Quality attributes and rheological properties of novel high milk protein-based extrudates made by supercritical fluid extrusion

Supercritical fluid extrusion (SCFX) process has opened up a new way of extruding heat-sensitive materials such as milk protein concentrate (MPC) into novel nutritional porous extrudates. Three formulations (30%:66.5%, 60%:36.5% and 90%:6.5% of MPC: rice flour, w/w) with 1% Dimodan, 1% lecithin and 1.5% salt were extruded by using SCFX. The physical, rheological and thermal properties of the extrudates were evaluated. The results showed that the increased MPC contents decreased gelatinisation enthalpy and increased the viscosity of the extrudates, which contributed to develop stable porous extrudates; and the increased MPC contents also helped to form a stronger gel network existed in dispersion of the extrudate samples, which resulted in a higher stress to break the gel and flow. The radial and overall expansions, crispness, porosity, rehydration ratio, moisture content and water activity increased while the axial expansion, hardness, piece density, apparent density, bulk density, decreased with higher amounts of MPC contents in extrudates. The overall results indicated that 90% MPC-containing extrudate was very suitable for developing highly nutritional and healthy cereals/snacks.