Multi-enzyme biosensors with amperometric detection for determination of lactose in milk and dairy products

Critical Parameters in an Enzymatic Way to Obtain the Unsweet Lactose-Free Milk Using Catalase and Glucose Oxidase Co-Encapsulated into Hydrogel with Chemical Cross-Linking

The presented work involves obtaining and characterising a two-enzymatic one-pot bioreactor, including encapsulated (co-immobilised) glucose oxidase and catalase. The enzymatic capsules were applied to produce unsweet, lactose-free milk during low-temperature catalysis. Furthermore, operational conditions, like pH and aeration, were selected in the paper, which sorts out discrepancies in literature reports. All experiments were carried out at 12 °C, corresponding to milk storage and transportation temperature. Preliminary studies (for reasons of analytical accuracy) were carried out in a buffer (pH, concentration of sugars mimicking conditions in the lactose-free milk, the initial glucose concentration 27.5 g/L) verified by processes carried out in milk in the final stage of the study. The presented results showed the need for regulating pH and the aeration of the reaction mixture in the continuous mode during the process. The procedure of co-immobilisation was performed in an alginate matrix with the cross-linking of glutaraldehyde or carbodiimide while carbodiimide showed better enzymes retention inside alginate capsules. Co-encapsulated enzymes could be used for nine cycles, preserving finally about 40% of the initial activity.

Sensitive electrochemical immunosensor using a bienzymatic system consisting of β-galactosidase and glucose dehydrogenase

Bienzymatic systems are often used with electrochemical affinity biosensors to achieve high signal levels and/or low background levels. It is important to select two enzymes whose reactions do not exhibit mutual interference but have similar optimal conditions. Here, we report a sensitive electrochemical immunosensor based on a bienzymatic system consisting of β-galactosidase (Gal, a hydrolase enzyme) and flavin adenine dinucleotide-dependent glucose dehydrogenase (FAD-GDH, a redox enzyme). Both enzymes showed high activities at neutral pH, the reactions catalyzed by them did not exhibit mutual interference, and the electrochemical-enzymatic redox cycling based on FAD-GDH coupled with enzymatic amplification by Gal enabled high signal amplification. Among the three amino-hydroxy-naphthalenes and 4-aminophenol (potential Gal products), 4-amino-1-naphthol showed the highest signal amplification. Glucose, as an electro-inactive, stable reducing agent for redox cycling, helped in achieving low background levels. Our bienzymatic system could detect parathyroid hormone at a detection limit of ∼0.2 pg mL-1, implying that it can be used for highly sensitive electrochemical detection of parathyroid hormone and other biomarkers in human serum.

Novel electrochemical sensing of galactose using GalOxNPs/CHIT modified pencil graphite electrode

For the construction of galactose biosensor, chitosan was electropolymerised onto the pencil graphite electrode. This chitosan modified pencil graphite electrode acts as good matrix for immobilization of enzyme nanoparticles of galactose oxidase. Development of this nanocomposite was further confirmed by Fourier transform infrared spectroscopy and scanning electron microscopy. The presence of chitosan makes the present galactose biosensor more efficient, reproducible and stable. The sensitivity was reported 7 × 10^-3 mA/mM/cm² with linear range from 0.05 to 25 mM and better detection limit of 0.05 mM. When the solution of galactose was spiked with 0.5 mM and 1 mM, the analytical recoveries were found 98.6% and 97.6%. A better storage stability was achieved (90days) when compared to earlier reported biosensors.

Expression, purification, and characterization of galactose oxidase of Fusarium sambucinum in E. coli

A gene encoding a galactose oxidase (GalOx) was isolated from Fusarium sambucinum cultures and overexpressed in Escherichia coli yielding 4.4mg enzyme per L of growth culture with a specific activity of 159Umg(-1). By adding a C-terminal His-tag the enzyme could be easily purified with a single affinity chromatography step with high recovery rate (90%). The enzyme showed a single band on SDS-PAGE with an apparent molecular mass of 68.5kDa. The pH optimum for the oxidation of galactose was in the range of pH 6-7.5. Optimum temperature for the enzyme activity was 35°C, with a half-life of 11.2min, 5.3min, and 2.7min for incubation at 40°C, 50°C, and 60°C, respectively. From all tested substrates, the highest relative activity was found for 1-methyl-β-galactopyranoside (226Umg(-1)) and the highest catalytic efficiency (kcat/Km) for melibiose (2700mM(-1)s(-1)). The enzyme was highly specific for molecular oxygen as an electron acceptor, and showed no appreciable activity with a range of alternative acceptors investigated. Different chemicals were tested for their effect on GalOx activity. The activity was significantly reduced by EDTA, NaN3, and KCN.

Quantifying the release of lactose from polymer matrix tablets with an amperometric biosensor utilizing cellobiose dehydrogenase

The release of lactose (hydrophilic) from polymer tablets made with hydrophobically modified poly(acrylic acid) (HMPAA) have been studied and compared to the release of ibuprofen, a hydrophobic active substance. Lactose is one of the most used excipients for tablets, but lactose release has not been widely studied. One reason could be a lack of good analytical tools. A novel biosensor with cellobiose dehydrogenase (CDH) was used to detect the lactose release, which has a polydiallyldimethylammonium chloride (PDADMAC) layer that increases the response. A sample treatment using polyethylenimine (PEI) was developed to eliminate possible denaturants. The developed methodology provided a good approach to detect and quantify the released lactose. The release was studied with or without the presence of a model amphiphilic substance, sodium dodecyl sulphate (SDS), in the release medium. Ibuprofen showed very different release rates in the different media, which was attributed to hydrophobic interactions between the drug, the HMPAA and the SDS in the release medium. The release of hydrophilic lactose, which did not associate to any of the other components, was rapid and showed only minor differences. The new methodology provides a useful tool to further evaluate tablet formulations by a relatively simple set of experiments.

Effects of temperature and glycerol and methanol-feeding profiles on the production of recombinant galactose oxidase in Pichia pastoris

Optimization of protein production from methanol-induced Pichia pastoris cultures is necessary to ensure high productivity rates and high yields of recombinant proteins. We investigated the effects of temperature and different linear or exponential methanol-feeding rates on the production of recombinant Fusarium graminearum galactose oxidase (EC 1.1.3.9) in a P. pastoris Mut⁺ strain, under regulation of the AOX1 promoter. We found that low exponential methanol feeding led to 1.5-fold higher volumetric productivity compared to high exponential feeding rates. The duration of glycerol feeding did not affect the subsequent product yield, but longer glycerol feeding led to higher initial biomass concentration, which would reduce the oxygen demand and generate less heat during induction. A linear and a low exponential feeding profile led to productivities in the same range, but the latter was characterized by intense fluctuations in the titers of galactose oxidase and total protein. An exponential feeding profile that has been adapted to the apparent biomass concentration results in more stable cultures, but the concentration of recombinant protein is in the same range as when constant methanol feeding is employed. © 2014 The Authors Biotechnology Progress published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers Biotechnol. Prog., 30:728–735, 2014

A comparative summary of expression systems for the recombinant production of galactose oxidase

BACKGROUND

The microbes Escherichia coli and Pichia pastoris are convenient prokaryotic and eukaryotic hosts, respectively, for the recombinant production of proteins at laboratory scales. A comparative study was performed to evaluate a range of constructs and process parameters for the heterologous intra- and extracellular expression of genes encoding the industrially relevant enzyme galactose 6-oxidase (EC 1.1.3.9) from the fungus Fusarium graminearum. In particular, the wild-type galox gene from F. graminearum, an optimized variant for E. coli and a codon-optimized gene for P. pastoris were expressed without the native pro-sequence, but with a His-tag either at the N- or the C-terminus of the enzyme.

RESULTS

The intracellular expression of a codon-optimized gene with an N-terminal His10-tag in E. coli, using the pET16b+ vector and BL21DE3 cells, resulted in a volumetric productivity of 180 U·L-1·h-1. The intracellular expression of the wild-type gene from F. graminearum, using the pPIC3.5 vector and the P. pastoris strain GS115, was poor, resulting in a volumetric productivity of 120 U·L-1·h-1. Furthermore, this system did not tolerate an N-terminal His10-tag, thus rendering isolation of the enzyme from the complicated mixture difficult. The highest volumetric productivity (610 U·L-1·h-1) was achieved when the wild-type gene from F. graminearum was expressed extracellularly in the P. pastoris strain SMD1168H using the pPICZα-system. A C-terminal His6-tag did not significantly affect the production of the enzyme, thus enabling simple purification by immobilized metal ion affinity chromatography. Notably, codon-optimisation of the galox gene for expression in P. pastoris did not result in a higher product yield (g protein·L-1 culture). Effective activation of the enzyme to generate the active-site radical copper complex could be equally well achieved by addition of CuSO4 directly in the culture medium or post-harvest.

CONCLUSIONS

The results indicate that intracellular production in E. coli and extracellular production in P. pastoris comprise a complementary pair of systems for the production of GalOx. The prokaryotic host is favored for high-throughput screening, for example in the development of improved enzymes, while the yeast system is ideal for production scale-up for enzyme applications.

Production, purification, and characterization of a novel galactose oxidase fromFusarium acuminatum

Extra-cellular production of a novel galactose oxidase from Fusarium acuminatum using submerged fermentation was studied. Glucose (1.0% w/v) was used as the sole carbon source. Maximum galactose oxidase production (approximately 4.0 U/ml) was obtained when fermentation was carried out at 25 degrees C, with orbital shaking (100 rpm) and an initial medium of pH 7.0, for 96 h, using a 2% (v/v) inoculum made from a homogenized four-day-old liquid culture, in the presence of copper, manganese, and magnesium. The enzyme was purified by one-step affinity chromatography, with a recovery of 42% of the initial activity. The purified enzyme ran as a single band of 66 kDa in SDS-PAGE. Optimal pH and temperature for the enzyme activity were 8.0 and 30 degrees C, respectively. The enzyme was thermoinactivated at temperatures above 60 degrees C. The purified enzyme was active toward various substrates, including galactose, dihydroxyacetone, guar gum, lactose, melibiose, methyl-galactopyranoside, and raffinose. SDS was an inhibitor but EDTA, Tween 80, NH(4)(+), Na(+), Mg(2+), K(+), and glycerol were not. The Michaelis-Menten constant (K(m)) for galactose was estimated to be 16.2 mM, while maximal velocity (V(max)) was 0.27 micromol of H(2)O(2) . ml(-1) . min(-1).

Autoanalyzer for milk quality control based on the lactose, fat, and total protein contents

A novel autoanalyzer was developed to assess the quality of milk samples according to the percentage of lactose, fat, and total protein they contain. The module comprises two pumps (one of high pressure), an injection valve, a filter, and an evaporative light-scattering detector. A volume of 15 microL of dilute milk was injected in an ethanol-water (50% v/v) stream for precipitation/retention of protein/fat, being the lactose content determined in the filtrate. The fat fraction was calculated using an ethanol stream, and total protein was finally dissolved by means of a 1.7 mol/L acetic acid solution. The simplicity of the proposed automatic module lies in the universal response of the detector, which permits the determination of the three macrocomponents in milk. In addition, the flow injection method allows their sequential analysis in the same injected sample by using selective reagents for each compound. The proposed method was validated with an SRM milk sample as well as by comparison of the results obtained with those provided by the IR method. In addition, the proposed analyzer is cheaper than its counterpart that is based on infrared technique.

Expression and stabilization of galactose oxidase in Escherichia coli by directed evolution

We have used directed evolution methods to express a fungal enzyme, galactose oxidase (GOase), in functional form in Escherichia coli. The evolved enzymes retain the activity and substrate specificity of the native fungal oxidase, but are more thermostable, are expressed at a much higher level (up to 10.8 mg/l of purified GOase), and have reduced negative charge compared to wild type, all properties which are expected to facilitate applications and further evolution of the enzyme. Spectroscopic characterization of the recombinant enzymes reveals a tyrosyl radical of comparable stability to the native GOase from Fusarium.