Dynamic viscoelastic properties and glass transition behavior of corn kernels

Information on viscoelastic properties is useful in industrial processing of foods as it provides insight into the structure of the material as a function of processing conditions. Corn kernels were hand sanded to obtain smooth and closely uniform samples with minimum damage to the kernel structure. The sample was tested using a dynamic mechanical analyzer. A miniature three point bending clamp was used to test the samples over a temperature range of 5-110C at frequencies of 1 and 10 Hz in the moisture content ranging from 11.9-%24.7% (db). The average value of storage modulus (G') showed a decreasing trend with increase in the moisture content. The corresponding tan curve showed a peak representing the glass transition temperature. The kernels exhibited a transition in the range of 20-60C, which is expected to be the glass transition range. The transition range is consistent with the results of similar studies on cornstarch. It embodies an average of several transition temperatures that arise due to the compositional diversity in the kernel. The individual corn kernels exhibit a wide sample-to-sample variation and structural heterogeneity. A very large number of test replications are required for consistent results. The accuracy and applicability of the dynamic testing in corn is limited due to the rigid sample specifications and testing conditions. Sample preparation and selection of appropriate loading conditions are also addressed.