Chemical and Biomolecular Engineering - Research Publications
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ItemThe effect of pH on the fat and protein within cream cheese and their influence on textural and rheological properties(Elsevier BV, 2020-12-01)The effect of variation in acid gel pH during cream cheese production was investigated. The gel microstructure was denser and cheese texture firmer, as the pH decreased from pH 5.0 to pH 4.3, despite the viscoelasticity of these gels remaining similar during heating. Protein hydration and secondary structure appeared to be key factors affecting both cheese microstructure and properties. Proteins within the matrix appeared to swell at pH 5.0, leading to a larger corpuscular structure; greater β-turn structure was also observed by synchrotron-Fourier transform infrared (S-FTIR) microspectroscopy and the cheese was softer. A decrease in pH led to a denser microstructure with increased aggregated β-sheet structure and a firmer cheese. The higher whey protein loss at low pH likely contributed to increased cheese hardness. In summary, controlling the pH of acid gel is important, as this parameter affects proteins in the cheese, their secondary structure and the resulting cream cheese.
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ItemEffects of shredding on the functionality, microstructure and proteolysis of low-moisture mozzarella cheese(ELSEVIER SCI LTD, 2021-06)Low-moisture mozzarella cheese (LMMC) is commonly shredded before packaging, however, the effects of shredding are not fully understood. Industrially-produced block and shredded LMMC were studied during 8 weeks of storage at 4 °C. Cheese shredded on 15 d and at 8 weeks of age, coated with microcrystalline cellulose and stored in a modified atmosphere (70% N₂ and 30% CO₂), had an altered microstructure after 8 weeks compared with vacuum-packed block cheese. In the latter case the fat formed a more dispersed phase. Proteolysis was higher in shredded samples and a higher level of two bacterial proteases was detected. Despite these differences, the meltability and stretchability of the block and shredded LMMC were similar. The microstructure and functionality of cheese shredded at 15 d and stored for a further 6 weeks was similar to cheese shredded at 8 weeks, suggesting there is a flexible period for performing cheese shredding processes.
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ItemStructure and functionality of almond proteins as a function of pH(ELSEVIER, 2021-10)Almond proteins have potential utility in a range of food and beverages but it is not clear how pH affects protein structure and function. The behaviour of almond protein isolate was examined under conditions of neutral and acidic pH (pH 7 and 4). The isolate was highly soluble (70–80%) at either pH. An increase in acidity lead to protein unfolding, an increase in random coil structure and the appearance of lower molecular weight proteins due to acidic hydrolysis. These structural changes at pH 4 increased the capacity for foam formation and foam stability, increased viscosity and led to concentration and age dependent thickening. Gels, similar in strength but with distinct microstructures and properties were obtained following heating. At pH 7, a particulate type gel with an interconnected protein network was formed, while the gel at pH 4 had a dense continuous protein matrix. The gels differed in their susceptibility to chemical disruption, suggesting different underlying molecular interactions. The ability to alter protein structure and properties as a function of pH and heating could be used to broaden the application of almond proteins and develop a variety of food products, such as protein supplements and vegan alternatives to traditional products.
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ItemPilot scale concentration of cheese whey by forward osmosis: A short-cut method for evaluating the effective pressure driving force(Elsevier, 2020-11-01)Cheese whey was concentrated to a concentration factor of 2.7 in a pilot scale forward osmosis filtration system, using a commercial cellulose triacetate membrane in a spiral-wound configuration. The whey was concentrated in a batch mode, using sodium chloride as the draw solution at initial osmotic pressures of 53–75 bar. During the process, flux was shown to reduce due to the simultaneous decrease in the bulk osmotic pressure of the draw solution, increase in the bulk osmotic pressure of the whey and the effect of concentration polarisation on both sides of the membrane. The flux is known to be driven by the effective osmotic pressures of whey and the draw solution on the surface of the membrane active layer. A short-cut approach that requires minimal information in advance about the osmotic pressure of whey and the geometry of the filtration system was implemented, enabling the determination of these effective osmotic pressures. The results obtained were shown to be in agreement with the fundamental forward osmosis flux model. The short-cut approach can be utilised for estimating effective osmotic pressures of other liquid food streams to be concentrated by forward osmosis, without the need of external measurements.
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ItemThe relevance of critical flux concept in the concentration of skim milk using forward osmosis and reverse osmosis(Elsevier BV, 2020-10-01)Skim milk was concentrated at 10 °C using forward osmosis (FO), reverse osmosis (RO) and pressure-assisted forward osmosis (PAFO). A pressure of 40 bar, in the form of draw solution osmotic pressure (FO and PAFO modes) or transmembrane hydraulic pressure (RO mode) was applied; an additional hydraulic pressure of 2 bar was applied in the PAFO mode. More severe protein fouling was observed in RO, followed by PAFO and then FO. This was credited to the difference in the initial permeate flux, induced by the different effective driving pressures, with RO having a greater deviation of the initial flux from the critical flux value. The critical flux was determined for the FO and RO modes using a step-wise increase of draw solution osmotic pressure or hydraulic pressure, at a constant milk solids content. The critical flux was between 5.4 L/m2h (1.5 × 10−6 m3/m2s) and 7.2 L/m2h (2 × 10−6 m3/m2s) for both the FO and RO modes at a cross flow velocity of 0.2 m/s. The similarities in the critical flux for FO and RO suggests that the critical flux does not depend on the nature of pressure applied on the system (hydraulic or osmotic). Therefore, when operated at the same flux and crossflow velocity, FO would not fundamentally provide a lower fouling environment compared to RO. An increase of the solids content from 8.7% to 17.3% caused a reduction in the critical flux from 5.4 L/m2h to 3.1 L/m2h (8.5 × 10−7 m3/m2s).
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ItemThe use of carbonic anhydrase to accelerate carbon dioxide capture processes(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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ItemConvective transport of boron through a brackish water reverse osmosis membrane(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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ItemFormation of a thick aromatic polyamide membrane by interfacial polymerisation(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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ItemWater vapor sorption and free volume in the aromatic polyamide layer of reverse osmosis membranes(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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ItemSynthesis of N-Acetyllactosamine and N-Acetyllactosamine-Based Bioactives(AMER CHEMICAL SOC, 2021-07-14)N-Acetyllactosamine (LacNAc) or more specifically β-d-galactopyranosyl-1,4-N-acetyl-d-glucosamine is a unique acyl-amino sugar and a key structural unit in human milk oligosaccharides, an antigen component of many glycoproteins, and an antiviral active component for the development of effective drugs against viruses. LacNAc is useful itself and as a basic building block for producing various bioactive oligosaccharides, notably because this synthesis may be used to add value to dairy lactose. Despite a significant amount of information in the literature on the benefits, structures, and types of different LacNAc-derived oligosaccharides, knowledge about their effective synthesis for large-scale production is still in its infancy. This work provides a comprehensive analysis of existing production strategies for LacNAc and important LacNAc-based structures, including sialylated LacNAc as well as poly- and oligo-LacNAc. We conclude that direct extraction from milk is too complex, while chemical synthesis is also impractical at an industrial scale. Microbial routes have application when multiple step reactions are needed, but the major route to large-scale biochemical production will likely lie with enzymatic routes, particularly those using β-galactosidases (for LacNAc synthesis), sialidases (for sialylated LacNAc synthesis), and β-N-acetylhexosaminidases (for oligo-LacNAc synthesis). Glycosyltransferases, especially for the biosynthesis of extended complex LacNAc structures, could also play a major role in the future. In these cases, immobilization of the enzyme can increase stability and reduce cost. Processing parameters, such as substrate concentration and purity, acceptor/donor ratio, water activity, and temperature, can affect product selectivity and yield. More work is needed to optimize these reaction parameters and in the development of robust, thermally stable enzymes to facilitate commercial production of these important bioactive substances.