Amylose and amylopectin are established components of starch with anhydroglucose units joined by glucosidic bonds and is potentially degradable by the amylolytic enzymes. Liquefaction of starch by ?-amylase is primarily an important process step in the food industries to produce syrups which are further used as additives with obvious functional properties in many processed food products. The hydrolysis/liquefaction curves of cornstarch in the present study by the tested ?-amylase both at 800C and 900C with the addition of 5 mM of Ca2+ at pH 5.5 are shown Fig.
4 and 5. These conditions of hydrolysis were chosen based on the results of observed viscosity measurements by RVA, whereby the readings were stable and showed no fluctuations in the viscosity curves. The hydrolysis/liquefaction of raw-starch corn at stipulated concentrations was determined and the results show that the % of hydrolysis increased as the incubation time increases. As shown, the enzyme liquefied cornstarch with varied percentages of hydrolysis, depending on temperature, starch concentration and incubation time. At 10% cornstarch slurry, the highest % of hydrolysis was 55% both at 800C and 900C after 30min of incubation. A similar tendency was observed for 20% (Fig.
), whereas at 30% initial corn starch concentration and at 900C, the % of hydrolysis reduced to (50% ?). Likely, this might be a result of incomplete gelatinization of starch due to less water mobility within the phases, which led to lower hydrolysis of the starch gel-enzyme complex or invariably, decreased enzyme stability and activity at this high temperature. In contrast, such decrease in activity was not observed at 800C , independent of the initial corn starch concentrations and, in this case, the % hydrolysis remained constant at 55% in all runs, indicating that the enzyme was active and stable at this temperature. This confirms the viscosity curve results obtained at 800C (Fig. 1,2 and 3) which showed similar tendency with final viscosity values < 0.01 Pa S-1, independent of initial starch concentration.
The attractive properties of the raw starch digesting ?-amylase in this study was the strong hydrolyzing power on high concentrations of the raw starch granule. In view of its raw corn digesting ability, it could have potential application in the food and fermentation industries.