Chemical and thermophysical properties of cold-pressed and unrefined vegetable oils between 293.15 K and 433.15 K

Vegetable oils are essential for human health, providing critical fatty acids and antioxidants such as carotenoids and tocopherols, including vitamin E. To preserve their nutritional value, texture, flavor, and shelf life, oil production must avoid conditions that promote degradation or the formation of harmful compounds. Understanding how transport properties change under various processing conditions is crucial. Among these, temperature significantly influences the physicochemical properties and flow behavior of oils in pipelines. This study analyzed the chemical and thermophysical properties of four cold-pressed, unrefined oils–peanut, sesame, golden flaxseed, and olive − across temperatures from 293.15 K to 433.15 K. Golden flaxseed oil had the highest linolenic acid content (50.68 %), while oleic acid predominated in peanut (41.72 %), sesame (42.04 %), and olive oils (71.44 %). Oxidative stability, measured by induction time, ranged from 0.96 h in golden flaxseed oil to 10.09 h in olive oil, with temperature causing a 73.84 % reduction in golden flaxseed oil stability. Tocopherol levels varied, with α-tocopherol ranging from 17.14 mg∙kg−1 in golden flaxseed to 1091.35 mg∙kg−1 in sesame oil. β-tocopherol was absent in peanut and sesame oils. Olive oil had the lowest smoke point (455.15 K), while golden flaxseed oil exhibited the highest (495.35 K). Temperature changes affected thermophysical properties: density decreased by 6.3 % in peanut oil and 2.05 % in golden flaxseed oil; heat capacity increased by 13.6 % in sesame oil and 36 % in olive oil; thermal conductivity increased by 6.6 % in golden flaxseed oil and 8.9 % in sesame oil; and viscosity decreased by 97.3 % in golden flaxseed oil and 98.3 % in sesame oil. These high-temperature data are vital for processes such as physical refining, where temperatures can reach up to 550 K.