Effect of Starch Hydrolysis Products on the Determination of Limit Dextrinase and Limit Dextrinase Inhibitors in Barley and Malt

Abstract

Abstract The activity of purified malt limit dextrinase was apparently increased by maltodextrins when enzyme activity was assayed by dyed pullulan substrates. At higher maltodextrin levels (different for each maltodextrin), the enzyme was inhibited. The apparent enzyme activation was not detected when assays were carried out with amylopectin β-limit dextrin, a more natural substrate for limit dextrinase, as substrate. Pullulanase (Aerobacter aerogenes) activity, when assayed with dyed pullulan, was not activated in the presence of maltodextrins. Barley extracts contained material that appeared to increase the activity of limit dextrinase. Results indicated that this material was a mixture of starch dextrins, which lost their activating ability when treated with amyloglucosidase. Treatment of malt extracts with amyloglucosidase prior to assaying for limit dextrinase significantly lowered the apparent limit dextrinase activities (when measured by dyed pullulan) and allowed for a more accurate estimate of both limit dextrinase and limit dextrinase inhibitor levels in the extracts. Enzyme and inhibitor levels in malt extracts, obtained using amyloglucosidase pre-treatments, showed that there was a strong relationship between inhibitor disappearance in malt extracts and the appearance of fully active limit dextrinase. These results confirm earlier conclusions that limit dextrinase is largely ineffective during the mashing stage of brewing because it is inhibited by two barley proteins still present in malt.