In Vitro Digestibility of Galactooligosaccharides: Effect of the Structural Features on Their Intestinal Degradation

In vitro and in vivo digestibility of prebiotic galactooligosacharides synthesized by β-galactosidase from Lactobacillus delbruecki subsp. bulgaricus CRL450

BACKGROUND

The general assumption that prebiotics reach the colon without any alterations has been challenged. Some in vitro and in vivo studies have demonstrated that 'non-digestible' oligosaccharides are digested to different degrees depending on their structural composition. In the present study, we compared different methods aiming to assess the digestibility of oligosaccharides synthesized by β-galactosidase (β-gal) of Lactobacillus delbruecki subsp. bulgaricus CRL450 (CRL450-β-gal) from lactose, lactulose and lactitol.

RESULTS

In the simulated gastrointestinal fluid method, no changes were observed. However, the oligosaccharides synthesized by CRL450-β-gal were partially hydrolyzed in vitro, depending on their structure and composition, with rat small intestinal extract (RSIE) and small intestinal brush-border membrane vesicles (BBMV) from pig. Digestion of some oligosaccharides increased when mixtures were fed to C57BL/6 mice used as in vivo model; however, lactulose-oligosaccharides were the most resistant to the physiological conditions of mice. In general β (1→6) linked products showed higher resistance compared to β (1→3) oligosaccharides.

CONCLUSION

In vitro digestion methods, without disaccharidases, may underestimate the importance of carbohydrates hydrolysis in the small intestine. Although BVMM and RSIE digestion assays are appropriate in vitro methods for these studies, in vivo studies remain the most reliable for understanding what actually happens in the digestion of oligosaccharides. © 2024 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

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.

Gastrointestinal metabolism characteristics and mechanism of a polysaccharide from Grifola frondosa

Grifola frondosa polysaccharide (GFP) is mainly composed of α-1,4 glycosidic bonds and possesses multiple pharmacological activities. However, the absence of pharmacokinetic studies has limited its further development and utilization. Herein, GFP was labeled with 5-DTAF (FGFP) and cyanine 5.5 amine (GFP-Cy5.5) to investigate its gastrointestinal metabolism characteristics and mechanism. Significant distributions of the polysaccharide in the liver and kidneys were observed by near infrared imaging. To investigate the specific distribution form of the polysaccharide, in vitro digestion models were constructed and revealed that FGFP was degraded in saliva and rat small intestine extract. The metabolites were detected in the stomach and small intestine, followed by further degradation in the distal intestine in the in vivo experiment. Subsequent investigations showed that α-amylase was involved in the gastrointestinal degradation of GFP, and its metabolite finally entered the kidneys, where it was excreted directly with urine.

Dietary Fiber and Its Potential Role in Obesity: A Focus on Modulating the Gut Microbiota

Dietary fiber is a carbohydrate polymer with ten or more monomeric units that are resistant to digestion by human digestive enzymes, and it has gained widespread attention due to its significant role in health improvement through regulating gut microbiota. In this review, we summarized the interaction between dietary fiber, gut microbiota, and obesity, and the beneficial effects of dietary fiber on obesity through the modulation of microbiota, such as modifying selective microbial composition, producing starch-degrading enzymes, improving gut barrier function, reducing the inflammatory response, reducing trimethylamine N-oxide, and promoting the production of gut microbial metabolites (e.g., short chain fatty acids, bile acids, ferulic acid, and succinate). In addition, factors affecting the gut microbiota composition and metabolites by dietary fiber (length of the chain, monosaccharide composition, glycosidic bonds) were also concluded. Moreover, strategies for enhancing the biological activity of dietary fiber (fermentation technology, ultrasonic modification, nanotechnology, and microfluidization) were subsequently discussed. This review may provide clues for deeply exploring the structure-activity relationship between dietary fiber and antiobesity properties by targeting specific gut microbiota.

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.

Non-dairy prebiotics: Conceptual relevance with nutrigenomics and mechanistic understanding of the effects on human health

The increasing health awareness of consumers has made a shift towards vegan and non-dairy prebiotics counterparts. Non-dairy prebiotics when fortified with vegan products have interesting properties and widely found its applications in food industry. The chief vegan products that have prebiotics added include water-soluble plant-based extracts (fermented beverages, frozen desserts), cereals (bread, cookies), and fruits (juices & jelly, ready to eat fruits). The main prebiotic components utilized are inulin, oligofructose, polydextrose, fructooligosaccharides, and xylooligosaccharides. Prebiotics' formulations, type and food matrix affect food products, host health, and technological attributes. Prebiotics from non-dairy sources have a variety of physiological effects that help to prevent and treat chronic metabolic diseases. This review focuses on mechanistic insight on non-dairy prebiotics affecting human health, how nutrigenomics is related to prebiotics development, and role of gene-microbes' interactions. The review will provide industries and researchers with important information about prebiotics, mechanism of non-dairy prebiotics and microbe interaction as well as prebiotic based vegan products.

The Effect of Encapsulating a Prebiotic-Based Biopolymer Delivery System for Enhanced Probiotic Survival

Orally delivered probiotics must survive transit through harsh environments during gastrointestinal (GI) digestion and be delivered and released into the target site. The aim of this work was to evaluate the survivability and delivery of gel-encapsulated Lactobacillus rhamnosus GG (LGG) to the colon. New hybrid symbiotic beads alginate/prebiotic pullulan/probiotic LGG were obtained by the extrusion method. The average size of the developed beads was 3401 µm (wet), 921 µm (dry) and the bacterial titer was 109 CFU/g. The morphology of the beads was studied by a scanning electron microscope, demonstrating the structure of the bacterial cellulose shell and loading with probiotics. For the first time, we propose adding an enzymatic extract of feces to an artificial colon fluid, which mimics the total hydrolytic activity of the intestinal microbiota. The beads can be digested by fecalase with cellulase activity, indicating intestinal release. The encapsulation of LGG significantly enhanced their viability under simulated GI conditions. However, the beads, in combination with the prebiotic, provided greater protection of bacteria, enhancing their survival and even increasing cell numbers in the capsules. These data suggest the promising prospects of coencapsulation as an innovative delivery method based on the inclusion of probiotic bacteria in a symbiotic matrix.

Nondigestible Functional Oligosaccharides: Enzymatic Production and Food Applications for Intestinal Health

Nondigestible functional oligosaccharides are of particular interest in recent years because of their unique prebiotic activities, technological characteristics, and physiological effects. Among different types of strategies for the production of nondigestible functional oligosaccharides, enzymatic methods are preferred owing to the predictability and controllability of the structure and composition of the reaction products. Nondigestible functional oligosaccharides have been proved to show excellent prebiotic effects as well as other benefits to intestinal health. They have exhibited great application potential as functional food ingredients for various food products with improved quality and physicochemical characteristics. This article reviews the research progress on the enzymatic production of several typical nondigestible functional oligosaccharides in the food industry, including galacto-oligosaccharides, xylo-oligosaccharides, manno-oligosaccharides, chito-oligosaccharides, and human milk oligosaccharides. Moreover, their physicochemical properties and prebiotic activities are discussed as well as their contributions to intestinal health and applications in foods.

Gastrointestinal Effects and Tolerance of Nondigestible Carbohydrate Consumption

Nondigestible carbohydrates (NDCs) are food components, including nonstarch polysaccharides and resistant starches. Many NDCs are classified as dietary fibers by the US FDA. Because of their beneficial effects on human health and product development, NDCs are widely used in the food supply. Although there are dietary intake recommendations for total dietary fiber, there are no such recommendations for individual NDCs. NDCs are heterogeneous in their chemical composition and physicochemical properties-characteristics that contribute to their tolerable intake levels. Guidance on tolerable intake levels of different NDCs is needed because overconsumption can lead to undesirable gastrointestinal side effects, further widening the gap between actual and suggested fiber intake levels. In this review, we synthesize the literature on gastrointestinal effects of NDCs that the FDA accepts as dietary fibers (β-glucan, pectin, arabinoxylan, guar gum, alginate, psyllium husk, inulin, fructooligosaccharides and oligofructose, galactooligosaccharides, polydextrose, cellulose, soy fiber, resistant maltodextrin/dextrin) and present tolerable intake dose recommendations for their consumption. We summarized the findings from 103 clinical trials in adults without gastrointestinal disease who reported gastrointestinal effects, including tolerance (e.g., bloating, flatulence, borborygmi/rumbling) and function (e.g., transit time, stool frequency, stool consistency). These studies provided doses ranging from 0.75-160 g/d and lasted for durations ranging from a single-meal tolerance test to 28 wk. Tolerance was NDC specific; thus, recommendations ranged from 3.75 g/d for alginate to 25 g/d for soy fiber. Future studies should address gaps in the literature by testing a wider range of NDC doses and consumption forms (solid compared with liquid). Furthermore, future investigations should also adopt a standard protocol to examine tolerance and functional outcomes across studies consistently.

Prebiotic Potential of a New Sweetener Based on Galactooligosaccharides and Modified Mogrosides

This study was conducted to investigate the sweetness intensity and the potential fecal microbiome modulation of galactooligosaccharides in combination with enzymatically modified mogrosides (mMV-GOS), both generated through a patented single-pot synthesis. Sweetness intensity was performed in vivo by trained sensory panelists. The impact on the human fecal microbiome was evaluated by in vitro pH-controlled batch fermentation, and bacterial populations and organic acid concentrations were measured by qPCR and GC-FID, respectively. Significant growth (p ≤ 0.05) during the fermentation at 10 h of bacterial populations includes Bifidobacterium (8.49 ± 0.44 CFU/mL), Bacteroides (9.73 ± 0.32 CFU/mL), Enterococcus (8.17 ± 0.42 CFU/mL), and Clostridium coccoides (6.15 ± 0.11 CFU/mL) as compared to the negative control counts for each bacterial group (7.94 ± 0.27, 7.84 ± 1.11, 7.52 ± 0.37, and 5.81 ± 0.08 CFU/mL, respectively) at the same time of fermentation. Likewise, the corresponding significant increase in production of SCFA in mMV-GOS at 10 h of fermentation, mainly seen in acetate (20.32 ± 2.56 mM) and propionate (9.49 ± 1.44 mM) production compared to a negative control at the same time (8.15 ± 1.97 and 1.86 ± 0.24 mM), is in line with a positive control (short-chain fructooligosaccharides; 46.74 ± 12.13 and 6.51 ± 1.91 mM, respectively) revealing a selective fermentation. In conclusion, these substrates could be considered as novel candidate prebiotic sweeteners, foreseeing a feasible and innovative approach targeting the sucrose content reduction in food. This new ingredient could provide health benefits when evaluated in human studies by combining sweetness and prebiotic fiber functionality.

Evaluation of Prebiotic Properties of Galactooligosaccharides Produced by Transgalactosylation Using Partially Purified β-Galactosidase from Enterobacter aerogenes KCTC2190

Transgalactosylation reaction is the penultimate step in the production of galactooligosaccharides (GOSs) which has prominent applications in the treatment of disorders. In the present study, partially purified β-galactosidase from Enterobacter aerogenes KCTC2190 was used for the synthesis of prebiotic GOSs. GOSs were produced using lactose as substrate. Structural elucidation of collected fractions of GOSs by liquid chromatography electrospray ionization mass spectrometry exhibited the appearance of major peaks of produced GOSs at m/z 241.20, 481.39, 365.11, 527.17, and 701.51 respectively. GOSs facilitated the growth of potential probiotic strains (Lactobacillus delbrueckii ssp. helveticus, Bifidobacterium bifidum, and Lactiplantibacillus plantarum) and liberated propionate and butyrate as principal short-chain fatty acids which established its prebiotic potency. Synbiotic combinations exhibited good antioxidant activities. Synbiotic combinations also exhibited antimicrobial activities against pathogenic microorganisms namely Staphylococcus aureus and Escherichia coli. Synbiotic combinations of GOSs and the respective probiotic microorganisms were able to decrease viable human bone cancer cells (MG-63).

Contribution of polysaccharides from crustacean in fermented food products

Fermented foods are of great importance for their role in preserving nutrients and enriching the human diet. Fermentation ensures longer shelf life and microbiological safety of food. Natural bioactive compounds have been paid attention as nutraceuticals or functional ingredients, which have health-promoting components since polysaccharides, especially chitosan, chitin and their derivatives, are biocompatible and biodegradable, biorenewable, without toxic properties and environmentally friendly. They have been applied in several fields such as medicine, agriculture, and food industry. This chapter provides information on polysaccharides obtained from crustacean as bioactive compounds as well as their effects in fermented foods.

Enzymatic Synthesis and Structural Characterization of Novel Trehalose-Based Oligosaccharides

Trehalose, α-d-glucopyranosyl-(1↔1)-α-d-glucopyranoside, is a disaccharide with multiple effects on the human body. Synthesis of new trehalose derivatives was investigated through transgalactosylation reactions using β-galactosidase from four different species. β-galactosidases from Bacillus circulans (B. circulans) and Aspergillus oryzae (A. oryzae) were observed to be the best biocatalysts, using lactose as the donor and trehalose as the acceptor. Galactosyl derivatives of trehalose were characterized using nuclear magnetic resonance spectroscopy. Trisaccharides were the most abundant oligosaccharides obtained followed by the tetrasaccharide fraction (19.5% vs 8.2% carbohydrates). Interestingly, the pentasaccharide [β-Galp-(1→4)]³-trehalose was characterized for the first time. Greater oligosaccharide production was observed using β-galactosidase from B. circulans than that obtained from A. oryzae, where the main structures were based on galactose monomers linked by β-(1→6) and β-(1→4) bonds with trehalose in the ending. These results indicate the feasibility of commercially available β-galactosidases for the synthesis of trehalose-derived oligosaccharides, which might have functional properties, excluding the adverse effects of the single trehalose.

Galacto-oligosaccharides as infant prebiotics: production, application, bioactive activities and future perspectives

Galacto-oligosaccharides (GOS) are non-digestible oligosaccharides characterized by a mix of structures that vary in their degree of polymerization (DP) and glycosidic linkage between the galactose moieties or between galactose and glucose. They have enjoyed extensive scientific scrutiny, and their health-promoting effects are supported by a large number of scientific and clinical studies. A variety of GOS-associated health-promoting effects have been reported, such as growth promotion of beneficial bacteria, in particular bifidobacteria and lactobacilli, inhibition of pathogen adhesion and improvement of gut barrier function. GOS have attracted significant interest from food industries for their versatility as a bioactive ingredient and in particular as a functional component of infant formulations. These oligosaccharides are produced in a kinetically-controlled reaction involving lactose transgalactosylation, being catalyzed by particular β-galactosidases of bacterial or fungal origin. Despite the well-established technology applied for GOS production, this process may still meet with technological challenges when employed at an industrial scale. The current review will cover relevant scientific literature on the beneficial physiological properties of GOS as a prebiotic for the infant gut microbiota, details of GOS structures, the associated reaction mechanism of β-galactosidase, and its (large-scale) production.

Structure-Specific Fermentation of Galacto-Oligosaccharides, Isomalto-Oligosaccharides and Isomalto/Malto-Polysaccharides by Infant Fecal Microbiota and Impact on Dendritic Cell Cytokine Responses

SCOPE

Next to galacto-oligosaccharides (GOS), starch-derived isomalto-oligosaccharide preparation (IMO) and isomalto/malto-polysaccharides (IMMP) could potentially be used as prebiotics in infant formulas. However, it remains largely unknown how the specific molecular structures of these non-digestible carbohydrates (NDCs) impact fermentability and immune responses in infants.

METHODS AND RESULTS

In vitro fermentation of GOS, IMO and IMMP using infant fecal inoculum of 2- and 8-week-old infants shows that only GOS and IMO are fermented by infant fecal microbiota. The degradation of GOS and IMO coincides with an increase in Bifidobacterium and production of acetate and lactate, which is more pronounced with GOS. Individual isomers with an (1↔1)-linkage or di-substituted reducing terminal glucose residue are more resistant to fermentation. GOS, IMO, and IMMP fermentation digesta attenuates cytokine profiles in immature dendritic cells (DCs), but the extent is dependent on the infants age and NDC structure.

CONCLUSION

The IMO preparation, containing reducing and non-reducing isomers, shows similar fermentation patterns as GOS in fecal microbiota of 2-week-old infants. Knowledge obtained on the substrate specificities of infant fecal microbiota and the subsequent regulatory effects of GOS, IMO and IMMP on DC responses might contribute to the design of tailored NDC mixtures for infants of different age groups.

Galactooligosaccharide pretreatment alleviates damage of the intestinal barrier and inflammatory responses in LPS-challenged mice

Galactooligosaccharides (GOS) have been identified as beneficial prebiotics for animals and human beings. Most studies have focused on the effect of GOS on the hindgut populated with abundant microbes. However, few research studies have been conducted on the small intestine, and many results are inconsistent due to the purity of GOS, commonly mixed with monosaccharides or lactose. Therefore, pure GOS with definite structures were prepared and used in the present study to evaluate their effects on intestinal barrier function, inflammatory responses and short-chain fatty acids (SCFAs) produced in the colon of mice challenged with lipopolysaccharide (LPS). The results of 1H and 13C nuclear magnetic resonance spectral analyses indicated that the main structures of GOS with a degree of polymerization of 3 (trisaccharide) and 4 (tetrasaccharide) are [β-Gal-(1 → 6)-β-Gal(1 → 4)-β-Glc] and [β-Gal-(1 → 6)-β-Gal-(1 → 6)-β-Gal-(1 → 4)-β-Glc], respectively. The results of an in vivo study in mice showed that intragastric administration of 0.5 g per kg BW GOS attenuated intestinal barrier damage and inflammatory responses induced by LPS in the jejunum and ileum, as indicated by increasing villus height and villus-to-crypt ratio, up-regulated intestinal tight junction (ZO-1, occludin, and claudin-1) gene expression, and down-regulated pro-inflammatory cytokines such as IL-1β, IL-6, IFN-γ, and TNF-α gene expression. Nevertheless, the protective effects of GOS on the intestinal barrier are independent of glucagon-like peptide 2. In addition, 0.5 g per kg BW GOS administration promoted the recovery of colonic acetate, propionate, butyrate, and total SCFA production reduced by LPS challenge. The obtained results provide practical evidence that pure GOS can act as protective agents for intestinal health.

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.

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.

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.

Bringing the digestibility of prebiotics into focus: update of carbohydrate digestion models

Oro-gastrointestinal digestion of dietary carbohydrates involves up to six different carbohydrases in a multistage process. Enzymes from the small intestinal brush border membrane play a major role in the digestibility of these substrates. However, to date, the inclusion of these small intestinal enzymes has been dismissed in most in vitro studies carried out, despite their importance in the degradation of carbohydrates. Several in vitro and in vivo studies have demonstrated the capability of brush border enzymes to degrade certain "non-digestible" carbohydrates to a different extent depending on their structural composition (monomeric composition, glycosidic linkage, etc.). In this sense, considering the available evidence, mucosal disaccharidases embedded in the small intestinal brush border membrane vesicles must be considered in addition to α-amylases; therefore, new approaches for the evaluation of the digestibility of carbohydrates have been recently reported. These new methods based on the utilization of the small intestinal enzymes present in the brush border membrane aim to fulfill the final and key step of the digestion of carbohydrates in the small intestine. Here, rat small intestinal extract enzymes as well as brush border membrane vesicles from pig have emerged as very reliable and useful tools to evaluate carbohydrate digestion. Thus, this review aims to go briefly through the most relevant digestion methods for carbohydrates that are currently available and to highlight the new improved methods, which include mammalian intestinal enzymes, and their current use in the evaluation of the digestibility of prebiotics.

Hydrolysis of Lactose and Transglycosylation of Selected Sugar Alcohols by LacA β-Galactosidase from Lactobacillus plantarum WCFS1

The production, biochemical characterization, and carbohydrate specificity of LacA β-galactosidase (locus lp_3469) belonging to the glycoside hydrolase family 42 from the probiotic organism Lactobacillus plantarum WCFS1 are addressed. The β-d-galactosidase activity was maximal in the pH range of 4.0-7.0 and at 30-37 °C. High hydrolysis capacity toward the β(1 → 4) linkages between galactose and glucose (lactose) or fructose (lactulose) was found. High efficiency toward galactosyl derivative formation was observed when lactose and glycerol, xylitol, or erythritol were used. Galactosyl derivatives of xylitol were characterized for the first time as 3-O-β-d-galactopyranosyl-xylitol and 1-O-β-d-galactopyranosyl-xylitol, displaying high preference of LacA β-galactosidase for the transfer of galactosyl residues from lactose to the C1 or C3 hydroxyl group of xylitol. These results indicate the feasibility of using LacA β-galactosidase for the synthesis of different galactosyl-polyols, which could be promising candidates for beneficial and appealing functional and technological applications such as novel prebiotics or hypocaloric sweeteners.

Selective Synthesis of Galactooligosaccharides Containing β(1→3) Linkages with β-Galactosidase from Bifidobacterium bifidum (Saphera)

The transglycosylation activity of a novel commercial β-galactosidase from Bifidobacterium bifidum (Saphera) was evaluated. The optimal conditions for the operation of this enzyme, measured with o-nitrophenyl-β-d-galactopyranoside, were 40 °C and pH around 6.0. Although at low lactose concentrations the property of this enzyme was basically hydrolytic, an increase of lactose concentration to 400 g/L resulted in a significant formation (107.2 g/L, 27% yield) of prebiotic galactooligosaccharides (GOS). The maximum amount of GOS was obtained at a lactose conversion of approximately 90%, which contrasts with other β-galactosidases, for which the highest GOS yield is achieved at 40-50% lactose conversion. Using high-performance anion-exchange chromatography with pulsed amperometric detection, semipreparative high-performance liquid chromatography-hydrophilic interaction liquid chromatography, mass spectrometry, and 1D and 2D NMR, we determined the structure of most of the GOS synthesized by this enzyme. The main identified products were Gal-β(1→3)-Gal-β(1→4)-Glc (3'-O-β-galactosyl-lactose), Gal-β(1→6)-Glc (allolactose), Gal-β(1→3)-Glc (3-galactosyl-glucose), Gal-β(1→3)-Gal (3-galactobiose), and the tetrasaccharide Gal-β(1→3)-Gal-β(1→3)-Gal-β(1→4)-Glc. In general, B. bifidum β-galactosidase showed a tendency to form β(1→3) linkages followed by β(1→6) and more scarcely β(1→4).

Evaluation of the impact of a rat small intestinal extract on the digestion of four different functional fibers

The degree of digestion, modulated by rat small intestinal extract on different functional fibers was investigated.

Prebiotic galactooligosaccharides production from lactose and lactulose by Lactobacillus delbrueckii subsp. bulgaricus CRL450

Galactooligosaccharides (GOS) are useful dietary ingredients recognized worldwide as prebiotics.

Hydrolysis and transgalactosylation catalysed by β-galactosidase from brush border membrane vesicles isolated from pig small intestine: A study using lactulose and its mixtures with lactose or galactose as substrates

Enzymatic transgalactosylation, in different concentrated carbohydrate solutions, was investigated using brush border membrane vesicles (BBMV) from the pig small intestine. When lactulose was incubated with BBMV, the hydrolytic activity of the enzyme towards the disaccharide was observed to be very low compared to that towards the lactose, but the linkage specificity β-(1 → 3), previously observed in lactose solutions, was not significantly affected. As in the case of lactose, lactulose transgalactosylation by BBMV synthesizes the corresponding 3'-galactosyl derivative (β-Gal-(1 → 3)-β-Gal-(1 → 4)-β-Fru). Fructose released during lactulose hydrolysis was found to be good acceptor for the transgalactosylation reaction, giving rise to the synthesis of the disaccharide β-Gal-(1 → 5)-Fru. When incubating an 80/20 mixture of lactulose/galactose, the presence of galactose did not affect the qualitative composition of the transglycosylated substrate but enhanced the synthesis of β-Gal-(1 → 5)-Fru and decreased the synthesis of β-(1 → 3) glycosidic bonds. The marked tendency for synthesizing this linkage indicates that under hydrolytic conditions, β-Gal-(1 → 3)-Gal- and β-Gal-(1 → 5)-Fru glycosidic bonds would be preferentially digested.

In vitro Gastrointestinal Models for Prebiotic Carbohydrates: A Critical Review

Background:

In the last decade, various consortia and companies have created standardized digestion protocols and gastrointestinal simulators, such as the protocol proposed by the INFOGEST Consortium, the simulator SHIME, the simulator simgi®, the TIM, etc. Most of them claim to simulate the entire human gastrointestinal tract. However, few results have been reported on the use of these systems with potential prebiotic carbohydrates.

Methods:

This critical review addresses the existing data on the analysis of prebiotic carbohydrates by different in vitro gastrointestinal simulators, the lack of parameters that could affect the results, and recommendations for their enhancement.

Results:

According to the reviewed data, there is a lack of a realistic approximation of the small intestinal conditions, mainly because of the absence of hydrolytic conditions, such as the presence of small intestinal brush border carbohydrases that can affect the digestibility of different carbohydrates, including prebiotics.

Conclusion:

There is a necessity to standardize and enhance the small intestine simulators to study the in vitro digestibility of carbohydrates.