Sustainable Valorisation of Coffee Waste as a Protein Source, Mycelium-Based Packaging Material and Renewable Energy Pellet

Abstract

This study investigates the valorization of spent coffee grounds (SCGs) through protein extraction and their application in mycelium-based packaging and renewable energy pellets. Three extraction methods-mechanical stirring, ultrasound-assisted, and CO₂-assisted extraction-were applied to SCGs. CO₂-assisted extraction yielded the highest protein content at 34.24%, followed by mechanical stirring (31.46%) and ultrasound-assisted extraction (28.51%). The total polyphenol content and antioxidant capacity were also highest in the CO₂ extracts, suggesting that this method preserves bioactive compounds most effectively. After protein extraction, SCGs were tested as a component in mycelium-based packaging, with results showing an apparent density of 0.551 g/cm³ and compression resistance of 3.354 MPa, indicating its suitability for structural applications. The energy value of SCGs remained high, with a calorific value of 19,887 J/g DW, slightly decreasing after extraction but still sufficient for renewable energy production. These findings highlight the potential of SCGs as a multi-functional resource, contributing to sustainable solutions across various industries.

Keywords: alternative protein; green extraction; mycelium-based packaging; renewable energy; spent coffee grounds.

Figure 1

Amino acid profile in the 3 extracts (Coffee extract stirring (CS), Coffee extract ultrasound (CU), Coffee extract CO₂ (CC)) in g/100g DW.

Figure 2

Sample image at (a) 16× and (b) 191× magnification.

Figure 3

(a) Elemental map and (b) EDX spectrum of the sample.

Figure 4

Energy content of SCGs before and after extraction. The extraction methods used are SCG-S (mechanical stirring), SCG-U (ultrasound-assisted), and SCG-C (CO₂-assisted).

Figure 5

(a) Mycelium-based packaging material after compression test and (b) Coffee waste and pine wood pellets.