Optimizing Chlorogenic Acid Extraction From Spent Coffee Grounds: A Comparative Review of Conventional and Non-Conventional Techniques.

Spent coffee grounds (SCGs) pose a significant environmental burden for coffee-producing industries due to the large quantities generated during coffee brewing. However, SCGs also represent an underexplored and sustainable source of bioactive compounds, particularly chlorogenic acid (CGA), known for its antioxidant, anti-inflammatory, and antimicrobial properties. This systematic review evaluates and compares various conventional and non-conventional extraction methods for CGA from SCGs, assessing their efficacy in terms of extraction yield, environmental impact, cost-efficiency, and processing time, factors often overlooked in earlier studies. Ultrasound-assisted extraction (UAE) emerged as the most effective technique, yielding the highest quantity of CGA (587.7 ± 46.6 mg/g), using ethanol as a solvent with a solid-to-liquid ratio of 1:30. UAE was also identified as the most environmentally friendly technique. In contrast, conventional solvent extraction (CSE) provided a moderate CGA yield (39.5 ± 2.1 mg/g) using water as a solvent and was the most cost-efficient technique. Microwave-assisted extraction (MAE) offered the fastest extraction time with a CGA yield of 84 ± 2.8 mg/g. By integrating technical performance with sustainability considerations, this study offers new insights into the optimization of SCG valorization. Furthermore, it supports the advancement of circular bioeconomy strategies through the efficient recovery of high-value bioactive compounds.