Optimization of White Tea Flavanol Extraction Process by the Ultrasonic-Assisted Deep Eutectic Solvent Method and Determination of the Antioxidant and Antibacterial Activity

Flavanols have a variety of health benefits and biological activities and become the hotspot of the food development and research. In this research, flavanols were extracted from white tea by ultrasonic-assisted deep eutectic solvent (DES) method. High-performance liquid chromatography was used to determine the content of flavanols. The influence of four factors on the flavanol extraction yield was analyzed by single factor experiments, including deep eutectic solvent mole ratio (the mole of hydrogen bond acceptors: the mole of hydrogen bond donors), solid-liquid ratio (white tea sample weight/g: the volume of DES/mL), extraction time and extraction temperature. On the basis of single factor experiments, the factors which had significant effects on the flavanol extraction yield were further optimized by the response surface test. The results showed that the optimized extraction conditions were as follows: the mole ratio of DES 1: 4 (choline chloride: 1,2-propanediol), the solid-liquid ratio 1:30, the extraction temperature 56 degrees C, the extraction time 53 min, and the ultrasonic power 341 W. Under the above parameters, the extraction yield of white tea flavanols was 9.63 mg/g. After purification with macroporous resin, antioxidation and antibacterial experiments were carried out. The results showed that the antioxidant and antibacterial effects of white tea flavanols were remarkable. The antibacterial effects performed best on Escherichia coli, followed by Bacillus subtilis and Staphylococcus aureus. The maximum diameter of the antibacterial zone on Escherichia coli was 0.95 +/- 0.11 mm. The best radical scavenging rates of OH, ABTS+ and DPPH were 97.1%, 97.5%, and 88.4%, respectively, when the flavanol concentration was 9.5 mg/mL. The conclusions of this research can provide theoretical foundation for the further study of white tea flavanols. Taking white tea as the research object, flavanol was extracted from white tea by ultrasonic-assisted low co-melting solvent method. High-performance liquid chromatograph was used to determine the content of flavanol. The influence of four factors on the flavanol extraction yield was analyzed by single factor experiments, including low co-melting soluble mol ratio, material-liquid ratio, extraction time, and extraction temperature. On the basis of single factor experiments, the factors which had significant effects on the flavanol extraction yield were further optimized by the response surface test. The results showed that the optimized extraction conditions were as follows: the molar ratio of low common melting solvent 1:4, the material-liquid ratio 1:30, the extraction temperature 56 degrees C, the extraction time 53 min, and the ultrasonic power 341 W. According to the above parameters, the extraction yield of white tea flavanol was 9.63 mg/g. After purification with macroporous resin, anti-oxidation experiments and bacteriostatic tests were carried out. The results showed that the antioxidant and bacteriostatic effects of white tea flavanol was remarkable and the bacteriostatic effects performed best on E. coli, followed by Bacillus subtilis and Staphylococcus aureus. The diameter of the bacteriostatic ring was 0.95 +/- 0.11 mm. The conclusions of this research can provide theoretical foundation for the further study of flavanols in white tea. image