Proteolytic Enzymes and Protein Modification in Malting Sorghum: A Review
MBAA TQ doi:10.1094/TQ-46-3-0714-01 |
VIEW ARTICLE
A. C. Ogbonna. Department
of Food Science & Technology, University of Uyo, P.M.B. 1017, Uyo,
Nigeria.
Abstract
Approximately 80% of the protein reserves,
composed mainly of alcohol-soluble prolamins (kaffirins), in the sorghum
grain are located in the starchy endosperm. During sorghum malting, the
proteolytic enzymes that are synthesized de novo and are not gibberellic
acid (GA(3)) dependent hydrolyze the glutelin and prolamin proteins in the
endosperm. The use of reducing agents such as dithiothreitol and cysteine
hydrochloride has made optimization of the extractability or activity of
sorghum malt proteases possible. All of the class-specific endoproteases,
i.e., serine, cysteine, and aspartic proteases and metalloproteases, have
been purified and characterized from different sorghum malt varieties.
However, unlike those of barley malts, these enzymes have not been
subjected to hydrolytic studies using kaffirin (the main sorghum reserve
protein) as substrate to establish what role each plays in sorghum protein
degradation. Nevertheless, because the optimum temperature (50�C) and pH
(5.0�6.0) for the activity of these class-specific enzymes are similar to
the conditions found in a brewery mash tun, their participation in protein
degradation is imperative when brewing with sorghum malt.
Keywords: malting, mobilization, protease, protein,
solubilization, sorghum
S�ntesis
Aproximadamente 80% de las reservas proteicas
(compuesta principalmente de prolaminas/kafirrinas) en el grano del sorgo
est� en la endosperma. En el malteo del sorgo, las enzimas proteol�ticas
que son sintetizados de novo y que no son dependientes del �cido
giber�lico (GA(3)), hidrolizan la glutelina y las prote�nas prolam�nicos en
la endosperma. El uso de agentes reductores, tales como dithiothreilol e
hidrocloruro de cisteina, hace posible optimizar la
actividad/extractabilidad de las proteasas de la malta de sorgo. Todas las
endoproteasas espec�ficas para determinadas clases (i.e., serina,
cisteina, metaloproteasas, y proteasas asp�rticas) han sido purificadas y
caracterizadas de diferentes variedades de malta de sorgo. Sin embargo,
contrario a aquellas de cebada malteada, estas enzimas no han sido objetos
de estudios hidrol�ticos usando kafirrina (la principal reserva proteica
de sorgo) como sustrato para establecer el rol que cada uno tiene en la
degradaci�n de prote�nas de sorgo. Pero dado que la temperatura �ptima
(50�C) y el pH �ptimo (5.0�6.0) para la actividad de estas enzimas es
similar a las condiciones encontradas en una mezcla en la paila de
maceraci�n de una cervecer�a, su participaci�n en la degradaci�n de
prote�nas es imperativa cuando se va a elaborar cerveza de malta de sorgo.
Palabras claves: malteo, movilizaci�n, proteasa, prote�na,
solubilizaci�n, sorgo
