Flavor and Texture in Cheddar Cheese. II. Carbonyl Compounds Produced by Mixed Strain Lactic Starter Cultures

Two mixed-strain lactic starters, A and C, selected for consistent production of normal and fruity-flavored Cheddar cheese, respectively, were cultured in 11% nonfat milk for 24 hr at 30 C, and the amounts and kinds of carbonyl compounds produced by each were compared. Tentative identification of 2,4-dinitrophenylhydrazones of the carbonyls showed the presence of acetaldehyde, propionaldehyde, acetone, pyruvie acid, diacetyl, glyoxal, and an alphaketo alkanal in Starter A. Starter C contained the same compounds but lacked propionaldehyde, which was replaced by formaldehyde. Striking differences were noted between A and C in the concentration of acetaldehyde, diacetyl, and pyruvie acid, the latter containing more than twice the eoneentration of these compounds found in Starter A. It appeared that cultures associated with high carbonyl production in milk also were responsible for fruity offflavor defects in Cheddar cheese.