Exploring the Effects of Reactive Extrusion on Spent Coffee Grounds: Chemical Composition, Bioactive Compounds and Techno-Functional Properties

The objective of this study was to investigate the effect of reactive extrusion (thermomechanical and chemical process) on the chemical composition, techno-functional properties, glucose and cholesterol adsorption capacity, and bioactive compound profile of spent coffee grounds (SCG). SCG was extruded using citric acid or alkaline hydrogen peroxide as reagents, and a control sample was extruded without reagents. Treatment with citric acid resulted in the highest levels of total dietary fiber (79.6 g/100 g) and insoluble fiber (76.2 g/100 g), especially cellulose, and significantly improved glucose (32.7 mmol/L) and cholesterol (4.5 mg/g) adsorption at neutral pH. Treatment with alkaline hydrogen peroxide increased water retention capacity (3.9 g/g). Although chemical treatments reduced total polyphenol and antioxidant activity, they effectively broke down the lignocellulosic matrix, thereby increasing fiber availability and functionality. Extrusion without reagents (processes induced by mechanical and thermal factors) favored the retention of caffeine and chlorogenic acids, increasing soluble fiber and maintaining antioxidant capacity. Therefore, reactive extrusion is a technological strategy that aligns with the principles of the circular economy, offering an environmentally friendly alternative to landfill disposal and adding value to spent coffee grounds by transforming lignocellulosic residue into functional ingredients with broad application potential.