Cereal Chem. 70:548-552   |  VIEW ARTICLE

Glass Transitions of Extrudates: Relationship with Processing-Induced Fragmentation and End- Product Attributes.

G. Kaletunc and K. J. Breslauer. Copyright 1993 by the American Association of Cereal Chemists, Inc. 

We used differential scanning calorimetry to measure glass transition temperatures (Tg) for two types of corn-flour extrudates that differed primarily in their amylose-to-amylopectin ratios. Our experiments were designed so that extrusion-induced fragmentation represented the primary cause of changes in Tg. We found that the extent of fragmentation, as monitored by reductions in the Tg of the extrudates, increased with the specific mechanical energy generated in the extruder. Further, the Tg of the extrudate decreased rapidly with increases in moisture content, thereby demonstrating that the glass phase of the extrudate is sensitive to the relative humidity of the storage environment. The Tg values of the extrudates also related to crispness and denseness, two important sensory-textural properties. Based on these results, we propose the use of Tg measurements on extrudates as a criterion for adjusting extruder operating conditions to produce extrudates with optimal textural properties, as well as to select optimum storage conditions (temperature and relative humidity) to improve stability and shelf life of extruded products.