Li Z.,Jiangnan University |
Wu X.,Jiangnan University |
Cai L.,University of South Carolina |
Duan S.,China National Research Institute of Food and Fermentation IndustriesBeijing |
And 4 more authors.
Bioorganic and Medicinal Chemistry Letters | Year: 2015
Abstract l-Rhamnulose-1-phosphate aldolase from a thermophilic source (Thermotoga maritima MSB8) (RhaDT.mari) was heterologously overexpressed in Escherichia coli and the stereoselectivity of this enzyme with or without Nus tag was investigated. We also applied this enzyme to the synthesis of rare sugars d-psicose, d-sorbose, l-tagatose and l-fructose using our one-pot four-enzyme system. To the best of our knowledge, this is the first use of RhaD from a thermophilic source for rare sugar synthesis and the temperature tolerance of this enzyme paves the path for large scale fermentation. © 2015 Elsevier Ltd.
Hu W.,Ocean University of China |
Wang D.,Ocean University of China |
Li H.,China National Research Institute of Food and Fermentation IndustriesBeijing
Journal of the American Society of Brewing Chemists | Year: 2015
Controlling the content of formaldehyde in beer is very important because of formaldehyde's toxicity. Nevertheless, accurate determination of its content in beer is difficult because of its low concentration in beer and reversible combination with sulfite. A selective and sensitive HPLC method for the determination of formaldehyde in beer, based on the derivatization of formaldehyde and 2,4-dinitrophenylhydrazine (DNPH), is described. Sample pretreatment was as follows: extraction of formaldehyde from beer through steam distillation of a beer sample preceded by adding 20 mL of phosphoric acid (concentration, 200 g/L) into 20 mL of beer and collection of 100 mL of distillate; mixing of 0.5 mL of the distillate and 1 mL of DNPH (concentration,1 g/L) in a 5-mL tube; and derivatizing for 20 min at 60°C. After derivatization, separation of the derivate was achieved using a C18 column (4 × 250 mm, 5 μm) and isocratic elution with 45% acetonitrile. This whole method enabled formaldehyde in beer to be determined with recoveries close to 100%, a repeatability error of less than 1%, and a limit of detection (LOD) of less than 3 μg/L. The overall method was successfully applied to the determination of formaldehyde in marketplace beers. The results showed that the concentration of formaldehyde in Chinese beers ranged from 0.062 to 0.453 mg/L, and the average content of formaldehyde in these beers was 0.134 mg/L. © 2015 American Society of Brewing Chemists, Inc.