VALORIZATION OF AN EMERGING FLOW OF FOOD WASTE: INFLUENCE OF EXTRACTION TECHNIQUES ON THE PHENOLIC COMPOUNDS AND ANTIOXIDANT CAPACITY OF SPENT COFFEE GROUNDS

One of the main challenges the world is facing today, is the substantial increase in generation of food waste as well as its valorisation and management. Spent coffee grounds (SCG), an important waste stream of coffee industry and coffee brewing, are a rich source of valuable compounds, such as polyphenols and antioxidants, but their profitable recovery is still a big challenge. This study aimed to assess the impact of different extraction techniques, namely maceration (MAc), homogenizer-assisted (HAE), ultrasound-assisted (UAE) and microwave-assisted (MAE) extractions on phenolic compounds (PC) and antioxidant capacity of espresso SCG obtained from Arabica coffee beans cultivated in the Pernambuco Agreste region, northeastern Brazil. Extractions were performed using 75mL, 30mL and 20mL of ethanol-water 80:20 (v/v) as solvent as well as 1.25g, 0.5g and 0.33g of SCG for MAc (magnetic stirrer at 25 °C for 4h), HAE (Ultra-turrax at 5000×g for 3min), UAE (ultrasonic-bath, 40 kHz, 35 ºC for 60 min) and MAE (microwave oven, 480 W, 50 ºC for 60 min), respectively. The extracts were then filtered and collected in amber glass bottles until further analysis. The content of PC by Folin–Ciocalteau method and antioxidant capacity by DPPH and ABTS assays were determined. All extracts showed large amounts of phenolic compounds. Ultrasound-assisted extraction technique (27.40±0.32 mggallic acid equivalent/gdried SCG) was more effective in extracting these compounds. In DPPH assay, we found that HAE, MAc and UAE produced extracts of SCG with the highest inhibition percentage (63.32%±0.44, 61.25%±0.87 and 60.84%±1.39, respectively), while the highest inhibition percentage of 70.13%±2.22 was found for the UAE extract by the ABTS assay, showing strong scavenging activity. These findings suggest the use of nonconventional extraction technologies for extracting bioactive compounds potentially available from spent coffee grounds, which may serve as a promising green, inexpensive and natural source to formulate new health-promoting food ingredientes.