The pasting properties of starches (peak viscosity, breakdown viscosity, setback viscosity and energy etc.) (Zeng et al., 2015; Reddy et al., 2014; Rittenauer et al., 2017) as well as mashing consistency can be studied using RVA method(Scrichuwong et al., 2009; Schntzenbaumer et al., 2013; ).. It has been reported that the use of RVA produces reproducible results that fit industrial applications with less sample requirement in a short (run) period of time compared to the well established Brandenber amylograph. In this paper, we analyzed the rheological behavior of cornstarch at different concentrations during hydrolysis/liquefaction processes using RVA with added raw- starch digesting ?- amylase (RSDA) produced by a novel strain Bacillus amyloliquefaciens. The results of the rheological behavior of different corn starch concentrations (10%, 20%, and 30%) with and without added Ca2+ during the hydrolysis/liquefaction processes by this method are shown in Fig. 1, 2 and 3.. Starch granule swelling in the presence of water is known to start in the bulk relatively mobile amorphous fraction and, in the most restrained amorphous region which is located adjacent to the crystalline regions (Donovan, 1979). Factors such as temperature, pH, and type of enzyme can greatly induce changes in the structure. During starch liquefaction at elevated temperatures in the present study, the viscosity of the starch paste initially increased rapidly due to rise in temperature which causes gelatinization of starch and, such starch gel behavior has been earlier observed by other authors. The onset of gelatinization of starch according to the rheological method described by MEBAK starts when the viscosity increases by 24 mPa.s within 1s (Rittenauer et al., 2017). Gelatinization temperature is defined as the temperature at which the starch granules swell tangentially and the same time loses their crystalline and amorphous regions. It is noteworthy that different initial starch concentration in the slurry (Fig. 1, 2 and 3) resulted in distinct viscosity profile (control result curves). Schnitzenbaumer et al.,2013, defined the “end point of liquefaction as the curve point at which the consistency after gelatinization is equal to the minimum consistency before gelatinization”. The start point A and the end point C incorporates the relevant integration limit (Fig. 1). As the initial starch concentration of the slurry increases, the higher the viscosity of the starch paste (Fig. 1,2 and 3), which thereafter decreased with time due to the action of the added thermostable ?- amylase. The presence of added enzyme did not delay the observed onset viscosity increase independent of the initial saturation (concentration) of starch. This could be explained that the initial swelling of starch granule is the prerequisite for enzymatic attack and subsequent hydrolysis. The reduction of viscosity by the action of the enzyme was accompanied with the initial increase induced by the gelatinized starch granule (Rittenauer et al., 2017). Values of the onset temperature for treated starches, independent of the concentration, confirmed that the thermostable ?-amylase treated starches swelled slowly and the viscosity peak was significantly (p ? 0.05) lower than its counterpart control (Fig. yyy). Likely, during the rise in temperature within 2min of heating to attain the desired temperature of liquefaction, there were some distinct levels of starch degradation by the added enzyme. This probably induced changes in the structure of starch lowered the initial peak viscosity due to the initial hydrolysis of the substrate by the added enzyme below the setpoint of liquefaction temperature for the starch treated enzyme.
The distortion of curves reading in form of a ” hump” that was observed after 5min of hydrolysis/liquefaction, occurred in all examined starch concentrations at 900C without the addition of Ca2+ion. This could be a result of initial peripheral hydrogel-enzyme complex formation caused by slow liquefaction of the complex during progression. Alternatively, the formed complex may affect the smash or torque, which invariably changed the curve reading during the process. Nevertheless, the final viscosity profiles (readings) at the end of liquefaction was smooth with a relatively low viscosity in all tested runs, independent of the initial corn starch concentration (Fig. xxx). In all the tested initial starch concentrations with the addition of Ca2+, the rheological amylographs showed smooth viscosity curves during the liquefaction process with substantial flowability characteristics (viscosity This could also lead to the design of a good reactor system and. reduction of cost in terms of energy input by 20-30% compared to the conventional method by jet-cooking. The energy input during jet cooking has been the rate-limiting economic factor in the gelatinization/liquefaction of starch.