Simulated processing with vinegar changes chemical structures of main terpenoids in Euphorbiae Ebracteolatae Radix

Abstract

This study aims to explore the chemical structure transformation mechanisms of the main terpenoids in the effective fraction of Euphorbiae Ebracteolatae Radix(EER) during the processing with vinegar. The terpenoids including ent-11α-hydroxyabicta-8(14),13(15)-dien-16,12-olide(HAO), jolkinolide B(JNB), fischeria A(FA), and eupractenoid A(EA) were heated at 160 ℃ with 6% acetic acid for 40 min, and then LC-MS/MS was employed to analyze the structural transformation rules of the terpenoids. Further, we analyzed the changes in the relative content of the four compounds and their transformation products in raw and vinegar processed EER to verify the transformation rules during the simulated processing with vinegar. In addition, JNB and FA were processed with single heating, heating with water or heating with acetic acid. We then employed HPLC to compare the content of these two terpenoids and their transformation products before and after processing, so as to investigate the effect of different processing methods on chemical structure transformation. The results showed that the lactone ring of the abietane-type diterpenoids HAO and JNB and the norditerpene lactone FA were opened by heating with acetic acid. When there were hydroxyl groups in the structures, terpenoids were esterized to esters and oxidized to form carbonyl groups. When there was epoxy ring in the structures, ring opening reaction was easy to occur. During the heating with acetic acid, the heterodimeric diterpenoid EA underwent the cleavage of ether bond to produce the rosane-type diterpenoid euphebracteolatin A(EHTA) and another abietane-type diterpenoid. The changes in the relative content of terpenoids and their transformation products in raw and vinegar-processed EER were basically consistent with those of simulated processing of components with vinegar. The HPLC results revealed that the effect of different simulated processing methods on structural transformation varied. Heating with acid can change JNB and FA into new components. Heating with water can also promote the structural transformation, with the efficiency obviously lower than that of heating with acid. Direct heating had no influence on the structure of JNB, while it significantly reduced the relative content of FA. The components treated with direct heating did not produce the products like those of the heating with acid. These results indicated that vinegar plays a key role in the structural transformation of diterpenoids during the processing of EER with vinegar. The structural transformation of diterpenoids in EER during the processing with vinegar may be the material basis for vinegar processed EER to reduce toxicity and preserve effect.