The innovative extraction and purification process of insoluble polyphenols from Paeonia ostii roots: Optimum study and in vitro activities

The oil tree peony (Paeonia ostii) is widely cultivated for their high value seed oil, and its roots also have high medicinal value, but they are often discarded and wasted as by-products. In this study, a set of steam explosion (SE) and ultrasound (US)-assisted extraction/purification methods of insoluble bound phenols (IPs) from oil peony roots (PR) were explored and developed. The IPs were obtained through SE pre-treatment (120 degrees C, 15 min) and US-assisted alkaline extraction (0.25 W/cm2, 4 h and 4 M NaOH). Their total phenolic content (TPC) significantly increased from 112.26 mg gallic acid/g dry weight (mg GAE/g dw) with traditional method to 185.59 mg GAE/g dw. Subsequently, the IPs were purified into PIPs using LX-83 resin. The optimized purification conditions were pH = 4, 3.0 mg GAE/mL of IPs, 0.25 W/cm2 adsorption for 120 min, as well as 60 % ethanol desorption solution, and 0.25 W/cm2 desorption for 30 min. The TPC of the PIPs increased to 254.74 mg GAE/g dw. Notably, typical compounds in IPs and PIPs were identified and quantified by HPLC-MS and their antioxidant and anti-tyrosinase activities were also evaluated by chronometry. The results showed that paeoniflorin and benzoyl-paeoniflorin increased by about 10-fold in the PIPs. Additionally, they demonstrated superior antioxidant and tyrosinase inhibitory activities compared to IPs. Therefore, the innovative extraction and purification process greatly improved the yield of bound phenols and recovered paeoniflorin from non-medicinal PR. The process may also provide a reference for the in-depth development of medicinal PR, ultimately achieving more efficient PR development and utilization.