The research has established a method to directly extract and determine free quercetin (aglycone form) from Flos Sophorae Immaturus methanol extract by using a simple HPLC method. Conducting experiment with system HPLC Agilent 1260 Infinity, reverse column ZORBAX SB-C18 (temperature 25oC), flow rate 0.5 ml/min, average pressure 30 and 35 bar, and diode array detector (DAD), we found that these parameters is suitbale: λmax = 370 nm, injection volume is 20 µl, analysis time 16 minutes, mobile phase (% volume) consists of methanol (15%), acetonitril (20%) and solvent C (65%, contains 1% acetic acid, methanol, acetonitril and H2O, 40%, 15% and 45% respectively. After using a combination of irocratic elution and standard addition, retention time of free quercetin in Flos Sophorae Immaturus methanol extract has found to be 8.84 ± 0,05 (min). Relative standard deviation (RSD) of retetion time, peak area and peak height have been less than 1%, this results have indicated that the proposed method has fullfilled the validation parameters such as selectivity/specitifity, precision/repeatability. This study provided useful information for screening activity of quercetin by using different methods.

Following the rising concern on environmental issues caused by conventional fossil-based plastics and depleting crude oil resources, polyhydroxyalkanoates (PHAs) are of great interest by scientists and biodegradable polymer market due to their outstanding properties which include high biodegradability in various conditions and processing flexibility. Many polyhydroxyalkanoate-synthesizing microorganisms, including normal and halophilic bacteria, as well as algae, have been investigated for their performance in polyhydroxyalkanoate production. However, to the best of our knowledge, there is still limited studies on PHAs-producing marine yeast. In the present study, a halophilic yeast strain isolated from Spratly Island in Vietnam were investigated for its potential in polyhydroxyalkanoate biosynthesis by growing the yeast in Zobell marine agar medium (ZMA) containing Nile red dye. The strain was identified by 26S rDNA analysis as Pichia kudriavzevii TSLS24 and registered at Genbank database under code OL757724. The amount of polyhydroxyalkanoates synthesized was quantified by measuring the intracellular materials (predicted as poly(3-hydroxybutyrate) -PHB) by gravimetric method and subsequently confirmed by Fourier transform infrared (FTIR) spectroscopic and nuclear magnetic resonance (NMR) spectroscopic analyses. Under optimal growth conditions of 35 °C and pH 7 with supplementation of glucose and yeast extract at 20 and 10 gL−1, the isolated strain achieved poly(3-hydroxybutyrate) content and concentration of 43.4% and 1.8 gL−1 after 7 days of cultivation. The poly(3-hydroxybutyrate) produced demonstrated excellent biodegradability with degradation rate of 28% after 28 days of incubation in sea water.

In this study, acidic hydrolysis to release the aglycone quercetin from plant extracts under ultrasound-assisted conditions was investigated. Based on the stability of quercetin, the suitable conditions were as follows: methanol/H2O (50:20, v/v) was added to the powder plants (ratio 50:1, ml/g), these mixtures were placed in ultrasonic bath of 37 kHz/550W; kept at 70°C within 30 min and then filtered. The filtrate was acidified with HCl (70:8, ml/ml). Lastly, the ultrasonication was carried out for hydrolysis for 1 hour (the second ultrasound) to obtain quercetin. We have obtained quercetin containing hydrolyzed extract from 10 plants to determine quercetin concentrations (using the HPLC optimized conditions) and evaluate the antioxidant activity (the capability to scavenge the DPPH radical). In 10 samples of plants that were obtained, both quercetin concentrations and antioxidant activity in the plant extract of the flower buds of Sophora japonica L have the highest value, then to the plant extract of Nelumbo nucifera Gaertn. In the Sophora flower-bud and the lotus leaf, quercetin content is calculated on dry material (mg/100g), 15423.04 and 5190.82  respectively; the average percentage inhibition of DPPH 100 µM (%) 55.26% and 32.23%., respectively. Keywords: Quercetin, HPLC, acid hydrolysis, ultrasound-assisted, antioxidant activity. References [1] S.G. Dmitrienko, V.A. Kudrinskaya, V.V. Apyari, Methods of extraction, preconcentration, and determination of quercetin, Journal of Analytical Chemistry 67 (4) (2012) 299-311. https://doi.org/ 101134/S106193481204003X.[2] H. Nishimuro, H. Ohnishi, M. Sato, M. Ohnishi-Kameyama, I. Matsunaga, S. Naito, K. Ippoushi, H. Oike, T. Nagata, H. Akasaka, S. Saitoh, K. Shimamoto, M. Konori, Estimated daily intake and seasonal food sources of quercetin in Japan, Nutrients 7 (4) (2015) 2345-2355. https://doi.org/ 10.3390/nu7042345.[3] C. Zhao, X. Ren, C. Li, H. Jiang, J. Guan, W. Su, Y. Li, Y. Tian, T. Wang, S. Li, Coupling ultrasound with heat-reflux to improve the extraction of quercetin, kaempferol, ginkgetin and sciadopitysin from Mairei Yew leaves, Applied Sciences 9 (4) (2019) 795-810. https://doi.org/10.3390/app9040795.[4] J. Azmir, M.S.I. Zaidul, M.M. Rahman, K.M. Sharif, A. Mohamed., F. Sahena, A.H.M. Jahurul, K. Ghafoor, N.A.N. Norulain, K.A.M. Omar, Techniques for extraction of bioactive compounds from plant materials : A review, Journal of Food Engineering 117 (4) (2013) 426-434. https://doi. org/10.1016/j.jfoodeng.2013.01.014.[5] L.H. Hoang, D.T.H. Anh, D.T. Hue, T.T.K. Oanh, N.Q. Huy, Determination of Quercetin Aglycone in Flos Sophorae japonicae Extract by High Performance Liquid Chromatography, VNU Journal of Science: Natural Sciences and Technology 33 (1S) (2017) 214-223 (in Vietnamese). https://doi.org/10.25073/2588-1140/ vnunst.4534. [6] A.M. Nuutila, K. Kammiovirta, M. Oksman-Caldentay, Comparison of methods for the hydrolysis of flavonoids and phenolic acids from onion and spinach for HPLC analysis, Food Chemistry 76 (4) (2002) 519-525. https://doi.org/ 10.1016/S0308-8146(01)00305-3.[7] L. Qiao, Y. Sun, R. Chen, Y. Fu, W. Zhang, X. Li, J. Chen, Y. Shen, X. Ye, Sonochemical effects on 14 flavonoids common in citrus : Relation to stability, Plos One 9 (2) (2014) e87766. https://doi. org/10.1371/journal.pone.0087766.[8] W. Brand-Williams, M.E. Cuvelier, C. Berset, Use of a free radical method to evaluate antioxidant activity, LWT - Food Science and Technology 28 (1995) 25-30. https://doi.org/10.1016/S0023-6438 (95)80008-5. [9] M. Biesaga, Influence of extraction methods on stability of flavonoids, Journal of Chromatography A 1218 (2011) 2505-2512. https://doi.org/10.1016/ j.chroma.2011.02.059.[10] L. Paniwnyk, E. Beaufoy, J.P. Lorimer, T.J. Manson, The extraction of rutin from flower buds of Sophora japonica, Ultrasonics Sonochemistry 8 (3) (2001) 299-301. https://doi.org/10.1016/S1350 -4177(00)00075-4.[11] X. He, Y. Bai, Z. Zhao, X. Wang, J. Fang, L. Huang, M. Zeng, Q. Zhang, Y. Zhang, Z. Zheng, Local and traditional uses, phytochemistry, and pharmacology of Sophora japonica L.: A review, Journal of Ethnopharmacology 187 (2016) 160-182. https://doi.org/10.1016/j.jep.2016.04.014.[12] I.Y. Bae, B.Y. Kwak, H.G. Lee, Synergistic antiradical action of natural antioxidants and herbal mixture for preventing dioxin toxicity, Food Science and Biotechnology 21 (2) (2012) 491-496. https://doi.org/10.1007/s10068-012-0062-9.