An efficient and green separation method of total alkaloids by resorcinol-formaldehyde aerogel during extraction of Coptis chinensis

Alkaloids are the most medicinally valuable ingredients in plant crop Coptis chinensis (C. chinensis). However, the separation of these small-molecule compounds is challenging because C. chinensis also contains a lot of impurities such as proteins and saccharides. Adsorption separation stands out in the field of biological separation by virtue of its efficiency and greenness. Here, this paper aimed to selectively separate the total alkaloids during extraction of C. chinensis by resorcinol-formaldehyde (RF) aerogel based on electrostatic interaction and size-sieving effect. First, RF aerogels with different surface area (40.6–674.9 m2/g) and pore size (2–25 nm approximately) were synthesized by adjusting the ratio of catalyst (C). The results of static adsorption showed that the optimum alkaloids selective separation was achieved at R/C of 10/1: alkaloids adsorption capacity (Qe), protein retention ratio (Pr), saccharides retention ratio (Sr) and the coefficient of selectivity were 487.93 mg/g, 87.40 %, 95.90 % and 2.23, respectively. Methanol containing 1 % hydrochloric acid was considered as the most suitable eluent with the desorption efficiency of 95.88 %. In addition, the adsorption process conformed to pseudo-second-order kinetics, intra-particle diffusion and Langmuir isotherm models, and was a spontaneous endothermic process. It was found from the dynamic adsorption experiment that the dynamic adsorption capacity was 497.81 mg/g, and the purity of total alkaloids increased from 39.19 % to 90.22 %. Compared with resin adsorption and salt precipitation method, RF aerogel separation could more efficiently separate the alkaloids from C. chinensis (the total alkaloids yield of 57.40 mg/g C. chinensis). In addition, the alkaloids separated by RF aerogel had better antioxidant and antibacterial activities than that separated by salt precipitation method. In summary, RF aerogel separation was potential as an efficient and green method for the separation of total alkaloids from C. chinensis.