Application of physical blowing agents in extrusion cooking of protein enriched snacks: Effects on product expansion, microstructure, and texture

Protein enriched snacks market is growing extensively due to the increasing demand for healthier and convenient food options. Extrusion cooking is the most common and commercially viable technique to manufacture protein enriched puffed snacks. However, the challenge lies in producing such snacks with uncompromised physical appeal. The present review summarizes the expansion, microstructure, and texture of extruded snacks produced at different protein levels to explain the role of protein content during extrusion and the effects of protein addition on final product quality, demonstrating the aforementioned challenge. Physical blowing agent (PBA)-assisted extrusion cooking is a recent modification to conventional food extrusion that enables better control and a certain degree of improvement to product physical quality. This review provides a detailed overview of the effects of various physical blowing agents on different phases in extrusion (e.g., melt expansion and melt shrinkage), and therefore the expansion, microstructure, and texture properties of the resultant snack products. Promising results were highlighted regarding the key improvement of physical properties, along with the additional benefits on nutritional qualities, presenting the great potential of this novel processing method. In order to provide some insights for future studies, the review further revealed the knowledge gap of PBA-assisted extrusion in food processing regarding the lack of studies focusing on how different PBA types, extrusion conditions, and feed formulas interact to affect extrudate expansion. Finally, the limited research in the applications of PBAs in manufacturing a broader range of extruded products, such as plant-based meat analogs, is identified.