Effect of UV-induced geometrical isomerization of hydroxyl-cinnamic acid-containing molecules of bush tea (Athrixia phylicoides DC.) using UHPLC-QTOF-MS

Abstract

Bush tea (Athrixia phyllicoides DC.) is a herbal tea which contains bioactive compounds. Naturally, these metabolites aid plants to defend themselves against a wide spectrum of biotic and abiotic stresses. The objective of the study was to identify hydroxyl-cinnamic acids affected by UV (Ultraviolet) light exposure of bush tea through ultra-high-performance liquid chromatography quadrupole time-of-flight mass spectrometry (UHPLC-QTOF-MS). A randomized complete block experimental design was used consisting of control and 80% white shade net replicated three times and samples were analyzed in triplicates. The methanolic leaf extracts of bush tea were exposed to UV light at 254 nm for 24 h and thereafter metabolites were measured and annotated through UHPLC-QTOF-MS. Hydroxyl-cinnamic acids (HCAs) have been shown to undergo photo-isomerization during post UV light exposure, evidenced by the emergence of photo-isomers. The findings showed that hydroxyl-cinnamic acids containing molecules to undergo photo-chemical isomerization, characterized by formation of isomeric molecules with cis geometry. Metabolites which underwent photo isomerization were found to be structurally related as they formed a very tight molecular family when molecular networking algorithm was used.