Biological pathways and enzymatic mechanisms in phytochemical biosynthesis: A review

Essential oils are complex mixtures of volatile secondary metabolites derived from plants, with significant ecological and therapeutic roles. Their chemical diversity arises from intricate biosynthetic pathways involving monoterpenoids, sesquiterpenoids, and phenylpropanoids. This review explores the biosynthetic mechanisms underlying the formation of these compounds in Citrus sinensisleaves, focusing on the mevalonate and non-mevalonate pathways. Additionally, how enzymatic activity and post-harvest metabolic processes influence the qualitative and quantitative variations in essential oil constituents was discussed. Understanding these pathways provides insights into optimizing plant-based products for pharmaceutical, cosmetic, and agricultural applications.