Some microorganisms can transform methyl ricinoleate into -decalactone, a valuable aroma compound, but yields of the bioconversion are low due to (i) incomplete conversion of ricinoleate (C₁₈) to the C₁₀ precursor of -decalactone, (ii) accumulation of other lactones (3-hydroxy--decalactone and 2- and 3-decen-4-olide), and (iii) -decalactone reconsumption. We evaluated acyl coenzyme A (acyl-CoA) oxidase activity (encoded by the POX1 through POX5 genes) in Yarrowia lipolytica in lactone accumulation and -decalactone reconsumption in POX mutants. Mutants with no acyl-CoA oxidase activity could not reconsume -decalactone, and mutants with a disruption of pox3, which encodes the short-chain acyl-CoA oxidase, reconsumed it more slowly. 3-Hydroxy--decalactone accumulation during transformation of methyl ricinoleate suggests that, in wild-type strains, -oxidation is controlled by 3-hydroxyacyl-CoA dehydrogenase. In mutants with low acyl-CoA oxidase activity, however, the acyl-CoA oxidase controls the -oxidation flux. We also identified mutant strains that produced 26 times more -decalactone than the wild-type parents.