Effects of aerobic and anaerobic germination on the debranching enzyme, limit dextrinase, in barley malt

Limit dextrinase exists in an active free form and in a soluble inhibited (latent) form. The total activity of limit dextrinase is measured after extracting the enzyme in the presence of dithiothreitol, and the free enzyme is measured following extraction without dithiothreitol. Limit dextrinase is normally in the inhibited form following malting. The activity of limit dextrinase in grains of barley, Hordeum vulgare L, variety Golden Promise, germinated using combinations of aerobic and anaerobic conditions, was studied. The total limit dextrinase measurable with dithiothreitol in the extraction increased with increasing days of aerobic germination until it came close to a plateau after six days. The transformation of this inhibited enzyme to the free and uninhibited enzyme required three to four days of anaerobic germination. The effect of an extract from an aerobically germinated malt on the uninhibited enzyme of an anaerobically germinated malt was studied. Mixing increasing amounts of aerobic malt (free limit dextrinase activity of 60 mU/g) with anaerobic malt led to the inhibition of the free enzyme in the anaerobic malt. The inhibition increased rapidly as the proportion of aerobic to anaerobic malt approached a ratio of 1:1. Thereafter, increasing amounts of aerobic malt only slightly decreased the small amount of residual free limit dextrinase activity remaining. Thus, in a mash, excess inhibitor from a normal malt would almost certainly inhibit free enzyme from an anaerobic malt.