Quantitative Description of Fracturability Changes in Puffed Corn Extrudates Affected by Sorption of Low Levels of Moisture

ABSTRACT Fracturability is a defining textural characteristic of extruded and crunchy products such as puffed snacks and cereals. Even low levels of moisture can significantly affect deformation properties and texture due to changes in the distribution of fracture intensities. The fracturability of puffed corn extrudates produced at two specific mechanical energy (SME) levels, which greatly influenced extrudate structure and deformation behavior, was measured by compression testing before and after equilibration of samples at 33% rh. Significant changes in fracturability due to moderate moisture sorption were manifest in a reduced total number of fractures occurring during compression, an indication of plasticization that was confirmed independently by differential scanning calorimetry (DSC) studies as reductions in glass transition temperature ( T g ). However, in both instances, mean fracture intensity and average compressive resistance increased after equilibration, indicating a qualitative toughening or hardening of the products, despite increased moisture and decreased T g . These textural developments were also reflected in changes in the parameters of fitted fracture intensity distributions. Thus, the influence of processing conditions (quantified in terms of SME) on the creation of new micro and macrostructures, and the effect of low levels of moisture on these structures, can be identified by using fracturability characteristics and T g . Furthermore, fracturability parameters can demonstrate complexity in the deformation patterns of products that thermal measurements confirm to be plasticized.