Spent coffee grounds – a coffee by-product abundant of bioactive compounds with antioxidant properties

The fulfilment of the circular economy concept requirements persuades scientists to implement new investigations of management of plant by-products. Spent coffee grounds (SCG) are considered to be incompletely utilized coffee-by product generated in notably amounts worldwide. For these reasons, the present research focused on the quality evaluation of SCG blend collected after coffee beverage preparation in local commercial establishments serving coffee. The conventional solid-liquid extraction with hexane and the ultrasound-assisted extraction with 60% hydroethanolic solution were performed to obtain SCG oil and extract, respectively. The quality of SCG blend was evaluated by carrying out the following determinations: fatty acids profile by means of gas chromatography with the flame ionization detection, oxidative induction time (OIT) by means of the pressure differential scanning calorimetry, total polyphenols content (TPC), ABTS and FRAP assays, browning index (BI) as well as caffeine and chlorogenic acids contents by using high-performance liquid chromatography. It was found that SCG oil mainly contained palmitic acid (37,18%) and linoleic acid (39,69%). Also the high share of unsaturated fatty acids (53%) was indicated. The OIT for SCG oil was determined at the level of 43,8 min. The SCG extract was characterised by a high TPC (34 mg GAE/ g SCG), BI (0,2) as well as caffeine (5,35 mg/g SCG) and chlorogenic acids (7,52 mg/ g SCG) contents. Additionally, ABTS and FRAP assays revealed the high antioxidant activity of SCG extract. In conclusion, SCG could be recognized as a coffee by-product abundant of bioactive antioxidant compounds, but further research will be recommended to examine possibility of the application of SCG in various forms as a new ingredient of functional food commodities.