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

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.

Spent Coffee Grounds as an Adsorbent for Malathion and Chlorpyrifos—Kinetics, Thermodynamics, and Eco-Neurotoxicity

“…The particle size distribution, determined by the fractional sieving method (Figure 1a), shows that the largest fraction of SCG particles is in the 100-200 µm range. Particle sizes in the order of 10 2 µm generally agree with previous reports of SCG properties, but the SCG particles reported here are somewhat smaller than in earlier reports [30,31], likely due to the grounding step we performed. We note that particle sizes of the same order of magnitude are frequently reported for biobased carbon materials used as adsorbents (see, for example, [32]).…”

The Potential of Spent Coffee Grounds in Functional Food Development

“…This scheme, termed as biorefinery, can generate many valuable components from the SCG biomass that is generally being discarded in landfill, potentially generating many avenues for generating commercially viable components [ 41 ]. Thus, biorefinery using SCG can provide many valuable products including biodiesel, hydrocarbon fuel, bio-hydrogen, glycerine, many pharmaceutical-grade bioactive compounds, bioethanol, bio-oil, biochar, polymers and biogas [ 75 ].…”

Green Solvent Extraction of Antioxidants from Herbs and Agro-Food Wastes: Optimization and Capacity Determination

“…Interestingly, herb residues and agro-food by-products still contain high amounts of bioactive components, such as polyphenols, vitamins, carotenoids, tannins, and other phytochemicals (minerals, dietary fibers, fatty acids, amino acids, prebiotics) with high nutritional value and antioxidant properties. Recently, the antioxidant potential of phenolic extracts from various by-products such as the distillation solid wastes of Greek oregano, rosemary, Greek sage, lemon balm, and spearmint [6], chestnut shell [7][8][9], berry biowaste [10], chokeberry pomace [11], grape pomace and skin [9,12], rapeseed, mustard, sesame meals and cakes [13,14], olive pomace and leaves, spent coffee grounds, brewer's spent grain, fruit and vegetable leaves, pulp, peel, pomace and seeds [9,15,16], gray and black alder bark [17], and buckwheat hulls [18,19] have been investigated.…”