Induced expression of bacterial β-glucosidase activity in saccharomyces

The bglA gene which encodes a β-glucosidase from Bacillus polymyxa, has been expressed in Saccharomyces cerevisiae under control of the yeast CYC-GAL promoter. Strains have been constructed which carry the gene in different locations: in a multicopy plasmid, a single integration at the URA3 locus, or multiple integrations at the RDN1 locus. Integrative transformation at RDN1 yielded genetically stable clones with a high level of β-glucosidase activity. Coordinated overexpression of the GAL4 inducer protein further increased the level of enzyme activity, although eventually caused the lysis of the cultures. Diploid, triploid and tetraploid strains derived from the transformants with multiple integrations were constructed and expression of β-glucosidase activity in different conditions of growth was assayed. While per-cell activity increased with ploidy, specific activity was about the same in strains of equivalent genotype regardless of ploidy. Genetically stable and regulated expression in Saccharomyces of β-glucosidase activity is interesting for the development of strains able to ferment β-glycosidic sugars (i.e. cellobiose and lactose). From another point of view, the bglA product proved to be a convenient reporter enzyme to monitor heterologous gene expression.     

Kinetics of continuous whey fermentation by Kluyveromyces fragilis

Continuous whey fermentation by Kluyveromyces fragilis was studied in a 30-dm³ stirred fermenter as a function of the dilution rate (D) and feed concentration of lactose (S_o). By using the concept of material and energy balances, it was possible not only to check the consistency of the experimental steady-state responses, but also to develop an unstructured model based on a Monod-type kinetic equation for cell growth and two independent linear equations for the consumption rates of lactose and oxygen. Moreover, a typical Lineweaver—Burk plot enabled the yeast specific growth rate to be described as that of an enzyme-catalysed reaction in the presence of an unknown noncompetitive inhibitor (that was identified with a reference intermediate compound produced by the microorganism itself under partially anaerobic conditions and expressed in terms of ethanol equivalent). In this way, the experimental cell concentrations were reconstructed with a mean standard error of about 10%, thus confirming the capability of this model to provide a reliable basis for further scale-up of this fermentation process.     

Electrocatalytic oxidation of lactose on gold nanoparticle modified carbon in carbonate buffer

The electrocatalytic oxidation of lactose has been studied on nanolength scale Au-colloids (5 nm) embedded in carbon felt as electrode (Au-NMC). A preliminary investigation by cyclic voltammetry, used to determine the optimized conditions of electrolysis, showed that the current densities were higher than those obtained on a gauze electrode of gold (Au-GE) with a surface area three times greater. Long-time electrolyses were carried out using a two potential plateau program with different values for the oxidation potentials. Chromatographic and NMR analyses showed that the oxidation of lactose led mainly to lactobionate (91%).     

Differences in characteristics of pellets prepared by different pelletization methods

Pellets are currently a very popular dosage form for oral application. They can be prepared by several pelletization techniques. Extrusion/spheronization, commonly used in the pharmaceutical industry, and modern agglomeration in a rotoprocessor were the methods chosen for pellet preparation in our study. Theophylline (in 10% to 65% concentration) was the model drug, lactose monohydrate was used as filler, microcrystalline cellulose Avicel® PH 101 was thespheronization enhancer, and the wetting agent was purified water. Both techniques led to the formation of pellets of appropriate shape and mechanical properties. Pellets of a higher density, hardness, lower friability, and slightly slower dissolution profiles were obtained by extrusion/spheronization. This method of pelletization also led to production of particles with narrower size distribution and bigger yield of pellets with the requested size.     

Determination of the surface energy distributions of different processed lactose

Particulate interactions between drug and lactose carrier in dry powder inhaler formulations are affected by the heterogenous energy distribution on the surface of the individual compounds. A new method based on Inverse Gas Chromatography at finite concentration is applied to study the energy heterogeneity of untreated, milled, and recrystallized lactose of similar particle size distribution. Energy distributions for the dispersive surface energy and the specific free energy of ethanol are obtained. Milling causes an increase in surface energy due to formation of amorphous regions. Untreated and recrystallized materials have similar surface energies at low surface coverages but show clear differences in energy distribution.     

A comparative study on the effects of glucose monohydrate, hot water, and sodium pyrophosphate on quality parameters and microbial flora of deboned and matured brisket

ABSTRACT:  Organic acids, hot water (HW), and chlorine have been commonly used in carcass decontamination for years. However, it has been observed that organic acids have adverse effects on color and are corrosive, while HW is discoloring. On the other hand, glucose fermentation by lactic acid bacteria in meat during the rigor period might be effective in microbial inhibition, without producing an adverse effect on the organoleptic quality of meat. Therefore, this study has aimed at finding an alternative meat decontamination procedure without any adverse effects. In this study, briskets were treated with 6 different applications: D (+) glucose monohydrate (GM) (16.51 g/100 mL, 15%) dip, HW dip, sodium pyrophosphate (SPP) and HW dip, GM + SPP + HW, and GM + HW combined dip. Then, the results of these applications were compared. First, GM + HW and GM + SPP + HW applications indicated more inhibition on Pseudomonas spp., Coliform and total Mesophile Aerob Bacteria growth, resulting in lower acidity loss ( P < 0.01). Second, additional use of SPP with GM and HW did not enhance microbial inhibition ( P < 0.01). Finally and most importantly, GM, 15%, improved a and b Hunter values significantly ( P < 0.01), producing a very intense red meat color that can be very attractive for meat producers and consumers.     

EFFECT OF IMPELLER SPEED AND VISCOSITY ON WHEY LACTOSE HYDROLYSIS AND β-GALACTOSIDASE STABILITY

In the present work, the effects of impeller speed and viscosity on the enzymatic hydrolysis of whey lactose and enzyme inactivation were studied. The experiments were carried out in 250 mL of 25 mM phosphate buffer solution containing 50 g/L whey lactose by using a commercial β-galactosidase produced from Kluyveromyces marxianus in a batch reactor system. The degree of lactose hydrolysis (%) and residual enzyme activity (%) was investigated versus impeller speeds from 100 to 600 rpm and viscosities from 1.005 to 13.43 cp for 30 minutes of processing time. The mathematical models depending on these process parameters were derived using the experimental data of residual lactose concentration and residual β-galactosidase activity. The predicted models have been confirmed with the experimental results.     

Ultrasound-enhanced lactose hydrolysis in milk fermentation with Lactobacillus bulgaricus

The effects of ultrasonic irradiation during milk fermentation have been investigated in terms of the cell viability, β-galactosidase activity, the pH value of the culture medium, the degree of lactose hydrolysis and glucose content. The results showed that the ultrasonic irradiation caused the intracellular β-galactosidase to be released from the lactic acid bacteria cells. The released β-galactosidase showed a higher lactose hydrolysis activity than that in the cells. The β-galactosidase that was released to the medium has been more effectively used in pH-controlled fermentation. The results also showed that the continuous sonication caused the cell viability to decrease, but the viable cell count was again increased with static incubation after sonication. High degrees of lactose hydrolysis and high cell viabilities were obtained with the combination of pH-controlled sonicated fermentation and static incubation.     

糖类手性固定相的合成及其色谱应用

制备了葡萄糖、纤维二糖、棉子糖、乳糖的高效液相色谱手性固定相,并在正相条件下对32种手性化合物进行了拆分,结果表明,四种手性固定相分别分开手性药物11,14,17,11种,拆分效果良好。