Effects of common cooking heat treatments on selenium content and speciation in garlic

The effect of traditional thermal treatments, normally applied during cooking practices, on the stability of Se-amino acids and Se-proteins present in Se-enriched garlic was studied. Five heat treatments including, convection oven (180 °C, 10 min), boiling (100 °C, 10 min), microwave oven (800 W, 3 min), steaming (10 min) and stir-frying (180 °C, 3 min) were assayed. Modifications on the molecular weight fractions profiles of protein extracts were evaluated by size exclusion chromatography with UV-visible and inductively coupled plasma mass spectrometry (ICP-MS) detection using a 0.05 M Tris(hidroxymethyl)aminomethane solution at pH 7.3 as the mobile phase. Possible modifications of Se-amino acids were evaluated by anion exchange chromatography (AEC), with a 30 mM Na2HPO4 solution (pH 6) as the mobile phase, coupled to ICP-MS after enzymatic hydrolysis. SEC chromatograms showed the incorporation of Se to high (7 kDa) and low molecular weight fractions (2-4 kDa) while AEC chromatograms showed mostly the presence of Se-methylselenocysteine. However, it could be observed that heat treatments significantly affect this important Se-amino acid.