Effect of screw speed and die temperature on physicochemical, textural, and morphological properties of soy protein isolate-based textured vegetable protein produced via a low-moisture extrusion

In this study, textured vegetable protein (TVP) based on soy protein isolate, wheat gluten, and corn starch was prepared at a 5:3:2 (w/w) ratio using a low-moisture extrusion process. To evaluate the effects of extrusion parameters, die temperature and screw rotation speed, on the properties of TVP, these two parameters were manipulated at a constant barrel temperature and moisture content. The results indicated that increasing the die temperature increased the expansion ratio while decreasing the density of the extrudates. Simultaneously, increasing the screw rotation speed clearly increased the specific mechanical energy of the TVP. Furthermore, mathematical modelling suggested that the expansion ratio increases exponentially to the die temperature. However, extreme process conditions bring about a decrease in water absorption capacity and expansion ratio, as well as undesirable texture and microstructure. The results suggested that the properties of SPI-based TVP are directly influenced by the extrusion process parameters, screw speed and die temperature.