Relationships between the gelatinization of starches and the textural properties of extruded texturized soybean protein-starch systems

• Thermal properties of SPI, gluten, starch, blend and extrudate were studied.
• Thermal transitions of SPI, gluten and starch appeared independent in blend.
• Extrusion decreased thermal transitions temperature and ΔH of starch.
• High blend ΔH increased tensile strength but reduced fibrous degree of extrudate.

Starches from diverse sources have different thermal properties and, thus, show different gelatinization degrees under a specific extrusion condition, which affects the quality of the extrudates. To find the appropriate ingredients for extruding texturized soybean protein-starch mixtures, the thermal properties of commercial-grade starches (wheat starch, corn starch, potato starch, sweet potato starch, cassava starch, mung bean starch, pea starch, amylose from potato, and amylopectin from waxy corn), blends of starches with soybean protein isolate (SPI) and wheat gluten were assessed. The extrusion response parameters (torque, pressure change, specific mechanical energy (SME), and on-line apparent viscosity) during extrusion and the thermal and textural properties of the extrudates were determined. Pearson correlation analysis showed that the enthalpy changes of the blends were directly correlated with the torque, pressure change, specific mechanical energy, and on-line apparent viscosity, whereas those parameters were inversely correlated with the fibrous degree of the extrudates. The hardness, tensile strength, lengthwise strength, and fibrous degree of the extrudates were correlated with the enthalpy changes of the blends. The springiness and fibrous degree of the extrudates were correlated with the half-peak height of the blends. It was concluded that a higher enthalpy changes of blends leads to a higher SME and a pressure change, which results in a higher hardness and tensile strength and a lower fibrous degree of the extrudates.