Production and physiological action of the disaccharide lactulose

Technological and sensory characteristics in development of innovative symbiotic boneless dry-cured lamb meat snack

Novel shelf-stable and high-protein meat products that are affordable, convenient, and healthy are hot topic in current food innovation trends. To offer technological databases for developing new functional lamb meat products, this study aimed to evaluate the technological and sensory aspects of dry-cured lamb meat snacks incorporated with the probiotic culture Lactobacillus paracasei and the prebiotic lactulose. Four formulations were analyzed: control (without prebiotic or probiotic); PREB (with 2% lactulose); PROB (with 107 CFU/g of L. paracasei); and SYMB (with 2% lactulose and 107 CFU/g of L. paracasei). Fitted curves revealed that weight-loss behavior during snack ripening was not affected (P > 0.05) by treatments. Snack moisture, water activity, pH, titratable acidity, lipid oxidation, and residual nitrite were affected (P < 0.05) only by ripening time. The target probiotic strain stood out against competitive flora and was detected at 107 CFU/g in the snack-supplemented formulations (PROB and SYMB). In snacks supplemented with prebiotics (PREB and SYMB), the lactulose content was maintained at 2.17%. Significant differences were not observed in the chemical composition, texture profiles, and CIE color indices between the proposed functional snacks and the control. In addition to texture, flavor, and overall impression evaluation, only color attributes were positively impacted (P < 0.05) in the acceptance and multiple comparison tests against the control. The proposed formulation and bench process parameters produced potential nutritionally and sensory-appreciated, microbiologically stable, and safe (multi-hurdle perspective) functional high-protein restructured lamb snacks.

Production of lactulose from lactose using a novel cellobiose 2-epimerase from Clostridium disporicum

Lactulose is a semisynthetic nondigestive sugar derived from lactose, with wide applications in the food and pharmaceutical industries. Its biological production routes which use cellobiose 2-epimerase (C2E) as the key enzyme have attracted widespread attention. In this study, a set of C2Es from different sources were overexpressed in Escherichia coli to produce lactulose. We obtained a novel and highly efficient C2E from Clostridium disporicum (CDC2E) to synthesize lactulose from lactose. The effects of different heat treatment conditions, reaction pH, reaction temperature, and substrate concentrations were investigated. Under the optimum biotransformation conditions, the final concentration of lactulose was up to 1.45 M (496.3 g/L), with a lactose conversion rate of 72.5 %. This study provides a novel C2E for the biosynthesis of lactulose from low-cost lactose.

Quantitative analysis of drug tablet aging by fast hyper-spectral stimulated Raman scattering microscopy

Pharmaceutical development of solid-state formulations requires testing active pharmaceutical ingredients (API) and excipients for uniformity and stability. Solid-state properties such as component distribution and grain size are crucial factors that influence the dissolution profile, which greatly affect drug efficacy and toxicity, and can only be analyzed spatially by chemical imaging (CI) techniques. Current CI techniques such as near infrared microscopy and confocal Raman spectroscopy are capable of high chemical and spatial resolution but cannot achieve the measurement speeds necessary for integration into the pharmaceutical production and quality assurance processes. To fill this gap, we demonstrate fast chemical imaging by epi-detected sparse spectral sampling stimulated Raman scattering to quantify API and excipient degradation and distribution.

A precise swaying map for how promiscuous cellobiose-2-epimerase operate bi-reaction

Promiscuous enzymes play a crucial role in organism survival and new reaction mining. However, comprehensive mapping of the catalytic and regulatory mechanisms hasn't been well studied due to the characteristic complexity. The cellobiose 2-epimerase from Caldicellulosiruptor saccharolyticus (CsCE) with complex epimerization and isomerization was chosen to comprehensively investigate the promiscuous mechanisms. Here, the catalytic frame of ring-opening, cis-enediol mediated catalysis and ring-closing was firstly determined. To map the full view of promiscuous CE, the structure of CsCE complex with the isomerized product glucopyranosyl-β1,4-fructose was determined. Combined with computational calculation, the promiscuity was proved a precise cooperation of the double subsites, loop rearrangement, and intermediate swaying. The flexible loop was like a gear, whose structural reshaping regulates the sway of the intermediates between the two subsites of H377-H188 and H377-H247, and thus regulates the catalytic directions. The different protonated states of cis-enediol intermediate catalyzed by H188 were the key point for the catalysis. The promiscuous enzyme tends to utilize all elements at hand to carry out the promiscuous functions.

Safety of 3-fucosyllactose (3-FL) produced by a derivative strain of Escherichia coli K-12 DH1 as a novel food pursuant to Regulation (EU) 2015/2283

Following a request from the European Commission, the EFSA Panel on Nutrition, Novel Foods and Food Allergens (NDA) was asked to deliver an opinion on 3-fucosyllactose (3-FL) as a novel food (NF) pursuant to Regulation (EU) 2015/2283. The NF is mainly composed of the human-identical milk oligosaccharide (HiMO) 3-FL, but it also contains d-lactose, l-fucose, 3-fucosyllactulose and a small fraction of other related saccharides. The NF is produced by fermentation by a genetically modified strain (Escherichia coli K-12 DH1 MDO MAP1834) of E. coli K-12 DH1 (DSM 4235). The information provided on the manufacturing process, composition and specifications of the NF does not raise safety concerns. The applicant intends to add the NF to a variety of foods, including infant formula and follow-on formula, food for special medical purposes and food supplements (FS). The target population is the general population. The anticipated daily intake of 3-FL from both proposed and combined (authorised and proposed) uses at their respective maximum use levels in all population categories does not exceed the highest intake level of 3-FL from human milk in infants on a body weight basis. The intake of 3-FL in breastfed infants on a body weight basis is expected to be safe also for other population groups. The intake of other carbohydrate-type compounds structurally related to 3-FL is also considered of no safety concern. FS are not intended to be used if other foods with added 3-FL or human milk are consumed on the same day. The Panel concludes that the NF is safe under the proposed conditions of use.

Effects of Flash Evaporation Conditions on the Quality of UHT Milk by Changing the Dissolved Oxygen Content in Milk

This study assessed the impact of reducing dissolved oxygen (DO) content on the quality of UHT milk using a flash deoxygenation treatment. Flash deoxygenation was designed based on preheated milk reaching boiling early under low-pressure conditions to remove DO from the milk. Two parameters were designed for flash deoxygenation: preheating temperature 65 °C, -0.08 Mpa, and 70 °C, -0.06 Mpa. The flash conditions were applied to two UHT sterilization conditions (135 °C for 10 s and 145 °C for 5 s). After deoxygenation, the total oxidation (TOTOX) value of UHT milk was reduced by 1.4~1.71, and the protein carbonyl (PC) value was reduced by 1.15~1.52 nmol/mg of protein. The maximum inhibition rates of furusine and 5-HMF were 33.23 ± 1.72% and 25.43 ± 3.14%, respectively. The particle size was reduced by 0.141~0.178 μm. The ketones and stale aldehydes causing oxidized taste in the UHT milk were significantly reduced. This study showed that the oxidation and Maillard reactions of UHT milk were significantly inhibited, stability was improved, and the content of undesirable volatile flavor substances was reduced after flash deoxygenation. Therefore, reducing DO content was beneficial to improving the quality of UHT milk.

Lactulose production from lactose isomerization by chemo-catalysts and enzymes: Current status and future perspectives

Lactulose, a semisynthetic nondigestive disaccharide with versatile applications in the food and pharmaceutical industries, has received increasing interest due to its significant health-promoting effects. Currently, industrial lactulose production is exclusively carried out by chemical isomerization of lactose via the Lobry de Bruyn-Alberda van Ekenstein (LA) rearrangement, and much work has been directed toward improving the conversion efficiency in terms of lactulose yield and purity by using new chemo-catalysts and integrated catalytic-purification systems. Lactulose can also be produced by an enzymatic route offering a potentially greener alternative to chemo-catalysis with fewer side products. Compared to the controlled trans-galactosylation by β-galactosidase, directed isomerization of lactose with high isomerization efficiency catalyzed by the most efficient lactulose-producing enzyme, cellobiose 2-epimerase (CE), has gained much attention in recent decades. To further facilitate the industrial translation of CE-based lactulose biotransformation, numerous studies have been reported on improving biocatalytic performance through enzyme mediated molecular modification. This review summarizes recent developments in the chemical and enzymatic production of lactulose. Related catalytic mechanisms are also highlighted and described in detail. Emerging techniques that aimed at advancing lactulose production, such as the boronate affinity-based technique and molecular biological techniques, are reviewed. Finally, perspectives on challenges and opportunities in lactulose production and purification are also discussed.

Altered Intestinal Production of Volatile Fatty Acids in Dogs Triggered by Lactulose and Psyllium Treatment

The intestinal microbiome of dogs can be influenced by a number of factors such as non-starch polysaccharides as well as some non-digestible oligo- and disaccharides. These molecules are only decomposed by intestinal anaerobic microbial fermentation, resulting in the formation of volatile fatty acids (VFAs), which play a central role in maintaining the balance of the intestinal flora and affecting the health status of the host organism. In the present study, the effects of lactulose and psyllium husk (Plantago ovata) were investigated regarding their influence on concentrations of various VFAs produced by the canine intestinal microbiome. Thirty dogs were kept on a standard diet for 15 days, during which time half of the animals received oral lactulose once a day, while the other group was given a psyllium-supplemented diet (in 0.67 and in 0.2 g/kg body weight concentrations, respectively). On days 0, 5, 10 and 15 of the experiment, feces were sampled from the rectum, and the concentration of each VFA was determined by GC-MS (gas chromatography−mass spectrometry). Lactulose administration caused a significant increase in the total VFA concentration of the feces on days 10 and 15 of the experiment (p = 0.035 and p < 0.001, respectively); however, in the case of psyllium supplementation, the concentration of VFAs showed a significant elevation only on day 15 (p = 0.003). Concentrations of acetate and propionate increased significantly on days 5, 10 and 15 after lactulose treatment (p = 0.044, p = 0.048 and p < 0.001, respectively). Following psyllium administration, intestinal acetate, propionate and n-butyrate production were stimulated on day 15, as indicated by the fecal VFA levels (p = 0.002, p = 0.035 and p = 0.02, respectively). It can be concluded that both lactulose and psyllium are suitable for enhancing the synthesis of VFAs in the intestines of dogs. Increased acetate and propionate concentrations were observed following the administration of both supplements; however, elevated n-butyrate production was found only after psyllium treatment, suggesting that the applied prebiotics may exert slightly different effects in the hindgut of dogs. These findings can be also of great importance regarding the treatment and management of patients suffering from intestinal disorders as well as hepatic encephalopathy due to portosystemic shunt.

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.

Low-Dose Lactulose as a Prebiotic for Improved Gut Health and Enhanced Mineral Absorption

Although medium and high doses of lactulose are used routinely for the treatment of constipation and hepatic encephalopathy, respectively, a wealth of evidence demonstrates that, at low doses, lactulose can also be used as a prebiotic to stimulate the growth of health-promoting bacteria in the gastrointestinal tract. Indeed, multiple preclinical and clinical studies have shown that low doses of lactulose enhance the proliferation of health-promoting gut bacteria (e.g., Bifidobacterium and Lactobacillus spp.) and increase the production of beneficial metabolites [e.g., short-chain fatty acids (SCFAs)], while inhibiting the growth of potentially pathogenic bacteria (e.g., certain clostridia). SCFAs produced upon microbial fermentation of lactulose, the most abundant of which is acetate, are likely to contribute to immune regulation, which is important not only within the gut itself, but also systemically and for bone health. Low-dose lactulose has also been shown to enhance the absorption of minerals such as calcium and magnesium from the gut, an effect which may have important implications for bone health. This review provides an overview of the preclinical and clinical evidence published to date showing that low-dose lactulose stimulates the growth of health-promoting gut bacteria, inhibits the growth of pathogenic bacteria, increases the production of beneficial metabolites, improves mineral absorption, and has good overall tolerability. Implications of these data for the use of lactulose as a prebiotic are also discussed.

Enhancement of the Isomerization Activity and Thermostability of Cellobiose 2-Epimerase from Caldicellulosiruptor saccharolyticus by Exchange of a Flexible Loop

Cellobiose 2-epimerase (CE) offers a promising enzymatic approach to produce lactulose. However, its application is limited by the unsatisfactory isomerization activity and thermostability. Our study attempted to optimize the catalytic performances of CEs by flexible loop exchange, for which four mutants were constructed using CsCE (CE from Caldicellulosiruptor saccharolyticus) as a template. As a result, all mutants maintained the same catalytic directions as the templates. Mutant RmC displayed a 2.2- and 1.34-fold increase in the isomerization activity and catalytic efficiency, respectively. According to the results of molecular dynamics (MD) simulations, it was revealed that the loop exchange in RmC enlarged the entrance of the active site for substrate binding and benefited proton transfer involved in the isomerization process. Besides, the t_1/2 of mutant StC at 70 °C was increased from 29.07 to 38.29 h, owing to the abundance of rigid residues (proline) within the flexible loop of StC. Our work demonstrated that the isomerization activity and thermostability of CEs were closely related to the flexible loop surrounding the active site, which provides a new perspective to engineer CEs for higher lactulose production.

Contribution to the Process Development for Lactulose Production through Complete Valorization of Whey Permeate by Using Electro-Activation Technology Versus a Chemical Isomerization Process

Whey permeate (WP) is a co-product of a cheese or casein production process that is regarded as an environmental pollutant because of its high organic load and is creating a major disposal problem for the dairy industry. However, it can be used as a suitable substrate to meet the increasing demand of producing a prebiotic lactulose through the isomerization of lactose present in the WP under adequate alkaline conditions. The goal of this study was to produce lactulose in situ of WP using electro-activation (EA) technology and compare the productivity of EA with conventional chemical isomerization at potassium hydroxide (KOH)-equivalent solution alkalinity in the feed medium. Electro-isomerization was conducted under different current intensities of 300, 600, and 900 mA for 60 min of EA with a 5 min sampling interval using 6, 12, and 18% (w/v) WP solutions. Chemical isomerization was carried out at the KOH-equivalent solution alkalinity to that measured in the EA solution at each 5 min interval using KOH powder as a catalyst. The outcomes of this study revealed that the production of lactulose using the EA approach was current intensity-, WP concentration-, and reaction time-dependent and produced the highest lactulose yield of 36.98% at 50 min of EA-time under 900 mA current intensity using 6% WP as a feed solution, whereas a maximum lactulose yield of 25.47% was achieved by the chemical isomerization at the solution alkalinity corresponding to that of the EA under 900 mA current intensity at 50 min in the 6% WP solution. Furthermore, a greater yield of lactulose was obtained using the EA technique for all reaction conditions compared to the chemical process at the equivalent solution alkalinity. Therefore, the results of this work suggest that the EA can be an emergent sustainable technology for achieving dual objectives of prebiotic lactulose production and concurrent valorization of WP using it as a feed medium.

Insight into the potential factors influencing the catalytic direction in cellobiose 2-epimerase by crystallization and mutagenesis

Cellobiose 2-epimerase (CE) is commonly recognized as an epimerase as most CEs mainly exhibit an epimerization activity towards disaccharides. In recent years, several CEs have been found to possess bifunctional epimerization and isomerization activities. They can convert lactose into lactulose, a high-value disaccharide that is widely used in the food and pharmaceutical industries. However, the factors that determine the catalytic direction in CEs are still not clear. In this study, the crystal structures of three newly discovered CEs, CsCE (a bifunctional CE from Caldicellulosiruptor saccharolyticus), StCE (a bifunctional CE from Spirochaeta thermophila DSM 6578) and BtCE (a monofunctional CE from Bacillus thermoamylovorans B4166), were determined at 1.54, 2.05 and 1.80 Å resolution, respectively, in order to search for structural clues to their monofunctional/bifunctional properties. A comparative analysis of the hydrogen-bond networks in the active pockets of diverse CEs, YihS and mannose isomerase suggested that the histidine corresponding to His188 in CsCE is uniquely required to catalyse isomerization. By alignment of the apo and ligand-bound structures of diverse CEs, it was found that bifunctional CEs tend to have more flexible loops and a larger entrance around the active site, and that the flexible loop 148-181 in CsCE displays obvious conformational changes during ligand binding. It was speculated that the reconstructed molecular interactions of the flexible loop during ligand binding helped to motivate the ligands to stretch in a manner beneficial for isomerization. Further site-directed mutagenesis analysis of the flexible loop in CsCE indicated that the residue composition of the flexible loop did not greatly impact epimerization but affects isomerization. In particular, V177D and I178D mutants showed a 50% and 80% increase in isomerization activity over the wild type. This study provides new information about the structural characteristics involved in the catalytic properties of CEs, which can be used to guide future molecular modifications.

One-Pot Synthesis of Lactose Derivatives from Whey Permeate

The simultaneous production of lactulose (LAU), lactobionic acid (LBA), and organic acids from sweet and acid whey permeate (SWP and AWP) via catalytic synthesis (5% Ru/C) was studied in a continuous stirred-tank reactor. At selected conditions (60 °C, 60 bar, and 600 rpm), a maximum conversion of lactose (37 and 34%) was obtained after 90 min for SWP and AWP, respectively. The highest yield calculated with respect to the initial concentration of lactose for LAU was 22.98 ± 0.81 and 15.29 ± 0.81% after only 30 min for SWP, and AWP, respectively. For LBA, a maximum yield was found in SWP (5.23%) after 210 min, while about 2.2% was found in AWP. Six major organic acids (gluconic, pyruvic, lactic, formic, acetic, and citric acid) were quantified during the one-pot synthesis of lactose.

Sustainable Valorization of Whey by Electroactivation Technology for In Situ Isomerization of Lactose into Lactulose: Comparison between Electroactivation and Chemical Processes at Equivalent Solution Alkalinity

The demand for production of prebiotics at a commercial scale is rising due to the consumers' growing health awareness. Whey, a coproduct of the dairy industries, is a suitable feed medium to produce a prebiotic lactulose through the isomerization of lactose under alkaline conditions. The aim of the present study was to compare the isomerization of lactose into lactulose in situ of whey by using electroactivation technology with the chemical isomerization method using KOH as catalysis under equivalent solution alkalinity. Electroisomerization of lactose into lactulose was performed by using whey solutions of 7, 14, and 21% (w/v) dry matter under current intensities of 300, 600, and 900 mA, respectively, during 60 min with a sampling interval of 5 min. The conventional chemical method was carried out using KOH powder as catalyst at the alkalinity that corresponded to that measured in the electroactivated whey at each 5 min interval. The results showed that lactulose production was dependent on the whey concentration, current intensity, and EA time. The highest lactulose yield of 32% was achieved under a 900 mA current intensity at 60 min for a 7% whey solution. Thereafter, the EA conditions were compared to those of a conventional chemical isomerization process by maintaining similar alkalinity in the feed solutions. However, no lactulose was produced by the chemical process for the equivalent solution alkalinity as in the EA technique. These results were correlated with the solution pH, which reached the required values in a 7% whey solution with values of up to pH 11.50, whereas the maximum pH values that were obtained at higher whey concentrations were around 10-10.50, which was not enough to initiate the lactose isomerization reaction. The outcomes of this study suggest that EA is an efficient technology to produce lactulose using whey lactose.

Sustainable Electroisomerization of Lactose into Lactulose and Comparison with the Chemical Isomerization at Equivalent Solution Alkalinity

The demand of lactulose production is increasing tremendously because of its bifidogenic (prebiotic) functionality. Therefore, the isomerization of lactose to synthesize lactulose through electroactivation (EA) technology is of great interest nowadays. However, lactulose production through electroisomerization is affected by several operational and experimental conditions, and the process needs to be optimized. In this context, the EA technique was applied to isomerize lactose into lactulose in an EA reactor modulated by anion and cation exchange membranes. The effect of lactose concentrations (5, 10, 15, and 20%), applied electric fields (300, 600, and 900 mA), and processing time (0-60 min) on lactose electroisomerization rate (lactulose formation) and coproduct (glucose, galactose, and fructose) formation has been investigated. The effect of different physicochemical parameters such as pH, alkalinity, temperature, ion migration, and oxidation-reduction potential (ORP) on the conversion of lactose into lactulose was correlated with the lactulose formation to understand the involved process mechanism of action. The conversion of lactose into lactulose was lactose-concentration-, electric-current-, and EA-time-dependent and reached the highest lactulose yield of 38% at 40 min using a 900 mA current intensity in a 10% lactose solution. The results were then compared to conventional chemical isomerization maintaining similar alkaline conditions at ambient temperature (22 ± 2 °C). A higher yield of lactulose was achieved in the EA process within a short reaction time compared to that of the chemical isomerization. The outcome of this study suggests that EA is a promising technique for the enhanced production of lactulose from lactose.

Sensory profile and technological characterization of boneless dry-cured ham with lactulose added as a prebiotic

OBJECTIVE

This study investigates the technological and sensory profile of boneless dry-cured ham added with different contents of lactulose as a prebiotic ingredient.

METHODS

In addition to the control samples (without the addition of lactulose), three treatments were formulated to contain 2, 4 or 6% lactulose. Technological (lactulose content, CIE color and texture profile analysis) and sensory (acceptance and check-all-that-applies tests) analyses were performed on the final product.

RESULTS

The lactulose content in the finished product (1.86±0.23%, 3.16±0.18% and 2.51±1.35%) was lower than the lactulose originally added (2, 4 and 6% respectively). The addition of 4% and 6% lactulose made (P &lt; 0.05) the products darker (lower L*) and redder (lower h) with higher hardness and chewiness values, when compared to control samples. The additions of 2% and 4% lactulose reduce the appearance acceptability of the products, but overall the treatments were well accepted.

CONCLUSION

The use of up to 4% lactulose as a prebiotic in the production of boneless dry-cured hams provides an alternative to improving its nutritional value with little alteration in the technological characteristics and still meeting the sensory characteristics desired by consumers.

Improvements in the production of Aspergillus oryzae β-galactosidase crosslinked aggregates and their use in repeated-batch synthesis of lactulose

Aspergillus oryzae β-galactosidase was immobilized by aggregation and crosslinking, obtaining catalysts (CLAGs) well-endowed for lactulose synthesis. Type and concentration of the precipitating agent were determinants of immobilization yield, specific activity and thermal stability. CLAGs with specific activities of 64,007, 48,374 and 44,560 IU_H g^-1 were obtained using 50% v/v methanol, ethanol and propanol as precipitating agents respectively, with immobilization yields over 90%. Lactulose synthesis was conducted at 50 °C, pH 4.5, 50% w/w total sugars, 200 IU_H g^-1 of enzyme and fructose/lactose molar ratio of 8 in batch and repeated-batch operation. Lactulose yields were 0.19 g g^-1 and 0.24 g g^-1 for fructose to lactose molar ratios of 4 mol mol^-1 and 8 mol mol^-1 while selectivities were 3.3 mol mol^-1 and 6.6 mol mol^-1 respectively for CLAGs obtained by ethanol and propanol precipitation. Based on these results, both CLAGs were selected for the synthesis in repeated-batch mode. The cumulative mass of lactulose in repeated-batch was higher with CLAGs produced by ethanol and propanol precipitation than with the free enzyme. 86 and 93 repeated-batches could have been respectively performed with those CLAGs considering a catalyst replacement criterion of 50% of residual activity, as determined by simulation.

Rapid HPLC method for monitoring of lactulose production with a high yield

An HPLC method suitable for rapid monitoring of lactulose production by isomerization from lactose was developed. The separation of lactose and lactulose under hydrophilic interaction liquid chromatography (HILIC) mode was achieved with resolution 1.5 within 5 min. Since isocratic elution was used, there is no extra time necessary for the column equilibration. Application of the method was illustrated on monitoring lactulose isomerization with catalysis of sodium hydroxide in the presence of sodium tetraborate at 70 °C (pH = 11). The conversion yield obtained for lactulose was 86%, and corresponding purity 76%. For the first time, a polyhydroxy stationary phase for separation of lactose and lactulose is reported.

Continuous enzymatic synthesis of lactulose in packed-bed reactor with immobilized Aspergillus oryzae β-galactosidase

Lactulose synthesis from fructose and lactose in continuous packed-bed reactor operation with glyoxyl-agarose immobilized Aspergillus oryzae β-galactosidase is reported for the first time. Alternative strategies to conventional batch synthesis have been scarcely explored for lactulose synthesis. The effect of flow rate, substrates ratio and biocatalyst-inert packing material mass ratio (M_B/M_IM) were studied on reactor performance. Increase in any of these variables produced an increase in lactulose yield (Y_Lu) being higher than obtained in batch synthesis at comparable conditions. Maximum Y_Lu of 0.6 g·g^-1 was obtained at 50 °C, pH 4.5, 50% w/w total sugars, 15 mL·min^-1, fructose/lactose molar ratio of 12 and M_B/M_IM of 1/8 g·g^-1; at such conditions yield of transgalactosylated oligosaccharides (Y_TOS) was 0.16 g·g^-1, selectivity (lactulose/TOS molar ratio) was 5.4 and lactose conversion (X_Lactose) was 28%. Reactor operation with recycle had no significant effect on yield, producing only some decrease in productivity.

A study of the prebiotic effect of lactulose at low dosages in healthy Japanese women

To investigate the prebiotic effect of lactulose at low dosages, we assessed changes in defaecation frequency following ingestion of 1, 2, or 3 g/day of lactulose for 2 weeks. Each test was carried out after a 2-week washout period. This was an open-label, before-after trial that enrolled 26 healthy Japanese women. The defaecation frequency, number of defaecation days, and number of faecal bifidobacteria increased significantly compared with before ingestion of 1, 2, and 3 g/day of lactulose. These results suggest that even 1 g/day of lactulose could have a prebiotic effect.

Microbiota stability in healthy individuals after single-dose lactulose challenge-A randomized controlled study

BACKGROUND AND AIMS

Lactulose is a common food ingredient and widely used as a treatment for constipation or hepatic encephalopathy and a substrate for hydrogen breath tests. Lactulose is fermented by the colon microbiota resulting in the production of hydrogen (H2). H2 is a substrate for enteropathogens including Salmonella Typhimurium (S. Typhimurium) and increased H2 production upon lactulose ingestion might favor the growth of H2-consuming enteropathogens. We aimed to analyze effects of single-dose lactulose ingestion on the growth of intrinsic Escherichia coli (E. coli), which can be efficiently quantified by plating and which share most metabolic requirements with S. Typhimurium.

METHODS

32 healthy volunteers (18 females, 14 males) were recruited. Participants were randomized for single-dose ingestion of 50 g lactulose or 50 g sucrose (controls). After ingestion, H2 in expiratory air and symptoms were recorded. Stool samples were acquired at days -1, 1 and 14. We analyzed 16S microbiota composition and abundance and characteristics of E. coli isolates.

RESULTS

Lactulose ingestion resulted in diarrhea in 14/17 individuals. In 14/17 individuals, H2-levels in expiratory air increased by ≥20 ppm within 3 hours after lactulose challenge. H2-levels correlated with the number of defecations within 6 hours. E. coli was detectable in feces of all subjects (2 x 10(2)-10(9) CFU/g). However, the number of E. coli colony forming units (CFU) on selective media did not differ between any time point before or after challenge with sucrose or lactulose. The microbiota composition also remained stable upon lactulose exposure.

CONCLUSION

Ingestion of a single dose of 50 g lactulose does not significantly alter E. coli density in stool samples of healthy volunteers. 50 g lactulose therefore seems unlikely to sufficiently alter growth conditions in the intestine for a significant predisposition to infection with H2-consuming enteropathogens such as S. Typhimurium (www.clinicaltrials.gov NCT02397512).

Lactulose production by a thermostable glycoside hydrolase from the hyperthermophilic archaeon Caldivirga maquilingensis IC-167

BACKGROUND

Lactulose has various uses in the food and pharmaceutical fields. Thermostable enzymes have many advantages for industrial exploitation, including high substrate solubilities as well as reduced risk of process contamination.

RESULTS

Enzymatic synthesis of lactulose employing a transgalactosylation reaction by a recombinant thermostable glycoside hydrolase (GH1) from the hyperthermophilic archaeon Caldivirga maquilingensis IC-167 was investigated. The optimal pH for lactulose production was found to be 4.5, while the optimal temperature was 85 °C, before it dropped moderately to 83% at 90 °C. However, the relative activity for lactulose synthesis dropped sharply to 35% at 95 °C. At optimal reaction conditions of 70% (w/w) initial sugar substrates with molar ratio of lactose to fructose of 1:4, 15 U mL^-1 enzyme concentration and 85 °C, the time course reaction produced a maximum lactulose concentration of 108 g L^-1 at 4 h, corresponding to a lactulose yield of 14% and 27 g L^-1  h^-1 productivity with 84% lactose conversion. The transgalactosylation reaction for lactulose synthesis was greatly influenced by the ratio of galactose donor to acceptor.

CONCLUSION

This novel GH1 may be useful for process applications owing to its high activity in very concentrated substrate reaction media and promising thermostability. © 2017 Society of Chemical Industry.

Restructured low-fat cooked ham containing liquid whey fortified with lactulose

BACKGROUND

Current health concerns have driven consumers to request products with nutritional and physiological advantages, which can be achieved by using prebiotic ingredients. Lactulose is a prebiotic with excellent functional properties and can be easily incorporated into meat products through the addition of liquid whey. This study investigated the technological and sensorial quality of restructured cooked ham elaborated without liquid whey added (control) and with liquid whey containing different contents (0, 30, 60 and 100 g kg^-1 ) of lactulose.

RESULTS

Liquid whey did not change any technological or sensorial characteristics of the product, but the general acceptability decreased due to addition of lactulose. Samples with higher lactulose concentrations had lower moisture content, pH and refreezing loss and increased carbohydrate content. Control and whey added samples had higher lightness and lower intense color than samples with lactulose. Liquid whey additions with higher lactulose content increased hardness and chewiness of the samples.

CONCLUSION

Restructured cooked hams formulated with liquid whey and 30 g kg^-1 of lactulose had minimal effects on the technological properties and sensory characteristics and, due to the possible benefits conferred by the prebiotic, is a potential alternative to provide meat products with prebiotic activity. © 2017 Society of Chemical Industry.

Fed-batch operation for the synthesis of lactulose with β-galactosidase of Aspergillus oryzae

Fed-batch synthesis of lactulose from lactose and fructose with Aspergillus oryzae β-galactosidase was evaluated, obtaining a concentration of 40.4g·L^-1, which is 20% higher than obtained in batch, while the concentration of transgalactosylated oligosaccharides (TOS) was reduced by 98%. Therefore, selectivity of lactulose synthesis can be significantly higher by operating in fed-batch mode. The enzyme-limiting substrate mass ratio (E/S) is a critical variable in fed-batch operation. Higher values favor lactose hydrolysis over transgalactosylation, being 400IU/g the limit for proper lactulose synthesis in fed-batch operation. Selectivity of lactulose synthesis increased with E/S being quite high at 800IU_H·g^-1 or higher. However, this increase was obtained at the expense of lactulose yield. Lactulose synthesis in fed-batch operation was a better option than conventional batch synthesis, since higher product concentration and selectivity of lactulose over TOS synthesis were obtained.

Efficient production of lactulose from whey powder by cellobiose 2-epimerase in an enzymatic membrane reactor

In this study, the gene encoding cellobiose 2-epimerase from Caldicellulosiruptor saccharolyticus (CsCE) was successfully expressed in Bacillus subtilis WB800. After the fermentation medium optimization, the activity of recombinant strain was 4.5-fold higher than the original medium in a 7.5L fermentor. The optimal catalytic pH and temperature of crude CsCE were 7.0 and 80°C, respectively. An enzymatic synthesis of lactulose was developed using cheese-whey lactose as its substrate. The maximum conversion rate of whey powder obtained was 58.5% using 7.5 U/mL CsCE. The enzymatic membrane reactor system exhibited a great operational stability, confirmed with the higher lactose conversion (42.4%) after 10 batches. To our best knowledge, this is the first report of lactulose synthesis in food grade strain, which improve the food safety, and we not only realize the biological production of lactulose, but also make good use of industrial waste, which have positive impact on environment.

Immobilization of Aspergillus oryzae β-galactosidase in an agarose matrix functionalized by four different methods and application to the synthesis of lactulose

Aspergillus oryzae β-galactosidase was immobilized in monofunctional glyoxyl-agarose and heterofunctional supports (amino-glyoxyl, carboxy-glyoxyl and chelate-glyoxyl agarose), for obtaining highly active and stable catalysts for lactulose synthesis. Specific activities of the amino-glyoxyl agarose, carboxy-glyoxyl agarose and chelate-glyoxyl agarose derivatives were 3676, 430 and 454IU/g biocatalyst with half-life values at 50°C of 247, 100 and 100h respectively. Specific activities of 3490, 2559 and 1060IU/g were obtained for fine, standard and macro agarose respectively. High immobilization yield (39.4%) and specific activity of 7700IU/g was obtained with amino-glyoxyl-agarose as support. The highest yields of lactulose synthesis were obtained with monofunctional glyoxyl-agarose. Selectivity of lactulose synthesis was influenced by the support functionalization: glyoxyl-agarose and amino-glyoxyl-agarose derivatives retained the selectivity of the free enzyme, while selectivity with the carboxy-glyoxyl-agarose and chelate-glyoxyl-agarose derivatives was reduced, favoring the synthesis of transgalactosylated oligosaccharides over lactulose.

Synthesis of lactulose in batch and repeated-batch operation with immobilized β-galactosidase in different agarose functionalized supports

Lactulose synthesis was done in repeated-batch mode with Aspergillus oryzae β-galactosidase immobilized in glyoxyl-agarose (GA-βG), amino-glyoxyl-agarose (Am-GA-βG) and chelate-glyoxyl-agarose (Che-GA-βG), at fructose/lactose molar ratios of 4, 12 and 20. Highest yields of lactulose in batch were obtained with Che-GA-βG (0.21, 0.29 and 0.32g·g^-1) for 4, 12 and 20 fructose/lactose molar ratios respectively; when operating in 10 repeated batches highest product to biocatalyst mass ratios were obtained with Am-GA-βG (1.82, 2.52 and 2.7g·mg^-1), while the lowest were obtained with Che-GA-βG (0.25, 0.33 and 0.39g·mg^-1). Operational stability of Am-GA-βG was higher than GA-βG and Che-GA-βG and much higher than that of the free enzyme, at all fructose/lactose molar ratios evaluated. Efficiency of biocatalyst use for GA-βG were 64.4, 35.5 and 18.4kg_lactulose/g_protein, for fructose/lactose molar ratios of 4, 12 and 20 respectively, while for Che-GA-βG were 1.46, 1.05 and 0.96kg_lactulose/g_protein.