Nonconventional Techniques in Plant Alkaloid Extraction: A Decade of Progress (2014-2023)

Plant metabolism encompasses primary and secondary pathways, with secondary metabolism yielding diverse natural products crucial for plant adaptation and ecosystem interactions. Among these products, plant-derived alkaloids are bioactive compounds of significant pharmacological interest, traditionally extracted using conventional solvents known for their environmental and health hazards. Historically, alkaloid extraction relied on acid-base methods, which separate these compounds based on their solubility under different pH conditions. Since the 19th century, extraction techniques have evolved from traditional methods to modern approaches such as supercritical fluid extraction (SFE), microwave-assisted extraction (MAE), ultrasound-assisted extraction (UAE), and the use of ionic liquids (ILs) and deep eutectic solvents (DESs). These advanced methods optimize yield, reduce extraction times, and enhance sustainability by minimizing solvent use and environmental impact. This review explores the evolution of alkaloid extraction methodologies from 2014 to 2023, emphasizing eco-friendly techniques. It discusses the principles and applications of SFE, MAE, UAE, ILs, and DESs in extracting alkaloids from plants, highlighting their pivotal role in modern natural product chemistry. These advancements underscore ongoing efforts to develop efficient and sustainable practices in alkaloid extraction, which is essential for pharmaceutical and medicinal applications.