Maltose Effects on Barley Malt Diastatic Power Enzyme Activity and Thermostability at High Isothermal Mashing Temperatures: II. α-Amylase

This study was conducted to determine if maltose, the primary product of starch degradation during mashing, would affect the activity of or increase the thermostability of barley malt α-amylase activity at high temperatures used in mashing and temperatures above those normally used in mashing. Malts of the two-row cultivar Harrington and the six-row cultivar Morex were mashed for 2 h with maltose concentrations of 0–500 mM at temperatures from 63 to 78°C. Worts were sampled every 30 min for 120 min and α-amylase activities determined utilizing the Megazyme Ceralpha assay. Mannitol, a polyhydric alcohol, was used for comparison. Polyhydric alcohols are known to enhance enzyme thermostability. At 63°C both cultivars had relatively thermostable α-amylase without the addition of maltose or mannitol. However, Morex, and to a lesser extent Harrington, α-amylase activity was significantly elevated by high levels of either maltose or mannitol, indicating a stimulatory effect on activity in which thermostability was apparently not involved. At 73 and 78°C increasing concentrations of maltose conferred considerable and highly significant (LSD analysis, P < 0.0001) thermal protection of α-amylase in both cultivars. For example, at 30 min of mashing at 73°C, maltose concentrations of 400 and 500 mM resulted in α-amylase activity in Harrington of 227 and 252% and in Morex 349 and 314%, respectively, of the 0 mM maltose activity. At 60 min of mashing at 73°C, concentrations of 400 and 500 mM maltose resulted in α-amylase activities of Harrington of 290 and 431% and Morex of 489 and 501%, respectively, of the 0 mM maltose activity. High mannitol incubations at higher temperatures such as at 73°C rendered lesser α-amylase thermal protection than maltose; however, it was also considerable and highly significant (P < 0.0001) for both cultivars (e.g., 30 min incubation at 73°C, with 400 and 500 mM maltose, respectively, α-amylase activities of Harrington were 163 and 174% and Morex were 188 and 260% of the 0 mM maltose activity). These data suggest that the production of maltose, as could be expected in high-gravity mashes, significantly increases the activity and thermostability of barley malt α-amylase.