Tailored recovery of antioxidant fractions enriched in caffeine and phenolic compounds from coffee pulp using ethanol-modified supercritical carbon dioxide

Coffee pulp (CP) is the by-product of coffee processing that urgently needs to be revalorized using sustainable technologies. This work applied a design of experiment (DoE) for modeling the extraction of bioactive compounds from CP using supercritical carbon dioxide (sc-CO₂) with ethanol as a co-solvent under variable conditions (temperature, pressure, and ethanol percentage). Considering extraction efficiency (per unit of CP) and extraction selectivity (per unit of extract), results showed that ethanol percentage significantly enhanced the efficiency of total phenolic content, as well as the selectivity of chlorogenic acid and protocatechuic acid (p < 0.05). The effects of temperature and pressure in EtOH-modified sc-CO₂ extraction exhibited non-linear patterns, highlighting the interaction between temperature and ethanol. Total phenolic content was responsible for the antioxidant activity of the EtOH-modified sc-CO₂ extracts, which was also affected by caffeine in the extracts. The extraction condition that balances both efficiency and selectivity was found at 65 °C, 23 MPa, and 9 % ethanol as co-solvent. The extraction yield (5.8 mg/g CP) was 3.8 times and 6.7 times lower than that of aqueous and ethanolic extraction, respectively, indicating a relatively lower efficiency of sc-CO₂. However, the selectivity of caffeine (106.3 mg/g extract) and sum of identified phenolic compounds (16.3 mg/g extract) such as chlorogenic, protocatechuic, and caffeic acids, especially for protocatechuic acid (14.9 mg/g extract), was superior to conventional extraction, resulting in the better ABTS chemical (182.3 mg TE/g extract) and cellular antioxidant (384.9 U/mg extract) activities. The notable enrichment of caffeine and protocatechuic acid, together with the antioxidant potential observed in the EtOH-modified sc-CO₂ extracts of CP could be promising for functional food, cosmetic, and pharmaceutical industries.