Amylose and amylopectin are established highly branched molecules 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 acquire different syrups that can be used as additives with obvious functional properties in one kind of processed food products. The hydrolysis/liquefaction percentages of cornstarch in the present study by the Bacillus amyloliquefaciens KU-20 ?-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 undesirable 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 various percentages of hydrolysis, depending on the 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 comparable effect 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 inside the phases (Xu e al., 2016), 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 final % 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 its strong hydrolyzing power on high concentrations of the starch granule. In view of its raw corn digesting ability, it could have potential application in the food and fermentation industries.