Metabolomic Analysis for Compositional Differences of Bush Tea (Athrixia phylicoides DC.) Subjected to Seasonal Dynamics

Abstract

Bush tea (Athrixia phylicoides DC.) is a South African indigenous herbal tea rich in secondary metabolites with medicinal significance. However, studies on the effects of seasonal changes on bush tea and quantification of its metabolites using untargeted approach have not been explored. Therefore, this study’s objective was to investigate the effects of seasonal variation on the metabolites of bush tea using LC-MS/MS (Liquid Chromatography with Tandem Mass Spectrometry) and 1H NMR (High-Resolution Proton Nuclear Magnetic Resonance) techniques. Bush tea leaves were plucked once in each season namely, autumn (March to May), winter (June to August), spring (September to November), and summer (December to February). The primary metabolites including non-essential amino acids, organic acids, and vitamins in bush tea were predominantly elevated during summer and spring. The 1H NMR-based metabolomic analysis revealed that bush tea metabolome was strongly affected by seasonal variations, using the partial least squares-discriminant analysis (PLS-DA) which demonstrated four distinct groups of seasons. Similarly, the 1H NMR based metabolic profiling of bush tea subjected to different seasons resulted in putative annotation of six phenolic compounds which included rutin, 4-(hydroxyphenyl) propyl coumarate, caffeic acid, hymenoxin, quercetin, and kaempferol. The phenolics and primary metabolites differed remarkably per season with enhanced accumulation observed in the summer and spring harvested bush tea. The LC-MS and 1H NMR metabolomics analysis suggests that summer and spring can be recommended as preferred plucking seasons for bush tea leaves and twigs.