Physical properties of puffed yellow pea snacks produced by nitrogen gas assisted extrusion cooking

Extrusion is an effective means of aerating foods, thereby converting dense, hard materials into lighter and more appealing forms. In this study, physical properties of yellow pea puffed snacks were manipulated using nitrogen assisted extrusion cooking. Extrudates were prepared at three feed moisture contents [low (0.14 g water/g feed material), medium (0.16 g water/g feed), high (0.18 g water/g feed)]. Nitrogen gas was injected into the extruder barrel (150 °C at the die) at five different pressures (100-500 kPa), making this study the first to employ nitrogen as a physical blowing agent during extrusion cooking. High correlations were found between extrudate expansion and hardness (r = −0.899), between bulk density and crunchiness (r = −0.874), and between nitrogen gas injection pressure and crispiness (r = 0.822). While extrudate expansion was feed moisture content and nitrogen pressure dependent; microstructure, texture and color were not substantially influenced by feed moisture content. These results show the potential of physical blowing agent assisted extrusion for improved extrudate physical, textural and microstructural properties.