Contribution of the Individual Small Intestinal α-Glucosidases to Digestion of Unusual α-Linked Glycemic Disaccharides

Comparative Study of Three Diverse Glycogen Branching Enzymes for Efficient Generation of Highly Surface Branched Starch Granules with Enhanced Digestive Resistance

Glycogen branching enzymes (GBEs) are widely applied to functionalize starch. However, modification of granular starch is challenging, and among GBEs, so far, only GBEs from Geobacillus thermoglucosidans (GtGBE) and Rhodothermus obamensis (RoGBE) have been used. To further develop their modification, starch granules of waxy, normal, and three types of high-amylose maize starches were treated with GBEs from Petrotoga mobilis (PmGBE), Rhodothermus marinus (RmGBE), and RoGBE as a benchmark. PmBE most effectively and rapidly added short branches, causing a reduced crystallinity and surface order of the starch granules. Furthermore, digestibility analysis indicated that PmGBE boosted the content of resistant starch. Along with its high activity, PmGBE showed a superior binding capacity to starch granules. Based on structural comparison, surface binding sites and the N-terminal domain of unknown function in PmGBE are proposed to influence activity and substrate specificity. Thus, PmGBE showed potential as an effective tool for the future modification of starch granules.

Activated effect of chondroitin sulfate on α-glucosidase: An in vitro and in silico approach

Chondroitin sulfate (CS), a glycosaminoglycan (GAG), plays a pivotal role in various physiological functions and is extensively utilized in medical and clinical applications. This study aimed to explore the enhancing effects and underlying mechanisms of three commonly encountered sulfated glycosaminoglycans CS-A, CS-C and CS-D on α-glucosidase activity. In vitro enzyme kinetic studies demonstrated that all three types of CS promoted α-glucosidase activity, with CS-D exhibiting the most pronounced effect, reaching 124.7 %. Fluorescence and circular dichroism (CD) spectroscopy, along with molecular docking experiments, revealed that CSs spontaneously interacted with the enzyme's active site, forming hydrogen bonds with Arg600 and His674. Additionally, hydrophobic interactions with Trp376 and Trp481 further strengthened these hydrogen bonds. These interactions increased the flexibility of the α-glucosidase polypeptide backbone, leading to greater solvent exposure of Trp residues and alterations in the enzyme's secondary structure composition. Furthermore, trajectory analysis from kinetic simulations indicated that activation of the α-glucosidase active site induced an inward folding and contraction of the region, thereby enlarging the internal cavity and enhancing its hydrophobic nature. This structural reconfiguration not only provided additional space for substrate hydrolysis but also minimized interference from water molecules, collectively contributing to an overall enhancement of α-glucosidase hydrolytic activity. In conclusion, this study identifies CS as an α-glucosidase activator and elucidates its interaction mechanisms through both in vitro and in silico approaches, highlighting its potential applications in the food industry.

Rat small intestine extract as a source of mammalian α- and β-glycosidases to study polyphenol bioaccessibility and deglycosylation in vitro: A case study with matrix-devoid and matrix-defined apple fractions

Most polyphenols are glycosylated, affecting their uptake, metabolism, and biological activity. However, the attached sugar must be removed before absorption and functionality can take place. Yet, despite the biological and chemical implications of polyphenol (de-)glycosylation, most in vitro digestion assays omit the utilization of intestinal brush border α- and/or β-glycosidases to study polyphenol bioaccessibility and deglycosylation. This study investigated the effect of rat small intestine extract (RSIE) as an affordable source of mammalian α- and β-glycosidases in different food matrices: matrix-devoid whole apple extract, whole apple, apple juice, and apple pomace. Using the INFOGEST 2.0 model, transepithelial polyphenol absorption, UHPLC-ESI-QTOF-MS/MS, and the inclusion of RSIE at the 15 U*mL-1 maltase activity reported in the human epithelium, the role of RSIE in polyphenol bioaccessibility and deglycosylation was explored. Moreover, the effect of the plant cell wall (PCW) matrix on the role of RSIE was mechanistically investigated by comparing whole apple (or pomace) with their respective extracts. 36 glycosylated polyphenols were identified, including 33 β-O-glycosides and 3 α-O-glycosides. The content of bioaccessible polyphenol β-O-glycosides and α-O-glycosides was significantly lower (p < 0.001) when RSIE was present, which resulted in a concomitant generation of the aglycone forms (phloretin, quercetin, ferulic acid, caffeic acid and p-coumaric acid). However, the concentration of aglycones was much lower than the reduction in the concentration of glycosylated polyphenols, strongly suggesting that polyphenols bind to RSIE. Matrix-devoid whole apple extract, or pomace extract, exhibited higher polyphenol bioaccessibility than whole apple or pomace, likely due to reduced interactions between polyphenols and the food matrix. Importantly, these differences in bioaccessibility diminished with RSIE, suggesting that RSIE α-glycosidases cleaved α-glucans and disrupted the PCW structure.

Design Optimization of a Novel Catalytic Approach for Transglucosylated Isomaltooligosaccharides into Dietary Polyols Structures by Leuconostoc mesenteroides Dextransucrase

Polyols, or sugar alcohols, are widely used in the industry as sweeteners and food formulation ingredients, aiming to combat the incidence of diet-related Non-Communicable Diseases. Given the attractive use of Generally Regarded As Safe (GRAS) enzymes in both academia and industry, this study reports on an optimized process to achieve polyols transglucosylation using a dextransucrase enzyme derived from Leuconostoc mesenteroides. These enzyme modifications could lead to the creation of a new generation of glucosylated polyols with isomalto-oligosaccharides (IMOS) structures, potentially offering added functionalities such as prebiotic effects. These reactions were guided by a design of experiment framework, aimed at maximizing the yields of potential new sweeteners. Under the optimized conditions, dextransucrase first cleared the glycosidic bond of sucrose, releasing fructose with the formation of an enzyme-glucosyl covalent intermediate complex. Then, the acceptor substrate (i.e., polyols) is bound to the enzyme-glucosyl intermediate, resulting in the transfer of glucosyl unit to the tested polyols. Structural insights into the reaction products were obtained through nuclear maneic resonance (NMR) and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) analyses, which revealed the presence of linear α(1 → 6) glycosidic linkages attached to the polyols, yielding oligosaccharide structures containing from 4 to 10 glucose residues. These new polyols-based oligosaccharides hold promise as innovative prebiotic sweeteners, potentially offering valuable health benefits.

Slowly hydrolyzable property of microbial dextrans at the small intestinal α-glucosidase levels leads to the modulated glycemic responses in the mouse model

Dextran-type α-glucans have been known as non-digestible ingredients that can be considered prebiotics to promote colon health. However, recent studies have revealed that various α-linked glucosyl units are hydrolyzed to glucose by small intestinal α-glucosidases. This study analyzed the structural characteristics of exopolysaccharides (EPSs) from Weissella species, and the hydrolysis properties at both in vitro/in vivo levels were investigated. Compared with a previous in vitro digestion model using fungal α-hydrolytic enzymes, dextrans, which mainly consist of α-1,6 linkages with small amounts of α-1,3 linked glucose units, were slowly hydrolyzed to glucose by mammalian mucosal α-glucosidases, resulting in attenuation of the initial glycemic response following administration of EPS samples to mice via oral gavage. The results of this study demonstrate the concept of dextran-type α-glucans as glycemic carbohydrates rather than dietary fibers or prebiotics. Slowly digestible dextrans can be applied as a functional ingredient to regulate postprandial glucose delivery throughout the gastrointestinal tract.

Detailed Analysis of Prebiotic Fructo- and Galacto-Oligosaccharides in the Human Small Intestine

Galacto-oligosaccharides (GOS) and fructo-oligosaccharides (FOS) are food ingredients that improve human health, but their degradation throughout the human small intestine is not well understood. We studied the breakdown kinetics of FOS and GOS in the intestines of seven healthy Dutch adults. Subjects were equipped with a catheter in the distal ileum or proximal colon and consumed 5 g of chicory-derived FOS (degree of polymerization (DP) DP2-10), and 5 g of GOS (DP2-6). Postprandially, intestinal content was frequently collected until 350 min and analyzed for mono-, di-, and oligosaccharides. FOS and GOS had recoveries of 96 ± 25% and 76 ± 28%, respectively. FOS DP ≥ 2 and GOS DP ≥ 3 abundances in the distal small intestine or proximal colon matched the consumed doses, while GOS dimers (DP2) had lower recoveries, namely 22.8 ± 11.1% for β-D-gal-(1↔1)-α-D-glc+β-D-gal-(1↔1)-β-D-glc, 19.3 ± 19.1% for β-D-gal-(1 → 2)-D-glc+β-D-gal-(1 → 3)-D-glc, 43.7 ± 24.6% for β-D-gal-(1 → 6)-D-gal, and 68.0 ± 38.5% for β-D-gal-(1 → 4)-D-gal. Lactose was still present in the distal small intestine of all of the participants. To conclude, FOS DP ≥ 2 and GOS DP ≥ 3 were not degraded in the small intestine of healthy adults, while most prebiotic GOS DP2 was hydrolyzed in a structure-dependent manner. We provide evidence on the resistances of GOS with specific β-linkages in the human intestine, supporting the development of GOS prebiotics that resist small intestine digestion.

Changes in the structure and enzyme binding of starches during in vitro enzymatic hydrolysis using mammalian mucosal enzyme mixtures

Starches are hydrolyzed into monosaccharides by mucosal α-glucosidases in the human small intestine. However, there are few studies assessing the direct digestion of starch by these enzymes. The objective of this study was to investigate the changes in the structure and enzyme binding of starches during in vitro hydrolysis by mammalian mucosal enzymes. Waxy maize (WMS), normal maize (NMS), high-amylose maize (HAMS), waxy potato (WPS), and normal potato (NPS) starches were examined. The order of the digestion rate was different compared with other studies using a mixture of pancreatic α-amylase and amyloglucosidase. NPS was digested more than other starches. WPS was more digestible than WMS. Hydrolyzed starch from NPS, NMS, WPS, WMS, and HAMS after 24 h was 66.4, 64.2, 61.7, 58.7, and 46.2 %, respectively. Notably, a significant change in the morphology, reduced crystallinity, and a decrease in the melting enthalpy of the three starches (NPS, NMS, and WPS) after 24 h of hydrolysis were confirmed by microscopy, X-ray diffraction, and differential scanning calorimetry, respectively. The bound enzyme fraction of NPS, NMS, and WPS increased as hydrolysis progressed. In contrast, HAMS was most resistant to hydrolysis by mucosal α-glucosidases in terms of digestibility, changes in morphology, crystallinity, and thermal properties.

Kinetics and molecular modeling studies on the inhibition mechanism of GH13 α-glycosidases by small molecule ligands

Alpha-glucosidase inhibitors play an important role in Diabetes Mellitus (DM) treatment since they prevent postprandial hyperglycemia. The Glycoside Hydrolase family 13 (GH13) is the major family of enzymes acting on substrates containing α-glucoside linkages, such as maltose and amylose/amylopectin chains in starch. Previously, our group identified glycoconjugate 1H-1,2,3-triazoles (GCTs) inhibiting two GH13 α-glycosidases: yeast maltase (MAL12) and porcine pancreatic amylase (PPA). Here, we combined kinetic studies and computational methods on nine GCTs to characterize their inhibitory mechanism. They all behaved as reversible inhibitors, and kinetic models encompassed noncompetitive and various mechanisms of mixed-type inhibition for both enzymes. Most potent inhibitors displayed Ki values of 30 μM for MAL12 (GPESB16) and 37 μM for PPA (GPESB15). Molecular dynamics and docking simulations indicated that on MAL12, GPESB15 and GPESB16 bind in a cavity adjacent to the active site, while on the PPA, GPESB15 was predicted to bind at the entrance of the catalytic site. Notably, despite its putative location within the active site, the binding of GPESB15 does not obstruct the substrate's access to the cleavage site. Our study contributes to paving the way for developing novel therapeutic strategies for managing DM-2 through GH13 α-glycosidases inhibition.

Mammalian maltase-glucoamylase and sucrase-isomaltase inhibitory effects of Artocarpus heterophyllus: An in vitro and in silico approach

Alpha-glucosidase (maltase, sucrase, isomaltase and glucoamylase) activities which are involved in carbohydrate metabolism are present in human intestinal maltase-glucoamylase (MGAM) and sucrase-isomaltase (SI). Hence, these proteins are important targets to identify drugs against postprandial hyperglycemia thereby for diabetes. To find natural-based drugs against MGAM and SI, Artocarpus heterophyllus leaf was explored for MGAM and SI inhibition in in vitro and in silico. A. heterophyllus leaf aqueous active fraction (AHL-AAF) was prepared using Soxhlet extraction followed by silica column chromatography. The phytoconstituents of AHL-AAF were determined using LC-ESI-MS/MS. AHL-AAF showed dose-dependent and mixed inhibition against maltase (IC50 = 460 µg/ml; Ki = 300 µg/ml), glucoamylase (IC50 = 780 µg/ml; Ki = 480 µg/ml), sucrase (IC50 = 900 µg/ml, Ki = 504 µg/ml) and isomaltase (IC50 = 860 µg/ml, Ki = 400 µg/ml). AHL-AAF phytoconstituents interaction with N-terminal (Nt) and C-terminal (Ct) subunits of human MGAM and SI was analyzed using induced-fit docking, molecular dynamics (MD), and binding free energy calculation. In docking studies, rhamnosyl hexosyl methyl quercetin (RHMQ), P-coumaryl-O-16-hydroxy palmitic acid (PCHP), and spirostanol interacted with active site amino acids of human MGAM and SI. Among these RHMQ stably interacted with all the subunits (Nt-MGAM, Ct-MGAM, Nt-SI and Ct-SI) whereas PCHP with Ct-MGAM and Nt-SI during MD analysis. In molecular docking, the docking score of RHMQ with NtMGAM, CtMGAM, NtSI and CtSI was -8.48, -12.88, -11.98 and -11.37 kcal/mol. The docking score of PCHP for CtMGAM and NtSI was -8.59 and -8.4 kcal/mol, respectively. After MD simulation, the root mean square deviation (RMSD) and root mean square fluctuation (RMSF) values further confirmed the stable protein-ligand interaction. The RMSD value of all the complexes were around 2.5 Å and the corresponding RMSF values were also quite low. In MM/GBSA analysis, the involvement of Van der Waals and lipophilic energy in the protein/ligand interactions are understood. Further binding free energy for Nt-MGAM-PCHP, Nt-MGAM-RHMQ, Nt-SI-PCHP, Nt-SI-RHMQ, Ct-MGAM-PCHP, Ct-MGAM-RHMQ and Ct-SI-RHMQ complexes was found to be -24.94, -46.60, -46.56, -44.48, -40.3, -41.86 and -19.39 kcal/mol, respectively. Altogether, AHL-AAF showed inhibition of α-glucosidase activities of MGAM and SI. AHL-AAF could be further studied for its effect on diabetes in in vivo.

α-Glucan-type exopolysaccharides with varied linkage patterns: Mitigating post-prandial glucose spike and prolonging the glycemic response

Microbial exopolysaccharides (EPSs) are traditionally known as prebiotics that foster colon health by serving as microbiota nutrients, while remaining undigested in the small intestine. However, recent findings suggest that α-glucan structures in EPS, with their varied α-linkage types, can be hydrolyzed by mammalian α-glucosidases at differing rates. This study explores α-glucan-type EPSs, including dextran, alternan, and reuteran, assessing their digestive properties both in vitro and in vivo. Notably, while fungal amyloglucosidase - a common in vitro tool for carbohydrate digestibility analysis - shows limited efficacy in breaking down these structures, mammalian intestinal α-glucosidases can partially degrade them into glucose, albeit slowly. In vivo experiments with mice revealed that various EPSs elicited a significantly lower glycemic response (p < 0.05) than glucose, indicating their nature as carbohydrates that are digested slowly. This leads to the conclusion that different α-glucan-type EPSs may serve as ingredients that attenuate post-prandial glycemic responses. Furthermore, rather than serving as mere dietary fibers, they hold the potential for blood glucose regulation, offering new avenues for managing obesity, Type 2 diabetes, and other related-chronic diseases.

The Synergistic Effect of Compound Sugar with Different Glycemic Indices Combined with Creatine on Exercise-Related Fatigue in Mice

In this study, a compound sugar (CS) with different glycemic index sugars was formulated via hydrolysis characteristics and postprandial glycemic response, and the impact of CS and creatine emulsion on exercise-related fatigue in mice was investigated. Thirty-five C57BL/6 mice were randomly divided into five groups to supply different emulsions for 4 weeks: initial emulsion (Con), glucose emulsion (62 mg/10 g MW glucose; Glu), CS emulsion (62 mg/10 g MW compound sugar; CS), creatine emulsion (6 mg/10 g MW creatine; Cr), and CS and creatine emulsion (62 mg/10 g MW compound sugar, 6 mg/10 g MW creatine, CS-Cr). Then, the exhaustion time of weight-bearing swimming and forelimb grip strength were measured to evaluate the exercise capacity of mice, and some fatigue-related biochemical indexes of blood were determined. The results demonstrated that the ingestion of CS significantly reduced the peak of postprandial blood glucose levels and prolonged the energy supply of mice compared to ingesting an equal amount of glucose. Mouse exhaustion time was 1.22-fold longer in the CS group than in the glucose group. Additionally, the supplementation of CS increased the liver glycogen content and total antioxidant capacity of mice. Moreover, the combined supplementation of CS and creatine increased relative forelimb grip strength and decreased blood creatine kinase activity. The findings suggested that the intake of CS could enhance exercise capacity, and the combined supplementation of CS and creatine has a synergistic effect in improving performance.

In vitro gastrointestinal digestion methods of carbohydrate-rich foods

The trend toward healthier food products has led to an increase in the research of in vitro gastrointestinal digestion methods. Among the most used models, static models are the simplest. Most static models have three stages: oral, gastric, and intestinal, simulating the enzymatic, electrolyte, pH, temperature, and bile salt conditions. The studies that have taken the most notice are those related to antioxidant activity, followed by those dealing with proteins and carbohydrates using most of them static in vitro digestion models. The number of these studies has increased over the years, passing from 45 to 415 in a 10-year period (2012-2023) and showing an interest in knowing the impact of food on human health. Nevertheless, published papers report different methodologies and analytical approaches. This review discusses the similarities and differences between the published static in vitro gastrointestinal digestion methods, with a focus on carbohydrates, finding that the most used protocol is Infogest, but with differences, mainly in the type of enzymes and their activity. Regarding in vitro gastrointestinal digestion of carbohydrates, many of the published studies are related to food and biomacromolecules, being the oral phase the most omitted, while the intestinal phase in the most diverse. Other methodologies to study the intestinal phase have been recommended, but the number of in vitro digestion studies using these methodologies (RSIE and BBMV) is still scarce but could represent a good alternative to analyze carbohydrates foods when combining with Infogest. More studies are required in this area.

Structural analysis of a water insoluble polysaccharide from pearl millet and evaluating its prebiotic activity

Epidemiological studies have shown an inverse correlation between dietary intake of prebiotics and the risk of chronic diseases. Pearl millet is a potential economic source to develop a new class of prebiotics in the form of its polysaccharide. In the present study, the chemical structure of a water insoluble homopolysaccharide (PMG), and its prebiotic properties were investigated. The structure of PMG was elucidated on the basis of total hydrolysis, methylation analysis, and 1D/2D NMR (1H, 13C, DEPT-135, HSQC, DQF-COSY, NOESY and ROESY) experiments. The results indicated that PMG was a glucan with an average molecular weight ~ 361 kDa having a backbone of (1 → 3) α-d-glucopyranosyl residues. Hydrolysis of PMG by salivary and pancreatic α amylase was 1.75 % ± 0.34 and 1.99 % ± 0.18 respectively. A positive prebiotic score of PMG with both L. acidophilus and L. brevis (0.446 ± 0.031 & 0.427 ± 0.016) hints towards its prebiotic potential. These observations suggest that PMG might be used as a potential prebiotic component in the food and pharmaceutical applications.

A comprehensive review on the properties, production, and applications of functional glucobioses

Glucobiose is a range of disaccharides consisting of two glucose molecules, generally including trehalose, kojibiose, sophorose, nigerose, laminaribiose, maltose, cellobiose, isomaltose, and gentiobiose. The difference glycosidic bonds of two glucose molecules result in the diverse molecular structures, physiochemical properties and physiological functions of these glucobioses. Some glucobioses are abundant in nature but have unconspicuous roles on health like maltose, whereas some rare glucobioses display remarkable biological effects. It is unpractical process to extract these rare glucobioses from natural resources, while biological synthesis is a feasible approach. Recently, the production and application of glucobiose have attracted considerable attention. This review provides a comprehensive overview of glucobioses, including their natural sources and physicochemical properties like structure, sweetness, digestive performance, toxicology, and cariogenicity. Specific enzymes used for the production of various glucobioses and fermentation production processes are summarized. Additionally, their versatile functions and broad applications are also introduced.

Transglycosylation catalysed by Caco-2 membrane disaccharidases: A new approach to understand carbohydrates digestibility

Under appropriate experimental conditions, some glycoside hydrolases can catalyze transglycosylation reactions; a hypothesis associated with this is that the glycosidic linkages formed will be preferentially hydrolyzed under optimal conditions. Therefore, the hydrolytic and transglycosylation activities of isolated membranes from differentiated Caco-2 cells on sucrose, maltose and isomaltulose were evaluated. After the enzymatic reactions, the di- and trisaccharides obtained were identified by gas chromatography coupled to a mass spectrometer. Differentiated Caco-2 cell membranes exerted hydrolytic and transglycosylation activities towards the studied disaccharides. The obtained di- and trisaccharides were detected for the first time using human cell models. Due to the absence of maltase-glucoamylase complex (MGAM) in Caco-2 cells, and the known hydrolytic activity of sucrase-isomaltase (SI) towards sucrose, maltose and isomaltulose, it is plausible that the glycosidic linkages obtained after the transglycosylation reaction, mainly α-glucosyl-fructoses and α-glucosyl-glucoses, were carried out by SI complex. This approach can be used as a model to explain carbohydrate digestibility in the small intestine and as a tool to design new oligosaccharides with low intestinal digestibility.

Macromolecular α-glucans with α-1,3/α-1,4 branching structures produced using dual glycosyltransferases: Elucidation of physicochemical and slowly digestible properties

Amylosucrase from Neisseria polysaccharea (NpAS) produces the linear amylose-like α-glucans by the elongation property from sucrose, and 4,3-α-glucanotransferase from Lactobacillus fermentum NCC 2970 (4,3-αGT) newly synthesizes the α-1,3 linkages after cleaving the α-1,4 linkages by the glycosyltransferring property. This study focused on the synthesis of high molecular α-1,3/α-1,4-linked glucans by combining NpAS and 4,3-αGT and analyzed their structural and digestive properties. The enzymatically synthesized α-glucans have a molecular weight of >1.6 × 10⁷ g mol^-1, and the α-4,3 branching ratios on the structures increased as the amount of 4,3-αGT increased. The synthesized α-glucans were hydrolyzed to linear maltooligosaccharides and α-4,3 branched α-limit dextrins (α-LDx) by human pancreatic α-amylase, and the amounts of produced α-LDx were increased depending on the ratio of synthesized α-1,3 linkages. In addition, approximately 80 % of the synthesized products were partially hydrolyzed by mammalian α-glucosidases, and the glucose generation rates decelerated as the amounts of α-1,3 linkages increased. In conclusion, new types of α-glucans with α-1,4 and α-1,3 linkages were successfully synthesized by a dual enzyme reaction. These can be utilized as slowly digestible and prebiotic ingredients in the gastrointestinal tract due to their novel linkage patterns and high molecular weights.

Mass Spectrometry Approach for Differentiation of Positional Isomers of Saccharides: Toward Direct Analysis of Rare Sugars

Rare sugars have gained popularity in recent years due to their use in antiaging treatments, their ability to sweeten with few calories, and their ability to heal infections. Rare sugars are found in small quantities in nature, and they exist typically as isomeric forms of traditional sugars, rendering some challenges in their isolation, synthesis, and characterization. In this work, we present the first direct mass spectrometric approach for differentiating structural isomers of sucrose that differ only by their glycosidic linkages. The method employed a noncontact nanoelectrospray (nESI) platform capable of analyzing minuscule volumes (5 μL) of saccharides via the formation of halide adducts ([M+X]-; X = Cl and Br). Tandem mass spectrometry analysis of the five structural isomers of sucrose afforded diagnostic fragment ions that can be used to distinguish each isomer. Detailed mechanisms showcasing the distinct fragmentation pattern for each isomer are discussed. The method was applied to characterize and confirm the presence of all five selected rare sugars in raw honey complex samples. Aside from the five natural α isomers of sucrose, the method was also suitable for differentiating some β isomers of the same glycosidic linkages, provided the monomeric sugar units are different. The halide adduct formation via the noncontact nESI source was also proven to be effective for oligosaccharides such as raffinose, β-cyclodextrin, and maltoheptaose. The results from this study encourage the future development of methods that function with simple operation to enable straightforward characterization of small quantities of rare sugars.

Production of a Series of Long-Chain Isomaltooligosaccharides from Maltose by Bacillus subtilis AP-1 and Associated Prebiotic Properties

Bacillus subtilis strain AP-1, which produces α-glucosidase with transglucosidase activity, was used to produce a series of long-chain isomaltooligosaccharides (IMOs) with degree of polymerization (DP) ranging from 2 to 14 by direct fermentation of maltose. A total IMOs yield of 36.33 g/L without contabacillusmination from glucose and maltose was achieved at 36 h of cultivation using 50 g/L of maltose, with a yield of 72.7%. IMOs were purified by size exclusion chromatography with a Superdex 30 Increase column. The molecular mass and DP of IMOs were analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF/MS). Subsequently, linkages in produced oligosaccharides were verified by enzymatic hydrolysis with α-amylase and oligo-α-1,6-glucosidase. These IMOs showed prebiotic properties, namely tolerance to acidic conditions and digestive enzymes of the gastrointestinal tract, stimulation of probiotic bacteria growth to produce short-chain fatty acids and no stimulating effect on pathogenic bacteria growth. Moreover, these IMOs were not toxic to mammalian cells at up to 5 mg/mL, indicating their biocompatibility. Therefore, this research demonstrated a simple and economical method for producing IMOs with DP2–14 without additional operations; moreover, the excellent prebiotic properties of the IMOs offer great prospects for their application in functional foods.

Rare Sugar Metabolism and Impact on Insulin Sensitivity along the Gut-Liver-Muscle Axis In Vitro

Rare sugars have recently attracted attention as potential sugar replacers. Understanding the biochemical and biological behavior of these sugars is of importance in (novel) food formulations and prevention of type 2 diabetes. In this study, we investigated whether rare sugars may positively affect intestinal and liver metabolism, as well as muscle insulin sensitivity, compared to conventional sugars. Rare disaccharide digestibility, hepatic metabolism of monosaccharides (respirometry) and the effects of sugars on skeletal muscle insulin sensitivity (impaired glucose uptake) were investigated in, respectively, Caco-2, HepG2 and L6 cells or a triple coculture model with these cells. Glucose and fructose, but not l-arabinose, acutely increased extracellular acidification rate (ECAR) responses in HepG2 cells and impaired glucose uptake in L6 cells following a 24 h exposure at 28 mM. Cellular bioenergetics and digestion experiments with Caco-2 cells indicate that especially trehalose (α1-1α), D-Glc-α1,2-D-Gal, D-Glc-α1,2-D-Rib and D-Glc-α1,3-L-Ara experience delayed digestion and reduced cellular impact compared to maltose (α1-4), without differences on insulin-stimulated glucose uptake in a short-term setup with a Caco-2/HepG2/L6 triple coculture. These results suggest a potential for l-arabinose and specific rare disaccharides to improve metabolic health; however, additional in vivo research with longer sugar exposures should confirm their beneficial impact on insulin sensitivity in humans.

Slow digestion properties of long-sized isomaltooligosaccharides synthesized by a transglucosidase from Thermoanaerobacter thermocopriae

Isomaltooligosaccharides (IMOs) are widely used as prebiotic ingredients that promote colon health; however, recent studies revealed that these are slowly hydrolyzed to glucose within the small intestine. Here, novel α-glucans with a higher number of α-1,6 linkages were synthesized from maltodextrins using the Thermoanaerobacter thermocopriae-derived transglucosidase (TtTG) to decrease susceptibility to hydrolysis and improve slow digestion properties. The synthesized long-sized IMOs (l-IMOs; 70.1% of α-1,6 linkages), comprising 10-12 glucosyl units, exhibited slow hydrolysis to glucose when compared to commercial IMOs under treatment with mammalian α-glucosidase level. In male mice, the ingestion of l-IMOs significantly decreased the post-prandial glycemic response compared to other samples (p < 0.05). Therefore, enzymatically synthesized l-IMOs can be applied as functional ingredients for the modulation of blood glucose homeostasis in obesity, Type 2 diabetes, and other chronic diseases.

Interaction between the α-glucosidases, sucrase-isomaltase and maltase-glucoamylase, in human intestinal brush border membranes and its potential impact on disaccharide digestion

The two major intestinal α-glycosidases, sucrase-isomaltase (SI) and maltase-glucoamylase (MGAM), are active towards α-1,4 glycosidic linkages that prevail in starch. These enzymes share striking structural similarities and follow similar biosynthetic pathways. It has been hypothesized that starch digestion can be modulated via “toggling” of activities of these mucosal α-glycosidases, suggesting a possible interaction between these two enzyme complexes in the intestinal brush border membrane (BBM). Here, the potential interaction between SI and MGAM was investigated in solubilized BBMs utilizing reciprocal pull down assays, i.e., immunoprecipitation with anti-SI antibody followed by Western blotting with anti-MGAM antibody and vice versa. Our results demonstrate that SI interacts avidly with MGAM concomitant with a hetero-complex assembly in the BBMs. This interaction is resistant to detergents, such as Triton X-100 or Triton X-100 in combination with sodium deoxycholate. By contrast, inclusion of sodium deoxycholate into the solubilization buffer reduces the enzymatic activities towards sucrose and maltose substantially, most likely due to alterations in the quaternary structure of either enzyme. In view of their interaction, SI and MGAM regulate the final steps in starch digestion in the intestine, whereby SI assumes the major role by virtue of its predominant expression in the intestinal BBMs, while MGAM acts in auxiliary supportive fashion. These findings will help understand the pathophysiology of carbohydrate malabsorption in functional gastrointestinal disorders, particularly in irritable bowel syndrome, in which gene variants of SI are implicated.

Isomaltooligosaccharides inhibit early colorectal carcinogenesis in a 1,2-dimethylhydrazine-induced rat model

Colon cancer (CC) is a multistage disease and one of the most common cancers worldwide. Establishing an effective treatment strategies of early colon cancer is of great significance for preventing its development and reducing mortality. The occurrence of colon cancer is closely related to changes in the intestinal flora structure. Therefore, remodelling the intestinal flora structure through prebiotics is a powerful approach for preventing and treating the occurrence and development of colon cancer. Isomaltooligosaccharides (IMOs) are often found in fermented foods and can directly reach the gut for use by microorganisms. In this study, a rat model of early colon cancer (DMH) was established by subcutaneous injection of 1,2-dimethylhydrazine, and the model rats were fed IMOs as a dietary intervention (DI). The untargeted faecal metabolomics, gut metabolome and intestinal function of the model rats were investigated. The results showed that DMH, DI and IMOs alone (IMOs) groups exhibited gut microbial community changes. In the DI group, there was an increased abundance of probiotics (Lactobacillus) and decreased abundance of CC marker bacteria (Fusobacterium). The key variations in the faecal metabolites of the DI group included decreased levels of glucose, bile acids (including deoxycholic acid and chenodeoxycholic acid) and amino acids (including L-glutamic acid and L-alanine). In addition, dietary intake of IMOs attenuated the intestinal inflammatory response, improved the intestinal microecological environment, and slowed the development of DMH-induced early CC in rats. This work provides a theoretical basis and technical support for the clinical prevention or treatment of CC with prebiotics.

6-Formyl Umbelliferone, a Furanocoumarin from Angelica decursiva L., Inhibits Key Diabetes-Related Enzymes and Advanced Glycation End-Product Formation

Over the years, great attention has been paid to coumarin derivatives, a set of versatile molecules that exhibit a wide variety of biological activities and have few toxic side effects. In this study, we investigated the antidiabetic potential of 6-formyl umbelliferone (6-FU), a novel furanocoumarin isolated from Angelica decursiva. Numerous pharmacological activities of 6-FU have been previously reported; however, the mechanism of its antidiabetic activity is unknown. Therefore, we examined the action of 6-FU on a few candidate-signaling molecules that may underlie its antidiabetic activity, including its inhibition of protein tyrosine phosphatase 1B (PTP1B), α-glucosidase, human recombinant aldose reductase (HRAR), and advanced glycation end-product (AGE) formation (IC₅₀ = 1.13 ± 0.12, 58.36 ± 1.02, 5.11 ± 0.21, and 2.15 ± 0.13 μM, respectively). A kinetic study showed that 6-FU exhibited mixed-type inhibition against α-glucosidase and HRAR and competitive inhibition of PTP1B. Docking simulations of 6-FU demonstrated negative binding energies and close proximity to residues in the binding pockets of those enzymes. We also investigated the molecular mechanisms underlying 6-FU's antidiabetic effects. 6-FU significantly increased glucose uptake and decreased PTP1B expression in insulin-resistant C2C12 skeletal muscle cells. Moreover, 6-FU (0.8-100 μM) remarkably inhibited the formation of fluorescent AGEs in glucose-fructose-induced human serum albumin glycation over the course of 4 weeks. The findings clearly indicate that 6-FU will be useful in the development of multiple target-oriented therapeutic modalities for the treatment of diabetes and diabetes-related complications.

New glucogenesis inhibition model based on complete α-glucosidases from rat intestinal tissues validated with various types of natural and pharmaceutical inhibitors

BACKGROUND

Inhibition of intestinal α-glucosidases from rat intestinal acetone powder (RIAP) has been widely used in research focused on regulating glucogenesis to be applied as a strategy to control obesity and type II diabetes. However, the crude extract has different compositions of α-glucosidases than a complete RIAP suspension due to enzymes anchored on the intestinal tissues after the extraction. Here, the inhibitory effects of different pharmaceutical and food-grade inhibitors on the enzymes in the RIAP suspension were investigated.

RESULTS

Instead of crude extracts from RIAP, the RIAP suspension without the extraction process was applied to optimize the α-glucosidase inhibitory model by pharmaceutical/natural inhibitors. The results clearly showed that the half-maximal inhibitory concentration ratios of four individual α-glucosidases by various inhibitors were different between the RIAP suspension and the crude extract. In particular, isomaltase from the RIAP suspension required more inhibitors than the crude extraction did, as this enzyme is still anchored to the remaining intestinal tissue from the extraction process.

CONCLUSION

The crude extract from RIAP contains only a portion of the enzymes, which poses limitations for determining the precise inhibitory properties by various types of enzyme inhibitors. On the contrary, an in vitro assay with RIAP suspension that has all the α-glucosidases is a more suitable method for determining digestibility of glycemic carbohydrates. This new approach can be applied to the development of natural/synthetic α-glucosidase inhibitors to attenuate the postprandial glycemic response more accurately. © 2022 Society of Chemical Industry.

Comprehensive utilization of sucrose resources via chemical and biotechnological processes: A review

Sucrose, one of the most widespread disaccharides in nature, has been available in daily human life for many centuries. As an abundant and cheap sweetener, sucrose plays an essential role in our diet and the food industry. However, it has been determined that many diseases, such as obesity, diabetes, hyperlipidemia, etc., directly relate to the overconsumption of sucrose. It arouses many explorations for the conversion of sucrose to high-value chemicals. Production of valuable substances from sucrose by chemical methods has been studied since a half-century ago. Compared to chemical processes, biotechnological conversion approaches of sucrose are more environmentally friendly. Many enzymes can use sucrose as the substrate to generate functional sugars, especially those from GH68, GH70, GH13, and GH32 families. In this review, enzymatic catalysis and whole-cell fermentation of sucrose for the production of valuable chemicals were reviewed. The multienzyme cascade catalysis and metabolic engineering strategies were addressed.

Functional oligosaccharide fermentation in the gut: Improving intestinal health and its determinant factors-A review

The human intestine is characterized by an abundance of nutrients and a complex microbiota that make crucial contributions to overall health. These nutrients facilitate the adaptation of resident commensals to extreme environments and the development of a robust ecological network in host species. Long-term deprivation of microbiota-accessible carbohydrates (MACs) in the gut results in a loss of bacterial diversity, disruption of intestinal barrier function, and inflammatory diseases. Functional oligosaccharides are excellent MACs possessing important prebiotic properties for intestinal health through their fermentation in the gut. Its mechanism of action is predominantly attributed to acting as carbon sources for specific probiotics, promoting short-chain fatty acids production, and regulating the gut microbiota. In this review, we describe the source and structural characteristics of functional oligosaccharides, provide a framework for strategies to improve intestinal health by oligosaccharide fermentation and discuss structural determinants influencing the functional properties of oligosaccharides.

Structural basis of the strict specificity of a bacterial GH31 α-1,3-glucosidase for nigerooligosaccharides

Carbohydrate-active enzymes are involved in the degradation, biosynthesis, and modification of carbohydrates and vary with the diversity of carbohydrates. The glycoside hydrolase (GH) family 31 is one of the most diverse families of carbohydrate-active enzymes, containing various enzymes that act on α-glycosides. However, the function of some GH31 groups remains unknown, as their enzymatic activity is difficult to estimate due to the low amino acid sequence similarity between characterized and uncharacterized members. Here, we performed a phylogenetic analysis and discovered a protein cluster (GH31_u1) sharing low sequence similarity with the reported GH31 enzymes. Within this cluster, we showed that a GH31_u1 protein from Lactococcus lactis (LlGH31_u1) and its fungal homolog demonstrated hydrolytic activities against nigerose [α-D-Glcp-(1→3)-D-Glc]. The k_cat/K_m values of LlGH31_u1 against kojibiose and maltose were 13% and 2.1% of that against nigerose, indicating that LlGH31_u1 has a higher specificity to the α-1,3 linkage of nigerose than other characterized GH31 enzymes, including eukaryotic enzymes. Furthermore, the three-dimensional structures of LlGH31_u1 determined using X-ray crystallography and cryogenic electron microscopy revealed that LlGH31_u1 forms a hexamer and has a C-terminal domain comprising four α-helices, suggesting that it contributes to hexamerization. Finally, crystal structures in complex with nigerooligosaccharides and kojibiose along with mutational analysis revealed the active site residues involved in substrate recognition in this enzyme. This study reports the first structure of a bacterial GH31 α-1,3-glucosidase and provides new insight into the substrate specificity of GH31 enzymes and the physiological functions of bacterial and fungal GH31_u1 members.

Sweet Biotechnology: Enzymatic Production and Digestibility Screening of Novel Kojibiose and Nigerose Analogues

In view of the global pandemic of obesity and related metabolic diseases, there is an increased interest in alternative carbohydrates with promising physiochemical and health-related properties as a potential replacement for traditional sugars. However, our current knowledge is limited to only a small selection of carbohydrates, whereas the majority of alternative rare carbohydrates and especially their properties remain to be investigated. Unraveling their potential properties, like digestibility and glycemic content, could unlock their use in industrial applications. Here, we describe the enzymatic production and in vitro digestibility of three novel glycosides, namely, two kojibiose analogues (i.e., d-Glc_p-α-1,2-d-Gal and d-Glc_p-α-1,2-d-Rib) and one nigerose analogue (i.e., d-Glc_p-α-1,3-l-Ara). These novel sugars were discovered after an intensive acceptor screening with a sucrose phosphorylase originating from Bifidobacterium adolescentis (BaSP). Optimization and upscaling of this process led to roughly 100 g of these disaccharides. Digestibility, absorption, and caloric potential were assessed using brush border enzymes of rat origin and human intestinal Caco-2 cells. The rare disaccharides showed a reduced digestibility and a limited impact on energy metabolism, which was structure-dependent and even more pronounced for the three novel disaccharides in comparison to their respective glucobioses, translating to a low-caloric potential for these novel rare disaccharides.

New insights suggest isomaltooligosaccharides are slowly digestible carbohydrates, rather than dietary fibers, at constitutive mammalian α-glucosidase levels

Isomaltooligosaccharides (IMOs) have been characterized as dietary fibers that resist digestion in the small intestine; however, previous studies suggested that various α-glycosidic linkages in IMOs were hydrolyzed by mammalian α-glucosidases. This study investigated the hydrolysis of IMOs by small intestinal α-glucosidases from rat and human recombinant sucrase-isomaltase complex compared to commonly used fungal amyloglucosidase (AMG) in vitro. Interestingly, mammalian α-glucosidases fully hydrolyzed various IMOs to glucose at a slow rate compared with linear maltooligosaccharides, whereas AMG could not fully hydrolyze IMOs because of its very low hydrolytic activity on α-1,6 linkages. This suggests that IMOs have been misjudged as prebiotic ingredients that bypass the small intestine due to the nature of the assay used. Instead, IMOs can be applied in the food industry as slowly digestible materials to regulate the glycemic response and energy delivery in the mammalian digestive system, rather than as dietary fibers.

Metabolism and Health Effects of Rare Sugars in a CACO-2/HepG2 Coculture Model

Non-alcoholic fatty liver disease (NAFLD) has become the most prevalent liver disease worldwide and is impacted by an unhealthy diet with excessive calories, although the role of sugars in NAFLD etiology remains largely unexplored. Rare sugars are natural sugars with alternative monomers and glycosidic bonds, which have attracted attention as sugar replacers due to developments in enzyme engineering and hence an increased availability. We studied the impact of (rare) sugars on energy production, liver cell physiology and gene expression in human intestinal colorectal adenocarcinoma (Caco-2) cells, hepatoma G2 (HepG2) liver cells and a coculture model with these cells. Fat accumulation was investigated in the presence of an oleic/palmitic acid mixture. Glucose, fructose and galactose, but not mannose, l-arabinose, xylose and ribose enhanced hepatic fat accumulation in a HepG2 monoculture. In the coculture model, there was a non-significant trend (p = 0.08) towards higher (20–55% increased) median fat accumulation with maltose, kojibiose and nigerose. In this coculture model, cellular energy production was increased by glucose, maltose, kojibiose and nigerose, but not by trehalose. Furthermore, glucose, fructose and l-arabinose affected gene expression in a sugar-specific way in coculture HepG2 cells. These findings indicate that sugars provide structure-specific effects on cellular energy production, hepatic fat accumulation and gene expression, suggesting a health potential for trehalose and l-arabinose, as well as a differential impact of sugars beyond the distinction of conventional and rare sugars.

Slowly digestible property of highly branched α-limit dextrins produced by 4,6-α-glucanotransferase from Streptococcus thermophilus evaluated in vitro and in vivo

Starch molecules are first degraded to slowly digestible α-limit dextrins (α-LDx) and rapidly hydrolyzable linear malto-oligosaccharides (LMOs) by salivary and pancreatic α-amylases. In this study, we designed a slowly digestible highly branched α-LDx with maximized α-1,6 linkages using 4,6-α-glucanotransferase (4,6-αGT), which creates a short length of α-1,4 side chains with increasing branching points. The results showed that a short length of external chains mainly composed of 1-8 glucosyl units was newly synthesized in different amylose contents of corn starches, and the α-1,6 linkage ratio of branched α-LDx after the chromatographical purification was significantly increased from 4.6% to 22.1%. Both in vitro and in vivo studies confirmed that enzymatically modified α-LDx had improved slowly digestible properties and extended glycemic responses. Therefore, 4,6-αGT treatment enhanced the slowly digestible properties of highly branched α-LDx and promises usefulness as a functional ingredient to attenuate postprandial glucose homeostasis.

The bifidogenic effects and dental plaque deformation of non-digestible isomaltooligosaccharides synthesized by dextransucrase and alternansucrase

Non-digestible isomaltooligosaccharides (NDIMOS) are functional food and beverage ingredients that contributed to human health benefits through metabolism of gastrointestinal microorganism. In this study, NDIMOS were synthesized by combine dextransucrase from Leuconostoc mesenteroides B512F/KM and alternansucrase from L. mesenteroides NRRL 1355CF10/KM using sucrose as substrate and maltose as acceptor. Their digestibility was confirmed by using digestive enzymes including α-amylase and amyloglucosidase. NDIMOS inhibited insoluble glucan formation through mutansucrase from Streptococcus mutans. The bifidogenic effect of NDIMOS was investigated by growth of four strains of Bifidobacterium in MRS broth containing NDIMOS, compared with MRS broth contain glucose and negative control. Additionally, Bifidobacterium bifidum or Bifidobacterium adolescentis inhibited the growth of Salmonella enterica serovar typhimurium when they were co-cultivation in MRS broth containing NDIMOS. These results suggested that NDIMOS is potential functional ingredient for food, beverage, and pharmaceutical application.

Preparation and Analysis of α-1,6 Glucan as a Slowly Digestible Carbohydrate

Carbohydrate materials that produce lower postprandial blood glucose increase are required for diabetic patients. To develop slowly digestible carbohydrates, the effect of degree of polymerization (DP) of α-1,6 glucan on its digestibility was investigated in vitro and in vivo. We prepared four fractions of α-1,6 glucan composed primarily of DP 3–9, DP 10–30, DP 31–150, and DP 151+ by fractionating a dextran hydrolysate. An in vitro experiment using digestive enzymes showed that the glucose productions of DP 3–9, DP 10–30, DP 31–150, and DP 151+ were 70.3, 53.4, 28.2, and 19.2 % in 2 h, and 92.1, 83.9, 39.6, and 33.3 % in 24 h relative to dextrin, respectively. An in vivo glycemic response showed that the incremental area under the curve (iAUC) of blood glucose levels of α-1,6 glucan with DP 3–9, DP 10–30, DP 31–150, and DP 151+ were 99.5, 84.3, 65.4, and 40.1 % relative to dextrin, respectively. These results indicated that α-1,6 glucan with higher DP had stronger resistance to digestion and produced a smaller blood glucose response. DP 10–30 showed significantly lower maximum blood glucose levels than dextrin; however, no significant difference was observed in iAUC, indicating that DP 10–30 was slowly digestible. In addition, α-1,6 glucan was also produced using an enzymatic reaction with dextrin dextranase (DDase). This produced similar results to DP 10–30. The DDase product can be synthesized from dextrin at low cost. This glucan is expected to be useful as a slowly digestible carbohydrate source.

Regulation of pancreatic exocrine in ruminants and the related mechanism: The signal transduction and more

The unique structure of the stomach, including the rumen, reticulum, omasum, and abomasum, indicates the differences between the ruminant and monogastric animals in the digestion of nutrients. This difference is reflected in the majority of dietary nutrients that may be fermented in the rumen. Significant proteins and a certain amount of starch can flow to the small intestine apart from rumen. The initial phase of small intestinal digestion requires pancreatic digestive enzymes. In theory, the enzymatic digestion and utilization efficiency of starch in the small intestine are considerably higher than that in the rumen, but the starch digestibility in the small intestine is quite low in ruminants. Therefore, improving the digestion of nutrients, especially starch in the small intestine is more urgent for high-yield ruminants. Although the pancreas plays a central role in nutrient digestion, the progress of research investigating pancreatic exocrine regulation in the ruminant is slow due to some factors, such as the complex structure of the pancreas, the selection of experimental model and duration, and internal (hormones or ages) and external (diet) influences. The present review is based on the research findings of pancreatic exocrine regulation of dairy animals and expounded from the physiological structure of the ruminant pancreas, the factors affecting the digestion and exocrine processing of carbohydrates, and the regulatory mechanism governing this process. The review aims to better understand the characteristics of enzymatic digestion, thereby advancing pancreatic exocrine research and improving the digestion and utilization of nutrients in ruminants. Additionally, this review provides the theoretical basis for improving nutrient utilization efficiency, reducing wastage of feed resources, and promoting the efficient development of the dairy industry.

Structural factors governing starch digestion and glycemic responses and how they can be modified by enzymatic approaches: A review and a guide

Starch is the most abundant glycemic carbohydrate in the human diet. Consumption of starch-rich food products that elicit high glycemic responses has been linked to the occurrence of noncommunicable diseases such as cardiovascular disease and diabetes mellitus type II. Understanding the structural features that govern starch digestibility is a prerequisite for developing strategies to mitigate any negative health implications it may have. Here, we review the aspects of the fine molecular structure that in native, gelatinized, and gelled/retrograded starch directly impact its digestibility and thus human health. We next provide an informed guidance for lowering its digestibility by using specific enzymes tailoring its molecular and three-dimensional supramolecular structure. We finally discuss in vivo studies of the glycemic responses to enzymatically modified starches and relevant food applications. Overall, structure-digestibility relationships provide opportunities for targeted modification of starch during food production and improving the nutritional profile of starchy foods.

Flavonoids as Human Intestinal α-Glucosidase Inhibitors

Certain flavonoids can influence glucose metabolism by inhibiting enzymes involved in carbohydrate digestion and suppressing intestinal glucose absorption. In this study, four structurally-related flavonols (quercetin, kaempferol, quercetagetin and galangin) were evaluated individually for their ability to inhibit human α-glucosidases (sucrase, maltase and isomaltase), and were compared with the antidiabetic drug acarbose and the flavan-3-ol(−)-epigallocatechin-3-gallate (EGCG). Cell-free extracts from human intestinal Caco-2/TC7 cells were used as the enzyme source and products were quantified chromatographically with high accuracy, precision and sensitivity. Acarbose inhibited sucrase, maltase and isomaltase with IC₅₀ values of 1.65, 13.9 and 39.1 µM, respectively. A similar inhibition pattern, but with comparatively higher values, was observed with EGCG. Of the flavonols, quercetagetin was the strongest inhibitor of α-glucosidases, with inhibition constants approaching those of acarbose, followed by galangin and kaempferol, while the weakest were quercetin and EGCG. The varied inhibitory effects of flavonols against human α-glucosidases depend on their structures, the enzyme source and substrates employed. The flavonols were more effective than EGCG, but less so than acarbose, and so may be useful in regulating sugar digestion and postprandial glycaemia without the side effects associated with acarbose treatment.

Barks of Three Wild Pyrus Taxa: Phenolic Constituents, Antioxidant Activity, and in Vitro and in Silico Investigations of α-Amylase and α-Glucosidase Inhibition

Dry MeOH extracts of the twig barks of Pyrus communis subsp. pyraster, P. spinosa and their hybrid P.×jordanovii nothosubsp. velenovskyi, collected in wild in Serbia, were analyzed. By LC/MS, the contents of arbutin (99.9-131.0 mg/g), chlorogenic acid (2.2-6.3 mg/g), catechin (1.0-5.3 mg/g) and total dimeric and trimeric procyanidins (42.2-61.3 mg/g), including procyanidin B2 (8.9-17.2 mg/g), were determined. Colorimetrically, high contents of total phenolics (436.2-533.4 mg GAE/g) and tannins (339.4-425.7 mg GAE/g), as well as strong total antioxidant activities (FRAP values 4.5-5.9 mmol Fe²⁺ /g), and DPPH (SC₅₀ =6.6-7.1 μg/ml) and hydroxyl radical (SC₅₀ =447.1-727.7 μg/ml) scavenging abilities were revealed. In vitro, all extracts exhibited notable inhibition of α-amylase (IC₅₀ =310.8-617.7 μg/ml) and particularly strong inhibition of α-glucosidase (IC₅₀ =2.1-3.7 μg/ml). Molecular docking predicted that among identified compounds procyanidin B2 is the best inhibitor of these carbohydrate-digesting enzymes. Obtained results showed that the barks of investigated Pyrus hybrid and its parent taxa have similar composition and bioactivity.

Inhibitory Activity and Mechanism Investigation of Hypericin as a Novel α-Glucosidase Inhibitor

α-glucosidase is a major enzyme that is involved in starch digestion and type 2 diabetes mellitus. In this study, the inhibition of hypericin by α-glucosidase and its mechanism were firstly investigated using enzyme kinetics analysis, real-time interaction analysis between hypericin and α-glucosidase by surface plasmon resonance (SPR), and molecular docking simulation. The results showed that hypericin was a high potential reversible and competitive α-glucosidase inhibitor, with a maximum half inhibitory concentration (IC₅₀) of 4.66 ± 0.27 mg/L. The binding affinities of hypericin with α-glucosidase were assessed using an SPR detection system, which indicated that these were strong and fast, with balances dissociation constant (KD) values of 6.56 × 10⁻⁵ M and exhibited a slow dissociation reaction. Analysis by molecular docking further revealed that hydrophobic forces are generated by interactions between hypericin and amino acid residues Arg-315 and Tyr-316. In addition, hydrogen bonding occurred between hypericin and α-glucosidase amino acid residues Lys-156, Ser-157, Gly-160, Ser-240, His-280, Asp-242, and Asp-307. The structure and micro-environment of α-glucosidase enzymes were altered, which led to a decrease in α-glucosidase activity. This research identified that hypericin, an anthracene ketone compound, could be a novel α-glucosidase inhibitor and further applied to the development of potential anti-diabetic drugs.

Inhibition of α-glucosidases by tea polyphenols in rat intestinal extract and Caco-2 cells grown on Transwell

Inhibition of maltase, sucrase, isomaltase and glucoamylase activity by acarbose, epigallocatechin gallate, epicatechin gallate and four polyphenol-rich tea extract from white, green, oolong, black tea, were investigated by using rat intestinal enzymes and human Caco-2 cells. Regarding rat intestinal enzyme mixture, all four tea extracts were very effective in inhibiting maltase and glucoamylase activity, but only white tea extract inhibited sucrase and isomaltase activity and the inhibition was limited. Mixed-type inhibition on rat maltase activity was observed. Tea extracts in combination with acarbose, produced a synergistic inhibitory effect on rat maltase activity. Caco-2 cells experiments were conducted in Transwells. Green tea extract and epigallocatechin gallate show dose-dependent inhibition on human sucrase activity, but no inhibition on rat sucrase activity. The opposite was observed on maltase activity. The results highlighted the different response in the two investigated model systems and show that tea polyphenols are good inhibitors for α-glucosidase activity.

Physicochemical properties of turanose and its potential applications as a sucrose substitute

Among the structural isomers of sucrose, turanose has been considered as one of good candidates as novel sweetener due to its mild taste, low calorie, and anti-cariogenicity. Here, various physicochemical properties of turanose, such as solubility, temperature and pH stabilities, viscosity, non-enzymatic browning reaction, and dynamic vapor sorption, were investigated by comparing them to those of other commercial sugars. Turanose did not significantly hydrolyze through the simulated digestion tract overall but in the artificial small intestinal environment specifically, turanose degraded by only 18% when sucrose was hydrolyzed by 36% after 4 h. In addition, physicochemical properties of turanose confirmed that it had a potential to replace sucrose due to similar or better product qualities as a food ingredient than other types of sugars with similar chemical structure. Thus, our study suggests that turanose can be applied as a functional sweetener or bulking agent in food processing.

Duplications and Functional Convergence of Intestinal Carbohydrate-Digesting Enzymes

Vertebrate diets and digestive physiologies vary tremendously. Although the contribution of ecological and behavioral features to such diversity is well documented, the roles and identities of individual intestinal enzymes shaping digestive traits remain largely unexplored. Here, we show that the sucrase-isomaltase (SI)/maltase-glucoamylase (MGAM) dual enzyme system long assumed to be the conserved disaccharide and starch digestion framework in all vertebrates is absent in many lineages. Our analyses indicate that independent duplications of an ancestral SI gave rise to the mammalian-specific MGAM, as well as to other duplicates in fish and birds. Strikingly, the duplicated avian enzyme exhibits similar activities to MGAM, revealing an unexpected case of functional convergence. Our results highlight digestive enzyme variation as a key uncharacterized component of dietary diversity in vertebrates.

Food Matrix Effects for Modulating Starch Bioavailability

As the prevalence of obesity and diabetes has continued to increase rapidly in recent years, dietary approaches to regulating glucose homeostasis have gained more attention. Starch is the major source of glucose in the human diet and can have diverse effects, depending on its rate and extent of digestion in the small intestine, on postprandial glycemic response, which over time is associated with blood glucose abnormalities, insulin sensitivity, and even appetitive response and food intake. The classification of starch bioavailability into rapidly digestible starch, slowly digestible starch, and resistant starch highlights the nutritional values of different starches. As starch is the main structure-building macroconstituent of foods, its bioavailability can be manipulated by selection of food matrices with varying degrees of susceptibility to amylolysis and food processing to retain or develop new matrices. In this review, the food factors that may modulate starch bioavailability, with a focus on food matrices, are assessed for a better understanding of their potential contribution to human health. Aspects affecting starch nutritional properties as well as production strategies for healthy foods are also reviewed, e.g., starch characteristics (different type, structure, and modification), food physical properties (food form, viscosity, and integrity), food matrix interactions (lipid, protein, nonstarch polysaccharide, phytochemicals, organic acid, and enzyme inhibitor), and food processing (milling, cooking, and storage).

In vitro digestion of polysaccharides: InfoGest protocol and use of small intestinal extract from rat

Starch, dextran, pectin and modified citrus pectin were subjected to intestinal digestion following InfoGest protocol and a rat small intestine extract (RSIE) treatment. Gastric stage did not show any modification in the structure of the carbohydrates, except for modified pectin. Regarding intestinal phases, starch was hydrolyzed by different ways, resulting in a complementary behavior between InfoGest and RSIE. Contrarily, digestion of dextran was only observed using RSIE. Similar situation occurred in the case of pectins with RSIE, obtaining a partial hydrolysis, especially in the modified citrus pectin. However, citrus pectin was the less prone to hydrolysis by enzymes. The results demonstrated that InfoGest method underestimates the significance of the carbohydrates hydrolysis at the small intestine, thus indicating that RSIE is a very reliable and useful method for a more realistic study of polysaccharides digestion.

Insulin-Mimetic Dihydroxanthyletin-Type Coumarins from Angelica decursiva with Protein Tyrosine Phosphatase 1B and α-Glucosidase Inhibitory Activities and Docking Studies of Their Molecular Mechanisms

As a traditional medicine, Angelica decursiva has been used for the treatment of many diseases. The goal of this study was to evaluate the potential of four natural major dihydroxanthyletin-type coumarins—(+)-trans-decursidinol, Pd-C-I, Pd-C-II, and Pd-C-III—to inhibit the enzymes, protein tyrosine phosphatase 1B (PTP1B) and α-glucosidase. In the kinetic study of the PTP1B enzyme’s inhibition, we found that (+)-trans-decursidinol, Pd-C-I, and Pd-C-II led to competitive inhibition, while Pd-C-III displayed mixed-type inhibition. Moreover, (+)-trans-decursidinol exhibited competitive-type, and Pd-C-I and Pd-C-II mixed-type, while Pd-C-III showed non-competitive type inhibition of α-glucosidase. Docking simulations of these coumarins showed negative binding energies and a similar proximity to residues in the PTP1B and α-glucosidase binding pocket, which means they are closely connected and strongly binding with the active enzyme site. In addition, dihydroxanthyletin-type coumarins are up to 40 µM non-toxic in HepG2 cells and have substantially increased glucose uptake and decreased expression of PTP1B in insulin-resistant HepG2 cells. Further, coumarins inhibited ONOO⁻-mediated albumin nitration and scavenged peroxynitrite (ONOO⁻), and reactive oxygen species (ROS). Our overall findings showed that dihydroxanthyletin-type coumarins derived from A. decursiva is used as a dual inhibitor for enzymes, such as PTP1B and α-glucosidase, as well as for insulin susceptibility.

Biosynthesis of Nondigestible Galactose-Containing Hetero-oligosaccharides by Lactobacillus plantarum WCFS1 MelA α-Galactosidase

This work describes the high capacity of MelA α-galactosidase from Lactobacillus plantarum WCFS1 to transfer galactosyl residues from melibiose to the C6-hydroxyl group of disaccharide-acceptors with β-linkages (lactulose, lactose, and cellobiose) or α-linkages (isomaltulose and isomaltose) to produce novel galactose-containing hetero-oligosaccharides (HOS). A comprehensive nuclear magnetic resonance characterization of the transfer products derived from melibiose:lactulose reaction mixtures revealed the biosynthesis of α-d-galactopyranosyl-(1 → 6)-β-d-galactopyranosyl-(1 → 4)-β-d-fructose as the main component as well as the presence of α-d-galactopyranosyl-(1 → 3)-β-d-galactopyranosyl-(1 → 4)-β-d-fructose and α-d-galactopyranosyl-(1 → 6)-α-d-galactopyranosyl-(1 → 6)-β-d-galactopyranosyl-(1 → 4)-β-d-fructose. Melibiose-derived α-galactooligosaccharides (α-GOS), manninotriose and verbascotetraose, were also simultaneously synthesized. An in vitro assessment of the intestinal digestibility of the novel biosynthesized HOS revealed a high resistance of α-galactosides derived from lactulose, lactose, cellobiose, and isomaltulose. According to the evidence gathered for conventional α-GOS and certain disaccharides used as acceptors in this work, these novel nondigestible α-galactosides could be potential candidates to selectively modulate the gut microbiota composition, among other applications, such as low-calorie food ingredients.

Prenatal and Postnatal Nutrition Influence Pancreatic and Intestinal Carbohydrase Activities of Ruminants

In ruminant livestock species, nutrition can play an important role in the long-term programming of gastrointestinal function. Pancreatic and small intestinal digestive enzymes are important for postruminal digestion of carbohydrates and protein. Carbohydrases have been shown to respond to changes in the level of feed intake and the dietary inclusion of specific nutrients, including arginine, butyrate, folic acid, fructose, and leucine. Understanding how diet influences enzyme development and activity during prenatal and postnatal life could lead to the development of dietary strategies to optimize offspring growth and development to increase digestive efficiency of ruminant livestock species. More research is needed to understand how changes in fetal or neonatal carbohydrase activities in response to nutrition influence long-term growth performance and efficiency in ruminant livestock species to optimize nutritional strategies.

Hydrolysis and transglycosylation activities of glycosidases from small intestine brush-border membrane vesicles

In order to know the catalytic activities of the disaccharidases expressed in the mammalian small intestinal brush-border membrane vesicles (BBMV) high concentrated solutions of sucrose, maltose, isomaltulose, trehalose and the mixture sucrose:lactose were incubated with pig small intestine disaccharidases. The hydrolysis and transglycosylation reactions generated new di- and trisaccharides, characterized and quantified by GC-MS and NMR, except for trehalose where only hydrolysis was detected. In general, α-glucosyl-glucoses and α-glucosyl-fructoses were the most abundant structures, whereas no fructosyl-fructoses or fructosyl-glucoses were found. The in-depth structural characterization of the obtained carbohydrates represents a new alternative to understand the potential catalytic activities of pig small intestinal disaccharidases. The hypothesis that the oligosaccharides synthesized by glycoside hydrolases could be also hydrolysed by the same enzymes was confirmed. This information could be extremely useful in the design of new non-digestible or partially digestible oligosaccharides with potential prebiotic properties.