Abstract
This study elucidated the comparative effects of steam extrusion (SX, 115 °C) and supercritical fluid extrusion (SCFX, 85 °C) on the physicochemical properties of extruded milk protein concentrate. SCFX with SC–CO2 injection at 2.5 (SC-2.5) and 5 (SC-5) wt % feed moisture temporarily lowered the pH of melt to 4.90 and 4.75, respectively, while the pH of 6.2 was maintained during SX. Acidic conditions during SCFX prevented temperature and shear-induced protein aggregation of calcium bridging and disulfide type. Compared to unextruded samples, the free sulfhydryl content was reduced by 12.6% in SC-5 and 75.9% in SX extrudates, indicating decreased sulfhydryl interactions in SCFX extrudates. The water-soluble protein fractions in SC-5 exhibited mean particle size and zeta potential of 166 nm and −28 mV, respectively, compared to 566 nm and −12.8 mV for SX. Thus, temporarily induced acidity and lower operating temperature of SCFX prevented protein aggregation and contributed to improving the physicochemical properties of milk protein extrudates.
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