Homogenization and lipase treatment of milk and resulting methyl ketone generation in blue cheese.

A specific range of methyl ketones contribute to the distinctive flavor of traditional blue cheeses. These ketones are metabolites of lipid metabolism by Penicillium mold added to cheese for this purpose. Two processes, namely, the homogenization of milk fat and the addition of exogenous lipase enzymes, are traditionally applied measures to control the formation of methyl ketones in blue cheese. There exists little scientific validation of the actual effects of these treatments on methyl ketone development. The present study evaluated the effects of milk fat homogenization and lipase treatments on methyl ketone and free fatty acid development using sensory methods and the comparison of selected volatile quantities using gas chromatography. Initial work was conducted using a blue cheese system model; subsequent work was conducted with manufactured blue cheese. In general, there were modest effects of homogenization and lipase treatments on free fatty acid (FFA) and methyl ketone concentrations in blue cheese. Blue cheese treatments involving Penicillium roqueforti lipase with homogenized milk yielded higher FFA and methyl ketone levels, for example, a ∼20-fold increase for hexanoic acid and a 3-fold increase in 2-pentanone.