Synthesis of β-Galactooligosaccharides from Lactose Using Microbial β-Galactosidases

Synthesis of galactooligosaccharides with four β-galactosidases: Structural comparison of the products by HPLC, ESI-MS and NMR

Galactooligosaccharides (GOS) are lactose-derived functional ingredients applied in food products and have great potential in health protection. The conversion of lactose to GOS commonly occurs using β-galactosidases of mould, yeast and bacterial origin. The yield and structure of the resulting GOS depend on the enzyme used and the reaction conditions. This work focuses on the structural analysis of the products obtained with four commercial β-galactosidases Maxilact LGI 5000 (ML), Maxilact A4 MG (MA), Saphera 2600 L (SA) and NOLA Fit 5500 (NL) to evaluate their efficiency and specificity. HPLC, ESI-MS and NMR spectroscopy were applied to characterise the GOS preparations. GOS were separated from the reaction mixture using activated charcoal treatment. HPLC analysis confirmed that most of the monosaccharides and a part of the lactose, but also some other disaccharides, probably allolactose and 6-galactobiose, were retained by charcoal. In all the products, ESI-MS analysis detects oligosaccharides up to hexamers. NMR spectra confirmed the presence of GOS of various configurations and polymerisation degrees and evaluated the specificity of used enzymes. MA preferably forms 1,6- and 1,4-glycosidic bonds, and bacterial enzymes NL and SA also form 1,2- and 1,3- glycosidic bonds, while yeast enzyme ML cannot produce new 1,4-glycosidic bonds. The mould enzyme MA showed the highest trans-galactosylation activity, forming longer GOS oligomers than the other enzymes.

The variable structural flexibility of the Bacillus circulans β-galactosidase isoforms determines their unique functionalities

β-Galactosidase from Bacillus circulans ATCC 31382 (BgaD) is a biotechnologically important enzyme for the synthesis of β-galactooligosaccharides (GOS). Among its four isoforms, isoform A (BgaD-A) has distinct synthetic properties. Here, we present cryoelectron microscopy (cryo-EM) structures of BgaD-A and compare them with the known X-ray crystal structure of isoform D (BgaD-D), revealing substantial structural divergences between the two isoforms. In contrast to BgaD-D, BgaD-A features a flexible Big-4 domain and another enigmatic domain. The newly identified flexible region in BgaD-A is termed as "barrier domain 8," and serves as a barricade, obstructing the access of longer oligosaccharide substrates into the active site of BgaD-A. The transgalactosylation reactions catalyzed by both isoforms revealed that BgaD-A has a higher selectivity than BgaD-D in the earlier stages of the reaction and is prevailingly directed to shorter galactooligosaccharides. This study improves our understanding of the structural determinants governing β-galactosidase catalysis, with implications for tailored GOS production.

Extraction, physicochemical properties, bioactivities and application of natural sweeteners: A review

Natural sweeteners generally refer to a sweet chemical component directly extracted from nature or obtained through appropriate modifications, mainly secondary metabolites of plants. Compared to the first-generation sweeteners represented by sucrose and the second-generation sweeteners represented by sodium cyclamate, natural sweeteners usually have high sweetness, low-calorie content, good solubility, high stability, and rarely toxic side effects. Historically, researchers mainly focus on the function of natural sweeteners as substitutes for sugars in the food industry. This paper reviews the bioactivities of several typical natural sweeteners, including anti-cancer, anti-inflammatory, antioxidant, anti-bacterial, and anti-hyperglycemic activities. In addition, we have summarized the extraction, physicochemical properties, and application of natural sweeteners. The article aimed to comprehensively collate vital information about natural sweeteners and review the potentiality of tapping bioactive compounds from natural products. Hopefully, this review provides insights into the further development of natural sweeteners as therapeutic agents and functional foods.

Freshwater microalgae Nannochloropsis limnetica for the production of β-galactosidase from whey powder

This study investigated the first-ever reported use of freshwater Nannochloropsis for the bioremediation of dairy processing side streams and co-generation of valuable products, such as β-galactosidase enzyme. In this study, N. limnetica was found to grow rapidly on both autoclaved and non-autoclaved whey-powder media (referred to dairy processing by-product or DPBP) without the need of salinity adjustment or nutrient additions, achieving a biomass concentration of 1.05-1.36 g L-1 after 8 days. The species secreted extracellular β-galactosidase (up to 40.84 ± 0.23 U L-1) in order to hydrolyse lactose in DPBP media into monosaccharides prior to absorption into biomass, demonstrating a mixotrophic pathway for lactose assimilation. The species was highly effective as a bioremediation agent, being able to remove > 80% of total nitrogen and phosphate in the DPBP medium within two days across all cultures. Population analysis using flow cytometry and multi-channel/multi-staining methods revealed that the culture grown on non-autoclaved medium contained a high initial bacterial load, comprising both contaminating bacteria in the medium and phycosphere bacteria associated with the microalgae. In both autoclaved and non-autoclaved DPBP media, Nannochloropsis cells were able to establish a stable microalgae-bacteria interaction, suppressing bacterial takeover and emerging as dominant population (53-80% of total cells) in the cultures. The extent of microalgal dominance, however, was less prominent in the non-autoclaved media. High initial bacterial loads in these cultures had mixed effects on microalgal performance, promoting β-galactosidase synthesis on the one hand while competing for nutrients and retarding microalgal growth on the other. These results alluded to the need of effective pre-treatment step to manage bacterial population in microalgal cultures on DPBP. Overall, N. limnetica cultures displayed competitive β-galactosidase productivity and propensity for efficient nutrient removal on DPBP medium, demonstrating their promising nature for use in the valorisation of dairy side streams.

Prebiotic galactooligosaccharide improves piglet growth performance and intestinal health associated with alterations of the hindgut microbiota during the peri-weaning period

BACKGROUND

Weaning stress reduces growth performance and health of young pigs due in part to an abrupt change in diets from highly digestible milk to fibrous plant-based feedstuffs. This study investigated whether dietary galactooligosaccharide (GOS), supplemented both pre- and post-weaning, could improve growth performance and intestinal health via alterations in the hindgut microbial community.

METHODS

Using a 3 × 2 factorial design, during farrowing 288 piglets from 24 litters received either no creep feed (FC), creep without GOS (FG-) or creep with 5% GOS (FG+) followed by a phase 1 nursery diet without (NG-) or with 3.8% GOS (NG+). Pigs were sampled pre- (D22) and post-weaning (D31) to assess intestinal measures.

RESULTS

Creep fed pigs grew 19% faster than controls (P < 0.01) prior to weaning, and by the end of the nursery phase (D58), pigs fed GOS pre-farrowing (FG+) were 1.85 kg heavier than controls (P < 0.05). Furthermore, pigs fed GOS in phase 1 of the nursery grew 34% faster (P < 0.04), with greater feed intake and efficiency. Cecal microbial communities clustered distinctly in pre- vs. post-weaned pigs, based on principal coordinate analysis (P < 0.01). No effects of GOS were detected pre-weaning, but gruel creep feeding increased Chao1 α-diversity and altered several genera in the cecal microbiota (P < 0.05). Post-weaning, GOS supplementation increased some genera such as Fusicatenibacter and Collinsella, whereas others decreased such as Campylobacter and Frisingicoccus (P < 0.05). Changes were accompanied by higher molar proportions of butyrate in the cecum of GOS-fed pigs (P < 0.05).

CONCLUSIONS

Gruel creep feeding effectively improves suckling pig growth regardless of GOS treatment. When supplemented post-weaning, prebiotic GOS improves piglet growth performance associated with changes in hindgut microbial composition.

β-Galactosidase: a traditional enzyme given multiple roles through protein engineering

β-Galactosidases are crucial carbohydrate-active enzymes that naturally catalyze the hydrolysis of galactoside bonds in oligo- and disaccharides. These enzymes are commonly used to degrade lactose and produce low-lactose and lactose-free dairy products that are beneficial for lactose-intolerant people. β-galactosidases exhibit transgalactosylation activity, and they have been employed in the synthesis of galactose-containing compounds such as galactooligosaccharides. However, most β-galactosidases have intrinsic limitations, such as low transglycosylation efficiency, significant product inhibition effects, weak thermal stability, and a narrow substrate spectrum, which greatly hinder their applications. Enzyme engineering offers a solution for optimizing their catalytic performance. The study of the enzyme's structure paves the way toward explaining catalytic mechanisms and increasing the efficiency of enzyme engineering. In this review, the structure features of β-galactosidases from different glycosyl hydrolase families and the catalytic mechanisms are summarized in detail to offer guidance for protein engineering. The properties and applications of β-galactosidases are discussed. Additionally, the latest progress in β-galactosidase engineering and the strategies employed are highlighted. Based on the combined analysis of structure information and catalytic mechanisms, the ultimate goal of this review is to furnish a thorough direction for β-galactosidases engineering and promote their application in the food and dairy industries.

Invited review: Properties of β-galactosidases derived from Lactobacillaceae species and their capacity for galacto-oligosaccharide production

β-galactosidase (enzymatic class 3.2.1.23) is one of the dairy industry's most important and widely used enzymes. The enzyme is part of a large family known to catalyze hydrolysis and transglycosylation reactions. Its hydrolytic activity is commonly used to decrease lactose content in dairy products, while its transglycosylase activity has recently been used to synthesize galacto-oligosaccharides (GOS). During the past couple of years, researchers have focused on studying β-galactosidase isolated and purified from lactic acid bacteria. This review will focus on β-galactosidase purified and characterized from what used to be the Lactobacillus genera. Furthermore, particular emphasis is given to its kinetics, biochemical characteristics, GOS production, market, and utilization by Lactobacilllaceae species.

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.

Involvement of Versatile Bacteria Belonging to the Genus Arthrobacter in Milk and Dairy Products

Milk is naturally a rich source of many essential nutrients; therefore, it is quite a suitable medium for bacterial growth and serves as a reservoir for bacterial contamination. The genus Arthrobacter is a food-related bacterial group commonly present as a contaminant in milk and dairy products as primary and secondary microflora. Arthrobacter bacteria frequently demonstrate the nutritional versatility to degrade different compounds even in extreme environments. As a result of their metabolic diversity, Arthrobacter species have long been of interest to scientists for application in various industry and biotechnology sectors. In the dairy industry, strains from the Arthrobacter genus are part of the microflora of raw milk known as an indicator of hygiene quality. Although they cause spoilage, they are also regarded as important strains responsible for producing fermented milk products, especially cheeses. Several Arthrobacter spp. have reported their significance in the development of cheese color and flavor. Furthermore, based on the data obtained from previous studies about its thermostability, and thermoacidophilic and thermoresistant properties, the genus Arthrobacter promisingly provides advantages for use as a potential producer of β-galactosidases to fulfill commercial requirements as its enzymes allow dairy products to be treated under mild conditions. In light of these beneficial aspects derived from Arthrobacter spp. including pigmentation, flavor formation, and enzyme production, this bacterial genus is potentially important for the dairy industry.

Probiotic potential and immunomodulatory properties in Enterococcus faecium GMB24 and Enterococcus hirae SMB16 isolated from goat and sheep milk

Probiotic attributes of lactic acid bacteria isolated from goat and sheep milk samples were analysed by culturing them on an MRS agar medium. The most potential isolates, GMB24 and SMB16, were identified by biochemical tests which had ability to tolerate different concentrations of acid and bile and phenol resistance. They were further identified as Enterococcus faecium GMB24 and Enterococcus hirae SMB16 by 16S rRNA gene sequencing approach. The probiotic potential of the isolates GMB24 and SMB16 were recorded including antimicrobial activity against pathogenic bacteria viz., Escherichia coli (MTCC118), Staphylococcus aureus (MTCC7443), Pseudomonas aeruginosa (MTCC424), Listeria monocytogens (MTCC657) and Salmonella typhimurium (MTCC733), and antibiotic susceptibility test. The isolates SMB16 and GMB24 exhibited a higher zone of inhibition against P. aeruginosa (19.00 ± 0.57 mm) and S. aureus (25.66 ± 0.88 mm), respectively. The data from these experiments were used for the principal component analysis (PCA) to assess the survivability of the isolates under different factors. The heatmap generated in this study clustered the bacterial isolates based on their phenotype properties. Further, immunomodulating activities of these probiotic bacteria were tested on neutrophil adhesion test, haemagglutinating antibody titer and delayed-type hypersensitivity. Probiotic E. faecium GMB24 and E. hirae SMB16, at 10⁹ cells/mL doses per day, increased the neutrophil adhesion, haemagglutinating antibody titer and DTH in comparison to the untreated control group. The isolates showed negative test for haemolytic and gelatinase activities and hence were considered safe. E. faecium GMB24 and E. hirae SMB16 were shown to have high probiotic potential and immune-stimulant action.

Biological activity of galacto-oligosaccharides: A review

Galacto-oligosaccharides (GOS) are oligosaccharides formed by β-galactosidase transgalactosylation. GOS is an indigestible food component that can pass through the upper gastrointestinal tract relatively intact and ferment in the colon to produce short-chain fatty acids (SCFAs) that further regulate the body’s intestinal flora. GOS and other prebiotics are increasingly recognized as useful food tools for regulating the balance of colonic microbiota-human health. GOS performed well compared to other oligosaccharides in regulating gut microbiota, body immunity, and food function. This review summarizes the sources, classification, preparation methods, and biological activities of GOS, focusing on the introduction and summary of the effects of GOS on ulcerative colitis (UC), to gain a comprehensive understanding of the application of GOS.

Effect of process parameters on the β-galactosidase hydrolysis of lactose and galactooligosaccharide formation in concentrated skim milk

The study aimed at evaluation of β-galactosidase activity for lactose hydrolysis (DH) and galactooligosaccharide (GOS) formation at 7 °C. β-galactosidase derived from K. lactis was more effective than B. lichenformis for DH and GOS formation in 16% lactose solution. β-galactosidase from K. lactis exhibited 96.61% DH and 7.28% GOS production after 12 h of reaction and hence was utilized for lactose hydrolysis in concentrated skim milk (40% total solids). Use of 9.53 U/mL enzyme resulted in significantly high DH (97.06%) after 12 h with 4.90 g/L of residual lactose. However, maximum GOS formation of 12.01% with 94.74% DH was obtained after 4 h. Further increase in reaction time up to 12 h resulted in breakdown of tri and tetrasaccharide GOS, thereby, reducing GOS content. Hence, reaction time of 12 h was finalized to obtain maximum DH along with additional benefit of GOS formation.

Engineered Glycosidases for the Synthesis of Analogs of Human Milk Oligosaccharides

Enzymatic synthesis is an elegant biocompatible approach to complex compounds such as human milk oligosaccharides (HMOs). These compounds are vital for healthy neonatal development with a positive impact on the immune system. Although HMOs may be prepared by glycosyltransferases, this pathway is often complicated by the high price of sugar nucleotides, stringent substrate specificity, and low enzyme stability. Engineered glycosidases (EC 3.2.1) represent a good synthetic alternative, especially if variations in the substrate structure are desired. Site-directed mutagenesis can improve the synthetic process with higher yields and/or increased reaction selectivity. So far, the synthesis of human milk oligosaccharides by glycosidases has mostly been limited to analytical reactions with mass spectrometry detection. The present work reveals the potential of a library of engineered glycosidases in the preparative synthesis of three tetrasaccharides derived from lacto-N-tetraose (Galβ4GlcNAcβ3Galβ4Glc), employing sequential cascade reactions catalyzed by β3-N-acetylhexosaminidase BbhI from Bifidobacterium bifidum, β4-galactosidase BgaD-B from Bacillus circulans, β4-N-acetylgalactosaminidase from Talaromyces flavus, and β3-galactosynthase BgaC from B. circulans. The reaction products were isolated and structurally characterized. This work expands the insight into the multi-step catalysis by glycosidases and shows the path to modified derivatives of complex carbohydrates that cannot be prepared by standard glycosyltransferase methods.

Galacto-Oligosaccharide (GOS) Synthesis during Enzymatic Lactose-Free Milk Production: State of the Art and Emerging Opportunities

Much attention has recently been paid to β-Galactosidases (β-D-galactoside galactohidrolase; EC 3.2.1.23), commonly known as lactases, due to the lactose intolerance of the human population and the importance of dairy products in the human diet. This enzyme, produced by microorganisms, is being used in the dairy industry for hydrolyzing the lactose found in milk to produce lactose-free milk (LFM). Conventionally, β-galactosidases catalyze the hydrolysis of lactose to produce glucose and galactose in LFM; however, they can also catalyze transgalactosylation reactions that produce a wide range of galactooligosaccharides (GOS), which are functional prebiotic molecules that confer health benefits to human health. In this field, different works aims to identify novel microbial sources of β-galactosidase for removing lactose from milk with the relative GOS production. Lactase extracted from thermophilic microorganisms seems to be more suitable for the transgalactosylation process at relatively high temperatures, as it inhibits microbial contamination. Different immobilization methods, such as adsorption, covalent attachment, chemical aggregation, entrapment and micro-encapsulation, have been used to synthesize lactose-derived oligosaccharides with immobilized β-galactosidases. In this mini-review, particular emphasis has been given to the immobilization techniques and bioreactor configurations developed for GOS synthesis in milk, in order to provide a more detailed overview of the biocatalytic production of milk oligosaccharides at industrial level.

Multitasking in the gut: the X-ray structure of the multidomain BbgIII from Bifidobacterium bifidum offers possible explanations for its alternative functions

β-Galactosidases catalyse the hydrolysis of lactose into galactose and glucose; as an alternative reaction, some β-galactosidases also catalyse the formation of galactooligosaccharides by transglycosylation. Both reactions have industrial importance: lactose hydrolysis is used to produce lactose-free milk, while galactooligosaccharides have been shown to act as prebiotics. For some multi-domain β-galactosidases, the hydrolysis/transglycosylation ratio can be modified by the truncation of carbohydrate-binding modules. Here, an analysis of BbgIII, a multidomain β-galactosidase from Bifidobacterium bifidum, is presented. The X-ray structure has been determined of an intact protein corresponding to a gene construct of eight domains. The use of evolutionary covariance-based predictions made sequence docking in low-resolution areas of the model spectacularly easy, confirming the relevance of this rapidly developing deep-learning-based technique for model building. The structure revealed two alternative orientations of the CBM32 carbohydrate-binding module relative to the GH2 catalytic domain in the six crystallographically independent chains. In one orientation the CBM32 domain covers the entrance to the active site of the enzyme, while in the other orientation the active site is open, suggesting a possible mechanism for switching between the two activities of the enzyme, namely lactose hydrolysis and transgalactosylation. The location of the carbohydrate-binding site of the CBM32 domain on the opposite site of the module to where it comes into contact with the catalytic GH2 domain is consistent with its involvement in adherence to host cells. The role of the CBM32 domain in switching between hydrolysis and transglycosylation modes offers protein-engineering opportunities for selective β-galactosidase modification for industrial purposes in the future.

β-Galactosidase from Kluyveromyces lactis: Characterization, production, immobilization and applications - A review

A review on the enzyme β-galactosidase from Kluyveromyces lactis is presented, from the perspective of its structure and mechanisms of action, the main catalyzed reactions, the key factors influencing its activity, and selectivity, as well as the main techniques used for improving the biocatalyst functionality. Particular attention was given to the discussion of hydrolysis, transglycosylation, and galactosylation reactions, which are commonly mediated by this enzyme. In addition, the products generated from these processes were highlighted. Finally, biocatalyst improvement techniques are also discussed, such as enzyme immobilization and protein engineering. On these topics, the most recent immobilization strategies are presented, emphasizing processes that not only allow the recovery of the biocatalyst but also deliver enzymes that show better resistance to high temperatures, chemicals, and inhibitors. In addition, genetic engineering techniques to improve the catalytic properties of the β-galactosidases were reported. This review gathers information to allow the development of biocatalysts based on the β-galactosidase enzyme from K. lactis, aiming to improve existing bioprocesses or develop new ones.

An improved method for galactosyl oligosaccharide characterization

Due to beneficial effects of galactosyl oligosaccharides (GOS) on digestive and immune health, their characterization has become increasingly important. This is especially so as GOS are synthesized enzymatically and contain oligosaccharides of different sizes and linkages. High performance anion exchange chromatography with pulsed amperometric detection (HPAE-PAD) is widely used for GOS characterization. With its high resolving power, it can separate structural isomers. Here we present a significant improvement to currently used methods. Our approach combines high resolution HPAE separation on a CarboPac PA300 column with 4 µm particle size with PAD and Orbitrap mass spectrometry (MS) detections to provide in-depth information on GOS composition. Oligosaccharide resolution, especially in the disaccharide region, is significantly improved and can be routinely achieved. Improvement in technology to remove sodium before MS results in minimal peak dispersion, allowing GOS degrees of polymerization 2 to 6 to be identified based on mass spectra obtained from intact oligosaccharides and confirmed using fragmentation patterns observed in MS/MS data. Combining HPAE with MS led to identification of 28 oligosaccharides in a commercial GOS sample. We attempted to correlate oligosaccharide structure with observed elution behavior. To our knowledge this is first such attempt and can form a basis for a comprehensive structure vs HPAE elution behavior database.

Composition analysis and oral administered effects on dextran sulfate sodium-induced colitis of galactooligosaccharides bioconverted by Bacillus circulans

Galactooligosaccharides have been known to have many health benefits as prebiotic ingredients. In this study, we examined the anti-inflammatory activity of the galactooligosaccharide, NeoGOS-P70 (Korean commercial product), in a dextran sodium sulfate-induced colitis model. Next, we performed compositional characterization of NeoGOS-P70, which confirmed that it was a 77.4% high-purity GOS products, including a large amount of 4'-galactosyllactose. Further experiments in DSS-induced colitis model showed that oral administration of NeoGOS-P70 could significantly improve DSS-induced colitis symptoms, such as weight loss, reduction in colon shortening, and suppression of inflammatory mediators, including interleukin-6, tumor necrosis factor-α, and myeloperoxidase secretion from colon of ulcerative colitis mice. Histological analysis of mucin expression in colon tissue revealed the protective effects of NeoGOS-P70. These results suggest the potential of the novel GOS, NeoGOS-P70, as an anti-ulcerative colitis agent that could regulate inflammatory responses.

Synthesis of magnetic nanoparticles functionalized with histidine and nickel to immobilize His-tagged enzymes using β-galactosidase as a model

The aim of this study was to synthesize iron magnetic nanoparticles functionalized with histidine and nickel (Fe₃O₄-His-Ni) to be used as support materials for oriented immobilization of His-tagged recombinant enzymes of high molecular weight, using β-galactosidase as a model. The texture, morphology, magnetism, thermal stability, pH and temperature reaction conditions, and the kinetic parameters of the biocatalyst obtained were assessed. In addition, the operational stability of the biocatalyst in the lactose hydrolysis of cheese whey and skim milk by batch processes was also assessed. The load of 600 U_enzyme/g_support showed the highest recovered activity value (~50%). After the immobilization process, the recombinant β-galactosidase (HisGal) showed increased substrate affinity and greater thermal stability (~50×) compared to the free enzyme. The immobilized β-galactosidase was employed in batch processes for lactose hydrolysis of skim milk and cheese whey, resulting in hydrolysis rates higher than 50% after 15 cycles of reuse. The support used was obtained in the present study without modifying chemical agents. The support easily recovered from the reaction medium due to its magnetic characteristics. The iron nanoparticles functionalized with histidine and nickel were efficient in the oriented immobilization of the recombinant β-galactosidase, showing its potential application in other high-molecular-weight enzymes.

Production of a synbiotic composed of galacto-oligosaccharides and Saccharomyces boulardii using enzymatic-fermentative method

Motivated by the search for healthy alimentation and sustainable technological processes, this study aimed to produce a synbiotic composed of the prebiotic galacto-oligosaccharides (GOS) and the probiotic yeast Saccharomyces boulardii, simultaneously, using cheese whey permeate as substrate by enzymatic-fermentative method. A central composite rotatable design with center point was used to evaluate the influence of temperature and enzyme concentration in the GOS and S. boulardii production. The best condition to obtain the prebiotic was at 32 °C and enzyme concentration of 0.175% (w/w), providing 56.84 g L^-1 of GOS concentration and Ln(3.59) 10⁷ viable cells mL^-1 of S. boulardii production. However, the condition that would favor the simultaneous production of GOS and S. boulardii studied through desirability function is 29.5 °C and 0.14% (w/w) of enzyme concentration. The simultaneous enzymatic-fermentative method showed promising results considering industrial application and can be easily incorporated into dairy production lines as functional food.

The impact of oligosaccharide content, glycosidic linkages and lactose content of galacto-oligosaccharides (GOS) on the expression of mucus-related genes in goblet cells

Galacto-oligosaccharides (GOS) have been reported to modulate the function of intestinal goblet cells and to improve mucus barrier function. However, GOS is available in many structurally different compositions and it is unknown how GOS structural diversity impacts this modulation of goblet cells. This study aims to investigate the effects of oligosaccharide content and glycosidic linkages of GOS on expression of genes associated with the secretory function of goblet cells. To investigate the effect of oligosaccharide content, LS174T cells were incubated with (β1 → 4)GOS of variable transgalactosylated oligosaccharides and lactose (Lac) composition. To investigate the effect of glycosidic linkages, we compared the effects of (β1 → 4)GOS with (β1 → 3)GOS, and with a mixture of α-linked oligosaccharides (lactose-derived oligosaccharides-LDO). The changes in mRNA expression of mucus-related genes were assessed by RT-PCR. GOS containing Lac significantly enhanced the expression of MUC2, TFF3 and RETNLB but not of Golgi sulfotransferases genes. In contrast, GOS without Lac did not impact these genes. Lac alone significantly enhanced MUC2, TFF3, RETNLB, CHST5, and GAL3ST2 genes suggesting that Lac might be responsible for goblet cell modulation in (β1 → 4)GOS preparations. (β1 → 3)GOS induced the expression of MUC2 and TFF3, and downregulated the RETNLB gene. Compared with the (β1 → 3) and GOS (β1 → 4)GOS, the α-linked LDO significantly upregulated the expression MUC2, TFF3, RETNLB and the Golgi sulfotransferases genes. We identify structural features of GOS that contribute to enhanced mucus integrity. Our study might lead to better GOS formulations for foods to prevent or treat different types of intestinal disorders.

Effect of the lactose source on the ultrasound-assisted enzymatic production of galactooligosaccharides and gluconic acid

It is well known that one of the main problems in galactooligosaccharide production (GOS) via tranglycosylation of lactose is the presence of monosaccharides that contribute to increasing the glycaemic index, as is the case of glucose. In this work, as well as studying the effect of ultrasound (US) on glucose oxidase (Gox) activation during gluconic acid (GA) production, we have carried out an investigation into the selective oxidation of glucose to gluconic acid in multienzymatic reactions (β-galactosidase (β-gal) and Gox) assisted by power US using different sources of lactose as substrate (lactose solution, whey permeate, cheese whey). In terms of the influence of matrix on GOS and GA production, lactose solution gave the best results, followed by cheese whey and whey permeate, salt composition being the most influential factor. The highest yields of GOS production with the lowest glucose concentration and highest GA production were obtained with lactose solution in multienzymatic systems in the presence of ultrasound (30% amplitude) when Gox was added after 1 h of treatment with β-gal. This work demonstrates the ability of US to enhance efficiently the obtainment of prebiotic mixtures of low glycaemic index.

Technological Aspects of the Production of Fructo and Galacto-Oligosaccharides. Enzymatic Synthesis and Hydrolysis

Fructo- and galacto-oligosaccharides (FOS and GOS) are non-digestible oligosaccharides with prebiotic properties that can be incorporated into a wide number of products. This review details the general outlines for the production of FOS and GOS, both by enzymatic synthesis using disaccharides or other substrates, and by hydrolysis of polysaccharides. Special emphasis is laid on technological aspects, raw materials, properties, and applications.

Trans-β-galactosidase activity of pig enzymes embedded in the small intestinal brush border membrane vesicles

This work highlights the utility of brush border membrane vesicles (BBMV) from the pig small intestine as a reliable model for gathering information about the reaction mechanisms involved in the human digestion of dietary carbohydrates. Concretely, the elucidation of the transgalactosylation mechanism of pig BBMV to synthesize prebiotic galacto-oligosaccharides (GOS) is provided, unravelling the catalytic activity of mammalian small intestinal β-galactosidase towards the hydrolysis of GOS. This study reveals that pig BBMV preferably synthesizes GOS linked by β-(1 → 3) bonds, since major tri- and disaccharide were produced by the transfer of a galactose unit to the C-3 of the non-reducing moiety of lactose and to the C-3 of glucose, respectively. Therefore, these results point out that dietary GOS having β-(1 → 3) as predominant glycosidic linkages could be more prone to hydrolysis by mammalian intestinal digestive enzymes as compared to those linked by β-(1 → 2), β-(1 → 4), β-(1 ↔ 1) or β-(1 → 6). Given that these data are the first evidence on the transglycosylation activity of mammalian small intestinal glycosidases, findings contained in this work could be crucial for future studies investigating the structure-small intestinal digestibility relationship of a great variety of available prebiotics, as well as for designing tailored fully non-digestible GOS.

Structural and functional characterization of a family GH53 β-1,4-galactanase from Bacteroides thetaiotaomicron that facilitates degradation of prebiotic galactooligosaccharides

Galactooligosaccharides (GOS) are prebiotic compounds synthesized from lactose using bacterial enzymes and are known to stimulate growth of beneficial bifidobacteria in the human colon. Bacteroides thetaiotaomicron is a prominent human colon commensal bacterial species that hydrolyzes GOS using an extracellular Glycosyl Hydrolase (GH) family GH53 endo-galactanase enzyme (BTGH53), releasing galactose-based products for growth. Here we dissect the molecular basis for GOS activity of this B. thetaiotaomicron GH53 endo-galactanase. Elucidation of its X-ray crystal structure revealed that BTGH53 has a relatively open active site cleft which was not observed with the bacterial enzyme from Bacillus licheniformis (BLGAL). BTGH53 acted on GOS with degree of polymerization ≤3 and therefore more closely resembles activity of fungal GH53 enzymes (e.g. Aspergillus aculeatus AAGAL and Meripileus giganteus MGGAL). Probiotic lactobacilli that lack galactan utilization systems constitute a group of bacteria with relevance for a healthy (infant) gut. The strains tested were unable to use GOS ≥ DP3. However, they completely consumed GOS in the presence of BTGH53, resulting in clear stimulation of their extent of growth. The extracellular BTGH53 enzyme thus may play an important role in carbohydrate metabolism in complex microbial environments such as the human colon. It also may find application for the development of synergistic synbiotics.

Heterologous Expression of a Thermostable β-1,3-Galactosidase and Its Potential in Synthesis of Galactooligosaccharides

A thermostable β-1,3-galactosidase from Marinomonas sp. BSi20414 was successfully heterologously expressed in Escherichia coli BL21 (DE3), with optimum over-expression conditions as follows: the recombinant cells were induced by adding 0.1 mM of IPTG to the medium when the OD600 of the culture reached between 0.6 and 0.9, followed by 22 h incubation at 20 °C. The recombinant enzyme β-1,3-galactosidase (rMaBGA) was further purified to electrophoretic purity by immobilized metal affinity chromatography and size exclusion chromatography. The specific activity of the purified enzyme was 126.4 U mg-1 at 37 °C using ONPG (o-nitrophenyl-β-galactoside) as a substrate. The optimum temperature and pH of rMaBGA were determined as 60 °C and 6.0, respectively, resembling with its wild-type counterpart, wild type (wt)MaBGA. However, rMaBGA and wtMaBGA displayed different thermal stability and steady-state kinetics, although they share identical primary structures. It is postulated that the stability of the enzyme was altered by heterologous expression with the absence of post-translational modifications such as glycosylation, as well as the steady-state kinetics. To evaluate the potential of the enzyme in synthesis of galactooligosaccharides (GOS), the purified recombinant enzyme was employed to catalyze the transgalactosylation reaction at the lab scale. One of the transgalactosylation products was resolved as 3'-galactosyl-lactose, which had been proven to be a better bifidogenic effector than GOS with β-1,4 linkage and β-1,6 linkages. The results indicated that the recombinant enzyme would be a promising alternative for biosynthesis of GOS mainly with β-1,3 linkage.

Immunomodulatory Effects of Enzymatic-Synthesized α-Galactooligosaccharides and Evaluation of the Structure-Activity Relationship

In this study, α-galactooligosaccharides (α-GOSs) were synthesized using galactose as the substrate and α-galactosidase from Aspergillus niger as the catalyst. In the reaction, synthesized products of U1, U2, U3, and U4 were detected by high-performance liquid chromatography. By mass spectrometry, nuclear magnetic resonance, and 1-phenyl-3-methyl-5-pyrazolone derivatization, U1 was the mixture of disaccharides of α-d-Gal p-(1→1)-α-d-Gal, α-d-Gal p-(1→2)-α-d-Gal, α-d-Gal p-(1→3)-α-d-Gal, α-d-Gal p-(1→4)-α-d-Gal, U2 was identified to be α-d-Gal p-(1→6)-α-d-Gal, U3 was the mixture of galactotrisaccharides linked by one α-(1→6)-glycosidic linkage and one other α-glycosidic linkage, and U4 was identified as α-d-Gal p-(1→6)-α-d-Gal p-(1→6)-α-d-Gal. Afterward, the synthesized α-GOSs (U1, U2, U3, U4, and their mixture) as well as α-GOSs (manninotriose, stachyose, ciceritol, and verbascose) obtained from natural materials were used as subjects to evaluate their immunomodulatory effects in vitro by culturing mouse macrophage RAW264.7 cells. The results showed that α-GOS with a higher degree of polymerization had better immunomodulatory activity, while to a certain extent, α-GOS linked with α-(1→6)-galactosidic linkage showed a better immunomodulatory effect.

Impact of ultrasound on galactooligosaccharides and gluconic acid production throughout a multienzymatic system

Galactooligosaccharides (GOS), recognised prebiotic, can be industrially produced from lactose and commercial β-galactosidase (β-gal) from Kluyveromyces lactis. Residual lactose and glucose limit GOS applications. To handle this problem, a multienzymatic system, with β-gal and glucose oxidase (Gox), was proposed to reduce glucose content in reaction media through its oxidation to gluconic acid (GA). Besides, ultrasound (US) probe effect over the multienzymatic system to produce GOS and GA has been evaluated. A production around 40% of GOS was found in all treatments after the first hour of reaction. However, glucose consumption and GA production was significantly higher (P < 0.05) for sequential reaction assisted by US, obtaining the best production of GOS (49%) and GA (28%) after 2 h of reaction. The conformational and residual activity changes of enzymes under US conditions were also evaluated, Gox being positively affected whereas in β-gal hardly any change was found.

Eu/Tb luminescence for alkaline phosphatase and β-galactosidase assay in hydrogels and on paper devices

Simple technologies for efficient detection of important (bio)molecules are always in great demand. We now report the detection and assay of two biologically important enzymes, alkaline phosphatase and β-galactosidase, in Eu- or Tb-based cholate hydrogels, respectively, and on filter paper discs coated with such hydrogels. Pro-sensitizers derived from 1-hydroxypyrene and 2,3-dihydroxynaphthalene were incorporated into Eu or Tb cholate hydrogels, respectively. Upon enzyme action, these artificial substrates liberate free sensitizers both in the gel and on gel-coated discs, resulting in turn-on luminescence, red/magenta for Eu, and green for Tb. The detection of enzymes was also demonstrated in natural/biological samples using low-cost systems.

Assessment of in Vitro Digestibility of Dietary Carbohydrates Using Rat Small Intestinal Extract

There are few studies on the assessment of digestibility of nondigestible carbohydrates, despite their increasingly important role in human health. In vitro digestibility of a range of dietary carbohydrates classified as digestible (maltose, sucrose, and lactose), well-recognized (lactulose, fructooligosaccharides (FOS), and two types of galactooligosaccharides (GOS) differing in the predominant glycosidic linkage), and potential (lactosucrose and GOS from lactulose, OsLu) prebiotics using a rat small intestinal extract (RSIE) under physiological conditions of temperature and pH is described. Recognized and potential prebiotics were highly resistant to RSIE digestion although partial hydrolysis at different extents was observed. FOS and lactulose were the most resistant to digestion, followed closely by OsLu and more distantly by both types of GOS and lactosucrose. In GOS, β(1 → 6) linkages were more resistant to digestion than β(1 → 4) bonds. The reported in vitro digestion model is a useful, simple, and cost-effective tool to evaluate the digestibility of dietary oligosaccharides.

Biochemical Characterization of the Functional Roles of Residues in the Active Site of the β-Galactosidase from Bacillus circulans ATCC 31382

The β-galactosidase enzyme from Bacillus circulans ATCC 31382 BgaD is widely used in the food industry to produce prebiotic galactooligosaccharides (GOS). Recently, the crystal structure of a C-terminally truncated version of the enzyme (BgaD-D) has been elucidated. The roles of active site amino acid residues in β-galactosidase enzyme reaction and product specificity have remained unknown. On the basis of a structural alignment of the β-galactosidase enzymes BgaD-D from B. circulans and BgaA from Streptococcus pneumoniae, and the complex of BgaA with LacNAc, we identified eight active site amino acid residues (Arg185, Asp481, Lys487, Tyr511, Trp570, Trp593, Glu601, and Phe616) in BgaD-D. This study reports an investigation of the functional roles of these residues, using site-directed mutagenesis, and a detailed biochemical characterization and product profile analysis of the mutants obtained. The data show that these residues are involved in binding and positioning of the substrate and thus determine the BgaD-D activity and product linkage specificity. This study provides detailed insights into the structure-function relationships of the B. circulans BgaD-D enzyme, especially regarding GOS product linkage specificity, allowing the rational mutation of β-galactosidase enzymes to produce specific mixtures of GOS structures.

Engineering of the Bacillus circulans β-Galactosidase Product Specificity

Microbial β-galactosidase enzymes are widely used as biocatalysts in industry to produce prebiotic galactooligosaccharides (GOS) from lactose. GOS mixtures are used as beneficial additives in infant formula to mimic the prebiotic effects of human milk oligosaccharides (hMOS). The structural variety in GOS mixtures is significantly lower than in hMOS. Since this structural complexity is considered as the basis for the multiple biological functions of hMOS, it is important to broaden the variety of GOS structures. In this study, residue R484 near +1 subsite of the C-terminally truncated β-galactosidase from Bacillus circulans (BgaD-D) was subjected to site saturation mutagenesis. Especially the R484S and R484H mutant enzymes displayed significantly altered enzyme specificity, leading to a new type of GOS mixture with altered structures and linkage types. The GOS mixtures produced by these mutant enzymes contained 14 structures that were not present in the wild-type enzyme GOS mixture; 10 of these are completely new structures. The GOS produced by these mutant enzymes contained a combination of (β1 → 3) and (β1 → 4) linkages, while the wild-type enzyme has a clear preference toward (β1 → 4) linkages. The yield of the trisaccharide β-d-Galp-(1 → 3)-β-d-Galp-(1 → 4)-d-Glcp produced by mutants R484S and R484H increased 50 times compared to that of the wild-type enzyme. These results indicate that residue R484 is crucial for the linkage specificity of BgaD-D. This is the first study showing that β-galactosidase enzyme engineering results in an altered GOS linkage specificity and product mixture. The more diverse GOS mixtures produced by these engineered enzymes may find industrial applications.

Infant food applications of complex carbohydrates: Structure, synthesis, and function

Professional health bodies such as the World Health Organization (WHO), the American Academy of Pediatrics (AAP), and the U.S. Department of Health and Human Services (HHS) recommend breast milk as the sole source of food during the first year of life. This position recognizes human milk as being uniquely suited for infant nutrition. Nonetheless, most neonates in the West are fed alternatives by 6 months of age. Although inferior to human milk in most aspects, infant formulas are able to promote effective growth and development. However, while breast-fed infants feature a microbiota dominated by bifidobacteria, the bacterial flora of formula-fed infants is usually heterogeneous with comparatively lower levels of bifidobacteria. Thus, the objective of any infant food manufacturer is to prepare a product that results in a formula-fed infant developing a breast-fed infant-like microbiota. The goal of this focused review is to discuss the structure, synthesis, and function of carbohydrate additives that play a role in governing the composition of the infant microbiome and have other health benefits.

The Influence of Prebiotics on Neurobiology and Behavior

Manipulating the intestinal microbiota for the benefit of the brain is a concept that has become widely acknowledged. Prebiotics are nondigestible nutrients (i.e., fibers, carbohydrates, or various saccharides) that proliferate intrinsic, beneficial gut bacteria, and so provide an alternative strategy for effectively altering the enteric ecosystem, and thence brain function. Rodent studies demonstrating neurobiological changes following prebiotic intake are slowly emerging, and have thus far revealed significant benefits in disease models, including antiinflammatory and neuroprotective actions. There are also compelling data showing the robust and favorable effects of prebiotics on several behavioral paradigms including, anxiety, learning, and memory. At present, studies in humans are limited, though there is strong evidence for prebiotics modulating emotional processes and the neuroendocrine stress response that may underlie the pathophysiology of anxiety. While the mechanistic details linking the enteric microbiota to the central nervous system remain to be elucidated, there are a number of considerations that can guide future studies. These include the modulation of intestinal endocrine systems and inflammatory cascades, as well as direct interaction with the enteric nervous system and gut mucosa. Our knowledge of gut microbiome-brain communication is steadily progressing, and thorough investigations validating the use of prebiotics in the treatment of neuropsychiatric disorders would be highly valued and are encouraged.