Physical properties of Jatropha curcas L. kernels after heat treatments

The drying characteristic and physical properties of kernels of Jatropha curcas L. after heat treatments were investigated. The treatments included drying at three different temperatures (40, 60, and 80 °C) and steaming. The drying characteristics studied included the relationship of moisture content, moisture ratio, and drying rate to drying time. The best fit for all parameters was the logarithmic model. Important physical properties of the kernels were measured. The kernels contained moisture 3.78, 4.01 and 2.82% wet basis at 40, 60 and 80 °C, respectively. The sphericity of dried kernels was 0.65–0.66 and 0.53 for steamed kernels. The bulk densities of dried kernels and steamed kernels were 403–513, and 509 kg m−3, solid densities were 951–971 and 1082 kg m−3, porosities were 46.00–59.31 and 52.86%, and specific surface areas were 177–241 and 154 m2 m−3, respectively. The static coefficient of friction and angle of repose of the steamed kernels were the highest because of their half section shape, lower sphericity, more viscous surface and soft texture. Drying at 80 °C gave the highest oil yield at 47.06% and the highest acid value. Drying at 40 °C gave a lower oil yield at 36.83% but the lowest acid value. Oil yield of steamed kernels was very low (18.13%). The temperature of the drying process had a minor effect on viscosity and ash content but had a significant effect on free fatty acid content and acid value. The viscosity of the kernel oil was 33.91–34.53 cSt at 40 °C.