Gek Kee Chua

Laccase application in medium density fibreboard to prepare a bio-composite

Laccase efficacy as a biological tool for the removal of lignin in pulp industries is evident and has scope for a wider application. In this research study, rubber wood (Hevea brasiliensis) fibres were treated with laccase enzyme to study its effect on the fibre surface and the enzyme hydrolysis lignin (EHL) was collected as a byproduct. Collected EHL was concentrated (con) until the solution reached a 3% solid content. Fibre surface modification was studied by FESEM, FTIR and XRD. A distinct fibre surface with an improved crystallinity index was observed. EHL and Con-EHL were analyzed on a viscometer, FTIR, DSC, and TGA. Con-EHL exhibits a lower stretching energy at the benzene range compared to EHL and a curing pattern similar to UF was reported. To evaluate the capability of modified fibre and Con-EHL, 6 mm medium density fibreboard (MDF) of 810 kg m−3 were prepared by using 10% Con-EHL solution (by weight of fibre). The MDF boards exhibit higher mechanical strength and have passed the ASTM D1037 standard for internal bonding and modulus of rupture.

A comparison of entrapped and covalently bonded laccase: Study of its leakage, reusability, and the catalytic efficiency in TEMPO-mediated glycerol oxidation

Abstract This article presents the comparison for reusability and leakage between entrapped and covalently bonded laccase and their performances towards the selective oxidation of glycerol. The reusability of immobilized laccase enzyme was studied by reacting a batch of immobilized laccase with ABTS for 15 cycles. The investigation of the leakage of immobilized laccase was carried out by storing the immobilized laccase in acetate buffer solution for 32 days. The data show that the retained enzyme activities of entrapped and covalently bonded enzyme after being reused for eight cycles were well above 60% and the leakages after storing for a month in the acetate buffer at 4 °C were well below 15%. The entrapped laccase coupled with TEMPO was found to perform better and gave a two-fold higher yield of glyceraldehyde and glyceric acid in the selective oxidation of glycerol compared to covalently bonded laccase. Hence, physical entrapment of laccase would be a suitable immobilization method in the laccase-mediated selective oxidation of glycerol.

Magnesium Sulphate and β-Alanine Enhanced the Ability of Kluyveromyces marxianus Producing Bioethanol Using Oil Palm Trunk Sap

ABSTRACT The abundance of oil palm trunk waste generated each year has encouraged research in using its sap for fermentation to produce value-added products. One of these value-added products is bioethanol production using yeast strains. In this study, the ability of Kluyveromyces marxianus ATCC 46537 to produce bioethanol using oil palm trunk sap (OPTS) was examined. The nutrients (ammonium sulphate, di-ammonium hydrogen phosphate, magnesium sulphate, β-alanine, calcium chloride and potassium dihydrogen phosphate) required to enhance production were screened and optimised. The concentrations of bioethanol and sugars were monitored with high performance liquid chromatography. The results showed that K. marxianus could attain maximum bioethanol concentration at 16 h with a higher productivity as compared to S. cerevisiae. Magnesium sulphate and β-alanine were found to increase bioethanol production. When 7.93 g/L of magnesium sulphate and 0.90 g/L of β-alanine were supplemented to OPTS, bioethanol production increased 20% with a bioethanol yield of 0.47 g/g and a productivity of 2.22 g/L.h. Therefore, minimum supplementation of OPTS with inorganic nutrients could enhance the bioethanol production of Kluyveromyces marxianus.

Development of a low serum medium for the production of monoclonal antibody against congenital adrenal hyperplasia by hybridoma culture

ABSTRACT Statistically designed experiments were used in developing a low-serum medium for the production of a diagnostic monoclonal antibody against congenital adrenal hyperplasia using hybridoma 192. A two-level half-fractional factorial design was used for screening six components (Minimum Essential Medium Eagle amino acids, 2-mercaptoethanol, ethanolamine, ferric citrate, zinc sulfate, and sodium selenite). The experimental design was then augmented to central composite design. The basal Dulbecco’s modified Eagle’s medium (DMEM; containing 4 mM L-glutamine, 1% antibiotic–antimycotic agent) supplemented with 0.4% by volume fetal bovine serum (FBS), 311.8 mM ferric citrate, 17.3 nM sodium selenite, and 4.5 mM zinc sulfate (LSD) was found to support the growth of the hybridoma. Specific cell growth rate in the LSD (0.033 ± 0.001/h) was slightly lower than in the control medium (i.e., basal DMEM supplemented with 2% FBS; 0.0045 ± 0.003/h). Nevertheless, the specific MAb production rate for LSD was higher (0.057 ± 0.015 pg/cell · h versus 0.004 ± 0.002 pg/cell · h in LSD and control, respectively). The antibody produced in the LSD showed high specificity and no cross-reactivity with the other structural resemblance’s steroid hormones, revealing no structural changes owing to the new medium formulation developed. The new medium formulation effectively reduced the medium cost by up to 64.6%.

Production and scale-up of a monoclonal antibody against 17-hydroxyprogesterone

The hybridoma 192 was used to produce a monoclonal antibody (MAb) against 17‐hydroxyprogesterone (17‐OHP), for possible use in screening for congenital adrenal hyperplasia (CAH). The factors influencing the MAb production were screened and optimized in a 2 L stirred bioreactor. The production was then scaled up to a 20 L bioreactor. All of the screened factors (aeration rate, stirring speed, dissolved oxygen concentration, pH, and temperature) were found to significantly affect production. Optimization using the response surface methodology identified the following optimal production conditions: 36.8°C, pH 7.4, stirring speed of 100 rpm, 30% dissolved oxygen concentration, and an aeration rate of 0.09 vvm. Under these conditions, the maximum viable cell density achieved was 1.34 ± 0.21 × 106 cells mL−1 and the specific growth rate was 0.036 ± 0.004 h−1. The maximum MAb titer was 11.94 ± 4.81 μg mL−1 with an average specific MAb production rate of 0.273 ± 0.135 pg cell−1 h−1. A constant impeller tip speed criterion was used for the scale‐up. The specific growth rate (0.040 h−1) and the maximum viable cell density (1.89 × 106 cells mL−1) at the larger scale were better than the values achieved at the small scale, but the MAb titer in the 20 L bioreactor was 18% lower than in the smaller bioreactor. A change in the culture environment from the static conditions of a T‐flask to the stirred bioreactor culture did not affect the specificity of the MAb toward its antigen (17‐OHP) and did not compromise the structural integrity of the MAb.