Rheology and Expansion of Starch-Water-CO₂ Mixtures with Controlled Gelatinization by Supercritical Fluid Extrusion

Figures & data

Figure 1 Typical screw configuration and corresponding pressure profile developed along the extruder barrel during SCFX processing.

Figure 2 Schematic of the slit die rheometer system attached to extruder outlet.

Table 1 Consistency index and flow behavior index as a function of degree of gelatinization and SC-CO₂ addition for starch-water mixtures with 42% water content

	Consistency index, K(kPa.s^n)		Flow behavior index, n		R^2
Degree of gelatinization	0 %	0.45% SC-CO2	0 %	0.45% SC-CO2	0 %	0.45% SC-CO2
100%	6383	3347	0.21	0.31	0.93	0.94
90%	2409	1809	0.37	0.39	0.80	0.81
80%	2191	711	0.37	0.57	0.78	0.95
60%	961	250	0.46	0.71	0.82	0.78

Figure 3 Viscosity of starch-water mixtures with starch of various degrees of gelatinization as a function of shear rate at 55°C.

Figure 4 Viscosity of starch-water-CO₂ mixtures with 0.45% wt CO₂ and starch with various degrees of gelatinization as a function of shear rate at 55°C.

Figure 5 Variation of viscosity reduction factors with respect to SC-CO₂ and DG levels for starch-water mixtures at the shear rate of 150/s.

Figure 6 Expansion of starch-water mixtures with 0.45 wt% SC-CO₂ injection using SCFX system with die diameter of 4.50 mm.

Table 2 Microstructure characteristics of starch-water mixtures with 0.45 wt% SC-CO₂ injection

Degree of gelatinization (DG)	Average cell size (μm)	Average cell density (cells/cm^3)	Polydispersity index (PDI)
100%	310	1.40E + 05	0.84
90%	340	6.87E + 04	0.82
80%	410	2.93E + 04	0.81
60%	NA	NA	NA

Figure 7 Characteristic SEM of expanded starch-based extrudates with 0.45 wt% SC-CO₂ injection using SCFX system with die diameter of 4.50mm. SEM were taken at 32× magnification.