Green Extraction Technologies for Herbal Bioactive Compounds: Methods, Pharmaceutical Applications, Challenges, and Future Perspectives

Herbal medicines are complex combinations of plants. The composition of the mixture depends on the part of the plant used, the type of plant, the conditions under which it was harvested, how it is processed and how it is extracted. Extraction is an important step to obtain phytochemicals for research and pharmaceutical development. While traditional techniques such as maceration, percolation, Soxhlet extraction and hydro distillation remain useful, they may involve a long processing time, large amounts of solvent, a lot of energy or heat exposure for delicate substances. Green extraction considers safer solvents, process intensifications, efficient energy utilization and responsible biomass management to enhance recovery and reduce occupational and environmental burdens. This review discusses the principles of green extraction and critically evaluates pressurized liquid extraction, enzyme-assisted extraction, supercritical fluid extraction, microwave-assisted extraction, ultrasound-assisted extraction, subcritical water extraction and natural deep eutectic solvents. Experimental optimization and comparative evaluation are considered along with important process variables including temperature, time, solvent composition, particle size, pH and solid to liquid ratio. Applications to alkaloids, polyphenols, terpenoids, essential oils, glycosides and other phytoconstituents are summarized and potential applications in herbal formulations and drug-delivery systems are discussed. Recent trends include hybrid technologies, environmentally benign solvent design, response-surface optimization and biorefinery techniques. There are still major hurdles to be overcome, including the need to differentiate laboratory bioactivity from therapeutic benefit, equipment costs, scale-up, solvent recovery, extract standardization and reproducibility. Instead of looking only at extraction yield, a green process should be assessed on the basis of product quality and safety but also on solvent, energy, waste and lifespan indicators.