Separation characteristics of ethanol precipitation for the purification of the water extract of medicinal plants

Ethanol precipitation is a widely applied separation technology in the production of botanical medicines, but the research on this technology is few. In this work, ethanol precipitation is used to purify the water extract of Danshen (Salvia miltiorrhiza Bge.) and Chuanxiong (Ligusticum chuanxiong Hort.) as a sample to describe its separation characteristics and mechanism. The effects of refrigeration temperature, ethanol addition, and supernatant pH value were investigated. Total saccharide removal and dry matter removal increased as refrigeration temperature decreased or ethanol addition increased. Danshensu (DSS) recovery and salvianolic acid B (SaB) recovery increased as supernatant pH value decreased or ethanol addition decreased. The purity of phenolic compounds increased after ethanol precipitation. The losses of caffeic acid (CA) and ferulic acid (FA) in ethanol precipitation were caused by chemical transformation. The losses of DSS and SaB were both caused by chemical transformation and precipitation. By using a simple model, the pKa values of DSS and SaB in supernatant can be calibrated, which were 3.63 and 3.56, respectively. The solubilities of DSS salt and SaB salt can also be calibrated. Most of DSS and SaB existed in supernatant in their ionic forms. The results of this work will contribute to the implementation of Quality by design (QbD) concept in the manufacture of botanical medicines.