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Jiang H.,Chinese Academy of Agricultural Sciences | Jiang H.,TU Braunschweig | Jiang H.,Key Laboratory of Tea Processing Engineering of Zhejiang Province | Engelhardt U.H.,TU Braunschweig | And 3 more authors.
Food Chemistry | Year: 2015

Abstract An UHPLC method for the determination of flavonol glycosides (FOG) from green and oolong tea vs. black tea has been developed for the first time. Sample clean-up method by means of polyamide column chromatography was optimized with multiple-step elution. Using UHPLC and HPLC with gradient elution and photodiode array detection, eighteen FOG compounds were determined with the aid of electrospray tandem mass spectrometry. These FOG compounds were qualified on both UHPLC and HPLC, and this UHPLC method successfully separated rutin (quercetin-3-O-rutinoside) and K-grg (kaempferol-3-O-glucorhamnoglucoside) while conventional HPLC method did not. The total amounts of FOG compounds in the tea samples were 2.32-5.67 g/kg dry weight (calculated as aglycones), and there is no significant difference for the total FOG content among green tea, oolong tea and black tea. However, kaempferol glycosides are more abundant in green teas, while oolong tea has more quercetin and myricetin glycosides. In black tea quercetin glycosides were most abundant. © 2015 Elsevier Ltd. All rights reserved. Source


Zhang J.,Chinese Academy of Agricultural Sciences | Zhang J.,Key Laboratory of Tea Processing Engineering of Zhejiang Province | Zhang J.,University of Chinese Academy of Sciences | Dong C.,Chinese Academy of Agricultural Sciences | And 7 more authors.
Journal of Chinese Institute of Food Science and Technology | Year: 2015

The eutectic point and the melting point are key control parameters of tea freeze-drying technology. In this paper, the varieties, grades, moisture content of green tea were studied and also their relation with eutectic point and melting point was analyzed. The results showed that different green tea varied in the eutectic point and the melting point. The eutectic point was lower than the melting point, and both the eutectic point and the melting point of first-class green tea were lower than those of third-class green tea. The positive linear correlation coefficient between moisture content of green tea and its eutectic point was up to 0.993 and down to 0.986, A negative linear correlation between water content of green tea and its melting point was found, correlation coefficient up to -0.993, down to -0.972. It proved that tea samples in vacuum freeze-drying process which based on the eutectic point and the melting point were better than those in traditional process in sensual shape and score, and the drying rate increased by 9.95%. ©, 2015, Chinese Institute of Food Science and Technology. All right reserved. Source


Xue J.,Chinese Academy of Agricultural Sciences | Xue J.,Key Laboratory of Tea Processing Engineering of Zhejiang Province | Xue J.,University of Chinese Academy of Sciences | Jiang H.,Chinese Academy of Agricultural Sciences | And 9 more authors.
Journal of Chinese Institute of Food Science and Technology | Year: 2014

A High Performance Liquid Chromatography (HPLC) method was established for the simultaneous determination of theasinensins (theasinensin A, theasinensin B, theasinensin C) and theaflavins(theaflavin, theaflavin-3-gallate, theaflavin-3'-gallate, theaflavin-3,3'-digallate) in tea. The determination was performed on a cosmosil 5C18-AR-II column(4.6 mm × 250 mm), 50 mmol/L H3PO4 and 100% acetonitrile were used as the mobile phases with a gradient elution. The flow rate was 0.8 mL/min. The column temperature was 35°C. The UV detection wavelength was at 280 nm. The external standard method was used for the quantitative analysis. Under the selected analytical condition, theasinensins and theaflavins in the samples got ideal resolution and had good linear relationship, the correlation coefficient square (R2) were more than 0.9925. The relative standard deviations (RSD) of repetitive test, precision test and stability test were 0.01% to 0.72%, 0.04% to 0.28% and 0.02% to 0.32%, respectively. The results of recovery test show that the average recoveries of theasinensins and theaflavins were 95.50% to 120.13% and 84.14% to 105.31%, respectively. The relative standard deviations (RSD) of the average recoveries of theasinensins and theaflavins were 0.41% to 4.24% and 1.59% to 4.59%, respectively. The method is reproducible, accurate, stable, and suitable for the simultaneous determination of theasinensins and theaflavins in tea. Source

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