Thermal Stability of Cold-Pressed Oil Blend with Balanced Fatty Acid Ratios of SFA:MUFA:PUFA and ω-6:ω-3 Under Continuous High-Temperature Heating

Edible oils are an important dietary source of energy and essential fatty acids (ω-6:ω-3). This study investigated the impact of thermal treatment on the nutritional and physicochemical properties of cold-pressed oils (groundnut, sunflower, palm, mustard, and coconut) and their blend, formulated to achieve a balanced fatty acid ratio of SFA:MUFA:PUFA (1:1.5:1) and ω-6:ω-3 (5:1). Oils were continuously heated at 230 ± 5 °C for 1, 2 and 4 h and analyzed for nutritional and physicochemical changes. Results showed that, compared with individual oils, blended oil (BO) exhibited greater thermal stability and maintained the recommended ω-6:ω-3 ratio throughout the heating period. However, the SFA:MUFA:PUFA ratio shifted from 1:1.5:1 to 1:1.24:0.58, with moderate trans fatty acid formation (2.29 ± 0.01%) after 4 h. The peroxide value of BO peaked at 1 h (9.26 ± 0.19 mEq O2/kg), while the acid value (4.58 ± 0.02 to 1.36 ± 0.01 mg KOH/g) and free fatty acids (2.53 ± 0.03 to 0.91 ± 0.02%) decreased steadily with thermal exposure. Conjugated dienes and trienes increased moderately, iodine value declined consistently, and oil color darkened with continuous heating. Overall, the blending of oils improved the fatty acid balance and moderate resistance to thermal degradation compared with individual oils. It supports the development of healthier, functional and sustainable edible lipids for food and health applications.