Real-time thermal imaging of expansion dynamics during extrusion of protein-fortified snacks: Effects of nitrogen gas and protein concentration

The physical quality challenges associated with incorporating proteins into puffed snacks can be mitigated using blowing agents. This study examined the effect of nitrogen gas as a physical blowing agent, on the expansion dynamics (e.g., bubble growth and shrinkage) of corn starch-based extrudates, across a wide range of protein contents (i.e., 0-50 %, d.b.). A real-time high-speed imaging system was used to characterize extrudate expansion along different axes. Nitrogen gas injection significantly impacted the expansion behavior (i.e., expansion dynamics and expansion in different directions) of extrudates, but the effect strongly depended on the protein content in the formula. For instance, at 0 and 20 % protein, nitrogen gas injection at 150 and 300 kPa significantly (p < 0.05) enhanced the longitudinal expansion compared to extrudates produced by conventional extrusion. In addition, at 50 % protein, nitrogen gas injection at 150 and 300 kPa resulted in a significant (p < 0.05) improvement in growth time and longitudinal expansion, respectively, compared to those produced with conventional extrusion. Overall, the results underscored the potential of nitrogen gas-assisted extrusion in manipulating extrudate expansion dynamics and therefore increasing the extent of expansion, especially at high protein content. This study contributes to the field of extrusion cooking by demonstrating how advanced processing techniques can improve the quality and consumer appeal of protein-enriched snacks, offering valuable insights into optimizing extrusion processes for high-protein snack formulations.