Subcritical water extraction, identification, antioxidant and antiproliferative activity of polyphenols from lotus seedpod

In this study, polyphenols from lotus seedpod were extracted by subcritical water. Based on single factor experiments, the extraction conditions were optimized by response surface methodology (RSM). Under optimal conditions [temperature of 140 degrees C, time of 20 min, liquid-solid ratio of 70 mL/g and 4%o (W/V) NaHSO3], the maximal yeild of lotus seedpod polyphenols (LSPP) was 178.32 mg of gallic acid equivalents (mg GAE) per gram dry weight (g DW), significantly higher than that of hot water extraction (HWE). This study further investigated antioxidant activity of LSPP. The results showed that, compared with HWE, LSPP extracted by SWE had better reducing power and ability to scavenge DPPII*, ABTS*(+) and NO2-, (P < 0.05). In addition, the antiproliferative ability on human hepatoma G2 (HepG2) cells of LSPP extracted by SWE was also evaluated to be significant (P < 0.05). Moreover, the antioxidant and antiproliferative activity of LSPP were found to be positively correlated with the polyphenols concentration. Detailed HPLC-ESI-MSn analyses with literatures and contrasted with authentic standards allowed the identification of 8 compounds (proanthocyanidin dimer 1, proanthocyanidin dimer 2, catechin, cyanidin-3-O-glucoside, quercetin-3-O-glucuronoside, isoquercetin, kaempferol-3-O-glucuronide and isorhamnetin) in LSPP (SWE). This work can provide a reference for the utilization of subcritical water extraction in the field of natural product extraction and the development and utilization of lotus seedpod as bioactive materials.