Recovery of Natural Antioxidants from Onion Solid Waste via Pressurized Liquid Extraction: Encapsulation and Application into a Food System

Onion solid wastes (OSW) are a promising source of natural antioxidants with potential applications in food preservation. This study optimized pressurized liquid extraction parameters-ethanol concentration, liquid-to-solid ratio, temperature, and time-using response surface methodology to maximize the recovery of total polyphenols, total anthocyanins, and antioxidant activity. The optimal extracts yielded 37.02 mg GAE/g dw for total polyphenols and 592.73 µg CyE/g dw for total anthocyanins. Antioxidant activity was evaluated using the FRAP assay and the DPPH method. HPLC-DAD analysis identified quercetin, spiraeoside, and protocatechuic acid as major polyphenolic compounds. The optimal extract was encapsulated via spray drying using gum arabic as the wall material. Parameters such as encapsulation efficiency, loading capacity, and process yield were evaluated. The encapsulated extract was incorporated into mayonnaise, and its effect on oxidative stability was monitored over 14 days. Results demonstrated significant antioxidant protection, comparable to synthetic preservatives such as potassium sorbate and butylated hydroxytoluene. This study highlights the potential of OSW-derived antioxidants as sustainable, natural additives for food systems.