Study of the physical and chemical properties and essential fatty acids of sunflower oil used for frying for a period of (1-5) hours

A portion of edible sunflower oil obtained from the local market was obtained and split into six segments. One segment served as the control sample, while the other five segments were used for frying for a duration of five hours. At each hour, a sample was extracted for inspection. The study included conducting chemical and physical testing on all samples. Additionally, gas chromatography (GC) analysis was performed to track the concentrations of essential fatty acids (namely linoleic and linolenic acids) in four oil samples. The obtained findings are as follows: Following a duration of five hours of frying, the melting point experienced a reduction of 2°C, the specific weight underwent a change from 0.9178 to 0.9255, the viscosity exhibited a rise from 40.82 to 48.70 CBP, and the refractive index had a modest alteration, transitioning from 1.4722 to 1.4735. The chemical tests yielded the following results: the free fatty acid content did not exceed 0.6%, the smoking point was reduced from 285°C to 245°C, the peroxide number remained within the permitted range without any modification, and the acidity level met the required specifications. The levels of unsaturated fatty acids in the control sample were as follows: oleic acid decreased from 263 ppm to 0.173 ppm, linoleic acid decreased from 102 ppm to 8.784 ppm, and linolenic acid decreased from 339 ppm to 17.27 ppm. Unsaturated acids exhibit less stability throughout the course of frying. The stability of the oil is directly correlated with the duration of frying. In general, sunflower oil is considered one of the most suitable oils for frying and remains stable for up to 5 hours of frying. The oil's essential acid concentration drops as the frying time increases, in addition to its physical qualities.