Coffee Pulp Valorization: Comparison of Conventional and Deep Eutectic Solvents Performance During Phenolic Compounds Extraction Optimization

Abstract

Abstract Coffee pulp, the main solid by-product of wet coffee processing, requires appropriate management to recover high-value compounds. This study focused on extracting phenolic compounds—total phenolics and total flavonoids—from coffee pulp using organic and deep eutectic solvents (DES). Among tested solvents, ethanol and choline chloride–citric acid (ChCl–CA) proved the most effective. Extraction was optimized via central composite design and response surface methodology, considering temperature, time, solvent concentration (or water content), and solvent-to-solid ratio. Ethanol extraction (40%) yielded 19.4 ± 0.8 mg gallic acid (GA)/g dry matter (DM) of total phenolics, 13.0 ± 0.6 mg catechin/g DM of total flavonoids, and 80.9 ± 0.8% antioxidant inhibition—used as baseline values. Using ChCl–CA, total phenolics increased by 34%, with antioxidant activity reaching 86.1 ± 1.0% inhibition, despite lower flavonoid content. This suggests enhanced extraction of other phenolic groups contributing to antioxidant capacity. Optimal conditions for ChCl–CA were 49.8% water content, 60.9 min extraction time, 26.8 mL/g solvent-to-solid ratio, and 70 °C. This work clearly presents elevated extraction yields with DES selection, specifically with ChCl–CA, paving the way for sustainable extraction promotion, which could close the loop and thus shift coffee processing and the derived by-products valorization to a greener and more circular holistic process. Graphical Abstract