Prakit Sukyai

Production of lactose-free galacto-oligosaccharide mixtures: comparison of two cellobiose dehydrogenases for the selective oxidation of lactose to lactobionic acid

Galacto-oligosaccharides, complex mixtures of various sugars, are produced by transgalactosylation from lactose using beta-galactosidase and are of great interest for food and feed applications because of their prebiotic properties. Most galacto-oligosaccharide preparations currently available in the market contain a significant amount of monosaccharides and lactose. The mixture of galacto-oligosaccharides (GalOS) in this study produced from lactose using recombinant beta-galactosidase from Lactobacillus reuteri contains 48% monosaccharides, 26.5% lactose and 25.5% GalOS. To remove efficiently both monosaccharides and lactose from this GalOS mixture containing significant amounts of prebiotic non-lactose disaccharides, a biocatalytic approach coupled with subsequent chromatographic steps was used. Lactose was first oxidised to lactobionic acid using fungal cellobiose dehydrogenases, and then lactobionic acid and monosaccharides were removed by ion-exchange and size-exclusion chromatography. Two different cellobiose dehydrogenases (CDH), originating from Sclerotium rolfsii and Myriococcum thermophilum, were compared with respect to their applicability for this process. CDH from S. rolfsii showed higher specificity for the substrate lactose, and only few other components of the GalOS mixture were oxidised during prolonged incubation. Since these sugars were only converted once lactose oxidation was almost complete, careful control of the CDH-catalysed reaction will significantly reduce the undesired oxidation, and hence subsequent removal, of any GalOS components. Removal of ions and monosaccharides by the chromatographic steps gave an essentially pure GalOS product, containing less than 0.3% lactose and monosaccharides, in a yield of 60.3%.

Comparing soluble and co-immobilized catalysts for 2-ketoaldose production by pyranose 2-oxidase and auxiliary enzymes

The tri-enzyme system pyranose 2-oxidase (P2O), laccase, and catalase was used to study major parameters in the homogeneous and heterogeneous application of a multi-component enzymatic machinery. P2O oxidizes aldoses to 2-ketosugars, which are interesting intermediates in carbohydrate chemistry, and concomitantly reduces oxygen or alternative electron acceptors. The enzyme was immobilized on eleven agarose or acrylic resins using various coupling methods. The binding capacity was determined and an acrylic carrier with the most suitable properties selected for detailed studies. As P2O shows higher turnover numbers with the electron acceptor 1,4-benzoquinone than with oxygen, the use of this alternative electron acceptor was enabled by employing laccase for the continuous reoxidation of hydroquinone. The laccase regeneration system was found to increase the specific productivity up to 3-fold. Catalase was used to disproportionate the formed hydrogen peroxide in close proximity to the oxygen consuming enzymes and applied in different amounts to adjust the hydrogen peroxide concentration, which was found to be the main reason for enzyme deactivation under turnover conditions. In contrast to homogeneous catalysis, the specific productivity of heterogeneous catalysts under the applied experimental conditions was limited primarily by oxygen transfer, an effect significantly reduced by the laccase regeneration system.

The Effect of Bacterial Cellulose on the Mechanical and Thermal Expansion Properties of Kenaf/Polylactic Acid Composites

The reinforcement of PLA matrix with natural fibers aims to generate the sustainable biocomposites. Kenaf fiber (KF) and bacterial cellulose (BC) were employed to reinforce and diminish the usage of PLA matrix. Particularly, BC is nano-cellulose which was anticipated to increased interfacial area and therefore low volume fractions of additives. That was consequently to attain mechanical property improvement. Thus, the incorporation of KF and BC reinforced PLA composites was investigated. The extrusion method was utilized and materials were mixed outside prior to adding. The specimens were examined mechanical testing, Dynamic Mechanical Analysis (DMA), Differential Scanning Calorimetry (DSC), Thermo Gravimetric Analysis (TGA) and Scanning Electron Microscopes (SEM). The mechanical study revealed that the increment of elastic modulus increased concomitantly with the augmentation of KF content. Interestingly, PLA/KF/BC sample at ratio of 60/39/1 wt.% was efficiently to maintain tensile and flexural strength comparing to 50% reduction of without BC sample with equal fiber volume. Therefore, it could recognize that mechanical properties was improved by using low amount of nano-cellulose. This would be a high aspect ratio of BC that capable to connect between PLA matrix and KF which enhanced a large contact surface and therefore excellent coherence. The temperature dependence of storage, loss and tan delta was determined by DMA. A decrease of storage modulus was consistent with increasing of temperature, result from softening of the composites. Loss modulus was increased approximately at Tg which related to storage modulus cause. In addition, the tan delta peaks of PLA and composites were around 60°C and it did not significantly shift when emerged of fiber. DSC of both composites indicated an influence of fiber on the crystallization and enthalpy. On the other hand, glass transition and melting temperature did not significantly affect. The composites exhibited a small reduction of thermal stability when examined by TGA analysis. Notwithstanding, BC showed an improvement of thermal stability of PLA/KF/BC sample at 40 wt.% total fiber content. The linkage of BC between PLA matrix and KF was monitored by SEM.

Fabrication and Characterisation of Functionalised Superparamagnetic Bacterial Nanocellulose Using Ultrasonic-Assisted In Situ Synthesis

Ultrasonic-assisted in situ synthesis was performed using bacterial nanocellulose (BNC) and magnetite nanoparticles (Fe3O4 NPs) to synthesise superparamagnetic membranes as BNC/Fe3O4 nanocomposite films (BNC/Fe3O4 NCFs). Vibrating sample magnetometry of these BNC/Fe3O4 NCFs exhibited superparamagnetic properties with high saturation magnetisation at 40.57 emu g-1. Morphology of BNC/Fe3O4 NCFs was studied by field-emission scanning electron microscopy. Results showed Fe3O4 NPs with diameter 30 to 50 nm trapped in a BNC structure. Fourier transform infrared spectroscopy analysis confirmed the incorporation of BNC and Fe3O4 NPs. Thermal properties of the nanocomposite films increased with Fe3O4 NPs in the BNC structure compared with native BNC. Surface wettability of BNC/Fe3O4 NCFs was determined by contact angle and revealed hydrophobic properties. Results showed that ultrasonic-assisted in situ synthesis of superparamagnetic BNC/Fe3O4 NCFs is an important property when utilising BNC/Fe3O4 NCFs with a hydrophobic nonpolar polymeric matrix in electronic device applications.

Homogenous isolation of individualized bacterial nanofibrillated cellulose by high pressure homogenization

Varying levels of high pressure homogenization (HPH) were applied to disintegrate bacterial nanofibrillated cellulose (BNFC) from bacterial cellulose (BC). HPH was considered as a simple, non-toxic and highly efficient physical method for nanofibrillated cellulose extraction. The blended BC passed through chambers at high pressures of 68, 138 and 207MPa for 30 cycles. The particle size confirmed disintegration of the BC network fibers to bundles of BNFC and the atomic force microscopy images showed the decreased diameter of individual BNFC in the range 36-67nm. Fourier transform infrared spectroscopy measurement indicated there were no change in the chemical functional groups of the BNFC compared with BC. The decreased crystallinity index and crystallite size of BNFC with increased pressure confirmed the effect of HPH on the BNFC. Nevertheless, BNFC at 207MPa had the lowest thermal stability due to having the highest surface area, which resulted in the minimum nanofiber diameter.

Production of hydroxyapatite-bacterial nanocellulose scaffold with assist of cellulose nanocrystals

Bacterial nanocellulose/hydroxyapatite/cellulose nanocrystal (BHC) composites were synthesized via in-situ synthesis using cellulose nanocrystals (CNCs) to improve colloidal stability and the dispersion of hydroxyapatite (HA) during the bacterial nanocellulose (BNC) cultivation period. Transmission electron microscopy images and energy dispersive spectroscopy (EDS) results confirmed the dispersion of HA on the CNC particles with a Ca/P ratio of 1.66 corresponding to that of the stoichiometric HA. The SEM images and EDS results showed that the integration of the HA and BNC network without CNC assistance (BHA (0.25 and 0.5 wt.%) composites) was less than that for BHC at both concentrations. Fourier-transform infrared analysis, XRD and thermal degradation revealed the effect of HA on the BHC composites with a decreased CrI% and improved thermal property. Cytotoxicity proved the potential for using BHC composites for bone tissue engineering scaffold with cell viability up to 83.4 ± 3.6% compared to the negative control (99.2 ± 0.08%).

The Effect of Thai Compost on Biodegradability of Polylactic Acid Based on ISO 14855-2 Method

The plastic requirements of earth inhabitant are enormous and have environment impacts of such consumption. An average person consumes many tons of those materials which ultimately disposed as wastes. Therefore, the trend of environmental awareness increases the demanding of biodegradable plastic. Presently, the biodegradability test has been reported in various kinds of standards. However, the biodegradation in aerobic condition under controlled composting system is the main focus of this research. As we have known that microorganisms in compost are the key player of biodegradation which differ from country to country. Therefore, our own compost was fermented from rice straw together with cow dropping and urea for 60 days. It was found that the properties of compost were acceptable the requirements of ISO 14855-2. Such that the compost was utilized for testing the biodegradation of cellulose and polylactic acid powder which operated by Microbial Oxidative Degradation Analyzer (MODA). The compost was designed to control the humidity, aeration ratio and temperature at 58oC. It was discovered that the percentage of biodegradability of cellulose and polylactic acid powder were 80 and 98, respectively after 60 days testing. Thus, from this report, we have confirmed that our compost attain the criterion of standard requirement.