Chemical and Biomolecular Engineering - Research Publications

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    The use of carbonic anhydrase to accelerate carbon dioxide capture processes
    Yong, JKJ ; Stevens, GW ; Caruso, F ; Kentish, SE (WILEY, 2015-01)
    The chemical absorption of CO2 into a monoethanolamine solvent is currently the most widely accepted commercial approach to carbon dioxide capture. However, the subsequent desorption of CO2 from the solvents is extremely energy intensive. Alternative solvents are more energy efficient, but their slow reaction kinetics in the CO2 absorption step limits application. The use of a carbonic anhydrase (CA) enzyme as a reaction promoter can potentially overcome this obstacle. Native, engineered and artificial CA enzymes have been investigated for this application. Immobilization of the enzyme within the gas absorber or in a membrane format can increase enzyme stability and avoid thermal denaturation in the stripper. However, immobilization is only effective if the mass transfer of carbon dioxide through the liquid phase to reach the immobilization substrate does not become rate controlling. Further research should also consider the process economics of large-scale enzyme production and the long-term performance of the enzyme under real flue gas conditions.
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    Convective transport of boron through a brackish water reverse osmosis membrane
    Kezia, K ; Lee, J ; Hill, AJ ; Kentish, SE (Elsevier, 2013-10-15)
    In this work, cross-flow filtration experiments using a brackish water reverse osmosis polyamide membrane have been performed to gather boron rejection data as function of feed concentration, pressure, pH and salinity. Increasing transmembrane pressure increases the permeation of boron indicating that convective flow is important. This result is in contrast to the normal assumption that solution diffusion dominates in such systems. The extended Nernst-Planck equation with a Donnan-steric partition coefficient is used to analyse the transport mechanisms of both neutral boric acid and negatively charged borate ions through the RO membrane. The contribution of surface charge is experimentally determined by streaming potential measurements and the electrokinetic surface charge density is then calculated as a function of ionic strength and pH. It is found that a 0.380 nm pore radius and an effective membrane porosity of 0.05 shows good agreement with experimental data. Charge screening becomes more dominant with increasing ionic strength and this contribution is readily incorporated into the model. The study extends our understanding of the transport mechanism of boric acid and borate ions which can assist in predicting the performance of polyamide reverse osmosis membranes. It also raises questions as to the true mechanism of transport through such a membrane.
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    Formation of a thick aromatic polyamide membrane by interfacial polymerisation
    Lee, J ; Hill, A ; Kentish, S (Elsevier, 2013-02-05)
    Thin film composite membranes (TFCs) consist of a thin film of polymer that is responsible for high salt rejection. This layer is made via interfacial polymerisation of two monomers 1,3 phenylene diamine and trimesoyl chloride, with the membrane reported to reach a self limiting thickness of less than 200 nm. This paper reports for the first time the formation of thick free-standing aromatic polyamide membranes of greater than 50 μm in thickness via the well-known interfacial polymerisation technique. The membrane thickness as a function of polymerisation time and monomer concentration was investigated. The polyamide layer formed through interfacial polymerisation is not necessarily homogeneous, but can indeed feature areas of porosity. A mechanism for such a porous structure is proposed and discussed. The ability to form thick free-standing polyamide membranes allows bulk polymer properties to be evaluated for the first time. In particular, in this work we are able to measure the zeta potential of the membrane surface that usually faces the membrane support. We show that this surface is still negatively charged for all pH values above 4.0.
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    Water vapor sorption and free volume in the aromatic polyamide layer of reverse osmosis membranes
    Lee, J ; Doherty, CM ; Hill, AJ ; Kentish, SE (Elsevier, 2013-01-01)
    Thin film composite membranes consist of an ultra thin active layer of polymer that governs the membrane's salt rejection and water permeation properties. However, the fragility of the ultrathin layer makes it challenging to select a technique capable of differentiating between the properties of this layer from the supporting layer. In this study, we isolated enough active layer material to characterise the water vapour sorption and free volume cavity size as functions of water activity. The sorption data were modelled using the Guggenheim–Anderson–De Boer (G.A.B.) isotherm and from this the number of sorption sites for water was calculated to be 189×1019 per gram for the active layer from a commercial Dow Filmtec SW30 membrane and 188×1019 per gram for an aromatic polyamide material prepared in house. The activation energy for diffusion of water through the active layer of SW30 was also evaluated and found to be 6.95 kcal/mol, lower than the heat of liquefaction of water. This suggests that water does not permeate as individual molecules in the vapour state, but rather as clusters of water molecules. The free volume cavity size in the active layer as a function of moisture uptake was also investigated and the results were explained using a pore filling and pore swelling mechanism. This study sheds light on the mechanisms of water entry into the active layer, water transport through the active layer, and the corresponding response of the polymer chains, thereby giving critical insight for the development of more novel systems.
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    A Comparison of the Effectiveness of Sonication, High Shear Mixing and Homogenisation on Improving the Heat Stability of Whey Protein Solutions
    Koh, LLA ; Chandrapala, J ; Zisu, B ; Martin, GJO ; Kentish, SE ; Ashokkumar, M (SPRINGER, 2014-02)
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    Effect of rennet on the composition, proteolysis and microstructure of reduced-fat Cheddar cheese during ripening
    Soodam, K ; Ong, L ; Powell, IB ; Kentish, SE ; Gras, SL (SPRINGER FRANCE, 2015-09)
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    A proteomic characterization shows differences in the milk fat globule membrane of buffalo and bovine milk
    Nguyen, HTH ; Ong, L ; Hoque, A ; Kentish, SE ; Williamson, N ; Ang, C-S ; Gras, SL (Elsevier, 2017-09-01)
    The proteins of the milk fat globule membrane (MFGM) have a number of functions, such as the regulation of milk fat secretion and metabolism, the uptake and transportation of fatty acids in the intestine, and potential protection from bacterial or viral infection. While the proteome of the MFGM in bovine milk has been extensively characterized, knowledge of these proteins in buffalo milk is limited. In this study, a proteomic approach was used to characterize the proteome of the buffalo MFGM. Multiple extraction techniques were used to increase the number of proteins identified, while label free relative quantitative liquid chromatography tandem mass spectrometry was used for comparison between the buffalo and bovine MFGM proteomes. A total of 220 buffalo MFGM proteins and 234 bovine MFGM proteins were identified after being filtered from the initial dataset of 757 and 680 proteins, respectively. A sixfold higher concentration of xanthine oxidoreductase was identified per mass of buffalo MFGM protein extracted, together with significantly greater concentrations of platelet glycoprotein 4, heat shock cognate and calcineurin B homologous protein. The expression of xanthine oxidoreductase in the MFGM of buffalo milk, which can affect milk shelf-life and flavor, was confirmed by Western blot analysis and a heterogeneous distribution of this protein observed in situ on the surface of the MFGM. The high concentration of fat in buffalo milk, together with the differences in the MFGM proteome provide insights into the differences in nutritional profile, biological function and properties of these two milk products.
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    The addition of calcium chloride in combination with a lower draining pH to change the microstructure and improve fat retention in Cheddar cheese
    Ong, L ; Soodam, K ; Kentish, SE ; Powell, IB ; Gras, SL (Elsevier, 2015-07-01)
    Calcium chloride addition and the whey draining pH are known to impact on cheese making. The effect of 100 or 300 mg kg−1 calcium chloride (CaCl2) and the whey draining pH (6.2 or 6.0) on the microstructure of Cheddar cheese was assessed using confocal and cryo scanning electron microscopy. The gel made with 300 mg kg−1 CaCl2 was found to have a denser protein network and smaller pores than the gel with lower or no CaCl2 addition. CaCl2 addition reduced fat lost to the sweet whey. The texture of the cheeses with a lower draining pH was harder and moisture content lower. Our results show that the combination of calcium addition and lower draining pH could be used to increase network formation at the early stages of cheese making to improve fat retention while maintaining a similar level of total calcium in the final cheese.
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    Small scale production of cream cheese: A comparison of batch centrifugation and cloth bag methods
    Ong, L ; Kentish, SE ; Gras, SL (Elsevier, 2018-06-01)
    Cream cheese production is well established at large scale but an effective small scale process could facilitate higher throughput and lower the cost of experimental studies. Whey was separated using centrifugation or the cloth bag method and the effect of heating prior to separation examined. Heat treatment and centrifugation resulted in cream cheese with a microstructure, composition and rheological properties comparable with that of a commercial scale cream cheese. Heating was necessary to achieve effective separation, the desired product microstructure and an adequate firmness and viscosity, with the heat induced denaturation of some whey proteins contributing to these properties. Whilst both whey separation methods resulted in a similar microstructure, centrifugation led to less fat loss and an optimal product. These data provide new insights into the development of cream cheese microstructure and provide a route to further understand and optimise this process.