Study on the Parameters of Extrusion Pretreatment of Corn Germ with Semi-Wet Milling in Solvent Oil Extraction

Efficiency of oil extraction from corn germ was improved by the extrusion pretreatment, and residual oil was taken as the index of this oil extraction process. An orthogonal rotation combination test design of five levels and four factors, consisting of the moisture of material, screw speed, barrel temperature, and die nozzle diameter, was employed to optimize the model and reaction condition. The optimum parameters of extrusion were as follows: moisture of material, W = 12%; extrusion temperature, T = 105 degrees C; screw speed, n = 185 rpm; die nozzle diameter, Phi = 9 mm x 3. Under these optimum conditions, residual oil of this process was 0.61-0.66%, which was lower than residual oil by pressing alone (residual oil of 5-6%) or by a combination of prepressing and hexane extraction (residual oil of nearly 2%). The corn oil obtained by the optimum extrusion parameters was analyzed, and iodine value, acid value, peroxide value, and saponification value were 1,250 g/kg, 400 mg/kg, 5.1 mmol/kg, and 189%, respectively.