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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A standardised static in vitro digestion method suitable for food – an international consensus

Food intake is regulated by the hypothalamus, including the melanocortin and neuropeptide Y (NPY) systems in the arcuate nucleus. The NPY Y2 receptor (Y2R), a putative inhibitory presynaptic receptor, is highly expressed on NPY neurons in the arcuate nucleus, which is accessible to peripheral hormones. Peptide YY3-36 (PYY3-36), a Y2R agonist, is released from the gastrointestinal tract postprandially in proportion to the calorie content of a meal. Here we show that peripheral injection of PYY3-36 in rats inhibits food intake and reduces weight gain. PYY3-36 also inhibits food intake in mice but not in Y2r-null mice, which suggests that the anorectic effect requires the Y2R. Peripheral administration of PYY3-36 increases c-Fos immunoreactivity in the arcuate nucleus and decreases hypothalamic Npy messenger RNA. Intra-arcuate injection of PYY3-36 inhibits food intake. PYY3-36 also inhibits electrical activity of NPY nerve terminals, thus activating adjacent pro-opiomelanocortin (POMC) neurons. In humans, infusion of normal postprandial concentrations of PYY3-36 significantly decreases appetite and reduces food intake by 33% over 24 h. Thus, postprandial elevation of PYY3-36 may act through the arcuate nucleus Y2R to inhibit feeding in a gut–hypothalamic pathway.

BRIEF COMMUNICATION ARISING: Gut hormone PYY3-36 physiologically inhibits food intake

Heteroatom doped carbon materials represent one of the most prominent families of materials that are used in energy related applications, such as fuel cells, batteries, hydrogen storage or supercapacitors. While doping carbons with nitrogen atoms has experienced great progress throughout the past decades and yielded promising material concepts, also other doping candidates have gained the researchers' interest in the last few years. Boron is already relatively widely studied, and as its electronic situation is contrary to the one of nitrogen, codoping carbons with both heteroatoms can probably create synergistic effects. Sulphur and phosphorus have just recently entered the world of carbon synthesis, but already the first studies published prove their potential, especially as electrocatalysts in the cathodic compartment of fuel cells. Due to their size and their electronegativity being lower than those of carbon, structural distortions and changes of the charge densities are induced in the carbon materials. This article is to give a state of the art update on the most recent developments concerning the advanced heteroatom doping of carbon that goes beyond nitrogen. Doped carbon materials and their applications in energy devices are discussed with respect to their boron-, sulphur- and phosphorus-doping.

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Doping carbons beyond nitrogen: an overview of advanced heteroatom doped carbons with boron, sulphur and phosphorus for energy applications

Developing a mechanistic understanding of the impact of food structure and composition on human health has increasingly involved simulating digestion in the upper gastrointestinal tract. These simulations have used a wide range of different conditions that often have very little physiological relevance, and this impedes the meaningful comparison of results. The standardized protocol presented here is based on an international consensus developed by the COST INFOGEST network. The method is designed to be used with standard laboratory equipment and requires limited experience to encourage a wide range of researchers to adopt it. It is a static digestion method that uses constant ratios of meal to digestive fluids and a constant pH for each step of digestion. This makes the method simple to use but not suitable for simulating digestion kinetics. Using this method, food samples are subjected to sequential oral, gastric and intestinal digestion while parameters such as electrolytes, enzymes, bile, dilution, pH and time of digestion are based on available physiological data. This amended and improved digestion method (INFOGEST 2.0) avoids challenges associated with the original method, such as the inclusion of the oral phase and the use of gastric lipase. The method can be used to assess the endpoints resulting from digestion of foods by analyzing the digestion products (e.g., peptides/amino acids, fatty acids, simple sugars) and evaluating the release of micronutrients from the food matrix. The whole protocol can be completed in ~7 d, including ~5 d required for the determination of enzyme activities.

https://hal.archives-ouvertes.fr/hal-02073386/document

INFOGEST static in vitro simulation of gastrointestinal food digestion

https://pubs.rsc.org/en/Content/ArticlePDF/2013/GC/C2GC36364J

Deconstruction of lignocellulosic biomass with ionic liquids

The formation of stable transparent nanoemulsions poses two challenges: the ability to initially create an emulsion where the entire droplet size distribution is below 80 nm, and the subsequent stabilization of this emulsion against Ostwald ripening. The physical properties of the oil phase and the nature of the surfactant layer were found to have a considerable impact on nanoemulsion formation and stabilization. Nanoemulsions made with high viscosity oils, such as long chain triglycerides (LCT), were considerably larger (D = 120 nm) than nanoemulsions prepared with low viscosity oils such as hexadecane (D = 80 nm). The optimization of surfactant architecture, and differential viscosity ηD/ηC, has led to the formation of remarkably small nanoemulsions. With average sizes below 40 nm they are some of the smallest homogenized emulsions ever reported. What is more remarkable is that LCT nanoemulsions do not undergo Ostwald ripening and are physically stable for over 3 months. Ostwald ripening is prevented by...

Impact of oil type on nanoemulsion formation and Ostwald ripening stability.

Oil-in-water emulsions are an important vehicles for the delivery of hydrophobic bioactive compounds into a range of food products. The preparation of very fine emulsions is of increasing interest to the beverage industry, as novel ingredients can be added with negligible impact to solution clarity. In the present study, both a batch and focused flow-through ultrasonic cell were utilized for emulsification with ultrasonic power generation at 20–24 kHz. Emulsions with a mean droplet size as low as 135 ± 5 nm were achieved using a mixture of flaxseed oil and water in the presence of Tween 40 surfactant. Results are comparable to those for emulsions prepared with a microfluidizer operated at 100 MPa. The key to efficient ultrasonic emulsification is to determine an optimum ultrasonic energy intensity input for these systems, as excess energy input may lead to an increase in droplet size. Industrial relevance The preparation of oil-in-water emulsions is a common feature of food processing operations. The use of ultrasound for this purpose can be competitive or even superior in terms of droplet size and energy efficiency when compared to classical rotor­stator dispersion. It may also be more practicable with respect to production cost, equipment contamination and aseptic processing than a microfluidisation approach. The present paper shows that ultrasound can be effective in producing nanoemulsions for use in a range of food ingredients.

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The use of ultrasonics for nanoemulsion preparation

Minimising oil droplet size using ultrasonic emulsification

The digestion and metabolism of lipids continues to generate considerable scientific interest, with food emulsions increasingly being seen as a mechanism by which lipid uptake may be controlled. Scientific advancement in this field is partly being driven by the ongoing need to address the obesity crisis, for which the enhancement of satiety and/or reduction of energy intake is seen as a positive solution in achieving more effective weight management. Yet the ability to regulate lipid uptake is also seen as beneficial in other areas, such as improved nutrition for the young and/or elderly and in cardiovascular protection. Because of the complexity of food digestion, the majority of research in this area has been applied to model or highly controlled systems. Through this approach it is becoming increasingly apparent that food emulsion structure and stability does have a contributing role on lipid digestion and metabolism. There is now a clear indication of how emulsion stability within the stomach affects emptying rates. There have been considerable developments in understanding the relationship between interfacial composition and lipolysis in both the gastric and intestinal regions, and how this relates to lipid uptake/metabolism. There is also an emerging understanding of the contribution of gastrointestinal biophysics to emulsion structure and stability, and how intestinal motility is in turn impacted by structural aspects, such as relative changes in particle size. Understanding of lipid digestion has been progressed through recent advancements in the sophistication of in vitro models. These are now seen as providing a more realistic representation of physiological conditions, both in terms of biochemical environment, and the biophysics of the gastrointestinal tract. Improvements in the validity of such models against in vivo and clinical behaviours is allowing aspects of emulsion digestion to be observed without the immediate need of costly human trials. Accordingly, emulsion systems with increasing structural complexity are now able to be characterised in terms of digestion behaviours. The ability to design food emulsions with specific lipid digestion profiles may allow the development of mainstream foods with particular physiological properties, such as enhanced satiation, or targeted delivery.

The influence of emulsion structure and stability on lipid digestion

Understanding and manipulating how emulsion structure impacts on fat digestion is an important step towards understanding the role of fat in our diet. This article reports on the nature of emulsion structuring within the digestive tract and how it affects the dynamics of fat digestion. Emulsions were designed a priori to have specific structuring behaviours (stable, coalesced, partially coalesced and fully broken) under gastrointestinal conditions, through careful emulsifier selection and control of solid fat composition. The impact these structures had on lipolysis was then assessed in vitro using a digestion model and in vivo by measuring the postprandial change in blood triglyceride concentration as a marker of fat absorption. The major factor controlling the rate of fat digestion in vitro was the droplet surface area available for lipase adsorption, which was governed by emulsion instability. The rate of fat absorption in vivo was only affected by large changes in the droplet surface area, and only if these changes remained until the droplets reached the small intestine. This was most evident in emulsions that had undergone extensive partial coalescence under gastric conditions. Partial coalescence resulted in a dramatic reduction in triglyceride absorption, in part because the network of fat crystals provided the agglomerates with an internal scaffold to resist re-dispersion as they passed through the pylorus. The differences in fat absorption profile achieved by controlling emulsion structural stability during digestion provide a basis for examining the physiological effects of food structure on lipid metabolism, which will be the subject of a follow-up clinical paper.

Tim J. Wooster

Papers

Impact of oil type on nanoemulsion formation and Ostwald ripening stability.

The use of ultrasonics for nanoemulsion preparation

Minimising oil droplet size using ultrasonic emulsification

The influence of emulsion structure and stability on lipid digestion

Impact of gastric structuring on the lipolysis of emulsified lipids