Kinetics of granular starch hydrolysis in corn dry-grind process

A promising modification to the dry grind process is the use of granular starch hydro- lyzing enzymes (GSHE) for corn fractionation and ethanol production. Modeling the kinetics of granular starch hydrolysis in the corn dry-grind process is challenging given the heterogeneity of the substrate and the combined activities of α-amylase and glucoamylase. By measuring reducing sugars, the hydrolysis progress in dry-grind corn slurry treated with a commercial GSHE was monitored during 3 h of reaction. Progress curves consisted initially of a rapid product formation phase (<15 min), followed by a longer range kinetics characterized by relatively slower product formation. The initial product from the accelerated kinetics was proportional to the adsorbed GSHE concentration, after accounting for the contribution of dissolved starch hydrolysis. The long range kinetics was modeled by an empirical equation that yielded two parameters: a which stood for the asymptotic limit of the product concentration, and ln (b) which was the time required to reach a product concentration of a/2. In response to increasing GSHE concentration, a increased and ln (b) decreased towards a saturation limit. In response to decreasing corn particle size (geometric mean diameter), a increased and ln (b) decreased linearly. These behaviors indicated both parameters were controlled by the concentration of accessible substrates in the starch granules. The findings have implications on the optimal usage of GSHE in dry-grind processes.