Drying of soybean seeds and effect on protein quality and oil extraction efficiency by extruding-expelling process

Abstract

Soybean seeds were dried under real scale conditions to different final moisture contents (m.c.) (9.1, 9.7, 10.9%, and control with 16.2%) and processed through extruding-expelling. Results indicated that soybean seed m.c. affected the composition of the soybean expeller and, hence, the oil extraction efficiency (OEE), which increased with the decrease in the seed m.c. A polynomic model was proposed to predict OEE as function of soybean m.c., indicating that drying soybean to 10% resulted in an OEE of about 65%. A thin layer drying experiment of soybean seeds indicated that the protein dispersibility index (PDI) was not affected for drying air temperatures up to approximately 69°C, and a bi-linear model with a non-pre-established break point was fitted. The real scale drying treatment in a rack type dryer (mixed flow) did not show a significant effect in the PDI at 80 °C, while at 115 °C a significant reduction was observed (PDI reduction were 0.8 and 2.1 percentage points, respectively).