Abstract
The objectives were to evaluate the properties of refined (ROO) and extra-virgin olive oil (EVOO) in their natural state (fresh) and after heating, while comparing them with each other and with refined soybean (SBO) and refined sunflower seed oil (SFO). The methodology was designed to simulate, in controlled laboratory conditions, the home-frying process, while evaluating fatty acid profile ( fatty acid methyl esters were separated by gas chromatography) , concentration of phenolic compounds (Gallic acid dosage), antioxidant activity (DPPH), and production of polar compounds (thin layer chromatography) before and after heating to 200 o C for six minutes. It was observed that, before and after heating, SBO and SFO are rich in polyunsaturated fatty acids (FA) and ROO and EVOO are rich in monounsaturated FA. Fresh or heated, ROO and EVOO do not have trans FA, which are present in SBO and SFO, and increase in SBO after heating (+ 32.8%). The concentrations of phenolic compounds are always higher in olive oils, despite the decrease that occurs after heating (-7.5% in the ROO and -24.6% in EVOO). Antioxidant activity is greater when olive oils are fresh and remains present in EVOO after heating. The concentration of polar compounds was similar for all oils after heating. In conclusion, ROO and EVOO are the richest in monounsaturated FA even after heating, with no production of saturated or trans FA. Despite losing some antioxidant activity, heated EVOO remains richer in monounsaturated FA than ROO, SBO and SFO in the fresh version. All oils suffer similar rates of degradation.
Highlights
Vegetable oils are widely used in home food preparation, either fresh as seasoning of cold dishes or added to the preparations that will be cooked, baked or fried by immersion
Olive oils (ROO and extra-virgin olive oil (EVOO)) are the richest in monounsaturated fatty acids and this profile remains after heating
soybean oil (SBO) and SFO are quite rich in polyunsaturated fatty acids, and SBO is especially rich in omega-3, and this profile persists after heating
Summary
Vegetable oils are widely used in home food preparation, either fresh as seasoning of cold dishes or added to the preparations that will be cooked, baked or fried by immersion. Heating modifies many properties of oils, such as the profile of fatty acids, antioxidant capacity, and nutritional quality (Nogueira-de-Almeida et al, 2015; Valderas-Martinez et al, 2016). Some of these can be evaluated by laboratory indicators, such as the composition of fatty acids, the antioxidant capacity, the amount of phenolic compounds, and degradation (Allouche, Jimenez, Gaforio, Uceda, & Beltran, 2007; Ballus, 2014; Cicerale, Conlan, Sinclair, & Keast, 2009; Daskalaki, Kefi, Kotsiou, & Tasioula-Margari, 2009; Freire, Ferreira, & Mancini-Filho, 2013; Nunes, de Souza, Correa, & da Costa e Silva, 2013; Santos, Cruz, Cunha, & Casal, 2013). This study intended to describe properties of two types of olive oil in their natural state and after heating at home-
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