation of the proposed model. This harmonised static, in vitro digestion method for food should aid the production of more comparable data in the future.

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Background:The digestive hydrolysis of dietary proteins leads to the release of peptides in the intestinal tract, where they may exert a variety of functions, but their characterization and quantification are difficult. Objectives: We aimed to characterize and determine kinetics of the formation of peptides present in the jejunum of humans who ingested casein or whey proteins by using mass spectrometry and to look for and quantify bioactive peptides. Design: Subjects were equipped with a double-lumen nasogastric tube that migrated to the proximal jejunum. A sample collection was performed for 6 h after the ingestion of 30 g 15 N-labeled casein (n = 7) or whey proteins (WPs; n = 6). Nitrogen flow rates were measured, and peptides were identified by using mass spectrometry. Results: After casein ingestion, medium-size peptides (750-1050 kDa) were released during 6 h, whereas larger peptides (1050-1800 kDa) were released from WPs in the first 3 h. A total of 356 and 146 peptides were detected and sequenced in the jejunum after casein and WP ingestion, respectively. b-casein was the most important precursor of peptides, including bioactive peptides with various activities. The amounts of b-casomorphins (b-casein 57-, 58-, 59-, and 60-66) and b-casein 108-113 released on the postprandial window were sufficient to elicit the biological action of these peptides (ie, opioid and antihypertensive, respectively). Conclusions: Clear evidence is shown of the presence of bioactive peptides in the jejunum of healthy humans who ingested casein. Our findings raise the question about the physiologic conditions under which these peptides can express their bioactivity in humans. This trial was registered at clinicaltrials.gov as NCT00862329.Am J Clin Nutr 2013;97:1314-23.