Sugar Ester Synthesis by Thermostable Lipase from <Emphasis Type="Italic">Streptomyces thermocarboxydus</Emphasis> ME168

The extracellular lipase from Streptomyces thermocarboxydus ME168 was purified to 9.5-fold with 20% yield, following concentration by acetone precipitation, ion exchange chromatography (Resource Q) and gel filtration chromatography (Superdex 200), respectively. The purified enzyme had an apparent molecular mass of 21 kDa by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). The N-terminal sequence of the lipase was ASDFDDQILG and was different from most other reported lipase. The enzyme showed maximum activity at 50 °C with the half-life of 180 min at 65 °C. It showed high stability at a broad pH range of 5.5–9.5 and was thermostable at the temperature range of 25–60 °C. The K _m and V _max were 0.28 mM and 1,428 U/mg, respectively, using p-nitrophenyl palmitate as substrate. It was active toward p-nitrophenyl ester with medium to long acyl chain (C₈–C₁₆). Lipase activity was inhibited by Zn²⁺, dithiothreitol (DTT), EDTA and some organic solvents, e.g., ethanol, acetone, dioxane, acetronitrile, tert-butanol and pyridine. Immobilized crude lipase of S. thermocarboxydus ME168 on celite could be used to synthesize sugar esters from glucose and vinyl acetate, vinyl butyrate or vinyl caproate in tert-butanol:pyridine (55:45 v/v) at 45 °C with conversion yields of 93, 67 and 55%, respectively.     

Morphology,Mechanical, and Water Barrier Properties of Carboxymethyl Rice Starch Films: Sodium Hydroxide Effect

Carboxymethyl rice starch films were prepared from carboxymethyl rice starch (CMSr) treated with sodium hydroxide (NaOH) at 10–50% w/v. The objective of this research was to determine the effect of NaOH concentrations on morphology, mechanical properties, and water barrier properties of the CMSr films. The degree of substitution (DS) and morphology of native rice starch and CMSr powders were examined. Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and differential scanning calorimetry (DSC) were used to investigate the chemical structure, crystallinity, and thermal properties of the CMSr films. As the NaOH concentrations increased, the DS of CMSr powders increased, which affected the morphology of CMSr powders; a polyhedral shape of the native rice starch was deformed. In addition, the increase in NaOH concentrations of the synthesis of CMSr resulted in an increase in water solubility, elongation at break, and water vapor permeability (WVP) of CMSr films. On the other hand, the water contact angle, melting temperature, and the tensile strength of the CMSr films decreased with increasing NaOH concentrations. However, the tensile strength of the CMSr films was relatively low. Therefore, such a property needs to be improved and the application of the developed films should be investigated in the future work.     

High Substitution Synthesis of Carboxymethyl Chitosan for Properties Improvement of Carboxymethyl Chitosan Films Depending on Particle Sizes

This study investigated the effect of chitosan particle sizes on the properties of carboxymethyl chitosan (CMCh) powders and films. Chitosan powders with different particle sizes (75, 125, 250, 450 and 850 µm) were used to synthesize the CMCh powders. The yield, degree of substitution (DS), and water solubility of the CMCh powders were then determined. The CMCh films prepared with CMCh based on chitosan with different particle sizes were fabricated by a solution casting technique. The water solubility, mechanical properties, and water vapor transmission rate (WVTR) of the CMCh films were measured. As the chitosan particle size decreased, the yield, DS, and water solubility of the synthesized CMCh powders increased. The increase in water solubility was due to an increase in the polarity of the CMCh powder, from a higher conversion of chitosan into CMCh. In addition, the higher conversion of chitosan was also related to a higher surface area in the substitution reaction provided by chitosan powder with a smaller particle size. As the particle size of chitosan decreased, the tensile strength, elongation at break, and WVTR of the CMCh films increased. This study demonstrated that a greater improvement in water solubility of the CMCh powders and films can be achieved by using chitosan powder with a smaller size.     

Optimization of Cellulase and Xylanase Productions by Streptomyces thermocoprophilus Strain TC13W Using Oil Palm Empty Fruit Bunch and Tuna Condensate as Substrates

The modified medium composed of the alkaline-pretreated oil palm empty fruit bunch (APEFB) and tuna condensate powder was used for cellulase and xylanase productions by Streptomyces thermocoprophilus strain TC13W. The APEFB contained 74.46% (w/w) cellulose, 15.72% (w/w) hemicellulose, and 6.40% (w/w) lignin. The tuna condensate powder contained 55.49% (w/w) protein and 11.05% (w/w) salt. In the modified medium with only 6.75 g/l tuna condensate powder, 10 g/l APEFB, and 0.5 g/l Tween 80, S. thermocoprophilus strain TC13W produced cellulase 4.9 U/ml and xylanase 9.0 U/ml. The enzyme productions in the modified medium were lower than cellulase (6.0 U/ml) and xylanase (12.0 U/ml) productions in the complex medium (CaCl₂ 0.1, MgSO₄·7H₂O 0.1, KH₂PO₄ 0.5, K₂HPO₄ 1.0, NaCl 0.2, yeast extract 5.0, NH₄NO₃ 1.0, Tween 80 0.5). When tuna condensate powder in the modified medium was reduced to 5.0 g/l and Tween 80 was increased to 1.5 g/l, S. thermocoprophilus strain TC13W produced cellulase and xylanase activities of 9.1 and 12.1 U/ml, respectively. This study shows that the cost of enzyme production could be reduced by using pretreated EFB and tuna condensate as a carbon and a nitrogen source, respectively.