Changes in Physical and Chemical Properties of Thermally and Oxidatively Degraded Sunflower Oil and Palm Fat

Abstract

Deep-fat frying is an important process used worldwide for the preparation of foods. Due to oxidation, hydrolysis, decomposition and oligomerization, numerous polar compounds are formed. These compounds change the physical, nutritional and sensory properties of the oil or fat. The standard methods of the German Society for Fat Science for the assessment of the quality of frying fats are time consuming and cost intensive. Therefore, alternative cost-effective and sensitive rapid methods, which ideally allow the quantitative determination of the quality of frying fats “in-line” in the deep-frying pan are needed. Sunflower oil and palm fat were thermally and oxidatively degraded in a beaker at atmospheric pressure under intensive stirring for 76 h at 175 °C. To evaluate the development of the physical properties during heat treatment, the viscosity and dielectric constant of these oils were measured. The temperature in a deep-frying pan can vary within a wide range (160–190 °C), and the viscosity and dielectric constant show a strong temperature dependence. Therefore, it was necessary to measure the temperature dependence of the viscosity and dielectric constant of the different degraded oils. Additionally, their chemical properties were characterized by high-performance gel permeation chromatography and Fourier-transform infrared spectroscopy (FTIR). The determination of the dielectric constant, which is directly correlated with the concentration of polar compounds, seems to be the best method for the assessment of the quality of used frying oils.

Evaluation of the Bioactive Compounds Found in Tomato Seed Oil and Tomato Peels Influenced by Industrial Heat Treatments

“…At temperatures higher that 50 °C the viscosity ranged between 10–22 mPa·s which was also observed in similar studies that analyzed polysaccharides in black tomato pomace [ 54 ]. Several types of oils have the same decreasing trend in viscosity (under 25 mPa·s) with the increase of temperature [ 55 , 56 ]. The decrease in viscosity can be explained by the fact that higher temperatures promote the motion of molecules and diminishes the forces between them, consequently is enabled the movement of each layer between each other [ 57 ].…”

Optimization and characterization of biodiesel from waste cooking oil using modified CaO catalyst derived from snail shell

“…WCO had a higher moisture content, densities, RI, AV, FFA, SV, IV, and PV than purified waste cooking oil (PWCO), but a lower pH. The frying process alters the physicochemical properties of oil, indicating that it has been degraded [ 41 , 42 ]. The low moisture content in PWCO samples revealed that they can improve the storability and suitability [ 43 ].…”

The relationship between commercial refined vegetable oils stabilities and health implications: A systematic review and meta-analysis

“…It is especially susceptible to heat, air, and light which accelerates SFO oxidation. SFO was reported to lose up to 76 % of tocopherols and reached > 25 % of total polar compounds (TPC) during a frying process (Wiege et al, 2020;Juarez et al, 2011). Thermal alterations were prevalent in HSFO including more than 10 % increase of polymeric and dimerized triacylglycerols.…”