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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Standardised recommendations for a physiologically relevant, semi-dynamic in vitro simulation of upper GI tract digestion.

During the last decade, there has been a growing interest in understanding food's digestive fate in order tostrengthen the possible effects of food on human health. Ideally, food digestion should be studied in vivoon humans but this is not always ethically and financially possible. Therefore, simple in vitro digestionmodels mimicking the gastrointestinal tract have been proposed as alternatives to in vivo experiments.Thus, it is no surprise that these models are increasingly used by the scientific community, although theirvarious limitations to fully mirror the complexity of the digestive tract. Therefore, the objective of thisarticle was to call upon the collective experiences of scientists involved in Infogest (an internationalnetwork on food digestion) to review and reflect on the applications of in vitro digestion models, theparameters assessed in such studies and the physiological relevance of the data generated when comparedto in vivo data. The authors provide a comprehensive review in vitro and in vivo digestion studiesinvestigating the digestion of macronutrients (i.e. proteins, lipids and carbohydrates) as well as studies of the bioaccessibility and bioavailability of micronutrients and phytochemicals. The main conclusion is thatevidences show that despite the simplicity of in vitro models they are often very useful in predictingoutcomes of the digestion in vivo. However, this has relies on the complexity of in vitro models and theirtuning towards answering specific questions related to human digestion physiology, which leaves a vastroom for future studies and improvements

The role of salivary α-amylase (HSA) in starch digestion is often overlooked in favour of that of pancreatic α-amylase due to the short duration of the oral phase. Although it is generally accepted that the amylase of salivary origin can continue to be active in the stomach, studies ascertaining its contribution are lacking. This study aimed to address this issue by coupling in vitro oral processing with an in vitro dynamic system that mimicked different postprandial gastric pH reduction kinetics observed in vivo following a snack- or lunch-type meal. The digestion of both starch and protein from wheat bread as well as the interplay between the two processes were studied. We have observed that the amylolytic activity of saliva plays a preponderant role hydrolysing up to 80% of bread starch in the first 30 min of gastric digestion. Amylolysis evolved exponentially and nearly superimposing curves were obtained regardless of the acidification profiles, revealing its high efficiency.

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