Talc and calcium carbonate inclusions in direct expanded pea starch extrudates exhibit different behavior under increasing screw speeds

The ability to modulate direct expanded product structures improves the versatility and range of product applications. The effect of nucleating agents, namely, talc and calcium carbonate (CC), on the expansion characteristics of pea starch extrudates as impacted by screw speed was explored. Pea starch blends with increasing levels of nucleating agents (0.25%, 1%, and 2%) at 18% moisture (w.b.) were extruded across a range of screw speeds (150, 250, 350, and 450 rpm). The water absorption index, water solubility index (WSI), expansion ratio (ER), unit density, and cell count were determined to evaluate the performance of nucleating agents. The nucleating efficiency of CC, as assessed by cell count, improved with increasing screw speeds. In contrast, the nucleating efficiency of talc was influenced by inclusion levels irrespective of screw speed. ER values ranged from 2.10 to 2.88, where higher nucleating agent inclusions and screw speeds corresponded with lower ER values. Increased nucleating agents and screw speeds corresponded to higher WSI values suggesting the nucleating agents promoted starch degradation. The nucleating agents appeared to promote flow instabilities indicated upon assessment of the extrudate surface. PRACTICAL APPLICATION: This study provides helpful information on the expanded extrudate structure of pea starch as influenced by screw speed and nucleating agents. These findings may help the food industry select processing parameters and appropriate nucleating agent inclusion levels when producing new expanded products with unique textures.