Enhanced Antioxidant Activity and Elevated Phenolic Content in Hydrolyzed Spent Coffee Ground Extracts for Stabilizing Edible Oils During Storage.

This study investigated how alkaline hydrolysis enhances the antioxidant activity of spent coffee ground (SCG) extracts in stripped soybean oil (SSBO) and stripped flaxseed oil (SFSO) during storage. Hydrolysis of SCG for 2 h markedly increased the concentrations of caffeic acid, p‑coumaric acid, ferulic acid, and total phenolic compounds, followed by gradual declines at 4 and 6 h. Among them, caffeic acid was the most abundant in the hydrolyzed SCG (HSCG) extracts, increasing from 992 to 17,862 µg/g in the ethanol extract and 965 to 20,540 µg/g in the acetone extract during the 2-h hydrolysis. These increases corresponded with the highest 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical‑scavenging activity observed in the 2‑h HSCG extracts. Storage studies with SSBO and SFSO containing ethanol extracts at 35°C revealed that hydrolysis decreased antioxidant effectiveness, suggesting that prooxidants were also produced during hydrolysis. In contrast, acetone extracts exhibited enhanced antioxidant activity after hydrolysis, with the 2‑ and 4‑h HSCG extracts providing the greatest protection against lipid oxidation in both SSBO and SFSO. These results indicate that acetone is a more suitable solvent for maximizing antioxidant activity, likely because it extracts less prooxidants while efficiently extracting antioxidants. Overall, this study demonstrates that alkaline hydrolysis can substantially enhance the antioxidant capacity of SCG extracts and highlights the advantages of acetone as an extraction solvent. The findings also provide insight into the activity of individual antioxidants during oil storage and suggest that antioxidant performance may be further improved by developing strategies to reduce prooxidant formation during hydrolysis. PRACTICAL APPLICATIONS: Hydrolyzed spent coffee grounds (HSCG), particularly when extracted with acetone, can be used as an effective natural antioxidant source to improve the oxidative stability of edible oils during storage. Food and oil manufacturers could incorporate optimized HSCG extracts into products to enhance shelf life while reducing reliance on synthetic antioxidants.