Spent Coffee Grounds Valorization in Biorefinery Context to Obtain Valuable Products Using Different Extraction Approaches and Solvents

Maris Lauberts; Inese Mierina; Matiss Pals; Mohammed Ammar Abdul Latheef; Andrei Shishkin

doi:10.3390/plants12010030

Spent Coffee Grounds Valorization in Biorefinery Context to Obtain Valuable Products Using Different Extraction Approaches and Solvents

Plants (Basel). 2022 Dec 22;12(1):30. doi: 10.3390/plants12010030.

Authors

Maris Lauberts¹, Inese Mierina², Matiss Pals¹, Mohammed Ammar Abdul Latheef³, Andrei Shishkin³

Affiliations

¹ Latvian State Institute of Wood Chemistry, LV-1006 Riga, Latvia.
² Institute of Technology of Organic Chemistry, Faculty of Materials Science and Applied Chemistry, Riga Technical University, Paula Valdena Str. 3, LV-1048 Riga, Latvia.
³ Riga Biomaterials Innovations and Development Centre of RTU, Institute of General Chemical Engineering, Faculty of Materials Science and Applied Chemistry, Riga Technical University, Pulka 3, K-3, LV-1007 Riga, Latvia.

Abstract

The valuable products that can be isolated from spent coffee ground (SCG) biomass consist of a high number of bioactive components, which are suitable for further application as raw materials in various production chains. This paper presents the potential value of the SCG obtained from large and local coffee beverage producers, for the production of valuable, biologically active products. Despite its high potential, SCG has not been utilized to its full potential value, but is instead discarded as waste in landfills. During its decomposition, SCG emits a large amount of CO₂ and methane each year. The main novelty of our work is the implementation of sequential extraction with solvents of increased polarity that allows for the maximal removal of the available extractives. In addition, we have compared different extraction techniques, such as conventional and Soxhlet extraction, with more effective accelerated solvent extraction (ASE), which has seen relatively little use in terms of SCG extraction. By comparing these extraction methods and highlighting the key differences between them in terms of extraction yield and obtained extract composition, this work offers key insights for further SCG utilization. By using sequential and one-step accelerated solvent extraction, it is possible to obtain a significant number of extractives from SCG, with a yield above 20% of the starting biomass. The highest yield is for coffee oil, which is obtained with n-hexane ranging between 12% and 14% using accelerated solvent extraction (ASE) according to the scheme: n-hexane→ethyl acetate→60% ethanol. Using single-stage extraction, increasing the ethanol concentration also increases the total phenolic content (TPC) and it ranges between 18.7-23.9 Gallic acid equivalent (GAE) mg/g. The iodine values in the range of 164-174 using ASE and Soxhlet extraction shows that the hexane extracts contain a significant amount of unsaturated fatty acids; coffee oils with a low acid number, in the range of 4.74-6.93, contain few free fatty acids. The characterization of separated coffee oil has shown that it mainly consists of linoleic acid, oleic acid, palmitic acid, stearic acid and a small number of phenolic-type compounds.

Keywords: coffee oil; extraction; extraction solvents; spent coffee grounds; total phenolic; value added products.

Grants and funding

The article was published with the financial support from the Riga Technical University Research Support Fund.