Type: Process Essays
Sample donated: Amelia Newton
Last updated: September 18, 2019
The pasting properties of starches (peak viscosity, breakdown viscosity, setback viscosity and energy etc.) can be studied using RVA method. It has been reported that the use of RVA produces reproducible results that fit several industrial applications with less sample requirement in a short run 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 rheological behaviour of different concentrations (10%, 20%, and 30%) of cornstarch with and without added Ca2+ during the hydrolysis/liquefaction processes by this method are shown in Fig. 1-3.. The obtained results were described and analyzed by means of recorded viscosity curves by using a software program.
Each analysis was performed in triplicate and a mean value was calculated for each curve to determine the reproducibility of the process. During starch liquefaction at elevated temperatures, the viscosity of the starch pastes initially increased rapidly due to rise in temperature which causes gelatinization of starch. Such starch gel behaviour observed in this study has been reported earlier by other authors. The onset of gelatinization of starch according to the RVA method described by MEBAK starts when the viscosity increases by 24 mPa.s within 1s. Gelatinization temperature is defined as the lowest temperature at which the aqueous starch granules begins to swell tangentially, and the same time loses their unique nature i.
e crystalline and amorphous regions. It is worthy of note that initial starch concentration in the slurry resulted in distinct viscosity profile (control result curves). Schnitzenbaumer et al.
, 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 starting point A and the end-point C define the relevant integration limit. As the initial starch concentration of the slurry increases due to heat treatment, the higher the viscosity of the starch paste, which thereafter decreased with time due to the action of the added thermostable ?- amylase.
This could be explained that the initial swelling of starch granule is the prerequisite for enzymatic attack and subsequent hydrolysis. In as much as the presence of the added enzyme in this study did not delay the observed onset viscosity acceleration independent of the saturation concentration as reported by Rittenauer et al., (2017), however, we observed a decrease in the initial viscosity compared to the control. In this study we observed a different pattern of hydrolysis, although the reduction of viscosity by the action of the enzyme was accompanied by the initial increase of viscosity induced by the gelatinized starch granule, but these values were found to be lower than observed for controls. (88%) This indicated that the added enzyme in this study was active towards raw starch prior to the onset of fitted temperature of hydrolysis and thus caused lowering of the initial viscosity of the processed starch compared to the control counterparts (Fig.4). Further analyses of this mechanism by integrating the logarithms of recorded parameters indicated the loss of viscosity at the onset of liquefaction within 2 min.