[Comparative study on free and bound phenolic acids before and after drying of Salvia miltiorrhiza]

There were significant differences in phenolic acid content between fresh and dried Salvia miltiorrhiza before and after drying. That is to say, the content of phenolic acid in S. miltiorrhiza significantly increased with the increase of dehydration during the drying process.In order to investigate the differences and transformation of free and bound phenolic acids before and after the drying process of S.miltiorrhiza, we studied hydrolysis method, hydrolysates and hydrolysis regularity of phenolic acids in S.miltiorrhiza. UPLC method was used to determine four main hydrolysates of bound phenolic acids, namely danshensu, caffeic acid dimer(SMND-309), caffeic acid, przewalskinic acid A(prolithosperic acid), and three main free phenolic acids in S.miltiorrhiza, namely rosmarinic acid, lithospermic acid, salvianolic acid B. The results of the acid-base hydrolysis experiment of salvianolic acid showed that the alkaline hydrolysis effect was significantly better than acid hydrolysis. The optimal alkaline hydrolysis condition was hydrolysis at 70 ℃ for 4 h with 2 mol·L~(-1) NaOH solution containing 1% ascorbic acid(Vit C). The hydrolysates of free phenolic acids were the same with the hydrolysates of bound phenolic acids. Fresh S.miltiorrhiza contains a low level of free phenolic acids and a high level of bound phenolic acids, which were exactly opposite to dried S.miltiorrhiza. It was suggested that a large amount of bound phenolic acids was accumulated during the growth of S.miltiorrhiza. These bound phenolic acids were coupled with polysaccharides on the cytoderm through ester bonds to form insoluble phenolic acids, which was not easy to be detected by conventional methods. However, during drying and dehydration processes, the bound phenolic acids were converted to a large amount of free phenolic acids under the action of the relevant enzyme.