Chemical monitoring of canola, corn, olive, soybean and sunflower oils after thermal treatment at conventional temperatures in domestic stoves

Abstract

The frying by immersion is a widely used cooking process and it improves the food texture and flavor. This study analyzed the initial thermal oxidation in five edible vegetable oils used for frying. Oils samples were heated twice for 30 minutes, at 180 °C and then at 240 °C simulating the domestic stoves temperatures. The oils decomposition temperatures were determined by TG, being all of them > 250 °C. The FA profile was analyzed by GC-FID and a slight decrease of UFA was found in corn and soybean oils. In canola, olive and sunflower oils, UFA was stable after heating treatment. Minor FA decomposition was found in canola oil, and followed by corn, olive, sunflower and soybean oils. NIR spectroscopy analyzes resulted in an extensive bands overlapping. The spectra were modeled by PCA and the oils were classified into two groups: fresh oil and heated oil, mainly by differing in 1900 nm region, associated with the carboxyl signal decrease, which might be related to the initial FA degradation in samples. It could partially understand what occurs to the vegetable oil in the beginning of its thermo-decomposition. These information are useful to consumers, food industry and health surveillance agency.