Monte Carlo simulation of the alpha-amylolysis of amylopectin potato starch. 2. alpha-amylolysis of amylopectin.

A model is presented that describes all the saccharides that are produced during the hydrolysis of starch by an alpha-amylase. Potato amylopectin, the substrate of the hydrolysis reaction, was modeled in a computer matrix. The four different subsite maps presented in literature for alpha-amylase originating from Bacillus amyloliquefaciens were used to describe the hydrolysis reaction in a Monte Carlo simulation. The saccharide composition predicted by the model was evaluated with experimental values. Overall, the model predictions were acceptable, but no single subsite map gave the best predictions for all saccharides produced. The influence of an alpha(1-->6) linkage on the rate of hydrolysis of nearby alpha(1-->4) linkages by the alpha-amylase was evaluated using various inhibition constants. For all the subsites considered the use of inhibition constants led to an improvement in the predictions (a decrease of residual sum of squares), indicating the validity of inhibition constants as such. As without inhibition constants, no single subsite map gave the best fit for all saccharides. The possibility of generating a hypothetical subsite map by fitting was therefore investigated. With a genetic algorithm it was possible to construct hypothetical subsite maps (with inhibition constants) that gave further improvements in the average prediction for all saccharides. The advantage of this type of modeling over a regular fit is the additional information about all the saccharides produced during hydrolysis, including the ones that are difficult to measure experimentally.

The effect of process conditions on the alpha-amylolytic hydrolysis of amylopectin potato starch: An experimental design approach.

The hydrolysis of amylopectin potato starch with Bacillus licheniformis alpha-amylase (Maxamyl) was studied under industrially relevant conditions (i.e. high dry-weight concentrations). The following ranges of process conditions were chosen and investigated by means of an experimental design: pH [5.6-7.6]; calcium addition [0-120 microg/g]; temperature [63-97 degrees C]; dry-weight concentration [3-37% [w/w]]; enzyme dosage [27.6-372.4 microL/kg] and stirring [0-200 rpm]. The rate of hydrolysis was followed as a function of the theoretical dextrose equivalent. The highest rate (at a dextrose equivalent of 10) was observed at high temperature (90 degrees C) and low pH (6). At a higher pH (7.2), the maximum temperature of hydrolysis shifted to a lower value. Also, high levels of calcium resulted in a decrease of the maximum temperature of hydrolysis. The pH, temperature, and the amount of enzyme added showed interactive effects on the observed rate of hydrolysis. No product or substrate inhibition was observed. Stirring did not effect the rate of hydrolysis. The oligosaccharide composition after hydrolysis (at a certain dextrose equivalent) did depend on the reaction temperature. The level of maltopentaose [15-24% [w/w]], a major product of starch hydrolysis by B. licheniformis alpha-amylase, was influenced mostly by temperature.