PROPANETHIAL S-OXIDE CONTENT IN SCALLIONS (ALLIUM-FISTULOSUM L VARIETY CAESPITOSUM) AS A POSSIBLE MARKER FOR FRESHNESS DURING COLD-STORAGE

Propanethial S-oxide (PSO), known as a precursor of flavor chemicals in Allium species, was analyzed in scallions (Allium fistulosum L. var. Caespitosum) stored at 0 and 5 degrees C for 1-5 weeks. The levels of PSO from scallions stored at 5 degrees C were much higher than those from scallions stored at 0 degrees C. PSO comprised 80-90% of the total volatiles of all the samples obtained from scallions. The amounts of total volatiles and PSO from scallions stored at 5 degrees C increased for the first week and then decreased slightly. They gradually increased from the second week to fourth week and then increased dramatically. The amount of PSO from scallions stored at 0 degrees C increased slightly for the first 4 weeks and then decreased. Over time, the visual changes of scallions stored at 5 degrees C correlated with the amount of PSO formed. Several sulfur-containing compounds known to be formed from PSO were also identified as main constituents of volatiles from scallions. The formation of PSO during cold storage can be used as a marker for the freshness of scallions.