Cell Nucleation Dynamic and Expansion Characteristics of Milk Protein Puffs Containing Fruit Pomace Made by Supercritical Fluid Extrusion

Grape and apple pomace powders, a good source of dietary fiber and nutrients, were incorporated in formulations containing milk protein concentrate with over 81% milk protein (MPC-81) to produce puffed products using supercritical fluid extrusion (SCFX). The cellular structure and cell nucleation dynamics in the extruded samples were evaluated as function of pressure drop and supercritical CO2 (SCCO2) injection rates. Results showed that SCFX generated pomace-based extruded products had an expansion ratio up to 12.3 and microcellular structure (ranging in cell size from 278 to 540 mu m) and cell density of the order of 10(4)-10(5) cells/cm(3). The general trend of increased cell density and decreased cell size of extrudates was observed by increasing pressure drop rate and SCCO2 content and exhibited a uniform cellular architecture when the injected SCCO2 level was close its saturation solubility in the aqueous phase of the dough, and the pressure drop rate was high, up to 141.04 MPa/s. Beyond these values, some structural collapse was observed in both extrudates. Although the extrudates had the same level of expansion, their hardness values gradually decreased, indicating that the textural qualities and microcellular structure in extrudates can be controlled by regulating the SCCO2 injection and pressure drop rates. It is thus reasonable to suggest that the SCFX technology provides a unique strategy to control cellular morphology, expansion, and physicochemical characteristics of nutritionally superior extruded products.