Annual Progress Report on Malting Barley Research March, 2007
Annual Progress Report on Malting Barley Research March, 2007
Annual Progress Report on Malting Barley Research March, 2007
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With starch as a substrate, iodine binding is impacted by both alpha-and beta-amylases.<br />
In order to make the method specific for alpha-amylase, beta-limit dextrin is used as<br />
substrate. Beta-limit dextrin is prepared by exhaustively reacting starch with a purified<br />
beta-amylase. Beta-amylase hydrolyzes starch from the n<strong>on</strong>-reducing end to yield<br />
maltose. As it can not pass alpha-1,6 linkages in the starch, a beta-limit dextrin product<br />
results in additi<strong>on</strong> to the maltose (figure 2).<br />
Beta-Amylase<br />
Alpha- 1, 6 branch<br />
+ Maltose<br />
starch<br />
Beta-Limit Dextrin<br />
Figure 2. Preparati<strong>on</strong> of beta-limit dextrin from starch using purified beta-amylase.<br />
Arrows show points at which beta-amylase can hydrolyze alpha-1,4 linkages in starch.<br />
In theory, the beta-limit dextrin can no l<strong>on</strong>ger be attacked by beta-amylase, and its use<br />
as a substrate makes the method specific for alpha-amylase. Alpha-amylase is an<br />
endo-enzyme, meaning it attacks the beta-limit dextrin internally and forms small<br />
oligosaccharides (figure 3). Loss of iodine binding is thus believed <strong>on</strong>ly to be associated<br />
<strong>on</strong>ly with the alpha-amylase in the malt sample.<br />
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