Change in organosulfur compounds in onion (Allium cepa L.) during heat treatment.

Changes in contents of the S-alk(en)yl-L-cysteine sulfoxides (ACSOs) methiin, isoalliin, propiin, and cycloalliin in onions after boiling, frying, steaming, and microwaving were investigated using Liquid Chromatography Electrospray Ionization-Tandem Mass Spectrometry (LC/ESI-MS/MS). ACSOs contents increased by 34.2-568.0% during frying, steaming and microwaving, whereas ACSOs contents decreased by 32.6-69.4% during boiling. The methiin level in heat-treated onions ranged from 0.18 to 0.47 g/100 g of dry weight (DW), and the cycloalliin concentration in heat-treated onions ranged from 0.31 to 3.50 g/100 g of DW. The amount of isoalliin in processed onions was 0.34-3.32 g/100 g of DW, and propiin was 0.15-1.67 g/100 g of DW. Changes in the ACSO concentrations were dependent on the cooking method. The quality of heat processed onions was evaluated.