Critical analysis of green extraction techniques used for botanicals: Trends, priorities, and optimization strategies-A review

Botanicals are widely used and marketed as food supplements or cosmetics with particular benefits for human health. Botanicals are products manufactured using natural components derived from plants, algae, fungi or lichens. Given the easy accessibility of such products, it is essential to ensure their safety by guaranteeing the absence of chemical or microbiological contamination. Furthermore, since botanicals are derived from natural products, they consist of a set of molecules called a phytocomplex, and it is important to develop standardised methods to ensure their reproducibility. Traditional approaches to the extraction of phytochemicals, as described in the monographs or pharmacopoeias of international authorities, guarantee product integrity with low levels of impurities and degradation products, but use large quantities of organic solvents with long timescales, high costs and environmental impact. A green chemistry approach is preferable to improve consumer safety, improve the extraction process and preserve the environmental status. This can be achieved by using advanced extraction methods that have proven effective in the extraction of natural molecules, such as microwave-assisted extraction (MAE), ultrasound-assisted extraction (UAE), supercritical fluid extraction (SFE) and pressurised liquid extraction (PLE) combined with GRAS solvents or unconventional solvents, such as natural deep eutectic solvents (NADES). In the chemistry of natural products, the extraction phase is a fundamental step and the one most responsible for environmental sustainability. There are usually many parameters that need to be monitored and optimised to ensure the optimized conditions of these techniques. More than the empirical One variable at a time (OVAT) approach, Design of Experiments (DoE) is required to understand the effects of multidimensionality and interactions of input factors on the output responses of the extraction phase. To date, there are no specific metrics for the extraction phase, therefore, it is necessary to identify the parameters responsible for the environmental impact of the extraction phase and to optimise them in order to increase the eco-sustainability of the analytical process. The actual review provides a critical analysis of the current green extraction procedures in natural product chemistry aimed to provide insights into strategies to improve both extraction efficiency and eco-sustainability.