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

Effect of different food matrices on the bioaccessibility of vitamin D3 in beverage systems: Comparison between juice and liquid milk

Vitamin D plays a crucial role in bone, immunology, and neurophysiological functions but has inadequate bioavailability in the human body. In this paper, six different liquid beverages were used for vitamin D3 fortification, investigating the effect of different food matrices on the bioaccessibility of vitamin D. Not from concentrate (NFC) apple juice (9.34%) and NFC orange juice (8.12%) presented about 20% higher bioaccessibility of vitamin D3 than soybean and skim milk, and achieved a similar value of whole milk (8.04%). Meanwhile, the bioaccessibility of NFC apple and orange juice was markedly about 120% higher than that of apple clear juice. From the correlation analysis, the bioaccessibility of VD3 indicated significant correlations with small intestine retention (0.82) and viscosity (0.66). But small intestinal particle size showed a negative effect on bioaccessibility (-0.78). Therefore, food components, delivery matrices, and physicochemical properties of digesta were key factors to achieve higher bioaccessibility for guiding formulation design.

Evaluation of the Effect of Thickeners in Enteral Formulas on the Gastric Emptying Rate of Proteins and Carbohydrates Using a Semi-Dynamic Gastric Model

The emptying rate of specific nutrients in enteral formulas is poorly understood, despite the importance of controlling the emptying rate in tube-fed patients. Because of their viscosity, thickened formulas are widely used to avoid gastric reflux and reduce the burden on caregivers. This study examined how thickeners in enteral formulas affected the gastric emptying rates of proteins and carbohydrates. A semi-dynamic gastric model was used to prepare and digest test enteral formulas that contained either no thickeners or agar (0.2%). The amounts of protein and carbohydrates in each emptied aliquot were determined, and the emptying rate was calculated. We found that agar accelerated protein emptying, and an exploratory experiment with agar (0.5%) suggested the possibility of concentration dependence. Additionally, experiments using gellan gum (0.08%), guar gum (0.2%), or carrageenan (0.08%, 0.2%) suggested that protein emptying could vary depending on the thickener type and that carrageenan might slow it. These results could help with the appropriate selection of thickeners added to liquid foods based on the patient's metabolic profile to manage nutrition, not only for tube-fed patients but also for those with oropharyngeal dysphagia or diabetes.

Microencapsulation of flaxseed oil in pea protein-gum arabic complex coacervates delays lipid digestion in liquid yoghurt

Flaxseed oil coacervates were produced by complex coacervation using soluble pea protein and gum arabic as shell materials, followed by either spray or electrostatic spray drying and their incorporation to yoghurt. Three yoghurt formulations were prepared: yoghurt with spray-dried microcapsules (Y-SD); with electrospray-dried microcapsules (Y-ES); with the encapsulation ingredients added in free form (Y). The standardised semi-dynamicin vitrodigestion method (INFOGEST) was employed to study the food digestion. The structure was analysed by confocal laser scanning microscopy and particle size distribution. Protein and lipid digestion were monitored by cumulated protein/free NH2 release and cumulated free fatty acids release, respectively. Stable microcapsules were observed during gastric digestion, but there was no significant difference in protein release/hydrolysis among samples until 55 min of gastric digestion. Formulation Y showed less protein release after 74 min (40.46 %) due to the free SPP being available and positively charged at pH 2-4, resulting in interactions with other constituents of the yoghurt, which delayed its release/hydrolysis. The total release of protein and free NH2 by the end of intestinal digestions ranged between 46.56-61.15 % and 0.83-1.57 µmol/g protein, respectively. A higher release of free fatty acids from formulation Y occurred at the end of intestinal digestion, implying that coacervates promoted the delayed release of encapsulated oil. In summary, incorporating protein-polysaccharides-based coacervates in yoghurt enabled the delay of the digestion of encapsulated lipids but accelerated the digestion of protein, suggesting a promising approach for various food applications.

Heat Treatment and Homogenization Influence the Gastric Digestion of Bovine Milk Protein in Growing Pigs as an Adult Human Model

BACKGROUND

Bovine milk processing influences the structure of the curd formed during gastric digestion, which may alter gastric protein hydrolysis and impact amino acid (AA) release into the small intestine.

OBJECTIVES

This study aimed to determine the influence of heat treatment and homogenization on the gastric protein digestion and AA emptying of bovine milk.

METHODS

Nine-wk-old pigs (n = 144) consumed either raw, pasteurized nonhomogenized (PNH), pasteurized homogenized (PH), or ultra-high-temperature homogenized (UHT) bovine milk for 10 d. On day 11, fasted pigs received the milk treatment (500 mL) before gastric contents were collected at 0, 20, 60, 120, 180, and 300 min postprandially. The apparent degree of gastric protein hydrolysis (based on the release of free amino groups), apparent gastric disappearance of individual proteins [based on sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) gel band intensity], and the gastric emptying of digested protein and AA were determined.

RESULTS

During the first 60 min, the rate of apparent gastric protein hydrolysis was fastest in pigs fed UHT milk (0.29%/min compared with on average 0.07%/min in pigs fed raw, PNH, and PH milk). Differences in the apparent degree of gastric protein hydrolysis and emptying were reflected in the rate of digested protein entering the small intestine. The AA gastric emptying half-time was generally shorter in pigs fed PH and UHT milk than in pigs fed raw and PNH milk. For example, the gastric release of total essential AA was >2-fold faster (P < 0.01) in pigs fed PH or UHT milk than that in pigs fed raw or PNH milk (i.e., homogenized compared with nonhomogenized milk).

CONCLUSIONS

Heat treatment and homogenization increased the apparent gastric degree of protein hydrolysis and the release of digested protein into the small intestine. However, the rate of AA entering the small intestine was mainly increased by homogenization.

A2 milk: Bioaccessibility of essential minerals and the release of amino groups under static in vitro digestion conditions

Alternative milk products such as A2 milk are gaining popular stand within consumer market, for their healthy profile and expected greater digestibility characteristics. However, total mineral content and its bioaccessible profile have lacked in studies through the years, even more because of their relevance in public health. The present study aimed to evaluate the mineral profile of commercial A2 bovine milk (AT) and estimate the bioaccessibility of calcium, phosphorus and magnesium using the INFOGEST protocol. Non-A2 samples (NAT) were evaluated for comparison purpose. The determination of Ca, Mg, Na and K was performed by FAAS and total P was quantified by colorimetric method. Total protein content was determined by Kjeldahl method. Free amino acids were quantified by OPA method along the in vitro digestion stages. Total content of Ca, Na and P exhibited equivalent results between samples, although A2 milk showed elevated levels of total Mg and K in the analyzed batches. AT showed protein content equivalent to NAT. In addition, levels of free NH2 were observed 2 times higher in AT, during the first hour of pancreatic phase in the intestinal digestion. Bioaccessibility of Ca showed equivalent percentages for AT (12-42 %) and NAT (10-39 %). The observed low values were possibly derived from interferences with saturated fatty acids and standardized electrolytes during digestion. Similar amounts of bioaccessible Mg were found for all milk samples (35-97 %), while A2 samples evidenced percentages of bioaccessible P exceeding 60 % across the three batches. Despite the health benefits associated to A2 milk, the study did not evidence clear distinction from non-A2 milk in terms of enhanced essential mineral solubility in digestive tract simulation, considering the association of greater digestibility expected for A2 milk.

Delivery of encapsulated bioactive compounds within food matrices to the digestive tract: recent trends and future perspectives

Encapsulation technologies have achieved encouraging results improving the stability, bioaccessibility and absorption of bioactive compounds post-consumption. There is a bulk of published research on the gastrointestinal behavior of encapsulated bioactive food materials alone using in vitro and in vivo digestion models, but an aspect often overlooked is the impact of the food structure, which is much more complex to unravel and still not well understood. This review focuses on discussing the recent findings in the application of encapsulated bioactive components in fabricated food matrices. Studies have suggested that the integration of encapsulated bioactive compounds has been proven to have an impact on the physicochemical characteristics of the finished product in addition to the protective effect of encapsulation on the fortified bioactive compound. These products containing bioactive compounds undergo further structural reorganization during digestion, impacting the release and emptying rates of fortified bioactive compounds. Thus, by manipulation of various food structures and matrices, the release and delivery of these bioactive compounds can be altered. This knowledge provides new opportunities for designing specialized foods for specific populations.

Dynamic Gastrointestinal Digestion of Bovine, Caprine and Ovine Milk Reconstituted from Commercial Whole Milk Powders

The global dairy market has been increasingly diversified with more dairy product offerings of milk products from different animal species. Meanwhile, milk powders remain the main exported dairy product format due to their ease of transportation. In this work, we studied the structural changes, protein hydrolysis and nutrient delivery during dynamic gastric digestion and small intestinal digestion of cow, goat and sheep milk reconstituted from commercial whole milk powders. The results show that the reconstituted milks digest similarly to processed fresh milk. The digestion behaviors of the three reconstituted ruminant milks are broadly similar (gastric coagulation, kinetics of gastric emptying of protein and fat and the high digestibility in the small intestine) with some differences, which are likely contributed by the processing history of the milk powders. The delivery of individual amino acids to the small intestine differed between the early and late stages of gastric digestion, which were primarily affected by the abundance of amino acids in caseins and whey proteins but also by the difference between milk types associated with their gastric coagulation behaviors. This work showed that powdered milk is similar to fresh processed milk in digestion behavior, and the inherent differences between ruminant milks can be modified by processing treatments.

The impact of heat treatment of bovine milk on gastric emptying and nutrient appearance in peripheral circulation in healthy females: a randomized controlled trial comparing pasteurized and ultra-high temperature milk

BACKGROUND

Heat treatments of dairy, including pasteurization and ultra-high temperature (UHT) processing, alter milk macromolecular structures, and ultimately affect digestion. In vitro, animal, and human studies show faster nutrient release or circulating appearance after consuming UHT milk (UHT-M) compared with pasteurized milk (PAST-M), with a faster gastric emptying (GE) rate proposed as a possible mechanism.

OBJECTIVES

To investigate the impact of milk heat treatment on GE as a mechanism of faster nutrient appearance in blood. We hypothesized that GE and circulating nutrient delivery following consumption would be faster for UHT-M than PAST-M.

METHODS

In this double-blind randomized controlled cross-over trial, healthy female (n = 20; 27.3 ± 1.4 y, mean ± SD) habitual dairy consumers, consumed 500 mL of either homogenized bovine UHT-M or PAST-M (1340 compared with 1320 kJ). Gastric content volume (GCV) emptying half-time (T50) was assessed over 3 h by magnetic resonance imaging subjective digestive symptoms, plasma amino acid, lipid and B vitamin concentrations, and gastric myoelectrical activity were measured over 5 h.

RESULTS

Although GCV T50 did not differ (102 ± 7 min compared with 89 ± 8 min, mean ± SEM, UHT-M and PAST-M, respectively; P = 0.051), GCV time to emptying 25% of the volume was 31% longer following UHT-M compared with PAST-M (42 ± 2 compared with 32 ± 4 min, P = 0.004). Although GCV remained larger for a longer duration following UHT-M (treatment × time interaction, P = 0.002), plasma essential amino acid AUC was greater following UHT-M than PAST-M (55,324 ± 3809 compared with 36,598 ± 5673 μmol·min·L-1, P = 0.006). Heat treatment did not impact gastric myoelectrical activity, plasma appetite hormone markers or subjective appetite scores.

CONCLUSIONS

Contrary to expectations, GE was slower with UHT-M, yet, as anticipated, aminoacidemia was greater. The larger GCV following UHT-M suggests that gastric volume may poorly predict circulating nutrient appearance from complex food matrices. Dairy heat treatment may be an effective tool to modify nutrient release by impacting digestion kinetics.

CLINICAL TRIAL REGISTRY

www.anzctr.org.au (ACTRN12620000172909).

Invited review: Camel milk and gut health-Understanding digestibility and the effect on gut microbiota

Camel milk (CM), known for its immune-regulatory, anti-inflammatory, antiapoptotic, and antidiabetic properties, is a natural healthy food. It is easily digestible due to the high levels of β-casein and diverse secreted antibodies, exhibiting superior antibacterial and antiviral activities compared with bovine milk. β-casein is less allergic and more digestible because it is more susceptible to digestive hydrolysis in the gut; therefore, higher levels of β-casein make CM advantageous for human health. Furthermore, antibodies help the digestive system by destroying the antigens, which are then overwhelmed and digested by macrophages. The connection between the gut microbiota and human health has gained substantial research attention, as it offers potential benefits and supports disease treatment. The gut microbiota has a vital role in regulating the host's health because it helps in several biological functions, such as protection against pathogens, immune function regulation, energy harvesting from digested foods, and reinforcement of digestive tract biochemical barriers. These functions could be affected by the changes in the gut microbiota profile, and gut microbiota differences are associated with several diseases, such as inflammatory bowel disease, colon cancer, irritable bowel disorder, mental illness, allergy, and obesity. This review focuses on the digestibility of CM components, particularly protein and fat, and their influence on gut microbiota modulation. Notably, the hypoallergenic properties and small fat globules of CM contribute to its enhanced digestibility. Considering the rapid digestion of its proteins under conditions simulating infant gastrointestinal digestion, CM exhibits promise as a potential alternative for infant formula preparation due to the high β-/αs-casein ratio and protective proteins, in addition to the absence of β-lactoglobulin.

Dairy Matrix Effects: Physicochemical Properties Underlying a Multifaceted Paradigm

When food products are often considered only as a source of individual nutrients or a collection of nutrients, this overlooks the importance of interactions between nutrients, but also interactions between nutrients and other constituents of food, i.e., the product matrix. This product matrix, which can be defined as 'The components of the product, their interactions, their structural organization within the product and the resultant physicochemical properties of the product', plays a critical role in determining important product properties, such as product stability, sensory properties and nutritional and health outcomes. Such matrix effects can be defined as 'the functional outcome of specific component(s) as part of a specific product matrix'. In this article, dairy matrix effects are reviewed, with particular emphasis on the nutrition and health impact of dairy products. Such matrix effects are critical in explaining many effects of milk and dairy products on human nutrition and health that cannot be explained solely based on nutrient composition. Examples hereof include the low glycemic responses of milk and dairy products, the positive impact on dental health, the controlled amino acid absorption and the absence of CVD risk despite the presence of saturated fatty acids. Particularly, the changes occurring in the stomach, including, e.g., coagulation of casein micelles and creaming of aggregated fat globules, play a critical role in determining the kinetics of nutrient release and absorption.

The role of food structure in gastric-emptying rate, absorption and metabolism

The high levels of non-communicable diseases such as CVD and type 2 diabetes mellitus are linked to obesity and poor diet. This continuing emphasis on health in relation to food is proving a powerful driver for the development of cheap but palatable and more functional foods. However, the efficacy of such foods is often hard to prove in human subjects. Thus, a suite of tools has been developed including in silico and in vitro simulations and animal models. Although animal models offer physiologically relevant platforms for research, their use for experimentation is problematic for consumers. Thus, in vitro methods such as Infogest protocols have been developed to provide digestion endpoints or even an indication of the kinetics of digestion. These protocols have been validated for a range of food systems but they still miss the final absorption step. This review discusses the use of such in vitro models and what further steps need to be included to make the bioaccessibility determination more relevant to bioavailability and human health.

Pea protein extraction method impacts the protein (micro)structural organisation and in vitro digestion kinetics

There is increasing interest in including pulse proteins into food products due to their nutrient-rich and sustainable character. However, little is known regarding the consequences of different extraction approaches on the pulse protein structure and the subsequent protein (micro)structural organization and protein digestion kinetics. Therefore, three green pea protein extracts were created: (i) cooking followed by cotyledon cell isolation, (ii) alkaline extraction followed by isoelectric precipitation, or (iii) salt extraction, and compared to the original pea flour as well as to sodium caseinate. The results showed that encapsulated, denatured protein inside pea cotyledon cells presented the (s)lowest digestion, while accessible and more native protein (e.g., pea flour, pea protein salt extract) presented much faster and higher digestion. Moreover, the alkali extracted pea protein was denatured to some extent, significantly lowering in vitro digestion kinetics. In the second part, three different in vitro approaches were applied to digest the salt extracted pea protein. Semi-dynamic gastric digestion approaches simulate in vivo conditions more closely which especially impacted the rate of digestion.

CCK and GLP-1 response on enteroendocrine cells of semi-dynamic digests of hydrolyzed and intact casein

A semi-dynamic gastrointestinal device was employed to explore the link between protein structure and metabolic response upon digestion for two different substrates, a casein hydrolysate and the precursor micellar casein. As expected, casein formed a firm coagulum that remained until the end of the gastric phase while the hydrolysate did not develop any visible aggregate. Each gastric emptying point was subjected to a static intestinal phase where the peptide and amino acid composition changed drastically from that found during the gastric phase. Gastrointestinal digests from the hydrolysate were characterized by a high abundancy of resistant peptides and free amino acids. Although all gastric and intestinal digests from both substrates induced the secretion of cholecystokinin (CCK) and glucagon-like peptide-1 (GLP-1) in STC-1 cells, GLP-1 levels were maximum in response to gastrointestinal digests from the hydrolysate. The enrichment of protein ingredients with gastric-resistant peptides by enzymatic hydrolysis is proposed as strategy to deliver protein stimuli to the distal gastrointestinal tract to control food intake or type 2 diabetes.

Casein structures differently affect postprandial amino acid delivery through their intra-gastric clotting properties

We aimed to assess if casein structure affects its digestion and its subsequent amino acid delivery kinetic. Higher nitrogen levels were recovered in dialysates after in vitro digestions of sodium caseinate (SC, formed of small aggregates) compared to micellar casein (MC, native form of casein) and calcium caseinate (CC, intermediate structure). Likewise, plasma indispensable amino-acid concentration peak was higher after SC compared to MC or CC ingestion in healthy volunteers in a randomized, double blind, cross-over study. In pigs, gamma-scintigraphy using labelled meals revealed that SC was mainly localized in the proximal part of the stomach whereas MC was distributed in the whole gastric cavity. Caseins were found in both solid and liquid phases and partly hydrolyzed casein in the solid phase shortly after SC drink ingestion. These data support the concept of slow (MC) and rapid (SC) casein depending of casein structure, likely due to their intra-gastric clotting properties.

The influence of protein oxidation on structure, pepsin diffusion, and in vitro gastric digestion of SPI emulsion

The stability behaviors of oxidized SPI emulsions under in vitro gastric conditions and the effects of pepsin diffusion on the proteolysis of emulsions were investigated using a static gastric model and the fluorescence recovery after photobleaching method. Results showed that protein oxidation increased the particle size of droplets and decreased the viscoelasticity of the interfacial layer. Compared to the control group (82.81 m²/s), the pepsin diffusivity decreased to 68.52 m²/s (7LA + LOX group) due to the space hindrance of oil droplets. After gastric digestion, protein hydrolysates were re-absorbed on the oil-water interface and formed a thick layer, thereby decreasing the size of oil droplets and reducing the contents of free amino acids in gastric digesta. The protein oxidation may affect the adsorption of interfacial proteins and alter the distribution of droplets, decreasing pepsin diffusion and ultimately impairing the emulsion gastric digestion. And this should be considered in the design of emulsion as the controllable delivery system.

Dairy and plant based protein beverages: In vitro digestion behaviour and effect on intestinal barrier biomarkers

The consumer demand for protein-enriched food products continues to grow, in parallel with consumers' interest in plant based alternatives. The replacement of milk protein by plant protein is likely to be occur predominantly in prepared consumer foods such as nutritional beverages. This study aimed to compare and contrast powder beverages formulated with commercially available dairy versus plant ingredients in terms of protein digestion and gut barrier health. After simulated static in vitro gastrointestinal digestion, the release of free amino acids increased for all model beverages. In addition, the majority of peptides present in digested beverages were < 0.8 kDa in size. Gastrointestinal digestion did not increase the degree of protein hydrolysis in beverages formulated with prehydrolysed milk protein, whey or pea ingredients. A 2 h permeability assessment of digested beverages across the intestinal barrier, using Caco-2/HT-29/MTX co-cultures, revealed reduced transcription of tight junction protein 1, claudin-1 and mucus protein 2 albeit gut barrier impedance was unchanged. IL-8 mRNA levels in cell monolayers was significantly increased with digested fluids treatment but even more so with digesta from hydrolysed milk protein beverage. Overall, the response observed on intestinal biomarkers with digested plant beverages was similar to dairy based beverages supporting the replacement of dairy with plant proteins in powder beverage formulations.

Coagulation and proteolysis of high-protein milks in the gastric environment

Gastric digestion of 2 commercial ultrafiltered milks and milk enriched with skim milk powder (to simulate concentration by reverse osmosis) was investigated and compared with the digestion of nonconcentrated milk. Curd formation and proteolysis of high-protein milks in simulated gastric conditions were studied using oscillatory rheology, extrusion testing, and gel electrophoresis. The presence of pepsin in the gastric fluid triggered coagulation at pH >6 and the elastic modulus of gels from high-protein milks was ∼5 times larger than the gel from reference milk. Despite similar protein concentrations, the coagulum from milk enriched with skim milk powder showed higher resistance to shear deformation than the coagula from ultrafiltered milks. The gel structure was also more heterogeneous. During digestion, the degradation of coagula from high-protein milks was slowed down compared with the coagulum from reference milk, and intact milk proteins were still detected after 120 min. Differences in the digestion patterns of coagula from high-protein milks were observed and were associated with the proportion of minerals bound to caseins and the denaturation rate of whey proteins.

In vitro gastric digestion of an experimental infant formula containing both intact and hydrolyzed milk proteins

Milk protein hydrolysates may have several benefits for digestion and digestion-related complications in infants, whereas intact milk proteins have been demonstrated to provide functionality beyond their nutritional value. In this study, in vitro digestion of an experimental infant formula containing both intact milk proteins and a milk protein hydrolysate was determined. Relative to an intact milk protein control formula, the experimental formula displayed a higher initial protein digestion during simulated gastric digestion as illustrated by a larger proportion of smaller peptides and higher level of available amino groups during digestion. Gastric protein coagulation was not affected by the hydrolysate addition. Further in vivo studies should demonstrate whether partial replacement of the protein source by a hydrolysate and observed differences in in vitro protein digestion result in overall altered protein digestion and absorption kinetics or affect functional gastrointestinal disorders as has been demonstrated for full hydrolysate formula.

Impact of Milk Storage and Heat Treatments on In Vitro Protein Digestibility of Soft Cheese

Cheese is an important source of protein in the human diet, and its digestibility depends on its macro and microstructure. This study investigated the effect of milk heat pre-treatment and pasteurization level on the protein digestibility of produced cheese. An in vitro digestion method was used considering cheeses after 4 and 21 days of storage. The peptide profile and amino acids (AAs) released in digestion were analyzed to evaluate the level of protein degradation following in vitro digestion. The results showed the presence of shorter peptides in the digested cheese from pre-treated milk and 4-day ripening while this trend was not observed after 21 days of storage, showing the effect of storage period. A significantly higher content of AAs was found in digested cheese produced from milk subjected to a higher temperature of pasteurization, and there was a significant increase in total AA content in the cheese after 21 days of storage, confirming the positive effect of ripening on protein digestibility. From these results emerges the importance of the management of heat treatments on the digestion of proteins in soft cheese.

Membrane filtration processing of infant milk formula alters protein digestion in young pigs

Reducing heat treatment (HT) during processing of infant milk formula (IMF) is desirable to produce a product that more closely resembles breast milk. By employing membrane filtration (MEM), we produced an IMF (60:40 whey to casein ratio) at pilot scale (250 kg). MEM-IMF had a significantly higher content of native whey (59.9 %) compared to HT-IMF (4.5 %) (p < 0.001). Pigs, at 28 days old, were blocked by sex, weight and litter origin and assigned to one of two treatments (n = 14/treatment): (1) starter diet containing 35 % of HT-IMF powder or (2) starter diet containing 35 % of MEM-IMF powder for 28 days. Body weight and feed intake were recorded weekly. Pigs at day 28 post weaning were sacrificed 180 min after their final feeding, for the collection of gastric, duodenal, jejunum and ileal contents (n = 10/treatment). MEM-IMF diet resulted in more water-soluble proteins and higher levels of protein hydrolysis in the digesta at various gut locations compared to HT-IMF (p < 0.05). In the jejunal digesta, a higher concentration of free amino acids were present post MEM-IMF consumption (247 ± 15 µmol g^-1 of protein in digesta) compared to HT-IMF (205 ± 21 µmol g^-1 of protein). Overall, average daily weight gain, average dairy feed intake and feed conversion efficiency were similar for pigs fed either MEM-IMF or HT-IMF diets, but differences and trends to difference of these indicators were determined in particular intervention periods. In conclusion, reducing heat treatment during processing of IMF influenced protein digestion and revealed minor effects on growth parameters providing in vivo evidence that babies who are fed with IMF processed by MEM are likely to have different protein digestion kinetics but minimal effect on overall growth trajectories as babies fed IMF processed by traditional thermal processing.

The Protein Composition and In Vitro Digestive Characteristics of Animal- versus Plant-Based Infant Nutritional Products

The protein composition and digestive characteristics of four commercially available infant formulae (IF) manufactured using bovine (B-IF), caprine (C-IF), soy (S-IF), and rice (R-IF) as a protein source were examined in this study. Plant-based formulae had significantly higher crude protein and non-protein nitrogen (NPN) concentrations. Static in vitro gastrointestinal digestion of these formulae, and subsequent analysis of their digestates, revealed significantly higher proteolysis of B-IF at the end of gastrointestinal digestion compared to the other formulae, as indicated by the significantly higher concentration of free amine groups. Furthermore, differences in structure formation during the gastric phase of digestion were observed, with formation of a more continuous, firmer coagulum by C-IF, while R-IF demonstrated no curd formation likely due to the extensive hydrolysis of these proteins during manufacture. Differences in digestive characteristics between formulae manufactured from these different protein sources may influence the bio-accessibility and bioavailability of nutrients, warranting additional study.

Influence of storage time on protein composition and simulated digestion of UHT milk and centrifugation presterilized UHT milk in vitro

The centrifugation presterilizing UHT (C-UHT) sterilization method removes 90% of the microorganism and somatic cells from raw milk using high-speed centrifugation following UHT treatment. This study aimed to study the changes in protein composition and plasmin in the UHT and C-UHT milk. The digestive characteristics, composition, and peptide spectrum of milk protein sterilized with the 2 technologies were studied using a dynamic digestive system of a simulated human stomach. The Pierce bicinchoninic acid assay, laser scanning confocal microscope, liquid chromatography-tandem mass spectrometry, and AA analysis were used to study the digestive fluid at different time points of gastric digestion in vitro. The results demonstrated that C-UHT milk had considerably higher protein degradation than UHT milk. Different processes resulted during the cleavage of milk proteins at different sites during digestion, resulting in different derived peptides. The results showed there was no significant effect of UHT and C-UHT on the peptide spectrum of milk proteins, but C-UHT could release relatively more bioactive peptides and free AA.

The plasma amino acid response to blended protein beverages: a randomised crossover trial

Soya-dairy protein blends can extend post-exercise muscle synthesis in young people more than whey protein control. Older adults differ metabolically from young people, and their ability to absorb amino acids from dietary protein is important for muscle function. The objective was to determine how protein source affects postprandial plasma amino acid response and/or metabolomic profile in older adults via a single-blind randomised crossover trial (n 16, males 50-70 years), using three nutritionally equivalent meal replacement drinks containing 30 g protein, from a 1:1 (mass ratio) soya:dairy blend, a 1:2 soya:dairy blend or whey protein. The outcome measures were plasma amino acid concentrations at 0-300 min postprandially and urine metabolomic fingerprint. Soya:dairy drinks gave similar amino acid response in plasma over time and similar urinary metabolite fingerprints. However, there were significant differences in plasma amino acid concentrations and AUC values for the soya:dairy drinks v. the whey protein drink. AUC for Leu, Trp and Lys was lower and AUC for Phe and Pro was higher for the soya:dairy drinks. Differences partly reflected the amino acid profiles of the drinks, but overall plasma amino acid response patterns were qualitatively unchanged. Plasma amino acid differences between the whey protein drink and the soya:dairy blends were reflected in urine metabolite patterns. In conclusion, postprandial plasma amino acid responses were broadly similar, irrespective of protein source (and soya:dairy ratio). There were significant differences for some plasma amino acid concentrations, reflecting different amino acid profiles of the protein source and influencing urine metabolite fingerprints.

Non-invasive monitoring of in vitro gastric milk protein digestion kinetics by 1H NMR magnetization transfer

Processing of milk involves heating, which can modify the structure and digestibility of its proteins. In vitro models are useful for studying protein digestion. However, validating these models with in vivo data is challenging. Here, we non-invasively monitor in vitro gastric milk protein digestion by protein-water chemical exchange detected by ¹H nuclear magnetic resonance (NMR) magnetization transfer (MT). We obtained either a fitted composite exchange rate (CER) with a relative standard error of ≤10% or the MT ratio (MTR) of the intensity without or with an off-resonance saturation pulse, from just a single spectral acquisition. Both CER and MTR, affected by the variation in the amount of semi-solid protons, decreased during in vitro gastric digestion in agreement with standard protein content analyses. The decrease was slower in heated milk, indicating slower breakdown of the coagulum. Our results open the way to future quantification of protein digestion in vivo by MRI.

Impact of Recombined Milk Systems on Gastrointestinal Fate of Curcumin Nanoemulsion

Milk powder is an important ingredient in various foods and pediatric formulations. The textural and digestion properties of the formulations depend on the preheat treatment of the milk powder during manufacture. Thus, it is interesting to know how these modifications can influence on the release of fortified bioactive compounds during digestion with a milk matrix. In this study, a curcumin nanoemulsion was incorporated into milks reconstituted from low-heat, medium-heat and high-heat skim milk powders (SMPs) and the milks were subjected to semi dynamic in vitro digestion. All the recombined milk systems formed a curd under gastric conditions, which reduced the gastric emptying of protein and curcumin-loaded oil droplets. Because of the formation of heat-induced casein/whey protein complexes, the open fragmented curd formed by the high-heat-treated reconstituted powder resulted in higher protein and oil droplets emptying to the intestine and higher curcumin bioaccessibility. This study provides useful information for how protein ingredients can govern the fate of added health-promoting compounds during digestion.

Milk proteins: Processing, gastric coagulation, amino acid availability and muscle protein synthesis

It is well-known that the postprandial muscle protein synthetic response to protein ingestion is regulated on various levels, including dietary protein digestion and amino acid (AA) absorption, splanchnic AA retention, the availability of dietary protein-derived AA in the circulation, delivery of AA to the muscle, uptake of AA by the muscle, and intramuscular signaling. AA availability after consumption of dairy products is primarily determined by the rate of gastric emptying of milk proteins, which is mainly linked to coagulation of milk proteins in the stomach. Caseins form gastric coagula, which make their gastric emptying and subsequent postprandial aminoacidemia notably slower than that of whey proteins. Only recently, the role of processing, food structure, preservation and matrix on coagulation herein has been getting attention. In this review we describe various processes, that affect gastric coagulation of caseins and therewith control gastric emptying, such as the conversion to caseinate, heat treatment in the presence of whey proteins, conversion to stirred yoghurt and enzymatic hydrolysis. Modulating product characteristics by processing can be very useful to steer the gastric behavior of protein, and the subsequent digestion and AA absorption and muscle anabolic response to maintain or increase muscle mass.

An evolving view on food viscosity regulating gastric emptying

Viscosity is a property of most foods. The consumption of the high-viscosity food is associated with a variety of physiological responses, one of which is their ability to regulate gastric emptying and modulate postprandial glycemic response. Gastric emptying has been proven to be a key step affecting the digestion and absorption of food, whereas, the relationship between viscosity and gastric emptying is still far away from being understood. Here, we reviewed the factors that influence food viscosity and food viscosity changes during digestion. Besides, the effect of food viscosity on gastric emptying and food-viscosity-physiological response were highlighted. Finally, "quantitative relationship" of viscosity and gastric emptying was discussed. This review can contribute to the understanding that how food viscosity affects gastric emptying, and help for developing foods that could control satiety and manage body weight for the specific populations.

High-pressure processing of bovine milk: Effects on the coagulation of protein and fat globules during dynamic in vitro gastric digestion

The effect of high-pressure processing (HPP) on the digestion behavior of skim and whole bovine milks was investigated using a human gastric simulator. Both milks formed clots during gastric digestion. HPP treatment led to the formation of a coagulum with a fragmented and crumbled structure, compared with the coagulum formed from untreated milk. At pressures over 400 MPa, more intense pressure resulted in looser and more fragmented gastric clot structures. The weight of the dried clots and the moisture content in the clots of the skim milk treated at 600 MPa were significantly lower and higher than that of untreated skim milk, respectively. The looser and more fragmented gastric clot structures consequently led to faster hydrolysis of the proteins by pepsin during gastric digestion. The denaturation of the whey proteins induced by HPP may have also altered the resistance of α-lactalbumin and β-lactoglobulin in the HPP-treated milk samples to pepsin hydrolysis. This study provides insights into the differences among untreated skim milk, untreated whole milk and HPP-treated milk under in vitro gastric digestion conditions. The structure of the clots formed in the gastric environment affects their breakdown and consequently their emptying rate into the intestine.

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High-pressure processing (HPP) modified physicochemical properties of bovine milk.

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HPP influenced the structure of bovine milk clots during in vitro gastric digestion.

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More intense pressure resulted in a looser and more fragmented clot structure.

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HPP resulted in more rapid hydrolysis of the caseins.

Gastric digestion of cow milk, almond milk and oat milk in rats

In this study, gastric digestion of isocaloric and iso-macronutrient cow milk, almond milk and oat milk were compared in rats euthanized at different post-feeding times.

In vitro simulated semi-dynamic gastrointestinal digestion: evaluation of the effects of processing on whey proteins digestibility and allergenicity

The effect of thermal processing on digestibility of milk proteins should be better understood as this can greatly affect their immunoreactivity. The aim of this study was to evaluate the...

Comparison of conventional heat-treated and membrane filtered infant formula using an in vitro semi-dynamic digestion method

Introducing membrane filtration steps into infant milk formula (IMF) manufacture can partly preserve native whey proteins in the final products. In this study, IMF produced by membrane filtration (MEM-IMF) and...

Formulation of infant formula with different casein fractions and their effects on physical properties and digestion characteristics

This study investigated whether casein (CN) fractions exhibit better physical properties and digestibility than native casein micelles presently used in the production of infant formula. The structural performance of native casein micelles (micellar casein concentrates, MCC), β-CN, κ-CN and β + κ-CN were explored, and physical properties and digestion characteristics (i.e., digestibility, particle size, zeta potential and microscopic morphology) of the infant formula with MCC, β-CN, κ-CN or β + κ-CN were determined to elucidate the applicability of these casein types in infant formula. Results indicated that the β + κ-CN infant formula solution had the largest particle size with the most unstable potential. Moreover, both β-CN and κ-CN infant formula showed high solubility, while κ-CN displayed the lowest foaming capacity and high foaming stability. β-CN infant formula expressed an effective digestibility property, however, it possessed the largest particle size after gastrointestinal digestion. Therefore, β-CN fraction infant formula showed better digestibility than casein infant formula, and thus this work provides a theoretical basis for the development of infant formula.

Pepsin activity as a function of pH and digestion time on caseins and egg white proteins under static in vitro conditions

The activity of pepsin, the gastric protease, is generally considered to be negligible for pH ≥ 4, based on the results obtained with a few purified globular proteins. The present study aimed at studying the activity of porcine pepsin on egg white proteins (EWP) and casein micelle micro-aggregates (CA) over a broad range of pH (from 1 to 7) for short (3 min) and long (2 h) digestion times. For a short time, the results confirmed a tendency for a higher rate of hydrolysis with decreasing pH, but with different pH activity profiles for both the substrates. More remarkably, the degree of hydrolysis of CA after 2 h of digestion was constant from pH 1 to pH 5, and was only reduced by half at pH 6. This finding demonstrates that pepsin can hydrolyse caseins from the very beginning of gastric digestion. Interestingly, the trend of the reaction kinetics over 2 h appeared to be rather characteristic of the type of the substrate and was largely independent in terms of pH. Most hydrolysis profiles could be accurately fitted by a power law, an empirical model that was then successfully applied to the static in vitro gastric proteolysis of 6 other food matrices. Overall, our results support the idea that pepsin activity under weakly acidic conditions (pH ≥ 4) should not always be neglected, in particular, for milk caseins, and that pepsin reaction kinetics during static in vitro gastric digestion seems to evolve proportionally to the power of the digestion time.

Explore Gastric Lipolysis and Lipid Oxidation of Conventional versus Pasture-Based Milk by a Semi-dynamic In Vitro Digestion Model

Research on gastric lipolysis of commercial cow's milk with different fatty acid (FA) compositions is scarce. Gastric lipase exhibits specificity for the sn-3 chain position of triacylglycerols, whose structure is influenced by milk FA composition. Therefore, during gastric digestion of conventional (C) vs pasture-based (P) milk, differences may occur on lipolysis, which has impact on free FA available, influencing their absorption/metabolism rate and physiological hormonal responses. Those two milk types were subjected to the INFOGEST semi-dynamic digestion model. Five gastric emptying points were analyzed for oxidative degradation of polyunsaturated fatty acids (PUFA) and individual free FA. The relative release of medium-chain FA (C8:0-C12:0) was higher than that of longer-chain FA (C14:0-C18:0), and a linear increase in markers of PUFA oxidative degradation occurred along gastric digestion. Quantitatively, C8:0, C18:2n-6, C18:3n-3, and CLAc9t11 were higher (P < 0.001) in P milk when compared with C milk.

Dynamic in vitro gastric digestion behavior of goat milk: Effects of homogenization and heat treatments

The gastric digestion behavior of differently processed goat milks was investigated using a dynamic in vitro gastric digestion model, the human gastric simulator. Homogenization and heat treatment of goat milk resulted in gastric clots with highly fragmented structures. They also delayed the pH reduction during digestion, altered the chemical composition of the clots and the emptied digesta, promoted the release of calcium from the clots, and accelerated the hydrolysis and the emptying of milk proteins. The apparent density of the protein particles and the location of the homogenized fat globules changed during the digestion process, as shown in the emptied digesta of the homogenized goat milks. The effects of processing on the digestion behavior of goat milk were broadly similar to those previously reported for cow milk. However, the overall gastric digestion process of goat milk was more affected by homogenization than by heat treatments.