Time course for the development of enzymes in barley

Abstract

Barley (Hordeum distichon var. Harrington) was steeped, germinated and extracted to observe the order of enzyme development. Different parts of the barley kernel were extracted to observe the order of enzyme development during the malting process. Five enzymes were investigated: carboxypeptidase (EC 3.4.16.1), endo-β1-3, 1-4-glucanase (EC 3.2.1.73), endo-B1-4-xylanase (EC 3.2.1.136), arabinofuranosidase (EC 3.2.1.55), and αamylase (EC 3.2.1.1). Early development of carboxypeptidase, followed by later development of β-glucanase, then α-amylase, confirmed earlier reports concerning the sequence of synthesis for these activities. However, xylanase developed during the steeping of barley and early in germination, whereas other authors found this enzyme to develop much later in the malting process. Enzyme activities developed to higher levels in the proximal end of kernels for all enzymes except xylanase, which was evenly distributed throughout the kernel. Enzyme development was tested in sterile barley annuli [embryo-less cross sections taken through the grain, and thus comprising rings of tissue with husk outermost and starchy endosperm innermost] under four effector conditions. Water controls mirrored the development pattern observed in whole barley kernels. Gibberellic acid (GA3) promoted higher total enzyme activity and development of all enzymes at the same time. Abscisic acid (ABA) promoted earlier development of late developing enzymes (xylanase, arabinofuranosidase and α-amylase) and significantly higher levels of xylanase than when treatment was with water alone. Mixtures of GA and ABA showed a non-exclusive, combined response of higher activity levels and a shifting of the initiation of enzyme development. Treatment with a combination of GA and calcium chloride triggered signifycantly higher carboxypeptidase activity and significantly lower xylanase activity as compared to treatment with GA or with GA/ABA mixtures. © 2007 The institute of brewing & distilling.