Optimization of ultrasonic-assisted extraction and UPLC-TOF/MS analysis of limonoids from lemon seed

•Ultrasonic-assisted extraction of limonoids from lemon seeds was optimized.•Three-factor-three-level Box-Behnken experimental design was used in this study.•The extraction has possessed significantly high antioxidant activity.•The major limonoids in the extraction were identified and quantified.

In this study, ultrasonic-assisted extraction of limonoids from lemon seed was optimized using Box-Behnken design with three-factor-three-level by evaluating the contents of limonoids. The optimized extraction conditions were as followings: extraction time of 56 min, temperature of 56 °C and ultrasonic power of 300 W. Under these optimized conditions, the extraction yield of limonoids reached 6.02 ± 0.07% (n = 3). The antioxidant activity of the extracted limonoids under the optimum extraction conditions was evaluated by DPPH radical scavenging assay and superoxide radical scavenging assay. UPLC-TOF/MS and HPLC-UV analyis showed that the major limonoids are limonin (715.40 mg/g), nomolin (277.20 mg/g) and obakunone (47.40 mg/g). Furthermore, high purity of limonin and nomilin were obtained by purification and recrystallization. The present study provides theoretical guidance for the industrial extraction of limonoids and improves the utilization of lemon seeds.