Chemical changes in microwave heated vegetable oils

Microwave (MW) heating of foods may cause the formation of cholesterol oxidation products (COPs). COPs formation depends on the conditions of MW heating and the composition of the food matrix. The aim of this work was to study the formation of major COPs from cholesterol incorporated into palm, extra virgin olive, soybean, or fish oils during MW heating, and to monitor changes in peroxide value and fatty acid (FA) profiles. Model systems composed of mixtures of cholesterol and oil (2.5 mg of cholesterol/g oil), were heated for 20 min in multimode (900 W), unimode MW (≈300 W) ovens, or convection oven at 180°C. Maximum total COPs contents largely varied (46.4–250.4 µg/g lipids), depending on the type of heating system and oil matrix. Multimode MW heating caused greater COPs formation than unimode MW. COPs formation trends in the conventional oven were similar to those of MW heating, except for fish oil. Results indicated that soybean oil, compared with the other oils tested, did not promote cholesterol oxidation during MW heating, while the opposite trend was observed for extra‐virgin olive oil and palm oil. FA profile and natural antioxidants influenced cholesterol and surrounding media oxidation during MW heating. Practical applications: This work explores the formation of oxysterols by microwave heating in model systems. This will help assess the possible risks for formation of these compounds during industrial and home cooking practices. Microwave (MW) heating of foods may cause formation of cholesterol oxidation products (COPs). In this work, a model system consisting of four types of edible oils with added cholesterol was employed and heated with three different forms (unimodal and multimodal MW, and conventional heating) for different time periods. Generation of COPs in all the model systems was monitored.

Section: Resultssupporting

confidence: 94%

Formation of cholesterol oxides in lipid medium during microwave heating

Leal-Castañeda

Hernández‐Becerra

Rodríguez‐Estrada³

et al. 2016

“…These results also confirmed Malheiro et al in virgin olive oils. But some authors determined two times lower tocopherol degradation in microwave‐heated oils than we did. Thus it appears that food nutrients (at least Vitamin E derivatives) are better preserved during frying and especially deep‐fat frying than they are during microwave heating.…”

Section: Resultscontrasting

confidence: 71%

“…In other types of microwave oven, this parameter can be at manufacture set to 25–30% of the total time, leaving more time for energy dissipation. Some authors found twice lower content of fatty acid hydroperoxides in oils heated with microwave oven adjusted with longer dissipation period of time.…”

Section: Resultsmentioning

confidence: 99%

Degradation of fatty acids and tocopherols to form tocopheryl quinone as risk factor during microwave heating, pan‐frying and deep‐fat frying

Kreps

Burčová

Schmidt

2016

Self Cite

We investigated degradation of tocopherols to form tocopheryl quinones (TQ) and cytotoxic γ‐tocopheryl quinone in oils and French fries during microwave heating, pan‐frying and deep‐fat frying. We proved that the microwave oven caused rapid increase of oil temperature, with the consequence of two to three times greater degradation of fatty acids and tocopherols than pan‐frying and deep‐fat frying. Pan‐frying with sunflower oil caused three‐time greater formation of fatty acids polymers, compare with rapeseed oil. The gentlest one was deep‐fat frying, which caused two times slower formation of fatty acid hydroperoxides and tocopheryl quinones in 900 g of oil. We found that not only the quantity but also the type of oil had critical effect on the formation of cytotoxic γ‐tocopheryl quinone. During 50 min of pan‐frying in rapeseed oil, 22 mg/kg of γ‐tocopheryl quinones was formed, of which 5–7 mg/kg penetrated into the homemade French fries. While the deep‐fat frying technique generated only 6 mg/kg of γ‐tocopheryl quinones in rapeseed oil. The rapid microwave heating caused formation of 8 mg/kg of γ‐tocopheryl quinones within 10 min. The emergence of γ‐tocopheryl quinones during culinary preparation of food has not yet been explored. Practical applications: Although an extensive research have been conducted in the area of microwave heating of foods, this is the first report about formation of cytotoxic γ‐tocopheryl quinone in microwave‐heated rapeseed oil. Formation of this reactive compound was also confirmed during frying process. The most γ‐tocopheryl quinone was formed during pan‐frying and subsequently entered into fried food. It was observed that the amount of oil used for frying has a major impact on slowing formation of cytotoxic γ‐tocopheryl quinone and other tocopherols and fatty acids degradation product. Formation of health‐promoting α‐tocopheryl quinone and cytotoxic γ‐tocopheryl quinone during pan‐frying.

“…Meanwhile, microwave oven applications showed to be harmful to vegetable oils, being possible to observe their deterioration in few minutes. Several reports highlight vegetable oils quality degradation, reduction in bioactive compounds and properties, fatty acids degradation, pigments destruction, sensorial changes, and color modifications, as well as physical and rheological changes [11][12][13][14][15][16][17][18][19][20]. In fact, comparatively to a conventional oven heating, microwave heating induces higher and faster oils deterioration [21][22][23].…”

Section: Introductionmentioning

confidence: 99%

Microwave heating induces changes in the physicochemical properties of baru (Dipteryx alataVog.) and soybean crude oils

Borges¹,

Malheiro

Souza³

et al. 2014

Baru oil is extracted from baru nuts (Dipteryx alata Vog.) by cold mechanical pressing, and is exploited as a source of vitamins, fatty acids and antioxidants in the Brazilian food and pharmaceutical sectors. No information is available on this oil under domestic culinary processes and thermal conditions. So, in the present study we evaluated the response of crude baru oil under microwave heating (0, 1, 3, 5, 10, and 15 min), using crude soybean oil as comparison. Physical and chemical parameters were evaluated (free acidity, peroxide value, specific extinction coefficient at 232 and 270 nm, ΔK and color by CIELAB method), fatty acid profile, tocopherol composition, antioxidant activity, and oxidative stability. Until 3 min (1000 W) no significant adverse changes were observed in either oil. However, higher exposition times are more adverse to baru oil than to soybean oil. Tocopherols, oils stability and antioxidant activity drop abruptly. The typical yellow coloration is lost with heating, giving a less appealing appearance to the oils. By a principal component analysis, it was verified that microwave heating differently influenced each oil, and within the same oil, exposure time also caused distinct effect on properties, quality, and composition. Based on the obtained results, we discourage the use of baru oil for culinary process. Practical applications: The use of baru oil for prolonged culinary processes is discouraged due to lower stability and low content in antioxidants. Baru oil is more suitable for seasoning for usage in domestic consumption at RT. Exposure to microwave heating is completely discouraged at an exposure higher than 3 min. Microwave heating changes appearence of baru and soybean crude oils.