Steven Le Feunteun

Monitoring protein hydrolysis by pepsin using pH-stat: In vitro gastric digestions in static and dynamic pH conditions

This study intends to demonstrate that acid titration at low pH is very well adapted to the monitoring of pepsin activity. After a description of the underlying principles, this approach was used during in vitro gastric digestions of a model of complex food containing 15wt% of whey proteins, according to both static (2h at pHxa0=xa03, Infogest protocol) and dynamic pH conditions (from pH 6.3 down to 2 in 1h). Pepsin activity was quantitatively assessed in all experiments through the calculation of degrees of hydrolysis (DH). Final values of 3.7 and 3.0% were obtained in static and dynamic pH conditions, respectively, and validated using an independent method. Results also show that about 92% of the peptides were detected at pHxa0=xa03, and 100% for pH≤2.5. Overall, the proposed approach proved to be very worthy to study protein hydrolysis during in vitro gastric digestions.

Exploring the breakdown of dairy protein gels during in vitro gastric digestion using time-lapse synchrotron deep-UV fluorescence microscopy

A novel time-lapse synchrotron deep-UV microscopy methodology was developed that made use of the natural tryptophan fluorescence of proteins. It enabled the monitoring in situ of the microstructural changes of protein gels during simulated gastric digestion. Two dairy gels with an identical composition, but differing by the coagulation mode, were submitted to static in vitro gastric digestion. The kinetics of gel particle breakdown were quantified by image analysis and physico-chemical analyses of digesta. The results confirm the tendency of rennet gels, but not acid gels, to form compact protein aggregates under acidic conditions of the stomach. Consequently, the kinetics of proteolysis were much slower for the rennet gel, confirming the hypothesis of a reduced pepsin accessibility to its substrate. The particle shapes remained unchanged and the disintegration kinetics followed an exponential trend, suggesting that erosion was the predominant mechanism of the enzymatic breakdown of dairy gels in these experimental conditions.

Lipo‐Protein Emulsion Structure in the Diet Affects Protein Digestion Kinetics, Intestinal Mucosa Parameters and Microbiota Composition

SCOPEnFood structure is a key factor controlling digestion and nutrient absorption. We test the hypothesis that protein emulsion structure in the diet may affect digestive and absorptive processes.nnnMETHODS & RESULTSnRats (n = 40) are fed for 3 weeks with two diets chemically identical but based on lipid-protein liquid-fine (LFE) or gelled-coarse (GCE) emulsions that differ at the macro- and microstructure levels. After an overnight fasting, they ingest a 15 N-labeled LFE or GCE test meal and are euthanized 0, 15xa0min, 1xa0h, and 5xa0h later. 15 N enrichment in intestinal contents and blood are measured. Gastric emptying, protein digestion kinetics, 15 N absorption, and incorporation in blood protein and urea are faster with LFE than GCE. At 15xa0min time point, LFE group shows higher increase in GIP portal levels than GCE. Three weeks of dietary adaptation leads to higher expression of cationic amino acid transporters in ileum of LFE compared to GCE. LFE diet raises cecal butyrate and isovalerate proportion relative to GCE, suggesting increased protein fermentation. LFE diet increases fecal Parabacteroides relative abundance but decreases Bifidobacterium, Sutterella, Parasutterella genera, and Clostridium cluster XIV abundance.nnnCONCLUSIONnProtein emulsion structure regulates digestion kinetics and gastrointestinal physiology, and could be targeted to improve food health value.

Oro-gastro-intestinal digestion of starch in white bread, wheat-based and gluten-free pasta: Unveiling the contribution of human salivary α-amylase

Starch is a major determinant of the glycemic responses elicited by our diets, but the exact contribution of the two main amylolytic enzymes (salivary and pancreatic α-amylases) remains a matter of debate. Our aim was to investigate the contribution of the oral, gastric and intestinal phases to the hydrolysis of starch in bread and pasta during dynamic in vitro digestions using DiDGI®. Before its inactivation by the low gastric pH, salivary α-amylase released about 80% of the starch in bread and 30% of that in pasta, hydrolysing over half of it into oligosaccharides. Accordingly, the contribution of pancreatic α-amylase during the intestinal phase was lower for bread than pasta. Our results are well correlated with in vivo data, and demonstrate the importance of salivary α-amylase during oro-gastric processing of starchy foods. This finding is discussed in relation with observations regarding salivary α-amylase from other fields of knowledge.

Structure of protein emulsion in food impacts intestinal microbiota, caecal luminal content composition and distal intestine characteristics in rats

SCOPEnFew studies have evaluated in vivo the impact of food structure on digestion, absorption of nutrients and on microbiota composition and metabolism. In this study we evaluated in rat the impact of two structures of protein emulsion in food on gut microbiota, luminal content composition, and intestinal characteristics.nnnMETHODS AND RESULTSnRats received for 3 weeks two diets of identical composition but based on lipid-protein matrices of liquid fine (LFE) or gelled coarse (GCE) emulsion. LFE diet led to higher abundance, when compared to the GCE, of Lactobacillaceae (Lactobacillus reuteri) in the ileum, higher β-diversity of the caecum mucus-associated bacteria. In contrast, the LFE diet led to a decrease in Akkermansia municiphila in the caecum. This coincided with heavier caecum content and higher amount of isovalerate in the LFE group. LFE diet induced an increased expression of (i) amino acid transporters in the ileum (ii) glucagon in the caecum, together with an elevated level of GLP-1 in portal plasma. However, these intestinal effects were not associated with modification of food intake or body weight gain.nnnCONCLUSIONnOverall, the structure of protein emulsion in food affects the expression of amino acid transporters and gut peptides concomitantly with modification of the gut microbiota composition and activity. Our data suggest that these effects of the emulsion structure are the result of a modification of protein digestion properties.