Vietnam Journal of Science, Technology and Engineering

3-8

Authors: Thi Thu Huong Tran, Thi Tuyet Mai Phan*, Van Boi Luu, Ngoc Lan Pham

This research illustrates the results of a study on the synthesis of maleic anhydride-vinyl acetate copolymers (MAVA) with the monomer molar ratio of 1:1 by the radical polymerisation method in which benzoyl per-oxide was used as a catalyst. The structure and compo-sition of MAVA were characterised by FTIR, 1H-NMR and 13C-NMR spectra. The molecular weight of the co-polymers was determined by the viscosity method. The copolymers were then modified by the esterification reaction with hexadecanol - a long alkyl chain alcohol. The modified copolymer products (MAVAC) were used as additives to improve the cold flow properties of palm oil-based biodiesel through pour point temperature measurement according to standard ASTM-D97 and dynamic viscosity according to ASTM D445-97. The re-sults showed that the MAVAC additives with the comb-shape structure at the concentration of 1000 ppm could decrease the pour point temperature of palm oil-based biodiesel by 5.5oC and dynamic viscosity by 0.17 cPs.

13-18

Authors: Trinh Nguyet Tran, Huynh Xuan Phong, Bui Thi Thao Anh, Bui Hoang Dang Long, Nguyen Ngoc Thanh, and Ngo Thi Phuong Dung*

Acerola (Malpighia emarginata) vinegar is one kind of fruit vinegar produced using acetic acid fermented by acetic acid bacteria. In this study, Acetobacter senegalensis A28 was applied in acerola vinegar production at a high temperature. With 1.0% (v/v) of A. senegalensis A28 inoculum, the suitable conditions for production of acerola vinegar were determined to be pH 6.5, 20°Brix, 106 cells/ml, as well as 4.0% (v/v) of ethanol added to acerola juice. Moreover, a temperature of 35°C was found to be suitable for fermentation in both 100 ml and 2 litre working volumes. Total acid concentrations of 5.45% (w/v) and 4.90% (w/v), respectively, were achieved after 4 days of fermentation. Acid concentrations of 5.40% (w/v) and 4.70% (w/v) were obtained at 37°C after 5 days of fermentation in volumes of 100 ml and 2 litres, respectively. At pilot-scale fermentation of 20 litres at 37°C, acid concentration of 3.68% (w/v) was achieved after 5 days of fermentation.

26-32

Authors: Van Dang Tran*, Dong Tran, Marc Oudjene

Timber is highly anisotropic. It behaves differently in diverse directions. Tension and compression perpendicular to the grain present a low strength with respect to the ones parallel to the grain. To compensate for the lack, the self-tapping screw is an excellent choice for reinforcing the timber. This paper focuses on the notched timber beam with the experimental and numerical results. In the first part, the experimental results of the unreinforced notched beams and the screw reinforced notched beams under bending load will be presented. The second part describes a numerical study in which a 3D finite element (FE) model and a fast FE model of the notched beam reinforced by a self-tapping screw are realised. In particular, the fast FE model is simplified with the use of the screw’s model as a beam element having one translational degree of freedom. This model not only presents a good result in comparison with the experiment as well as the 3D FE model but also requires six times less computational times as compared to the 3D FE model.

37-41

Authors: Quoc Sinh Nguyen*, Chi Bao Nguyen, Thanh Long Le, Sy Vuong Ho, Thi Diem Huong Nguyen, Van Quoc Bao Vo, Van Toan Nguyen

Gamma(γ)-Aminobutyric acid (GABA), which provides a variety of health benefits, is an important bioactive component of tea (Camellia sinensis). A special tea product, GABA tea, contains high levels of γ-Aminobutyric acid which is produced by anaerobic fermentation. Tea fermentation is affected by a number of factors, including anaerobic conditions (vacuum, and the kind of gas used), temperature, and the duration of anaerobic fermentation. In this study, the levels of bioactive compounds in tea leaves produced by fermenting fresh tea leaves in nitrogen gas are investigated. The fermentation was conducted at different temperatures: room temperature (28±2), 35, and 40ºC; and for each temperature setting, the fermentation times were 6, 9, 12, and 15 hours. The results show that the GABA content increased significantly with fermentation temperature. The most appropriate temperature and time for the anaerobic fermentation to produce GABA and other bioactive compounds were, respectively, 40ºC and 9 hours. Under these conditions, GABA content reached the maximum value (202.77 mg/100 g of dry tea); that of total polyphenols was 22.30% of dry matter (DM); caffeine was 2.39% DM; and soluble solids were 36.25% DM.

48-54

Authors: Tran Thi Thuy Ha, Thai Thi Lam, Nguyen Thanh Huyen, Nguyen Xuan Canh*

To isolate and characterise free nitrogen-fixing bacteria, we collected randomly soil samples from different areas of Ha Noi. Nitrogen-fixing bacteria were isolated using Burk’s medium without nitrogen mineral supplement. The ammonia (NH4+) synthesis of these bacterial strains after biomass production was determined by means of Nessler reagent. Based on the results of isolation, we observed and evaluated colony and cellular morphology, pigment production, and metabolic activities of twenty-five isolates. Among the isolated bacteria, two bacterial strains (6.2 and 8.2) with high NH4+ concentration in the cultural medium were selected as the best strains for nitrogen-fixing ability. The optimal pH and temperature for their growth and nitrogen fixation are 7.0 and 30°C, respectively. Growth is best favored in the presence of sucrose. We sequenced the 16S rRNA gene of selected strains and compared the homology of them in GenBank using BLAST search. The result of the comparison shows that the 6.2 and 8.2 strains have 99% and 100% 16S rRNA-sequence similarity with Pseudomonas sp. and Bacillus sp., respectively

59-66

Authors: Hanh Dung Thai, Van-Tuan Tran*

The filamentous fungus Aspergillus oryzae, also named as the koji mold, is a preferred host for enzyme production due to its prominent secretion ability into the culture medium. Fungal laccases are widely used in different industrial processes, especially in removing environmental pollutants. Up till now, little was known about the roles of some laccase genes from the black mold Aspergillus niger. The McoD laccase gene from A. niger includes three exons interrupted by two short introns. The respective coding sequence of the gene is computationally predicted to encode a secreted laccase of 563 amino acids. In this study, a binary vector carrying the A. nigerMcoD gene was successfully constructed for heterologous expression in the edible fungus A. oryzae. This vector was transformed into A. oryzae using the Agrobacterium tumefaciens-mediated transformation method. The transformation efficiency was relatively high in two different auxotrophic A. oryzae strains, including RIB40∆pyrG and VS1∆pyrG. All the tested transformants possess in their genomes the construct for expression of the McoD laccase gene under control of the strong A. oryzae amyB promoter. The selected transformants were examined for the laccase activity using the ABTS substrate. The results showed that in comparison to the wild-type fungal strains, the transgenic strains could oxidise ABTS to form the sea green colour, which can be seen directly on the agar plate

74-80

Authors: Le Anh Tuan*

The Vietnamese Mekong river delta (MD) is recognised as the biggest agriculture and aquaculture region of Vietnam. The MD plays an important role in ensuring food security for the country. The MD also has many sensitive ecosystems reliant on the ecology of the Mekong river basin. However, during the last decade, many electricity generation plants, both renewable and non-renewable power projects, have been built and some will be built in the near future in the MD. These energy plants’ construction and operation may prove to be a challenge to the national energy strategy.This paper is a monograph review of two sides of energy sector industrialisation in the MD with a focus on ‘green’ and ‘grey’ socio-economic development (as ‘xanh’ and ‘xám’ in Vietnamese respectively). ‘Green’ energy is understood as the electricity generated from inexhaustible sources and known as renewable energy. It emits fewer greenhouse gases and causes less harm to habitats in comparison to traditional fossil fuels and hydropower. ‘Grey’ energy is another word for non-renewable energy or polluting energy, which can have negative effects on human health, environment, and climate. This paper finds that the MD’s energy development plans at present might not be as ‘green’ as expected, due to more ‘grey’ power plans in the planning pipeline. This paper also considers an outlook on energy prices and impacts on long-term sustainable development of the MD.

89-96

Authors: Mau Nguyen-Dang*, Truong Nguyen-Minh, Hidetaka SASAKI, Izuru TAKAYABU

This article presents analyses of changes in the seasonal characteristics of the far future climate (2080-2099) across Vietnam as projected by the Non-Hydrostatic Regional Climate Model (NHRCM) in terms of the RCP 8.5 (Representative Concentration Pathways 8.5) scenario. The results show significant changes in seasonal rainfall in Vietnam compared with the 1982-2003 baseline period. Specifically, the June-August rainfall is projected to increase in South Central (SCVN), Central Highlands (CHVN), and South Vietnam (SVN), but to decrease by approximately 50% in North Central (NCVN) and off the Central coast. In the September-November season, the NHRCM detects an increase in rainfall of about 50% in North Vietnam (NVN) and CHVN. The increase and decrease in rainfall are due to the convergence and divergence of moisture flux that might be associated with the westward expansion of the Northwestern Pacific High Pressure in the far future