Annual Progress Report on Malting Barley Research March, 2007

Figure 6. Degradation of beta-limit dextrin with alpha-amylase (30 DU) and alpha- and
beta-amylase. End-point line indicates the normal color endpoint of the manual assay.
As shown in figure 6, supplementation with beta-amylase did change in the initial rate of
color loss. However, the impact on the final endpoint was only about 1 min. The would
translate to about 4 DU. The value for alpha-amylase in the absence of added beta-
was 40, and in the presence of beta was 44. These results are significant but perhaps
the magnitude is not of great concern in routine analytical situations.
Beta-limit dextrin is prepared by exhaustive treatment of soluble starch with betaamylase.
In the next series of experiments we tested the beta-limit dextrin substrate for
the presence of residual enzyme activity. The beta-limit dextrin substrate was assayed
both as normal, and following heat treatment. As shown in figure 7, the heat treated
beta-limit dextrin substrate took over 20 min to reach the color endpoint when digested
with only alpha-amylase (■-■-■). However, when assayed as normal, with no heat
treatment conversion was in approximately 12 min (▲-▲-▲). This translates to 24 DU
in the heat treated substrate and 40 in the normal assay. Residual beta-amylase in the
beta-limit dextrin substrate is clearly making a very large contribution to the value for
malt alpha-amylase.
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