Abstract
In brewing, 2(E)-nonenal is considered to be the major contributor to the cardboard flavor that arises when a beer is stored for a prolonged period. We found that lipoxygenase-1, fatty acid hydroperoxide lyase (HPL) and 3Z:2E- isomerase in malt are involved in the production of 2(E)-nonenal. In this cascade pathway, linoleic acid from malt is transformed into linoleic acid 9-hydroperoxide (9-HPOD), and then 9-HPOD is cleaved into 3(Z)-nonenal, and finally 3(Z)-nonenal is isomerized to 2(E)-nonenal. These HPL and 3Z:2E-isomerase found in malt were the first enzymes appeared in monocots. We screened candidate barley EST and cloned a full length cDNA that code for this type of HPL, and designated as HvHPL2. Recombinant protein of HvHPL2 cleaved both 9-HPOD and linoleic acid 13-hydroperoxide, indicating HvHPL2 belongs to CYP74C subfamily of cytochrome P450. Flavor stability of beer could be improved by developing barley mutant lines of HvHPL2.
