Effects of particle size distribution and processing conditions on the techno-functional properties of extruded soybean meal

Abstract

Soybean meal (SBM) is a protein-rich, soybean oil industry by-product which can be extruded for improved techno-functionality and potential utilization as a food ingredient. The effects of SBM particle size distribution [PSD] (small, medium and large), extrusion feed moisture content (15, 21 and 27 g water/100 g dry SBM) and barrel temperature (110, 130 and 150 °C at the die) on techno-functional properties of SBM extrudates were investigated. A decrease in barrel temperature from 150 to 110 °C generally improved nitrogen solubility index, gel forming capacity, oil holding capacity and emulsion capacity of extrudates. In addition, increasing feed moisture content from 15 to 27 g water/100 g dry SBM generally enhanced oil and water holding capacities. Nitrogen solubility index of extrudates made from large PSD feed was generally higher than that of medium PSD extrudates. PSD of SBM also affected the torque and specific mechanical energy requirements during extrusion cooking, SBM with large PSD requiring a higher level of mechanical energy input to be processed when compared to that with medium PSD. This work provided a comprehensive understanding of how feed particle size, extrusion moisture and barrel temperature can be manipulated to provide new opportunities in producing novel food ingredients from SBM.