Microwave heating of edible vegetable oils: hydrolytic and oxidative modifications

Microwave heating is a common and rapid procedure for food preparation and offers many advantages for both home and industrial food applications such as baking, cooking, thawing, blanching, dehydration, pasteurization, sterilization and tempering. Microwaves are commonly found in both domestic and food catering operations and are very popular due to their high speed and convenience, as compared to conventional heating methods. Among macrocomponents of food, lipids are particularly sensitive to microwave heating as the specific heat for lipids is low and they are heated quickly. Vegetable oils are commonly used as a heat transfer medium in food processing, and it is well known that heat treatments accelerate hydrolysis and oxidation of glycerides and also cause degradation of minor compounds. In this chapter, chemical modifications of major and minor components of vegetable oils induced by microwave heating will be overviewed and compared to these caused by conventional heating. Specifically, variations in free fatty acids and their isomeric forms, triacylglycerol and fatty acid dimers and polymers, along with changes in hydrophilic and lipophilic antioxidant compounds will be detailed.