Abstract: The volatile flavor components of three commercial Cheddar cheeses with different ripening times were analyzed by solvent-assisted flavor evaporation (SAFE) or solid phase micro-extraction (SPEM) combined with gas chromatography-mass spectrometry (GC-MS) and electronic nose. The results showed that a total of 78 volatile aroma compounds were identified, mainly including 13 fatty acids, 9 esters, 8 lactones, 9 aldehydes, 5 ketones, 12 alcohols, 19 aromatic or heterocyclic compounds, and 3 sulfur-containing compounds. Principal component analysis (PCA) performed on the volatile compounds identified in Cheddar samples showed that the main volatile aroma components of mild Cheddar cheese were fatty acids, methyl ketones and heterocyclics, the main volatile substances of medium Cheddar cheese were fatty acids, methyl ketones and lactones, and the main volatile aroma components of mature Cheddar cheese were fatty acids, esters，methyl ketones and lactones. Moreover, the Cheddar samples with different ripening times could be perfectly distinguished by electronic nose.

Key words: Cheddar cheese; solvent-assisted flavor evaporation; solid phase micro-extraction; electronic nose discrimination; principal component analysis