Abstract:

Response surface methodology was applied to optimize the ultrasonic extraction of polyphenols from chestnut shells. In order to establish a method for the separation of phenolic antioxidants from crude polyphenol extract, the static adsorption and desorption of phenolics on macro adsorption resin were kinetically studied and the optimum conditions for static adsorption and desorption were explored. Besides, polyphenols obtained from chestnut shells by different methods were tested for DPPH radical scavenging capacity and Fe3+ reducing power. Ethanol concentration and ultrasonic power were identified as main factors that influence extraction efficiency. The optimum conditions for the ultrasonic extraction of polyphenols from chestnut shells were found to be three extraction cycles with 43% ethanol at a solid-to-solvent ratio of 1:18.5 (g/mL) for 17.5 min with an ultrasonic power of 305 W. Under these conditions, the extraction efficiency of polyphenols was 2.86 g/100 g. LX-17 resin was found to be the best resin for the purification of phenolics from chestnut shells and the optimum purification conditions were determined as adsorption at 25 ℃ for 1.5 h followed by desorption with 50% ethanol at 20 ℃ for 4 h. Phenolics with stronger DPPH radical scavenging activity and reducing power from chestnut shells were obtained using ultrasonic extraction than reflux extraction. The antioxidant activity of crude polyphenol extract was improved after macroporous resin purification.

Key words: chestnut shell, polyphenols, ultrasonic extraction, macroporous resin, antioxidant, response surface methodology