Advanced extraction of caffeine and polyphenols from coffee pulp: Comparison of conventional and ultrasound-assisted methods

Abstract

Two extraction methods of caffeine and total polyphenols from coffee pulp waste were evaluated using water as solvent: conventional solid-liquid extraction (CSLE) and ultrasound-assisted extraction (USAE). A central rotary experimental design was applied in each case, after evaluating the effect of the substrate:solvent ratio. The highest concentration of caffeine in the extractant using CSLE was found to be 49.9 ± 1.3 mg/L (equivalent to 3.7 ± 0.1 g/kg pulp, dry basis (d.b.)), after 5.5 min at 96 °C, and at a substrate:solvent ratio of 1:10 w/v. In parallel, the concentration of total polyphenols reached 128.3 ± 4.3 mg gallic acid equivalent (GAE)/L (9.7 ± 0.3 g/kg) at 75 °C (equal time and ratio). USAE was found to be also affected by power, leading to 206.6 ± 0.1 mg caffeine/L and 164.9 ± 5.2 mg GAE/L (15.6 ± 0.3 g/kg and 12.4 ± 0.2 g/kg, respectively) (396 W, 5.5 min, 75–90 °C). These results indicate extraction yields as high as 85%, at a markedly lower energy requirement using USAE. Consequently, USAE using water as a solvent might be a promising and innovative alternative to improve the extraction performance of highly demanded biocompounds from coffee pulp waste, with the consequent environmental and social benefits within a markedly relevant agro-industrial sector.