Effect of Dairy Structures on Gastric Behaviour and Nutrient Digestion Kinetics using a Semi-Dynamic Model

Dairy products, due to manufacturing processes, exhibit an array of possible structures at different length scales and are associated with beneficial nutritional and health effects. However, to date there is very little mechanistic understanding of such links. Unravelling the fate of food in the gastrointestinal tract is essential to better understand the health effects of food. The investigation of different dairy structured matrices was performed using a semi-dynamic model of gastric digestion, developed in this thesis, to simulate the main dynamics of the adult stomach, i.e. gradual gastric acidification, fluid secretion and emptying. It was validated with two dairy matrices obtaining a similar gastric behaviour compared to the corresponding in vivo digestion. The ‘fast’ and ‘slow’ digestion kinetics of whey proteins and caseins were shown to be due to their behaviour in the stomach, presenting soluble aggregates and solid, firm coagulation, respectively, which was linked to a higher ex vivo Leu absorption at early and late stages of digestion. The gastric restructuring of caseins was modulated by changing the whey protein to casein ratio, addition of lipid, and processing by heating and homogenisation. The most intensive processing resulted in weaker, fragmented coagulation, leading to quicker kinetics of nutrient emptying and rapid protein hydrolysis. The latter was linked to an easier access of pepsin into the weaker structure. The modulation of nutrient digestion kinetics was also obtained by comparing specific dairy macrostructures of semi-solid versus liquid through different gastric behaviours, which could be linked to the satiety responses observed in vivo. This thesis clearly demonstrated the key role of the gastric phase on nutrient bioaccessibility, which can be associated to physiological responses of dairy products. The modulation of gastric behaviour should be further studied and can be exploited to develop food structures with improved and/or tailored biofunctional properties addressing health/nutritional requirements

Dairy food structures influence the rates of nutrient digestion through different in vitro gastric behaviour

peer-reviewedThe purpose of this study was to investigate in vitro the extent to which specific food structures alter gastric behaviour and could therefore impact on nutrient delivery and digestion in the small intestine. Results obtained from a specifically developed gastric digestion model, were compared to results from a previous human study on the same foods. The semi-dynamic model could simulate the main gastric dynamics including gradual acidification, lipolysis, proteolysis and emptying. Two dairy-based foods with the same caloric content but different structure were studied. The semi-solid meal comprised a mixture of cheese and yogurt and the liquid meal was an oil in water emulsion stabilised by milk proteins. Our findings showed similar gastric behaviour to that seen previously in vivo. Gastric behaviour was affected by the initial structure with creaming and sedimentation observed in the case of liquid and semi-solid samples, respectively. Lipid and protein digestion profiles showed clear differences in the amount of nutrients reaching the simulated small intestine and, consequently, the likely bioaccessibility after digestion. The semi-solid sample generated higher nutrient released into the small intestine at an early stage of digestion whereas nutrient accessibility from liquid sample was delayed due to the formation of a cream layer in the gastric phase. This shows the strong effect of the matrix on gastric behaviour, proteolysis and lipolysis, which explains the differences in physiological responses seen previously with these systems in terms of fullness and satiety.This work has funded by the Irish Dairy Levy Research Trust (project number MDDT6261). Ana-Isabel Mulet-Cabero was funded under Teagasc Walsh Fellowship scheme and BBSRC in the UK (grant BB/J004545/1)

Impact of caseins and whey proteins ratio and lipid content on in vitro digestion and ex vivo absorption

Caseins and whey proteins are known as ‘slow’ and ‘fast’ proteins, respectively, based on their amino acid absorption rate. However, there is limited understanding of the mechanisms controlling their behaviour during gastro-intestinal transit. A protein model system (8% total protein) with varying casein:whey protein ratios (0:100, 20:80, 50:50 and 80:20) were subjected to in vitro gastro-intestinal digestion using a semi-dynamic gastric model, a static intestinal model and an ex vivo absorption model (Ussing chambers). The casein-rich (≥ 50%) samples showed the formation of solid coagula that were persistent throughout gastric digestion, which caused a delay in nutrient emptying, slower digestion and leucine absorption kinetics. In contrast, whey proteins formed more soluble aggregates during the gastric phase, which led to faster gastric emptying, rapid intestinal hydrolysis, and higher and faster leucine absorption. This work shows the key role of the gastric restructuring for the overall digestive mechanism and kinetics of food, in particular proteins

Standardization of in vitro digestibility and DIAAS method based on the static INFOGEST protocol

Resumen de la conferencia invitada presentada en el 7th International Conference on Food Digestion. Cork, Irlanda. 3-5 Mayo (2022

Structural mechanism and kinetics of in vitro gastric digestion are affected by process-induced changes in bovine milk

Bovine milk is commonly exposed to processing, which can alter the structure, biochemical composition, physico-chemical properties and sensory quality. While many of these changes have been studied extensively, little is known about their effect on digestive behaviour. In this study, heat treatments of pasteurisation at 72 °C for 15 s or Ultra-High-Temperature (UHT) treatment at 140 °C for 3 s and homogenisation at pilot-plant scale were applied to whole milk. The gastric behaviour was investigated using a recently developed semi-dynamic adult in vitro model. The emptied digesta were analysed to assess the nutrient delivery kinetics, changes in microstructure and protein digestion. All samples showed protein aggregation and coagulum formation within the first 15 min of gastric digestion at which time the pH ranged from 5.5 to 6. Homogenised samples creamed regardless of heat treatment, whereas all non-homogenised samples exhibited sedimentation. The consistency of the coagulum of the heated samples was more fragmented compared to those of the non-heated samples. Rheological analysis showed that the higher the temperature of the heat treatment, the softer the obtained coagulum and the higher the protein hydrolysis at the end of digestion. The study also confirmed that gastric emptying of caseins from milk is delayed due to coagulation in the stomach, while β-lactoglobulin was emptied throughout the gastric phase, except for UHT-treated milk. The gastric behaviour also had an impact on the lipid and protein content of the emptied chyme. The homogenised samples seemed to release more nutrients at the end of gastric digestion

Dairy food structures influence the rates of nutrient digestion through different in vitro gastric behaviour

The purpose of this study was to investigate in vitro the extent to which specific food structures alter gastric behaviour and could therefore impact on nutrient delivery and digestion in the small intestine. Results obtained from a specifically developed gastric digestion model, were compared to results from a previous human study on the same foods. The semi-dynamic model could simulate the main gastric dynamics including gradual acidification, lipolysis, proteolysis and emptying. Two dairy-based foods with the same caloric content but different structure were studied. The semi-solid meal comprised a mixture of cheese and yogurt and the liquid meal was an oil in water emulsion stabilised by milk proteins. Our findings showed similar gastric behaviour to that seen previously in vivo. Gastric behaviour was affected by the initial structure with creaming and sedimentation observed in the case of liquid and semi-solid samples, respectively. Lipid and protein digestion profiles showed clear differences in the amount of nutrients reaching the simulated small intestine and, consequently, the likely bioaccessibility after digestion. The semi-solid sample generated higher nutrient released into the small intestine at an early stage of digestion whereas nutrient accessibility from liquid sample was delayed due to the formation of a cream layer in the gastric phase. This shows the strong effect of the matrix on gastric behaviour, proteolysis and lipolysis, which explains the differences in physiological responses seen previously with these systems in terms of fullness and satiety

Effects of grain source and processing methods on the nutritional profile and digestibility of grain amaranth

Amaranth grain is reputed to have a high nutritional value, and as a plant, be tolerant to adverse weather conditions. This suggests that grain amaranth could be useful in tackling malnutrition and the growing burden of cardiometabolic diseases. However, there is insufficient knowledge at present about how the nutrient composition and digestibility of amaranth grain varies with growing environment, crop genotype, and post-harvest processing. We investigated the effect of the source and processing of amaranth grains on the digestibility of protein and lipid present in the grains. There was variation in the composition and digestibility of raw grains from different sources, indicating a role of genotype and/or growing environment which warrants further investigation. The greatest differences in digestibility were measured between the different processing techniques. This indicates that efforts to increase the cultivation and consumption of grain amaranth need to be supported by education about effective processing and preparation techniques

Inter-laboratory comparability of the in vitro digestibility method based on the static INFOGEST method

Poster presentado en: International Symposium Dietry Protein for Human Health. Utrecht, Paises Bajos. 14-16 septiembre (2023

Standardization of in vitro digestibility and DIAAS method based on the static INFOGEST protocol

Background: The FAO recommends the digestible indispensable amino acid score (DIAAS) as the measure for protein quality, for which the true ileal digestibility needs to be assessed in humans or pigs. However, due to high costs and ethical concerns, the FAO strongly encourages as well the development of validated in vitro methods, which complement the in vivo experiments. Method: Recently, an in vitro workflow, based on the validated static INFOGEST protocol, was developed and compared towards in vivo data. In parallel to the validation with in vivo data, the repeatability and reproducibility of the in vitro protocol were tested in an international ring trial (RT) with the aim to establish an international ISO standard method within the International Dairy Federation (IDF). Five different dairy products (skim milk powder, whole milk powder, whey protein isolate, yoghurt, and cheese) were analyzed in 32 different laboratories from 18 different countries, across 4 continents. Results: in vitro protein digestibilities based on Nitrogen, free R-NH2, and total amino acids as well as DIAAS values were calculated and compared to in vivo data, where available. Conclusion: The in vitro method is suited for quantification of digestibility and will be further implemented to other food matricesinfo:eu-repo/semantics/publishedVersio

Impact of pectin on the gastric digestibility of sodium caseinate

Trabajo presentado a las III Jornadas Científicas CIAL Fórum, celebradas del 22 al 23 de noviembre de 2018 en el Instituto de Investigación en Ciencias de la Alimentación (CIAL).Pectin is an anionic polysaccharide used in food applications which, due to its physical and chemical properties can modify the absorption of nutrients. The fact that there is a protection by polysaccharides to protein digestion can be very important when considering the absorption of nutrients and allergens in the small intestine such is the case of casein. One possible mechanism is through electrostatic binding to proteins, depending on the pH. Thus, the adsorption of pectin to casein can take place at pH 3.5-5.0 by the electrostatic attraction between the carboxylate group of pectin and cationic residue of casein. Hardly any investigation has been done on the interaction casein/pectin during digestion of the protein. In this work, we studied the effect of citrus pectin on the gastric digestion of sodium caseinate in a semi-dynamic gastric model. Different mixtures of caseinate and pectin (1/0.08-1/3.4) were assayed and the changes in the protein fraction due to the gastric digestion were followed by SDS-PAGE. After digestion, diffuse bands corresponding to the formation of peptides, whose intensity was greater when the ratio caseinate/pectin was lower, were observed. In addition, a slight displacement to areas of lower molecular mass was also detected. This was probably due to a protective effect of pectin, mainly after 1 h of gastric digestion. The best ratio caseinate/pectin was 1/0.08, since the other values (1/0.85 and 1/3.4) gave rise to lower initial pH values (4.83 and 4.38, respectively) near to the optimum pH of pepsin (1.5-4.5) that could have favored the digestion. With the aim to investigate if other parameters such as the molecular mass could affect, citrus pectin treated with pectinolytic enzymes such as Viscozyme® and Glucanex®200 G were used. SDS-PAGE analyses indicated that, besides pH that affect the electrostatic bindings between the polysaccharide and protein, the degree of polymerization of pectin plays also an important role in the casein digestion by steric hindrance. Although more investigation should be carried out to go more insight in the involved mechanism, the obtained results underline the protection of pectin on the digestion of sodium caseinate, particularly evident at times lower than two hours.This work has been funded by MINECO of Spain: Project AGL2014-53445-R. MV thanks Salvador de Madariaga Program for the economic support of this project.Peer reviewe