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Annual Progress Report on Malting Barley Research March, 2007

Annual Progress Report on Malting Barley Research March, 2007

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These automated methods have been the subject of numerous ASBC technical<br />

subcommittees, but a rugged, reproducible method has not been accepted. Principle<br />

problems with the methods have included alternative calibrati<strong>on</strong> methods and<br />

chemistries (starch-iodine and ferricyanide). The iodine reacti<strong>on</strong> with beta-limit dextrin is<br />

the foundati<strong>on</strong> of the original 1939 Sandstedt-Kneen-Blish (SKB) publicati<strong>on</strong> and<br />

subsequently, the ASBC manual method (ASBC Methods 1992). The method is based<br />

up<strong>on</strong> indirect measurement of a substrate property, and is perhaps of questi<strong>on</strong>able<br />

kinetic soundness. On the other hand, reducing sugar methods, such as the ferricyanide<br />

method are based up<strong>on</strong> the direct measurement of reducing sugars formed as a result<br />

of hydrolysis of alpha-1, 4 glucosidic linkages in starch by alpha-amylase. We c<strong>on</strong>tend<br />

that some of the difficulties in inter-lab measurement of malt alpha-amylase can be<br />

resolved by improving the understanding of the kinetics involved in various methods.<br />

The objective of the project is to compare various methods <strong>on</strong> a kinetic basis.<br />

Background and Hypothesis. The standard ASBC method for alpha-amylase in malt<br />

is based up<strong>on</strong> the reacti<strong>on</strong> of beta-limit dextrin (starch) with iodine (figure 1). Iodine<br />

binds within helical secti<strong>on</strong>s of the starch or beta-limit dextrin chain and yields a blue<br />

color. As amylases degrade starch, this helical structure and iodine binding are lost, and<br />

the color gradually changes to red. The measurement of alpha-amylase is based <strong>on</strong> this<br />

color change.<br />

Iodine<br />

Figure 1. Iodine binding within a cyclodextrin. This is analogous to binding within helical<br />

secti<strong>on</strong>s of the starch chain.<br />

77

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