Eng-Seng Chan

Production of biodiesel using immobilized lipase--a critical review.

Increase in volume of biodiesel production in the world scenario proves that biodiesel is accepted as an alternative to conventional fuel. Production of biodiesel using alkaline catalyst has been commercially implemented due to its high conversion and low production time. For the product and process development of biodiesel, enzymatic transesterification has been suggested to produce a high purity product with an economic, environment friendly process at mild reaction conditions. The enzyme cost being the main hurdle can be overcome by immobilization. Immobilized enzyme, which has been successfully used in various fields over the soluble counterpart, could be employed in biodiesel production with the aim of reducing the production cost by reusing the enzyme. This review attempts to provide an updated compilation of the studies reported on biodiesel production by using lipase immobilized through various techniques and the parameters, which affect their functionality.

Prediction models for shape and size of ca-alginate macrobeads produced through extrusion-dripping method

The aim of this work was to develop prediction models for shape and size of ca-alginate macrobeads produced through extrusion-dripping method. The relationship between the process variables on the shape and size of the alginate drops before and after gelation was established with the aid of image analysis. The results show that a critical Ohnersorge number (Oh)>0.24 was required to form spherical beads. The shape transition of ca-alginate beads could be typically distinguished into three phases along the collecting distance and it was affected by the combined influence of the solution properties, the collecting distance and the drop size. Mathematical equations and a master shape diagram were developed to reveal a clear operating region and the overall process limits within which spherical ca-alginate beads could be formed. In terms of bead size, the overall size correction factor (K) which accounted for the liquid loss factor (k(LF)) and the shrinkage factor (k(SF)), varied between 0.73 and 0.85 under the experimental conditions. The size prediction model correlated well with the experimental data. The approach and the outcome could be used as a model to develop prediction tools for similar bead production systems.

Nanostructured Tungsten Trioxide Thin Films Synthesized for Photoelectrocatalytic Water Oxidation: A review

The recent developments of nanostructured WO3 thin films synthesized through the electrochemical route of electrochemical anodization and cathodic electrodeposition for the application in photoelectrochemical (PEC) water splitting are reviewed. The key fundamental reaction mechanisms of electrochemical anodization and cathodic electrodeposition methods for synthesizing nanostructured WO3 thin films are explained. In addition, the effects of metal oxide precursors, electrode substrates, applied potentials and current densities, and annealing temperatures on size, composition, and thickness of the electrochemically synthesized nanostructured WO3 thin films are elucidated in detail. Finally, a summary is given for the general evaluation practices used to calculate the energy conversion efficiency of nanostructured WO3 thin films and a recommendation is provided to standardize the presentation of research results in the field to allow for easy comparison of reported PEC efficiencies in the near future.

Biodiesel production from Jatropha curcas: a critical review

The fuel crisis and environmental concerns, mainly due to global warming, have led researchers to consider the importance of biofuels such as biodiesel. Vegetable oils, which are too viscous to be used directly in engines, are converted into their corresponding methyl or ethyl esters by a process called transesterification. With the recent debates on “food versus fuel,” non-edible oils, such as Jatropha curcas, are emerging as one of the main contenders for biodiesel production. Much research is still needed to explore and realize the full potential of a green fuel from J. curcas. Upcoming projects and plantations of Jatropha in countries such as India, Malaysia, and Indonesia suggest a promising future for this plant as a potential biodiesel feedstock. Many of the drawbacks associated with chemical catalysts can be overcome by using lipases for enzymatic transesterification. The high cost of lipases can be overcome, to a certain extent, by immobilization techniques. This article reviews the importance of the J. curcas plant and describes existing research conducted on Jatropha biodiesel production. The article highlights areas where further research is required and relevance of designing an immobilized lipase for biodiesel production is discussed.

A CRITICAL REVIEW: SURFACE AND INTERFACIAL TENSION MEASUREMENT BY THE DROP WEIGHT METHOD

The drop weight method has been used as a standard method for surface and interfacial tension measurement. However, lack of appropriate guidelines in using this method has resulted in errors. The specific objective of this critical review is to present the experimental setup, the limitations on the correction factors, and the principle of the drop weight method. Mathematical models of correction factors were evaluated by using a proposed error analysis. The use of the proposed Lee-Chan-Pogaku model and HG-Equation 2 for correction factor determination is suggested. However, further investigations would be required to justify the validity of the correction factors at low r/V 1/3 range and their use for viscous fluids. The physics of drop detachment is complicated; more investigations would be required to form a rigid theory of this method.

Encapsulation of Probiotic Bacteria Lactobacillus Acidophilus by Direct Compression

The objective of the work is to evaluate the potential use of compression coating as an alternative method for the encapsulation of probiotic bacteria Lactobacillus acidophilus to improve their storage stability. Microbial cell containing powders were first compressed into a pellet, which was then encapsulated with a coating material of a combination of sodium alginate and hydroxypropyl cellulose by further compression. The effect of compression pressure on cell viability was studied. Results showed that compression of the microbial cell containing powders at pressures up to 90 MPa caused little loss of viability of the bacteria. Beyond 90MPa, the cell viability decreased almost linearly with the compression pressure. Further compression to form a coating did not cause significant reduction in the cell viability. The stability of the encapsulated bacteria using the compression pressures up to 60MPa was approximately 10 times higher than free cell containing powders and cell pellets after 30 days storage at 25°C.

Comparison of alginate and pectin based beads for production of poultry probiotic cells

A comparative study on the stability and potential of alginate and pectin based beads for production of poultry probiotic cells using MRS medium in repeated batch fermentation was conducted. The bead cores, made of three types of materials, i.e., ca-alginate, ca-pectinate and ca-alginate/pectinate, were compared. The effect of single and double layer coatings using chitosan and core material, respectively, on the bead stability and cell production were also studied. The pectin based beads were found to be more stable than that of the alginate beads and their stability was further improved by coating with chitosan. The cell concentration in pectin based beads was comparable to that in the alginate beads. On the other hand, pectin based beads gave significantly lower cell concentration in the growth medium for the initial fermentation cycles when compared to the alginate beads. In conclusion, pectin was found to be potential encapsulation material for probiotic cell production owing to its stability and favourable microenvironment for cell growth.

Surface tension of viscous biopolymer solutions measured using the du Nouy ring method and the drop weight methods

The discrepancy of the existing literature data on the surface tension values of biopolymer solutions could be affected by the measurement technique. The aim of the study was to compare the surface tension values of biopolymer solutions, measured using the du Nouy ring method and the drop weight methods (Harkins–Brown correction factors method and the LCP coefficient method). Four biopolymers were chosen (sodium alginate, carboxymethyl cellulose, xanthan gum and pectin) and the surface tensions of the solutions were measured as a function of biopolymer concentration. The surface tension was found to increase with biopolymer concentration when measured using the du Nouy ring method. On the other hand, the drop weight methods gave an opposite trend. The results verified the discrepancy of the existing literature data. The error may be caused by the correction factors calculation and the solution viscosity when the du Nouy ring method was used. The LCP coefficient method which is independent of correction factors and liquid properties is proposed for measurement of the surface tension of viscous biopolymer solutions.

Effects of process variables on the encapsulation of oil in ca-alginate capsules using an inverse gelation technique

The objective of this study was to investigate the effects of process variables on the encapsulation of oil in a calcium alginate membrane using an inverse gelation technique. A dispersion of calcium chloride solution in sunflower oil (water-in-oil emulsion) was added dropwise to the alginate solution. The migration of calcium ions to the alginate solution initiates the formation of a ca-alginate membrane around the emulsion droplets. The membrane thickness of wet capsules and the elastic modulus of dry capsules increased following first-order kinetics with an increasing curing time. An increase in the calcium chloride concentration increased the membrane thickness of wet capsules and the elastic modulus of dry capsules. An increase in the alginate concentration decreased the mean diameter of wet capsules but increased the elastic modulus of dry capsules.

Particle designs for the stabilization and controlled-delivery of protein drugs by biopolymers: A case study on insulin

Natural biopolymers have attracted considerable interest for the development of delivery systems for protein drugs owing to their biocompatibility, non-toxicity, renewability and mild processing conditions. This paper offers an overview of the current status and future perspectives of particle designs using biopolymers for the stabilization and controlled-delivery of a model protein drug--insulin. We first describe the design criteria for polymeric encapsulation and subsequently classify the basic principles of particle fabrication as well as the existing particle designs for oral insulin encapsulation. The performances of these existing particle designs in terms of insulin stability and in vitro release behavior in acidic and alkaline media, as well as their in vivo performance are compared and reviewed. This review forms the basis for future works on the optimization of particle design and material formulation for the development of an improved oral delivery system for protein drugs.