Sustainable valorization of spent coffee grounds via microwave-assisted extraction and spray-dried microencapsulation

Spent coffee grounds (SCGs), an abundant agro-industrial by-product, are rich in phenolics, caffeine, and melanoidins but are limited by inefficient extraction and poor stability. This study optimized microwave-assisted extraction (MAE) of SCG bioactives using response surface methodology and stabilized the extracts via spray-drying microencapsulation. The optimized MAE conditions (4 mg/mL, 77 °C, 10 min) yielded 3.3-, 1.5-, and 2.0-fold higher phenolics, caffeine and melanoidins than conventional extraction, respectively. The optimized extract was microencapsulated using maltodextrin (MD), gum arabic (GA), and their combinations with whey protein isolate (WPI) or inulin (INL). MD-based systems provided higher yields, whereas GA + WPI achieved the highest microencapsulation efficiency (87.5-99.4%). The microcapsules exhibited low moisture content (2.8-6.5%) and water activity (0.16-0.35), high solubility (74.0-88.2%), good dispersibility (71.8-91.8%), and rapid wettability (1.5-10.0 min).Structural analyses confirmed successful encapsulation via non-covalent interactions. This study demonstrates a sustainable valorization pathway transforming SCGs into stable, antioxidant-rich microcapsules for functional food applications.