Ultrasound-enhanced subcritical water extraction of polysaccharides from Lycium barbarum L.

• The polysaccharides were extracted from Lycium barbarum L. using USWE.
• A Box–Behnken design (BBD) was used to optimize the USWE conditions.
• The USWE method was compared with three conventional methods.
• The antioxidant activities against superoxides, hydroxyl radicals and DPPH were investigated.

Recent studies have shown that polysaccharides are the main component of Lycium barbarum L. that is responsible for its medicinal effects. The main purpose of this study was to extract the valuable natural polysaccharides from L. barbarum L. using ultrasound-enhanced subcritical water extraction (USWE). A Box–Behnken design (BBD), based on the results of a single-factors test, was used to optimize the USWE conditions of the L. barbarum polysaccharides (LBP). Four independent variables (extraction temperature, extraction time, liquid-to-solid ratio, and ultrasonic electric power) were investigated. The USWE method was also compared with the other three methods in terms of the extraction conditions and recovery yields for LBP. The antioxidant activities against superoxides, hydroxyl radicals, and 2,2-diphenyl-1-picryl-hydrazyl (DPPH) were also evaluated. The maximum yields of LBP were obtained at an extraction temperature of 100 °C, an extraction time of 53 min, a liquid-to-solid ratio of 26 mL/g and an ultrasonic electric power of 160 W. USWE was superior to the other extraction methods in terms of its easy pretreatment and high recovery yields for LBP. The antioxidant activity assay revealed the significant antioxidant activities of LBP, and there were little differences in the antioxidant effects of the polysaccharides obtained by USWE, subcritical water extraction (SWE) and hot water extraction (HWE).