Change in some physical characteristics of ultrasound pre-treated corn during hot-air convection and vacuum drying

Abstract

The objective of this study was to investigate the effect of ultrasound pre-treatment (50% US and 100% US-soaking), temperature (80, 90 and 100 ᵒC) and dryer type (hot-air convection and vacuum) on some physical characteristics such as hectoliter weight, thousand kernel weight, dimensions (thickness, length, width, equivalent diameter and sphericity) of corn during drying. Before drying, corn samples were pre-treated without ultrasound (conventional-soaking) and with ultrasound (40 kHz 200 W, 50 and 100% amplitude) during 1 hour soaking. Pre-treated samples were dried at 80, 90 and 100 ᵒC in the laboratory type vacuum dryer and hot-air convection dryer. Moisture content, dimensions (length, width, thickness, equivalent diameter and sphericity), thousand kernel weight and hectoliter weight of pre-treated corn samples at each temperature were analyzed for every 60 min during 240 minutes of drying processes. When the research results were analyzed, the length, width and equivalent diameter values of the corn samples dried in vacuum and hot air convection dryer were found significantly different between 0-60 minutes (P≤0.05), but insignificant (P>0.05) in the following periods. While the decrease in thickness of corn samples dried in vacuum dryer was significant (P≤0.05), the decrease in thickness of corn samples dried in hot air convection dryer was found insignificant (P>0.05). The increase in sphericity of the corn samples dried in vacuum dryer during drying was significant (P≤0.05), but the increase in the hot air convection dryer was insignificant (P>0.05). The effect of ultrasonic pre-treatment and dryer temperature on the size of the corn samples was found to be insignificant (P>0.05), while the effect of vacuum drying on the size of the corn samples was significant (P≤0.05). The effect of ultrasound pre-treatment, drying temperature and drying time on moisture content, thousand kernel weight and hectoliter weight of corn grains were found to be significant (P≤0.05). As a result, the vacuum dryer, allowed the corn to dry in a short time without much change in the structure of the corn.