|Chang, Shih-Ying - U.MARYLAND,CHEMICAL ENGR.|
|Wang, Nam - U.MARYLAND,CHEMICAL ENGR.|
Submitted to: Biotechnology and Bioengineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 8, 2002
Publication Date: September 30, 2002
Citation: CHANG, S., DELWICHE, S.R., WANG, N.S. HYDROLYSIS OF WHEAT STARCH AND ITS EFFECT ON THE FALLING NUMBER PROCEDURE: MATHEMATICAL MODEL. BIOTECHNOLOGY AND BIOENGINEERING. 2002. Interpretive Summary: Produced by higher plants as a means of energy storage, starch is the major source of carbohydrates in the human diet. Synthesized within the storage organs (amyloplasts) of the cereals, such as wheat, starch molecules form tiny (around 10 micrometers) white granules that are insoluble in cold water. Within the molecule, starch consists of hundreds of glucose units, which, by enzymatic hydrolysis, are cleaved in the presence of heat and hydration. In addition to extensive study at the molecular level, starch hydrolysis has been widely examined at the macro level through the rheological changes that occur to a heated starch-water solution as granules swell and rupture. However, scant information exists on mathematical modeling to describe the competing kinetic events of gelatinization, hydrolysis, and enzyme (alpha amylase) activity. The current research was directed toward developing such a model, then using this model to describe the behavior of a viscometer-type instrument (i.e., Falling Number) used worldwide to measure the starch-related processing characteristics of wheat and barley. Through modeling of starch hydrolysis, grain-testing apparatus can be better utilized to ascertain the subtle but significant cooking properties of cereals. Moreover, traders and processors will gain an enhanced understanding of the processing characteristics of grain lots during scale-up operations.
Technical Abstract: A population balance model was developed for wheat starch hydrolysis to simulate the performance parameters of a viscosity-based device, known as the Falling Number (FN) instrument. The instrument is widely used as an indirect means to gauge the level of preharvest sprout activity in cereal grains such as wheat and barley. The model consisted of three competing kinetics: starch gelatinization, enzymatic hydrolysis, and enzyme thermal deactivation. Using established principles of starch rheology and fluid mechanics, the model simulated the velocity profiles of the falling stirrer, starch gel viscosity, and the FN readings at various levels of alpha amylase. Model predictions for the velocity of the stirrer at any time during the downward fall, as well as the prediction of the total time needed for the fall, defined as the falling number, closely matched experimental measurements. There was better agreement between the modeled viscosity and the final viscosity of the starch gel as measured by a precision rheometer than there was with the measured FN.