Impact of in vitro gastrointestinal digestion on peptide profile and bioactivity of cooked and non-cooked oat protein concentrates

Oat (Avena sativa) is one of the most cultivated and consumed cereals worldwide. Recognized among cereals for its high protein content (12% to 24%), it makes it an excellent source of bioactive peptides, which could be modified during processes such as heating and gastrointestinal digestion (GID). This work aims to evaluate the impact of heat treatment on the proteolysis of oat proteins and on the evolution of antioxidant peptide release during in vitro static GID, in terms of comparative analysis between cooked oat protein concentrate (COPC) and non-heated oat protein concentrate (OPC) samples. The protein extraction method and cooking procedure used showed no detrimental effects on protein quality. After GID, the proportion of free amino acids/dipeptides (40% for both samples (OPC and COPC), thus producing peptides with low molecular weight and enhanced bioactivity. Furthermore, during GID, the amino acid profile showed an increase in essential, positively-charged, hydrophobic and aromatic amino acids. At the end of GID, the reducing power of OPC and COPC increased >0.3 and 8-fold, respectively, in comparison to the non-digested samples; while ABTS•+ and DPPH• showed a >20-fold increase. Fe2+ chelating capacity of OPC and COPC was enhanced >4 times; similarly, Cu2+ chelation showed a >19-fold enhancement for OPC and >10 for COPC. β-carotene bleaching activity was improved 0.8 times in OPC and >9 times in COPC; the oxygen radical antioxidant capacity assay increased 2 times in OPC and >4.7 times in COPC, respectively. This study suggests that OPC after cooking and GID positively influenced the nutritional and bioactive properties of oat peptides. Thus, COPC could be used as a functional food ingredient with health-promoting effects, as hydrothermal treatment is frequently used for this type of cereals

The impact of liquid preloads varying in macronutrient content on postprandial kinetics of amino acids relative to appetite

status: publishe

The impact of liquid preloads varying in macronutrient content on postprandial kinetics of amino acids relative to appetite in healthy adults

The underlying mechanisms for the effect of proteins on appetite regulation, especially in presence of variable macronutrient composition, are not fully elucidated. The present study investigated the absorption kinetics of proteins after co-ingestion with the other macronutrients and examined the impact of circulating amino acids on appetite and satiety-related gut hormones. A randomized, within-subjects, 2-level full factorial design was implemented, where thirty six healthy subjects consumed seven preloads with similar energy density (3.1 kJ/g) and volume (670 mL) but with varying macronutrient content. The energy from protein (%) and the CHO:fat ratio were the two factors combined in three levels of 9, 24, 40 and 0.4, 2, 3.6 respectively. Blood and appetite parameters were evaluated until the serving of the ad libitum lunch after 210 min and the amino acid concentrations were measured in a subgroup of seven male subjects. The amino acid concentrations peaked at 90 min after all preloads and returned to the baseline values until 210 min. Protein intake affected amino acid profiles (P 0.05) were detected between the two high protein preloads despite the different CHO:fat ratio (40%/0.4 CHO:fat and 40%/3.6 CHO:fat), indicating that neither carbohydrate nor fat influenced the profiles. Most of the amino acids were not related to appetite sensations or gut hormones (P > 0.05), while glutamate was positively associated with prospective consumption and inversely related to ghrelin (P < 0.05). Valine, leucine, isoleucine, lysine and α-aminobutyric acid were inversely associated with energy intake (P < 0.05). Overall, postprandial amino acid profiles were solely affected by protein content and were not consistently related to appetite regulation. Further investigation of glutamate's effect on appetite is needed

Differences in endosperm cell wall integrity in wheat (Triticum aestivum L.) milling fractions impacts on the way starch responds to gelatinization and pasting treatments and its subsequent enzymatic in vitro digestibility

Wheat grain roller milling disrupts the starch containing endosperm cell walls and extracts white flour. Many wheat based food processes involve simultaneous use of heat and water which then cause starch to gelatinize and enhance its digestibility. In this study, the impact of starch enclosure in intact endosperm cell walls on starch physicochemical properties and digestibility was investigated. Wheat kernels milled into coarse farina (average particle size 705 µm) contained a substantial portion of intact cells and exhibited 15 - 30% lower Rapid Visco Analyzer peak viscosity readings than flour and fine farina (average particle size 85 and 330 µm, respectively) since its higher level of intact cell walls limited the swelling of the enclosed starch. Xylanase use in situ substantially degraded coarse farina cell walls and increased its swelling and viscosifying potential. Following full gelatinization of the different samples, the starch in coarse farina was digested at a 40% lower rate in an in vitro gastrointestinal digestion assay, but still to a similar extent than that in fully gelatinized flour. This indicates that while wheat endosperm cell walls are permeable to pancreatic amylase, they can sufficiently slow down enzyme diffusion. When xylanase treatment was performed after starch gelatinization and pasting, the rates of starch digestion were similar for all samples evidencing that cell walls act as physical barrier to enzyme diffusion and thus retard its digestion. The present findings offer ways to produce wheat-based foods with sustained energy release benefits.status: accepte

The impact of liquid preloads varying in macronutrient content on postprandial kinetics of amino acids relative to appetite in healthy adults

The underlying mechanisms for the effect of proteins on appetite regulation, especially in presence of variable macronutrient composition, are not fully elucidated. The present study investigated the absorption kinetics of proteins after co-ingestion with the other macronutrients and examined the impact of circulating amino acids on appetite and satiety-related gut hormones. A randomized, within-subjects, 2-level full factorial design was implemented, where thirty six healthy subjects consumed seven preloads with similar energy density (3.1 kJ/g) and volume (670 mL) but with varying macronutrient content. The energy from protein (%) and the CHO:fat ratio were the two factors combined in three levels of 9, 24, 40 and 0.4, 2, 3.6 respectively. Blood and appetite parameters were evaluated until the serving of the ad libitum lunch after 210 min and the amino acid concentrations were measured in a subgroup of seven male subjects. The amino acid concentrations peaked at 90 min after all preloads and returned to the baseline values until 210 min. Protein intake affected amino acid profiles (P  0.05) were detected between the two high protein preloads despite the different CHO:fat ratio (40%/0.4 CHO:fat and 40%/3.6 CHO:fat), indicating that neither carbohydrate nor fat influenced the profiles. Most of the amino acids were not related to appetite sensations or gut hormones (P > 0.05), while glutamate was positively associated with prospective consumption and inversely related to ghrelin (P < 0.05). Valine, leucine, isoleucine, lysine and α-aminobutyric acid were inversely associated with energy intake (P < 0.05). Overall, postprandial amino acid profiles were solely affected by protein content and were not consistently related to appetite regulation. Further investigation of glutamate's effect on appetite is needed.status: publishe

The effect of in vitro gastrointestinal conditions on the structure and conformation of oat β-glucan

A plethora of studies have shown that the physicochemical properties of oat β-glucan determine its health benefits. However, the impact of the passage through the gastrointestinal tract on the conformational and structural characteristics is not fully understood. The present study aims to elucidate the structure and conformation of gently extracted oat β-glucan before and after in vitro gastric and gastrointestinal digestion utilizing asymmetric flow field-flow fractionation (AF4) and NMR spectroscopy. The structural features and the bile acid-binding capacity of oat β-glucan were probed with NMR. Oat β-glucan without digestion presented primary aggregates with fringed micelle structure, and other high molar mass supramolecular secondary aggregates were detected. Under gastric conditions, the molar mass was reduced and an increase in apparent density, suggesting more compact and disrupted aggregates, was observed. In the intestinal phase, the conformation was restored as prior digestion. No effect of the digestive enzymes on the conformation of oat β-glucan was shown, except from a modest effect of pepsin under gastric conditions. In contrast, the bile acids induced alterations to the apparent density of the oat β-glucan aggregates indicating a molecular interaction which was further confirmed with NMR by observing numerous changes in the resonance of bile acids' carbons in presence of oat β-glucan. In conclusion, the examination of oat β-glucan under in vitro gastrointestinal conditions with AF4 and NMR sheds light on the aggregation behavior and interaction mechanisms and enables a rich gain of knowledge for its physiological effects

Effect of wheat endosperm cell wall structures on starch physico-chemical properties and digestibility

Starch is the most abundant glycemic carbohydrate in a normal human diet. Lowering the rate of its digestion in the small intestine provides a unique opportunity to maintain optimal blood glucose and insulin levels. Wheat milling into white flour disrupts the endosperm cell walls. One can assume that these cell walls can act as a physical barrier to the amylolytic enzymes during digestion. Against this background, the aim of this study was to investigate the impact of the degree of starch enclosure in wheat endosperm cellular structures on its physico-chemical properties and digestibility before and after hydrothermal processing. Hard wheat (Triticum aestivum L) kernels were milled and separated into different size fractions: regular flour (average particle diameter: 85 μm), fine (330 μm) and coarse (710 μm) farina. Epifluorescence microscopy images showed that the coarse particles had a significantly higher level of intact cells than regular flour. The coarse farina particles exhibited substantially retarded and, at the same time, up to 25% lower starch swelling than flour and fine farina, clearly indicating that the surrounding matrices impose physical restraints to starch swelling. Rapid Visco Analyzer (RVA) peak viscosity values at a dry matter content of 12% w/w were 4,121 cP for fine farina and 3,316 cP for coarse farina as a result of the increased cell walls intactness. At the same time, coarse farina exhibited lower breakdown values (1,005 cP) than did fine farina (2042 cP), since intact cells are more resistant to the applied shear. To fully comprehend the impact of the cell walls on starch pasting, Bacillus subtilis xylanase was added during RVA analysis to in situ hydrolyze arabinoxylan, the main cell wall component of wheat endosperm tissue. The peak viscosity values of coarse farina increased from 3,316 to 3,597 cP upon cell wall hydrolysis indicating that removing the physical barriers allowed starch granules to swell to a larger extent. Moreover, the breakdown values increased from 1,005 to 1,436 cP since the granules were more susceptible for disintegration once the cell walls were (partly) broken down. Nevertheless, the starch gelatinization properties such as measured by Differential Scanning Calorimetry were not affected by the degree of cell wall intactness. Finally, the rate and extent of in vitro starch digestibility went hand in hand with the degree of cell wall disintegration of the study samples indicating that the cell walls have a substantial impact on starch digestibility by acting as physical barrier and/or changing starch physico-chemical properties. In conclusion, intact wheat endosperm cell walls drastically limit the swelling and viscosity development of starch and, at the same time, retard (and limit) in vitro digestibility, offering innovative opportunities to design novel cereal-based products with potential claims on sustained energy release.status: publishe