Ultrasound-assisted extraction to improve the recovery of phenols and antioxidants from spent espresso coffee ground: a study by response surface methodology and desirability approach

The ultrasound-assisted extraction was studied to improve the recovery of antioxidants from spent espresso coffee ground (SECG). The response surface methodology and the desirability approach were used to study and define the best recovery conditions in terms of time length of ultrasound (US) pulse, the extraction time and methanol/water mass ratio. The methanol/water mass ratio was the most important variable followed by the length of US pulse. Phenols between 19.29 and 24.95 mg GAE/g and antioxidant capacity from 134.90 to 174.73 μmol Trolox/g were recovered. A methanol/water ratio of 1.25, US pulse of 4 min and treatment time of 60 min enabled to reach a maximum desirability of 0.903. Through these conditions, an antioxidant activity of 172 μmol Trolox/g SECG and phenolic content of 24 mg GAE/g SECG were recovered. Contrarily, without US pulse a desirability value of only 0.605 could be obtained. This suggests that ultrasound-assisted extraction improves the recovery of antioxidants from SECG enabling to reduce of the methanol consumption and/or the treatment time.