Recovery of phenolic compounds from spent coffee grounds through optimized extraction processes

Abstract

The aim of the present study was to compare novel methods and technologies of phenolics extraction from spent coffee grounds, as “green” alternative techniques of the conventional ethanol extraction. Three extraction techniques, ultrasound- and microwave-assisted extraction, along with the use of β-cyclodextrin as a solvent have been studied and optimized as the eco-friendly solutions for the efficient extraction of phenolic compounds from Spent Coffee Grounds (SCG). The investigated factors were temperature (20–60 °C), solvent concentration (0–100% v/v water ethanol, EtOH), amplitude (20–60%), and liquid/solid ratio (5–60 mL/g) for ultrasound-assisted extraction (UAE). In the case of microwave extraction (MAE), the effects of solvent concentration (0–100% v/v), liquid/solid ratio (5–60 mL/g), and power (100–600 Watt) were studied. Ethanol (0–100% v/v) and β-cyclodextrin (β-CD, 1–18.5 mg/mL) were also compared as solvents, under the same range of liquid/solid ratio (5–60 mL/g) and temperatures (20–60 °C). In addition, the effect of the drying method (oven drying and freeze-drying), as well as a defatting pretreatment of SCG, were studied under the optimum conditions of each extraction method. The optimum extraction yield (31.79 ± 0.25 mg GAE/g SCG) was achieved using MAE with a liquid/solid ratio of 60 mL/g, a power level 600 W, and a solvent concentration of 68% v/v EtOH. While the maximum yield (34.43 mg GAE/g SCG) was also obtained by the same method from the freeze-dried sample.