| Soy protein fortification in starch-based half-products employing extrusion process was studied to improve nutritional profile of snack foods. The effects of soy protein isolate (SPI) (0, 20, 40, 60%), nitrogen solubility index (NSI) (low, high), starch source (corn, tapioca), additives (sugar, salts), screw speed (100, 250, 400 rmp), and product temperature (75, 90$spcirc$C) on the properties of extruded products were investigated. SPI-starch blends were processed via twin-screw extruder. Dough sheet obtained from the die was cut and dried at room temperature. Extrudates were later expanded by deep frying. Rheology, gelatinization extent, water absorption index (WAI), and water solubility index (WSI) were the physicochemical properties investigated for the extrudates, while the expanded products were tested for volume expansion, breaking strength and morphology. Results indicated that both corn starch and tapioca starch were appropriated to fabricate extruded half-products. SPI was incorporated in half-products up to 40% with still maintaining good expansion. Higher NSI also improved expansion. The more protein incorporation, the higher breaking strength of the products. Results from rheology during extrusion, feed viscosity, extrudate rheology, scanning electron microscopy and differential scanning calorimetry helped explain ingredient interactions during formation of half-product structure. SPI drew water from starch and consequently delayed starch gelatinization process. Gelatinization was an important process in extrudate structure formation. It correlated well with product expansion. Screw speed and temperature had a significant effect on the extent of starch gelatinization. Addition of sugar lowered expansion, but addition of salts did not. However, additives assisted in improving expansion characteristics by a moisture migration effect.;This study indicated the high potential of extrusion technology to produce soy protein-fortified half-product snacks with good texture and superior nutritional profile. |
