Abstract
Current paper reveals the impact of thermal treatment on the quality of two seed oils – pumpkin and melon compared to the quality of the most used oil – sunflower oil. Conventional and microwave heating were used for processing the oils. The duration of the thermal treatment was 9, 12 and 18 min for the conventional heating. The microwave heating was performed with two microwave powers of the equipment (600 W and 900 W) for 3, 6, 9 and 12 min. At every stage of the thermal processing were determined acid and peroxide value, the absorbance of the oils at 232 and 268 nm, tocopherol and fatty acid composition. It was observed that the degree of oxidation of the examined oils during microwave and conventional heating increased with the duration of the thermal process and the power of the microwaves. Also, the two methods of heating had a little impact on the processes leading to the formation of free fatty acids. Total tocopherols of the melon seed oil were more stable to thermal treatment. The amount of linoleic acid decreased in the pumpkin and sunflower oils during microwave treatment, while that of oleic and palmitic acid relatively increased. The biggest change in the fatty acid composition of both oils was found during microwave heating at 900W. The changes in fatty acid composition of thermally treated melon seed oil were insignificant. Overall, melon seed oil was observed to be more thermally stable than pumpkin and sunflower oils.
Highlights
Conventional heating is the most commonly used method in the world for food preparation
Reactive free radicals are formed during the heating, which rapidly interact with atmospheric oxygen to form hydroperoxides, and they can be determined with the peroxide value that depicts the degree of oil oxidation
The greatest changes in the fatty acid composition were observed in pumpkin and sunflower oils, while in melon seed oil, there were no significant changes in the main fatty acids
Summary
Conventional heating is the most commonly used method in the world for food preparation. The thermal treatment is carried out at high temperature and in the presence of moisture and atmospheric oxygen, whereby the processes of oxidation and hydrolysis of the oils are activated. These reactions lead to a change in the functional, sensory and nutritional qualities of the processed foods and have great impact on human health. In the heat treatment of food products, microwave heating is widely used (Lukesova et al, 2009). It is more efficient method and reduces the cooking time of the products.
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