Effect of Roasting and Oil Extraction Method on the Nutritive Value of Soybean Seed Cake

This study was conducted to evaluate the effect of roasting and method of oil extraction on the chemical composition, Metabolizable energy (ME), and in vitrogas production of soybean seed cake: from un-roasted or roasted (at 164.5 °C for 10 minutes) soybean seeds oil was extracted mechanically or by solvent (hexane). A complete randomized design was used with 2×2 factorial arrangements (un-roasted × mechanical extraction, un-roasted × solvent extraction, roasted × mechanical extraction, and roasted × solvent extraction). The results revealed that although roasting had no significant effect on the chemical composition of the seed cake, it resulted in a significant (P<0.05) reduction in total gas production throughout the different incubation periods. More oil was retained in mechanically extracted soybean cake (24.51%) compared with solvent extracted cake (5%). The high oil content of mechanically extracted soybean cake was reflected in high ME content (14.1 MJ/kg DM) compared with solvent extracted cake (11.2 MJ/kg DM). Crude protein content was higher in solvent extracted cake (48.8%) compared with mechanically extracted cake (35.1%). The study concluded that the heat or roasting reduced the fermentation process resulting in less in vitrogas production, and the same trend was observed for mechanically extracted cake. Solvent extraction increased crude protein content and enhanced the fermentation process.