Response Surface Methodology as a Tool for Optimization of Extraction Process of Bioactive Compounds from Spent Coffee Grounds

Abstract

Featured Application: The coffee processing industry is nowadays confronted with urgent challenges associated with the implementation of profitable and environmentally safe technological solutions for managing plant waste matter. Therefore, this sector of the food industry is cooperating with scientific communities to explore the possibility of using coffee by-products, especially spent coffee grounds, which can be considered as a valuable natural alternative to plant material with plentiful quantities of various components with antioxidant activity. However, additional investigations are needed to evaluate the potential for using spent coffee grounds in different forms as an ingredient of newly designed food products with functional properties or as a component of biodegradable packaging materials used in the agri-food processing system. These applications are in accordance with EU policies regarding the circular economy and sustainability of the food industry. The main goal of this research was to model and optimize the extraction process of bioactive compounds from spent coffee grounds (SCG). This study utilized response surface methodology (RSM) to determine the significance of the effects of independently tested extraction process conditions and their interactions. The quality of the SCG extracts was evaluated by performing the following determinations: total polyphenols content (TPC), ABTS and FRAP assays, browning index (BI), and caffeine and chlorogenic acids contents by high-performance liquid chromatography. The resultant optimal extraction conditions, which maximized recovery of antioxidant bioactive compounds, were 65% hydroethanolic solution (v/v) in a solvent–matrix ratio of 51 mL/g CS, followed by ultrasound-assisted extraction carried out for 30 min at 60 °C. The SCG extract obtained by this extraction variant had values for TPC, ABTS, FRAP and BI of approximately 38 mg GAE (gallic acid equivalent) per g d.m. SCG, 73 mg Trolox/g d.m. SCG, 81 µmol Fe (II)/g d.m. SCG, and 0.22, respectively. The sample was also characterized by a high content of caffeine (5 mg/g d.m. SCG) and chlorogenic acids (8 mg/g d.m. SCG). Based on the obtained results, SCG may be recognized as a coffee by-product that has abundant components with antioxidant activity and broad possible applications in agri-food processing fields.