Effects of Particle Size Distribution and Feed Moisture Content on the Techno-functional Properties of Extruded Soybean Meal

Abstract

Soybean protein products are the most widely used ingredients in the plant-based foods category. However, soybean meal (SBM), a by-product of the soybean oil extraction process, is still underutilized in human food products due to its inferior techno-functional properties in its raw form. In this research work, mechanically pressed SBM that was milled to three different particle sizes (0.5, 0.75, and 1 mm) was processed using extrusion cooking at three different feed moisture contents (15, 21, and 27 % based on dry SBM weight), and the techno-functional properties of the resulting extruded SBM were characterized. As compared to their raw SBM counterparts, the oil holding capacity of the SBM extrudates significantly (p < 0.05) improved at the highest (27 %) feed moisture content. As expected with thermal treatment, the nitrogen solubility index of SBM significantly (p < 0.05) decreased after extrusion cooking at all the processing conditions studied. Among SBM extrudates, the nitrogen solubility index generally increased when the feed moisture content was decreased from 27 to 15 %, and PSD was increased from 0.75 to 1 mm. Moreover, an increase in feed moisture content generally resulted in enhanced water holding capacity and oil holding capacity of the SBM extrudates. Among all the processing conditions studied, the SBM extrudates produced at 27 % feed moisture content and 0.5 mm PSD showed relatively higher water holding capacity, oil holding capacity, and gel forming capacity. Overall, this research work provided a comprehensive understanding about the techno-functional properties of raw and extruded SBM, offering new possibilities in producing novel ingredients from this food industry by-product through the optimization of processing conditions.