Biomedical subjects

Meng Heng

Publications and source records attributed to Meng Heng.

6 recordsLinked to original sources

PubMed2006

Broth conditions determining specific cake resistance during microfiltration of Bacillus subtilis.

The effects of broth pH, pressure, temperature, and fermentation medium on specific cake resistance were studied for dead-end microfiltration of Bacillus subtilis. Decreases in pH and transmembrane pressure decreased the specific cake resistance for cells grown in both complex and defined media. With the complex medium, the reduction in resistance with temperature decrease did not offset the flux decrease caused by the increase in viscosity. The greatest decrease in specific cake resistance occurred with adjustment of pH to 7.5 for cells grown in defined medium. For those cells the change in pH resulted in aggregation leading to a large increase in flux.

Bacillus subtilis↗

PubMed2006

High-throughput process development for recombinant protein purification.

Methods development in chromatographic purification processes is a complex operation and has traditionally relied on trial and error approaches. The availability of a large number of commercial media, choice of different modes of chromatography, and diverse operating conditions contribute to the challenging task of accelerating methods development. In this paper, we describe a novel microtiter-plate based screening method to identify the appropriate sequence of chromatographic steps that result in high purities of bioproducts from their respective culture broths. Protein mixtures containing the bioproduct were loaded on aliquots of different chromatographic media in microtiter plates. Serial step elution of the proteins, in concert with bioproduct-specific assays, resulted in the identification of "active fractions" containing the bioproduct. The identification of a successful chromatographic step was based on the purity of the active fractions, which were then pooled and used as starting material for screening the next chromatographic dimension. This procedure was repeated across subsequent dimensions until single band purities of the protein were obtained. The sequence of chromatographic steps and the corresponding operating conditions identified from the screen were validated under scaled-up conditions. Various modes of chromatography including hydrophobic interaction, ion exchange (cation and anion exchange) and hydrophobic charge-induction chromatography (HCIC), and different operating conditions (pH, salt concentration and type, etc.) were employed in the screen. This approach was employed to determine the sequence of chromatographic steps for the purification of recombinant alpha-amylase from its cell-free culture broth. Recommendations from the screen resulted in single-band purity of the protein under scaled-up conditions. Similar results were observed for an scFv-beta-lactamase fusion protein. The use of a miniaturized screen enables the parallel screening of a wide variety of actual bioprocess media and conditions and represents a novel paradigm approach for the high-throughput process development of recombinant proteins.

Anion Exchange Resins↗

PubMed2005

Quantitative analysis of chloride in brackish water: an application to the hyperchromic effect of copper(II) ion with chloride ion.

A new modified method was applied to the determination of chloride anion in brackish water by using a common copper(II) sulfate solution and a spectrophotometer. The result of the quantitative analysis demonstrated that chloride concentrations were 1.61% w/v and 1.74% w/v at ebb tide and flood tide, respectively, of the Muya River. On the other hand, chloride concentrations were 1.17% w/v at ebb tide and 1.65% w/v at flood tide of the Yoshino River. The new method proved that chloride concentration corresponded well with results from Mohr and conductive methods. Therefore, the newly developed method can be exploited as common means to measure chloride concentration in aqueous solutions. Moreover, it is also valuable for application to other types of environmental samples.

Journal Article↗

PubMed2004

Zeta potential as a measure of polyelectrolyte flocculation and the effect of polymer dosing conditions on cell removal from fermentation broth.

Characterization of flocculation for cell removal from fermentation broth via polyelectrolyte addition is commonly based on qualitative methods such as physical appearance of the floc. The use of zeta potential as a quantitative measure of floc character was evaluated as an indicator of optimal polymer addition. Zeta potential was found to increase with increasing cationic polyelectrolyte dosage, but never reached zero regardless of the total amount of polymer added, indicating flocculation occurs at least partially through a bridging type mechanism. Experiments were conducted using various polymer concentrations (25-75 g/L) and dosing methods (batch, incremental and continuous addition) that resulted in variable overall polymer requirements to achieve optimum flocculation. Zeta potential was found to be constant at optimal floc character regardless of the total amount of polymer added, polymer concentration, or method of polymer addition. Experiments with two additional types of fermentation broth also showed characteristic zeta potentials at optimal flocculation. Polymer requirements to achieve a particular floc character can vary greatly, depending on polymer dosing conditions and fermentation batch. The effect of polymer dosing conditions on the polymer requirement to obtain optimal floc character was evaluated. Polymer dosing method and calcium concentration were both found to have a significant effect (P < 0.0001) with continuous polymer addition and high calcium concentration requiring less polymer than did batch polymer addition and low calcium concentration, respectively. Polymer dosing concentration did not significantly affect polymer requirement for optimal flocculation.

Bacillus↗

PubMed2004

Extracellular enzyme loss during polyelectrolyte flocculation of cells from fermentation broth.

Association of extracellular protein product with flocculated cells reduces product yield. Here, partitioning of the enzyme subtilisin between the liquid and polyelectrolyte-flocculated and sedimented Bacillus increased as the polymer dosage was increased beyond that necessary to obtain optimum floc character (brain floc) for cell removal by centrifugation. Partitioning to the cell floc is partly physical entrapment at all polymer dosages; however, at higher levels there is also direct interaction between the polyelectrolyte and enzyme. Enzyme loss was not likely due to pH denaturation during the flocculation process because conditions were within the stable pH range of the enzyme. The direct interaction between polyelectrolyte and enzyme was characterized through turbidimetric titrations and partitioning studies. Neither changes in the polymer feed concentration nor the method of polymer addition reduced the enzyme loss at dosages optimal for cell removal.

Bacillus↗

PubMed2004

Aging of concrete buildings and determining the pH value on the surface of concrete by using a handy semi-conductive pH meter.

A new method was devised for measuring the pH of a concrete surface by pHBOY-P2 with a piece of filter paper by extracting the pH value from concrete. This is a simple and inexpensive method that does not damage the concrete building, and is easy to apply on concrete samples for monitoring. By using the method mentioned above, a drastic decrease of the pH value of concrete bridges and buildings has investigated. The method is environmentally friendly to detect the pH value change of concrete as an environmental sample investigation.

Journal Article↗