Preparation of paeoniflorin from the stems and leaves of Paeonia lactiflora Pall. ‘Zhongjiang’ through green efficient microwave-assisted extraction and subcritical water extraction

The aims of this study were to establish a green and efficient process for extracting paeoniflorin (PF) from the stems and leaves of the Paeonia lactiflora Pall. ‘Zhongjiang’ (PLP-SL). The microwave-assisted extraction (MAE) and subcritical water extraction (SWE) conditions of PF that was from PLP-SL were optimized through the response surface methodology. The optimal conditions of MAE were as follows: extraction solvent, 70% EtOH; microwave extraction temperature, 61℃; liquid-to-solid ratio (LSR), 22 mL/g; and extraction time (ET), 9.5 min, and the PF extraction yield was 2.30% ± 0.19% (n = 3). The best extraction conditions of SWE were subcritical water temperature of 176℃, ET of 16 min, and LSR of 32 mL/g, and the PF extraction yield was 2.21% ± 0.11% (n = 3). Compared with SWE and ultrasonic-assisted extraction, MAE significantly reduced the amounts of organic solvent and ET. The SWE only uses water as the extraction solvent, and the obtained extracts have high PF contents (19.83% ± 0.31%) and low amounts of low-polar impurities and pigments (41.82% ± 0.80%). These features effectively simplify the subsequent purification process and reduce purification costs. Crude PF content of 67.19% was obtained by purifying PF extracted through SWE with an AB-8 macroporous resin. The recovery rate was 84.13%. Further purification with silica gel column chromatography can obtain PF with purity of ≥ 95% (HPLC). This research shows that MAE and SWE are green and efficient techniques for extracting PF from PLP-SL, although SWE is more environmentally friendly. The promotion of these green and efficient technologies can lead to the use of PLP-SL as a new source of PF, effectively promoting the green and sustainable development of the PLP industry and increasing farmers’ income.