Enzymes that Transform Linoleic Acid into Di- and
Trihydroxyoctadecenoic Acids
in Malt
MBAA TQ vol. 40, no. 1, 2003, pp. 11-16 |
VIEW ARTICLE
Hisao Kuroda, Hideo Maeba, and Masachika
Takashio. Brewing Research Laboratories, Sapporo Breweries Ltd., 10
Okatome, Yaizu, Shizuoka 425-0013, Japan.
Abstract
The qualities of beer are deteriorated by the presence of either di- or
trihydroxyoctadecenoic acids (DHOD and THOD, respectively), which reduce
the beer �head� and produce an astringent flavor. Production of
these hydroxy fatty acids is reduced when the mashing-in temperature is
raised, which suggests that some enzymatic activities in the malt are
involved in the formation of these acids. During the characterization of
the factors that transform linoleic acid into DHOD and THOD in the mash
extract, it was revealed that these acids are produced by both
lipoxygenase (LOX) and a heat-stable enzyme present in the malt. This
newly found enzyme is considered to be an enzyme related to peroxygenase
(POX) that catalyzes the epoxidation of linoleic acid hydroperoxide to
produce epoxy fatty acid and epoxyalcohol. The enzyme, which we named
�POX-like activity,� has a high level of heat stability and is
supposed to be a rate-limiting enzyme for the production of DHOD and THOD.
The presence of POX-like activity poses the possibility of developing a
new malting barley that produces less DHOD and THOD by screening for
POX-like activity. In addition, it suggests the presence of other
uncharacterized enzymes in malt, known as cytochrome P450s, that catalyze
the transformation of fatty acid or lipid hydroperoxide into hydroxy fatty
acids, ketols, and carbonyl compounds, offering a new insight into the
mechanism of lipid oxidation during mashing in which catalysts besides LOX
may play an important role in the formation of these products.
Keywords: dihydroxyoctadecenoic acid, lipid oxidation,
lipoxygenase, malt, peroxygenase, trihydroxyoctadecenoic acids
S�ntesis
La calidad de una cerveza es deteriorada por la presencia
tanto de �cido di- � trihidroxi-octadecen�ico (DHOD y THOD,
respectivamente), los cuales reducen la formaci�n y/o estabilidad de la
espuma y producen un sabor astringente. La producci�n de estos �cidos
grasos hidrox�licos es reducido al utilizar temperaturas iniciales de
maceraci�n m�s altas, lo que sugiere que alguna actividad enzim�tica
en la malta est� involucrada en la formaci�n de estos �cidos. Al
caracterizar los factores que transforman �cido linol�ico en DHOD y
THOD en la maceraci�n, se pudo determinar que estos �cidos son
producidos tanto por lipoxigenasa (LOX) y una enzima termo-estable
presente en la malta. Esta nueva enzima parece estar relacionado con
peroxigenasa (POX), la que cataliza la epoxidaci�n de �cido linol�ico
hidroper�xido para producir �cido graso ep�xico y alcohol ep�xico.
Esta enzima, a la que hemos denominado de �actividad similar al POX�,
tiene una alta estabilidad t�rmica y se supone que es una enzima que
limita la velocidad de reacci�n para la producci�n de DHOD y THOD. La
presencia de esta actividad �POX-like� pareciera indicar que podr�a
ser posible desarrollar un nuevo tipo de cebada cervecera que produzca
menos DHOD y THOD mediante el triaje de la actividad �POX-like�. Es
m�s, tambi�n sugiere la presencia de otras enzimas no caracterizadas en
la malta, conocidas como citocromos P450, las cuales catalizan la
transformaci�n de �cidos grasos o l�pidos hidroper�xidos en �cidos
grasos hidrox�licos, ketoles y compuestos carbon�licos, ofreciendo una
nueva �ptica al mecanismo de la oxidaci�n l�pida durante la
maceraci�n, dado que catalizadores diferentes a LOX pueden tener un papel
importante en la formaci�n de estos productos.
Palabras claves: �cido dihidroxi-octadecen�ico, oxidaci�n de
l�pidos, lipoxigenasa, malta, peroxigenasa, �cidos
trihidroxi-octadecen�icos
