Enhancement of the oxidative stability of soybean/sunflower oils and margarine enriched with tomato peel powder

This study evaluated the direct use of tomato peel powder to enrich margarine, sunflower oil, soybean oil, and a 1:1 (w/w) sunflower–soybean oil mixture. Dried tomato peels were ground and physicochemically characterised, showing low moisture content (3.11 ± 0.04%), acidic pH (4.10 ± 0.03), and high levels of carotenoids, including lycopene (94.16 ± 1.50 mg/100 g) and β -carotene (19.50 ± 0.75 mg/100 g). Antioxidant activity, determined using the 1,1-diphenyl-2-picrylhydrazyl assay, showed a half maximal effective concentration of 54.46 ± 1.81 mg antioxidant per gram of radical, compared to 120.15 ± 3.18 mg antioxidant per gram for vitamin E, and 67.05 ± 1.92 mg antioxidant per gram for butylated hydroxytoluene. Margarine and oil samples containing 0.25–3.0% tomato peel powder were prepared, and oxidative stability was evaluated over 45 days at 35 °C using peroxide value, conjugated dienes, malondialdehyde content, and induction time. Tomato peel powder significantly reduced lipid oxidation and increased induction times. Oxidative stability improved in margarine (14.81 ± 0.40 h vs . 13.12 ± 0.20 h) and soybean oil (17.67 ± 0.20 h vs. 13.12 ± 0.20 h), extending shelf life. These findings highlight tomato peel powder as an effective natural stabiliser for lipid-based products without solvent extraction.