Proximate composition and vitamin E levels in egg yolk: losses by cooking in a microwave oven

The proximate composition, fatty acid and tocopherol levels of egg yolk were determined in raw eggs and after different cooking processes: boiling for 3 and 10 min, heating in a microwave oven, and frying. Of the protein, lipid, ash and moisture contents, only the last decreased with microwave cooking. The predominant fatty acid was oleic (18:1) (36.10–42.6%), followed in decreasing amounts by palmitic (16:0), linoleic (18:2), linolenic (18:3) = arachidonic(20:4) = docosanoic (22:0), docosahexanoic (22:6) and myristic acid (14:0). Of the polyunsaturated fatty acids, 18:2, 18:3, 20:4 and 22:6 decreased in the samples subjected to microwaves. α-Tocopherol (6.1–2.9 mg per 100g) was the predominant isomer in all the samples followed by (β + γ)-tocopherol and δ-tocopherol, while α-tocotrienol was detected in trace amounts. All these tocopherols were reduced during cooking by up to 50% in omelettes and microwave treatments. © 1999 Society of Chemical Industry