Abstract
Waste cooking oil is an abundant food-related residue that can be valorized into useful products within circular economy strategies. This study aimed to prepare five soap formulations from waste edible oil-derived raw materials and to evaluate their physicochemical properties and antioxidant activity in order to identify the most balanced formulation. The waste oil was purified and used for soap production by alkaline saponification. The obtained formulations were assessed in terms of moisture content, foam height, pH, total fatty substances, total alkali content, and DPPH radical scavenging activity. The moisture content ranged from 8.78% to 20.53%, with the lowest value observed for F3 and the highest for F5. Foam height varied from 9.63 to 24.67 cm, and the highest foaming performance was recorded for F3. The pH values ranged from 7.03 to 10.21, indicating clear differences in alkalinity among the formulations. Total fatty substances ranged from 66.11% to 83.91%, with F4 showing the highest value, while total alkali content ranged from 0.19% to 1.10% and remained below the cited limit in all samples. Antioxidant activity was weak for all formulations, although F4 showed the lowest IC₅₀ value and therefore the strongest activity among the soap samples. The integrated evaluation indicated that F3 had the most balanced physicochemical profile, whereas F4 showed the most favorable antioxidant performance. These findings confirm that waste edible oil can serve as a promising raw material for soap production, although formulation optimization remains essential.