Expansion and Functional Properties of Corn Starch Extrudates Related to their Molecular Degradation, Product Temperature and Water Content

Abstract

Expansion and functional properties of corn starch extrudates were related to the weight average of the molecular weight (M̄ w) of the extrudate molecules, the product temperature (PT), and the water content of the extruded mass. Expansion of the extrudates was investigated by determining sectional, longitudinal and volumetric expansion indexes. The expansion indexes of extrudates depended to various degrees on M̄ w' PT and water content of plasticised starch. Taking into consideration that functional properties of extrudates are dependent both on the disintegration of the crystalline structure and the molecular degradation of the molecules of the starch granules, it was demonstrated that functional properties depend both on M̄ w and PT. An increase in molecular degradation led to a decreasing cold paste viscosity (CPV) at constant PT. The influence of the PT on the CPV was more pronounced at higher values of M̄ w than at lower ones. Cold water solubility (CWS) of extrudates was dependent both on M̄ w and PT. This dependency was similar to that of the CPV. The sediment volume depended on M̄ w' PT and water content of the material on extrusion of the starch.