Experimental study on the effect of glass transition on moisture profiles and stress-crack formation during continuous and time-varying drying of maize kernels

The concept of glass transition can help understand the drying process and provide insight into the stress-cracking behaviour of maize (Zea mays) kernels. Thin-layer drying experiments using continuous and time-varying temperature and humidity profiles were conducted and the stress crack index was evaluated. Overlaying glass-transition regimes over the continuous drying profiles demonstrated a broader transition region at lower temperatures and a narrower transition region at higher temperatures. The time taken by maize kernels to pass through the glass-transition regime was directly related to the stress-crack formation. High temperature drying at 90 degrees C decreased the drying time but showed a higher cracking index. Low temperature drying at 30 degrees C had the longest drying time but this caused the least amount of cracking in the samples. Time-varying temperature profiles were also tested using a combination of temperatures in the glass-transition zone. Introduction of a high humidity step along with high temperature in the time-varying drying profile offered advantages in terms of drying time and reduced cracking in comparison to continuous single temperature drying at 70 degrees C. To extend the findings of this study, future studies should be conducted using additional drying conditions and computer simulations. Published by Elsevier Ltd on behalf of IAgrE.