Comparison of moisture-dependent physical and mechanical properties of two varieties of corn (Sc 704 and Dc 370)

This study was carried out to determine the effect of moisture content on some physical properties and mechanical behavior of corn grains under compression load of two varieties of corn (Sc704 and Dc370) which are the most cultivated varieties by Iranian farmers. Four levels of moisture content ranging from 4.73-22% wet base (w.b.) and 5.15-22% w.b. for Sc704 and Dc370, respectively were used. The average length, width, thickness, geometric mean diameter, equivalent diameter, arithmetic diameter, sphericity, grain volume, surface area and aspect ratio were studied. The thousand grain weight increased linearly from 271.0 to 321.4 g for Sc704 and from 267.7 to 305.8g for Dc370. As the moisture content increased, bulk density was found to decrease from 710 to 649 kgm-3 and 679 to 632 kgm-3 for Sc704 and Dc370, respectively whereas true density and porosity were found to increase from 1250 to 1325 kgm-3 and 43.2% to 51.02% for Sc704 and 997 to 1170 kgm-3 and 31.90% to 45.98% for Dc370. The static coefficients of friction on various surfaces, namely, galvanized iron, plywood and plastic also increased linearly with an increase in moisture content. The linearity of coefficients of friction data of galvanized iron and plastic for Sc704 was higher with moisture content than Dc370. The results showed higher correlation with moisture content for the static angle of repose of Sc704 compared to Dc370 variety. The mechanical properties of corn were determined in terms of average rupture force and rupture energy. The rupture force decreased for compression while rupture energy of the corn grains generally increased in magnitude with an increase in moisture content. Dc370 had higher rupture force than Sc704 in all moisture content levels. The variance of rupture energy data for Sc704 was greater than those of Dc370. The results showed that the thousand grain weight had the best linear relationship with moisture content while the surface area and true density had the worst relationship with moisture content.