首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 15 毫秒
1.
The beta-galactosidases (beta-Gals) of Lactobacillus reuteri L103 and L461 proved to be suitable biocatalysts for the production of prebiotic galacto-oligosaccharides (GOS) from lactose. Maximum GOS yields were 38% when using an initial lactose concentration of 205 g/L and at approximately 80% lactose conversion. The product mixtures were analyzed by capillary electrophoresis (CE) and high-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD). Disaccharides other than lactose and trisaccharides made up the vast majority of GOS formed. The main products were identified as beta-d-Galp-(1-->6)-d-Glc (allolactose), beta-d-Galp-(1-->6)-d-Gal, beta-d-Galp-(1-->3)-d-Gal, beta-d-Galp-(1-->6)-Lac, and beta-d-Galp-(1-->3)-Lac. There were no major products with beta1-->4 linkages formed. Both intermolecular and intramolecular transgalactosylation were observed. d-Galactose proved to be a very efficient galactosyl acceptor; thus, a relatively large amount of galactobioses was formed. Monosaccharides could be conveniently separated from the mixture by chromatography using a strong cation-exchange resin.  相似文献   

2.
The production of galactooligosaccharides (GOSs) by transgalactosylation using beta-galactosidase from Bifidobacterium longum BCRC 15708 was studied. Other than lactose, galactose, and glucose, two types of GOSs, tri- and tetrasaccharides, were formed after beta-galactosidase action on 40% lactose. Trisaccharides were the major type of GOS formed. Generally, an increase of the initial lactose concentration in the reaction mixture resulted in a higher GOS production. A maximum yield of 32.5% (w/w) GOSs could be achieved from 40% lactose solution at 45 degrees C, pH 6.8, when the lactose conversion was 59.4%. The corresponding productivity of GOSs was 13.0 g/(L.h). Transgalactosylation activity of beta-galactosidase from a test organism showed a relatively lower sensitivity toward glucose and galactose than that from other organisms. The addition of 5% or 10% glucose or galactose to the reaction mixture did not significantly (p>0.05) reduce the transgalactosylation reaction of beta-galactosidase.  相似文献   

3.
The β-galactosidase activity of 15 Kluyveromyces strains isolated from cheese belonging to Kluyveromyces lactis and Kluyveromyces marxianus species was tested for the production of oligosaccharides derived from lactose (GOS) and lactulose (OsLu). All Kluyveromyces crude cell extracts (CEEs) produced GOS, such as 6-galactobiose and 3'-, 4'-, and 6'-galactosyl-lactose. At 4 h of reaction, the main trisaccharide formed was 6'-galactosyl-lactose (20 g/100 g of total carbohydrates). The formation of OsLu was also observed by all CEEs tested, with 6-galactobiose, 6'-galactosyl-lactulose, and 1-galactosyl-lactulose being found in all of the reaction mixtures. The synthesis of trisaccharides predominated over other oligosaccharides. K. marxianus strain O3 produced the highest yields of GOS and OsLu after 4 h of reaction, reaching 42 g/100 g of total carbohydrates (corresponding to 80% lactose hydrolysis) and 45 g/100 g of total carbohydrates (corresponding to 87% lactulose hydrolysis), respectively. Therefore, the present study contributes to a better insight into dairy Kluyveromyces β-galactosidases and shows the feasibility of these enzymes to transglycosylate lactose and lactulose, producing high yields of prebiotic oligosaccharides.  相似文献   

4.
The intracellular beta-galactosidase (beta-gal) enzymes from two strains of Lactobacillus reuteri, L103 and L461, were purified by ammonium sulfate fractionation, hydrophobic interaction, and affinity chromatography. Both enzymes are heterodimers with a molecular mass of 105 kDa, consisting of a 35 kDa subunit and a 72 kDa subunit. Active staining of L. reuteri L103 and L461 beta-gal with 4-methylumbelliferyl beta-d-galactoside showed that the intact enzymes as well as the larger subunits possess beta-galactosidase activity. The isoelectric points of L. reuteri L461 and L103 beta-gal were found to be in the range of 3.8-4.0 and 4.6-4.8, respectively. Both enzymes are most active in the pH range of 6-8; however, they are not stable at pH 8. The L. reuteri beta-galactosidases are activated by various mono- and divalent cations, including Na(+), K(+), and Mn(2+), and are moderately inhibited by their reaction products d-glucose and d-galactose. Because of their origin from beneficial and potentially probiotic lactobacilli, these enzymes could be of interest for the synthesis of prebiotic galacto-oligosaccharides.  相似文献   

5.
Prebiotic galacto-oligosaccharides (GOS) were effectively synthesized from lactose in organic-aqueous biphasic media by a novel metagenome-derived β-galactosidase BgaP412. A maximum GOS yield of 46.6% (w/w) was achieved with 75.4% lactose conversion rate in the cyclohexane/buffer system [95:5 (v/v) cyclohexane/buffer] under the optimum reaction conditions (initial lactose concentration = 30% (w/v), T = 50 °C, pH 7.0, and t = 8 h). The corresponding productivity of GOS was approximately 17.5 g L(-1) h(-1). The GOS mixture consisted of tri-, tetra-, and pentasaccharides. Trisaccharides were the chief component of reaction products. These experimental results showed that a low water content, a high initial lactose concentration, and an elevated reaction temperature could significantly promote the transgalactosylation activity of β-galactosidase BgaP412; at the same time, the enhanced GOS yield in an organic-aqueous biphasic system is because of the fact that thermodynamic equilibrium can be shifted to the synthetic direction by reversing the normal hydrolysis.  相似文献   

6.
The transgalactosylation activity of Kluyveromyces lactis cells was studied in detail. Cells were permeabilized with ethanol and further lyophilized to facilitate the transit of substrates and products. The resulting biocatalyst was assayed for the synthesis of galacto-oligosaccharides (GOS) and compared with two soluble β-galactosidases from K. lactis (Lactozym 3000 L HP G and Maxilact LGX 5000). Using 400 g/L lactose, the maximum GOS yield, measured by HPAEC-PAD analysis, was 177 g/L (44% w/w of total carbohydrates). The major products synthesized were the disaccharides 6-galactobiose [Gal-β(1→6)-Gal] and allolactose [Gal-β(1→6)-Glc], as well as the trisaccharide 6-galactosyl-lactose [Gal-β(1→6)-Gal-β(1→4)-Glc], which was characterized by MS and 2D NMR. Structural characterization of another synthesized disaccharide, Gal-β(1→3)-Glc, was carried out. GOS yield obtained with soluble β-galactosidases was slightly lower (160 g/L for Lactozym 3000 L HP G and 154 g/L for Maxilact LGX 5000); however, the typical profile with a maximum GOS concentration followed by partial hydrolysis of the newly formed oligosaccharides was not observed with the soluble enzymes. Results were correlated with the higher stability of β-galactosidase when permeabilized whole cells were used.  相似文献   

7.
The synthesis of galacto-oligosaccharides (GOS) catalyzed by a novel commercial preparation of β-galactosidase from Bacillus circulans (Biolactase) was studied, and the products were characterized by MS and NMR. Using 400 g/L lactose and 1.5 enzyme units per milliliter, the maximum GOS yield, measured by HPAEC-PAD analysis, was 165 g/L (41% w/w of total carbohydrates in the mixture). The major transgalactosylation products were the trisaccharide Gal-β(1→4)-Gal-β(1→4)-Glc and the tetrasaccharide Gal-β(1→4)-Gal-β(1→4)-Gal-β(1→4)-Glc. The GOS yield increased to 198 g/L (49.4% w/w of total carbohydrates) using a higher enzyme concentration (15 U/mL), which minimized the enzyme inactivation under reaction conditions. Using skim milk (with a lactose concentration of 46 g/L), the enzyme also displayed transgalactosylation activity: maximum GOS yield accounted for 15.4% (7.1 g/L), which was obtained at 50% lactose conversion.  相似文献   

8.
Galactooligosaccharides (GOS) obtained during the enzymatic hydrolysis of lactose contain large amounts of glucose, galactose, and unreacted lactose, which do not have prebiotic properties and increase the calorific value of the product. In this work, the isomerization of the GOS mixture by the action of sodium aluminate has been studied. During the reaction, lactose, glucose, and galactose were isomerized to lactulose, fructose, and tagatose, respectively, and in addition allolactose, 6-galactobiose, and 6'-galactosyl-lactose were also converted to the corresponding keto-sugars. The effect of time, temperature, and aluminate/initial lactose ratio has been studied. After 9 h at 40 degrees C and molar ratio aluminate/lactose 3:1, the isomerization yield was >60%, and the amount of final carbohydrates was close to 90% of the initial product. This process considerably decreases the amount of lactose, glucose, and galactose.  相似文献   

9.
The influence of methanol on the adsorption of the fungicide cyprodinil by a crop soil was studied by equilibrium measurements and by determining the retention-release dynamics in a continuous stirred flow tank reactor (CSTR). Equilibrium measurements showed the effective coefficient of partition of cyprodinil between soil and solution, K(dc), decreases linearly as the concentration of methanol in the solution increases until a percentage of 20% is reached. In CSTR experiments, the retention of cyprodinil was found to be almost reversible; up to a 95% of the fungicide was desorbed. The retention-release dynamics showed biphasic behavior and was partially controlled by diffusion. This behavior was reproduced by a model of diffusion into micropores identifying the soil particles as spheres and taking into account both intraparticle nonlinear adsorption and nonlinear adsorption at external surfaces. In all cases, the sorption kinetics was not the limiting step. The main effect of methanol in the retention-release dynamics ended up being based on the changes produced in the adsorption equilibrium. Methanol also increased the effective diffusion coefficient and decreased the mass transfer coefficient. The optimized Freundlich's isotherm coefficients for <5% methanol were lower than those obtained from the batch experiments.  相似文献   

10.
The lacLM genes from Lactobacillus sakei Lb790, encoding a heterodimeric β-galactosidase that belongs to glycoside hydrolase family GH2, were cloned and heterologously expressed in Escherichia coli . Subsequently, the recombinant β-galactosidase LacLM was purified to apparent homogeneity and characterized. The enzyme is a β-galactosidase with narrow substrate specificity because o-nitrophenyl-β-D-galactopyranoside (oNPG) was efficiently hydrolyzed, whereas various structurally related oNP analogues were not. The K(m) and k(cat) values for oNPG and lactose were 0.6 mM and 180 s(-1) and 20 mM and 43 s(-1), respectively. The enzyme is inhibited competitively by its two end-products D-galactose and D-glucose (K(i) values of 180 and 475 mM, respectively). As judged by the ratio of the inhibition constant to the Michaelis constant, K(i)/K(m), this inhibition is only very moderate and much less pronounced than for other microbial β-galactosidases. β-Galactosidase from L. sakei possesses high transgalactosylation activity and was used for the synthesis of galacto-oligosaccharides (GalOS), employing lactose at a concentration of 215 g/L. The maximum GalOS yield was 41% (w/w) of total sugars at 77% lactose conversion and contained mainly non-lactose disaccharides, trisaccharides, and tetrasaccharides with approximately 38, 57, and 5% of total GalOS formed, respectively. The enzyme showed a strong preference for the formation of β-(1→6)-linked transgalactosylation products, whereas β-(1→3)-linked compounds were formed to a lesser extent and β-(1→4)-linked reaction products could not be detected.  相似文献   

11.
Galactooligosaccharides (GOS), prebiotic nondigestible oligosaccharides derived from lactose, have the potential for improving mineral balance and bone properties. This study examined the dose-response effect of GOS supplementation on calcium and magnesium absorption, mineral retention, bone properties, and gut microbiota in growing rats. Seventy-five 4-week-old male Sprague-Dawley rats were randomized into one of five treatment groups (n = 15/group) and fed a diet containing 0, 2, 4, 6, or 8% GOS by weight for 8 weeks. Dietary GOS significantly decreased cecal pH and increased cecal wall weight and content weight in a dose-dependent manner (p < 0.0001). Fingerprint patterns of the 16S rRNA gene PCR-DGGE from fecal DNA indicated the variance of bacterial community structure, which was primarily explained by GOS treatments (p = 0.0001). Quantitative PCR of the samples revealed an increase in the relative proportion of bifidobacteria with GOS (p = 0.0001). Net calcium absorption was increased in a dose-response manner (p < 0.01) with GOS supplementation. Dietary GOS also increased (p < 0.02) net magnesium absorption, femur ??Ca uptake, calcium and magnesium retention, and femur and tibia breaking strength. Distal femur total and trabecular volumetric bone mineral density (vBMD) and area and proximal tibia vBMD increased (p < 0.02) with GOS supplementation. Trabecular-rich bones, that is, those that rapidly turn over, were most benefited. Regression modeling showed that GOS benefited calcium and magnesium utilization and vBMD through decreased cecal pH, increased cecal wall and content weight, and increased proportion of bifidobacteria.  相似文献   

12.
Bacterial leaching of heavy metals from sewage sludge was studied to assess the potential of agricultural application of the decontaminated sludge. Experiments were conducted in both batch processes (at 28 ?C) and continuous process (at 30 ?C) using a culture of Thiobacillus ferrooxidans and a mixted culture of Thiobacillus ferrooxidans and Thiobacillus thiooxidans. Reagent grade ferrous sulfate, spent ferrous sulfate and pyrite were used as the energy substrates. A first order kinetic model of Cu solubilization was proposed. It was shown that the processes in the continuously stirred tank reactor (CSTR) and the air lift reactor (ALR) with 20% cell recycling were more efficient than the others for metal solubilization due to a relatively large bacterial population.  相似文献   

13.
This study aimed to achieve the conversion of cereal proteins to the alternative end products glutamate or γ-aminobutyrate (GABA). Rye malt, fungal proteases, and lactobacilli were employed to convert wheat gluten or barley proteins. Glutamate and GABA formations were strain-dependent. Lactobacillus reuteri TMW1.106 and Lactobacillus rossiae 34J accumulated glutamate; L. reuteri LTH5448 and LTH5795 accumulated GABA. Glutamate and GABA accumulation by L. reuteri TMW1.106 and LTH5448 increased throughout fermentation time over 96 h, respectively. Peptides rather than amino acids were the main products of proteolysis in all doughs, and barley proteins were more resistant to degradation by rye malt proteases than wheat gluten. However, addition of fungal protease resulted in comparable degradation of both substrates. Glutamate and GABA accumulated to concentrations up to 63 and 90 mmol kg(-1) DM, respectively. Glutamate levels obtained through bioconversion of cereal proteins enable the use of hydrolyzed cereal protein as condiment.  相似文献   

14.
Prebiotic galactosyl oligosaccharides (GOS) are produced from lactose by the enzyme β-galactosidase. It is widely reported that the highest GOS levels are achieved when the initial lactose concentration is as high as possible; however, little evidence has been presented to explain this phenomenon. Using a system composed of the commercial β-galactosidase derived from Bacillus circulans known as Biolacta FN5, lactose and sucrose, the relative contribution of water activity, and substrate availability were assessed. Oligosaccharide levels did not appear to be affected by changes in water activity between 1.0 and 0.77 at a constant lactose concentration. The maximum oligosaccharide concentration increased at higher initial concentrations of lactose and sucrose, while initial reaction rates for transfer increased but remained constant for hydrolysis. This suggests that the high oligosaccharide levels achieved at the raised initial saccharide concentration are due to increases in reactions that form oligosaccharides rather than decreases in concurrent reactions, which degrade oligosaccharides. There were different effects from changing the initial concentration of lactose compared to sucrose, suggesting that the ability of lactose to act as a donor saccharide may be more important for increasing maximum oligosaccharide concentrations than the combined ability of both saccharides to act as galactosyl acceptors.  相似文献   

15.
Fermentation properties of oligosaccharides derived from lactulose (OsLu) and lactose (GOS) have been assessed in pH-controlled anaerobic batch cultures using lactulose and Vivinal-GOS as reference carbohydrates. Changes in gut bacterial populations and their metabolic activities were monitored over 24 h by fluorescent in situ hybridization (FISH) and by measurement of short-chain fatty acid (SCFA) production. Lactulose-derived oligosaccharides were selectively fermented by Bifidobacterium and lactic acid bacterial populations producing higher SCFA concentrations compared to GOS. The highest total SCFA production was from Vivinal-GOS > lactulose > OsLu > GOS. Longer incubation periods produced a selective fermentation of OsLu when they were used as a carbon source reaching the highest selective index scores. The new oligosaccharides may constitute a good alternative to lactulose, and they could belong to a new generation of prebiotics to be used as a functional ingredient for improving the composition of gut microflora.  相似文献   

16.
Dry mixtures of lactose and caseinate were heated at 60 degrees C for up to 96 h at different relative humidities (RHs) ranging from 29 to 95%. The resulting nonenzymatic browning was studied by determining lactulosyl lysine formation in the caseinate (as measured by the conversion to furosine), amount of reacted lactose, loss of lysine, color formation, and fluorescent intensity. For each measurement, the maximum reaction occurred at intermediate RHs. While there is general agreement between the results obtained by different methods, discrepancies are understandable given the complex nature of nonenzymatic browning. It was shown that the degradation of the Amadori product, lactulosyl lysine, increased with RH. Moreover, the Maillard reaction, as opposed to caramelization of lactose, was the major pathway at all RHs. Visible browning occurred when the destruction of Amadori product became dominant, and interactions between sugar fragments and caseinate were not the rate-limiting steps in the nonenzymatic browning.  相似文献   

17.
The aim of this study was to display a rumen bacterial β-glucanase on the cell surface of a probiotic Lactobacillus reuteri strain. The β-glucan degrading ability and the adhesion capability of the genetically modified strain were evaluated. The β-glucanase (Glu) from Fibrobacter succinogenes was fused to the C-terminus of collagen-binding protein (Cnb) from L. reuteri and then expressed by L. reuteri Pg4 as a recombinant Cnb-Glu-His(6) fusion protein. Confocal immunofluorescence microscopy and flow cytometric analysis of the transformed strain L. reuteri pNZ-cnb/glu demonstrated that Cnb-Glu-His(6) fusion protein was displayed on its cell surface. In addition, L. reuteri pNZ-cnb/glu acquired the capacity to break down barley β-glucan and showed higher adhesion capability, in comparison with the parental strain L. reuteri Pg4. To the best of the authors' knowledge, this is the first report of successful display of fibrolytic enzymes on the cell surface of intestinal lactobacilli.  相似文献   

18.
6-O-decanoyl, 6-O-dodecanoyl, or 6-O-tetradecanoyl L-ascorbate was continuously produced at 50 degrees C using a continuous stirred tank reactor (CSTR) with an immobilized lipase, Chirazyme L-2 C2, from Candida antarctica. Acetone was used as the reaction medium. For each saturated acyl L-ascorbate, the productivity of ca. 60 g/L reactor/day was achieved for at least 11 days. The solubility of the saturated acyl L-ascorbate in the soybean oil or water was measured at various temperatures. The solubilities in both the soybean oil and the water were higher for L-ascorbate with a shorter acyl chain. The acyl chain dependence of the solubility in water was stronger than that of the solubility in soybean oil. The temperature dependences of the solubility in both soybean oil and water could be expressed by the van't Hoff equation, and the dissolution enthalpy (DeltaH) values for the soybean oil and water were about 20 and 90 kJ/mol, respectively, irrespective of the acyl chain length. The radical scavenging activities of L-ascorbic acid and the saturated acyl L-ascorbates against 1,1-diphenyl-2-picrylhydrazyl free radical were ca. 95% for all of the compounds, and the introduction of a saturated acyl group to the L-ascorbic acid did not affect the activity.  相似文献   

19.
[目的]对湖南省益阳市安化县澄坪村"7·16"泥石流灾害成因机理及力学特征进行分析,为类似灾害的防灾减灾研究提供科学参考。[方法]通过灾后野外调查开展相关分析。[结果]湖南省安化县马路镇澄坪村梨树坪让家沟流域在地形地貌,地层岩性以及气象水文方面具备良好的孕灾条件;由于2014年7月16日的持续性强降雨作用,沟道上游一侧形成了一个约5.20×10~4 m~3的滑坡堰塞湖,随后堰塞湖迅速溃决并形成了强大的溃决型泥石流,冲溃了下游的两道拦砂坝,并形成了高达190.65m~3/s的峰值流量。[结论]安化县澄坪村"7·16"泥石流灾害是一次典型的滑坡灾害转换成泥石流的灾害链,而下游两道堵塞坝的堵溃过程进一步放大了泥石流的峰值流量及规模,具有典型的堵溃放大效应。  相似文献   

20.
The enzymatic transgalactosylation from lactose to fructose leading to the prebiotic disaccharide lactulose was investigated using the beta-galactosidase from Aspergillus oryzae and the hyperthermostable beta-glycosidase from Pyrococcus furiosus (CelB). The conditions for highest lactulose yields relative to the initial lactose concentration were established on a 1 mL scale. Dependent on the initial molar ratio of lactose to fructose, more or fewer oligosaccharides other than lactulose were generated. Bioconversions on a 30 mL scale in a stirred glass reactor were performed, and lactulose yields of 46 mmol/L (44% relative to lactose) for CelB and 30 mmol/L (30% relative to lactose) for A. oryzae beta-galactosidase were achieved. Only <5% of other oligosaccharides were detectable. The corresponding productivities were 24 and 16 mmol/L/h, respectively. The molecular structure of lactulose was investigated in detail and confirmed after purification of the reaction solution by LC-MS and 1D and 2D NMR. Lactulose (4-O-beta-D-galactopyranosyl-D-fructose) was unambiguously proved to be the major transglycosylation disaccharide.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号