In this paper, we report the chemical constituents, larvicidal and antimicrobial activities of essential oils from Zingiber castaneum Škorničk. & Q.B. Nguyễn and Zingiber nitens M.F. Newman growing in Vietnam. The main constituents of Z. castaneum leaf were bicyclogermacrene (24.8%), germacrene D (12.9%), cis -β-elemene (11.2%) and β-pinene (10.3%), while the pseudo-stem contained bicyclogermacrene (15.8%), cis -β-elemene (9.8%) and germacrene D (9.2%). The significant compound of the rhizome oil was sabinene (22.9%), along with α-pinene (7.8%), β-pinene (6.5%), bornyl acetate (6.1%) and γ-terpinene (5.5%). However, β-pinene (45.8%), α-pinene (10.7%) and bicyclogermacrene (7.8%) were the dominant compounds in the leaf oil of Z. nitens . Terpinen-4-ol (77.9%) occurred as the compound occurring in higher amount in the rhizome oil. The rhizome oil of Z. castaneum exhibited 100% mortality towards Ae. aegypti (concentration, 200 µg/mL; 24 h and 48 h) and Ae. albopictus (concentration, 100 µg/mL; 24 h and 48 h). However, mortality of 81.3% was observed against Cx. quinquefasciatus at 48 h (concentration 100 µg/mL). The leaf also exhibited 100% mortality against Ae. aegypti (concentration, 100 µg/mL; 24 h and 48 h) and Cx. quinquefasciatus (concentration, 150 µg/mL; 24 h and 48 h). The rhizome oil displayed a minimum lethal concentration LC 50 of 121.43 µg/mL and 110.31 µg/mL against Ae. aegypti respectively at 24 h and 48 h while values of 49.85 µg/mL and 43.93 µg/mL at 24 h and 48 h were observed against Ae. albopictus respectively. In addition, LC 50 values of 88.86 µg/mL and 48.08 µg/mL were recorded respectively against Cx. quinquefasciatus . Also, the leaf oil displayed significant larvicidal activity against Ae. aegypti with LC 50 of 39.30 µg/mL (24 h) and 31.78 µg/mL (48 h) while LC 50 values of 84.97 µg/mL (24 h) and 47.40 µg/mL (48 h) were recorded respectively against Cx. quinquefasciatus . The leaf oil of Z. nitens exhibited 100% mortality against Ae. aegypti at 24 h and 48 h period (concentration 50 µg/mL) while the rhizome oil displayed maximum mortality at concentration of 100 µg/mL. The rhizome oil attained only mortality of 93% against Cx. quinquefasciatus at test period. No significant mortality was recorded against Cx. quinquefasciatus by the leaf oil. The LC 50 values of 17.58 µg/mL (24 h) and 15.12 µg/mL (48 h) were displayed by the leaf oil against Ae. aegypti while values of 29.60 µg/mL (24 h) and 26.21 (48 h) were exhibited by the rhizome oil. Only the rhizome oil was toxic against Cx. quinquefasciatus with LC 50 of of 64.18 µg/mL (24 h) and 59.06 µg/mL (48 h). The pseudo-stem oil of Z. castaneum inhibited the growth of Pseudomonas aeruginosa (ATCC 25923) with minimum inhibitory concentration (MIC) of 12.5 µg/mL, while all other tested samples recorded MIC of 50 µg/mL. However, only the pseudo-stem oil of Z. castaneum displayed antimicrobial activity against Aspergillus niger (ATCC 9763) and Fusarium oxysporum (ATCC 48112) with MIC of 50 µg/mL.

Since Vietnam is integrating internationally in all aspects of social life, more and more foreigners are learning Vietnamese. However, there are still very few quantitative studies on teaching and learning Vietnamese idioms effectively. This study aims to fill the theoretical gap and provide more evidence on the factors affecting Vietnamese idiom learning effectiveness. This study was conducted through a cross-sectional survey using a targeted sampling technique (n=100). The multiple linear regression models is applied to prove the hypotheses. The R language is used to analyze research data. The research results show that the willingness to learn Vietnamese and the strategy to learn Vietnamese have a positive and significant impact on the effectiveness of learning Vietnamese idioms. The results of this study continue to confirm the role of cognitive techniques in learning idioms as the results of previous studies.

Rice bran is a subsidised product of rice processing. It is rich in carbohydrate, especially xylan therefore, has being used for production of soluble fiber oligosaccharide including xylooligosaccharides (XOS). XOS is an oligomer of 2-7 xylose residues and has been proven to be fermented by beneficial bacteria Bifidobacterium and Lactobacillus in colon. The market for XOS is increasing rapidly due to its advantages in biological and technological properties, compared to other common oligosaccharides, such as fructooligosaccharide or galactooligosaccharide. XOS can be produced from rice bran using either chemical or enzymatic hydrolysation technologies. The hydrolyzation using β-1,4-xylanase is commonly used to produce XOS from rice bran. However, an appropriate technology for XOS production from rice bran with high purity and food safety in Vietnam is not available yet. This paper presents new data on optimisation of rice bran hydrolyzation by xylanase to produce XOS using the quadratic model of Box-Behnken. The theoretically optimized conditions for the hydrolyzation are 0.25% enzyme at pH 5.5, temperature of 50°C for 18 hours. Experimental data confirmed the selected condition. The XOS product contains mainly xylobiose, xylotriose and xylotetraose.

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