Physicochemical Changes and Resistant-Starch Content of Extruded Cornstarch with and without Storage at Refrigerator Temperatures

Abstract

Effects of extrusion cooking and low-temperature storage on the physicochemical changes and resistant starch (RS) content in cornstarch were evaluated. The cornstarch was conditioned at 20%-40% moisture contents and extruded in the range 90-130 • C and at screw speeds in the range 200-360 rpm. The extrudates were stored at 4 • C for 120 h and then at room temperature. The water absorption, solubility index, RS content, viscoelastic, thermal, and microstructural properties of the extrudates were evaluated before and after storage. The extrusion temperature and moisture content significantly affected the physicochemical properties of the extrudates before and after storage. The RS content increased with increasing moisture content and extrusion temperature, and the viscoelastic and thermal properties showed related behaviors. Microscopic analysis showed that extrusion cooking damaged the native starch structure, producing gelatinization and retrogradation and forming RS. The starch containing 35% moisture and extruded at 120 • C and 320 rpm produced the most RS (1.13 g/100 g) after to storage at low temperature. Although the RS formation was low, the results suggest that extrusion cooking could be advantageous for RS production and application in the food industry since it is a pollution less, continuous process requiring only a short residence time.

Nutritional, physical and sensory properties of extruded products from high-amylose corn grits

“…The extrusion process damaged the native RS, caused gelatinization and retrogradation, and reformed the RS (Nedersuárez et al, 2016). However, the extrudates of HACG and NCG had RS contents of 2.89% and 1.01%, respectively, which indicated a minor amount of RS was rebuilt during the extrusion.…”

“…The increased RS content could be due to the higher amylose content in HACG. The higher amylose content results in more chances to avoid starch retrogradation or excessive dextrinization which limit the formation of RS (Nedersuárez et al, 2016).…”

Optimization of an Extrusion Cooking Process to Increase Formation of Resistant Starch from Corn Starch with Addition of Citric Acid

“…Figure a shows corn starch granules with a round or elliptical shape, a defect‐free surface, and an approximate size of 12 µm . Figure b illustrates an RS standard from an enzymatic kit (Megazyme International Ireland Ltd., Co., Wicklow, Ireland) with 52% of RS, showing agglomeration of 50 or more granules with an approximate size of 40 µm . Figure c reveals the best treatment for RS production: 18% moisture content and 5.1% of citric acid with the yield of 1.15 g 100 g −1 (Table ), and Figure d shows the optimized conditions of ECP at 21.4% moisture content with 2.18% of citric acid, generating RS at 0.85 g 100 g −1 ( Figure ); both treatments were carried out at 127 °C and 233 rpm.…”

“…Figure a shows corn starch granules with a round or elliptical shape, a defect‐free surface, and an approximate size of 12 µm . Figure b illustrates an RS standard from an enzymatic kit (Megazyme International Ireland Ltd., Co., Wicklow, Ireland) with 52% of RS, showing agglomeration of 50 or more granules with an approximate size of 40 µm .…”

“…Processing temperature was first Section 35 °C, second Section 42 °C, third Section 51 °C, and fourth Section 127 °C and screw speed 233 rpm according to the optimized conditions obtained by Neder‐Suárez et al . Extrusion temperature was controlled by a TT‐137N water heater (Tool‐temp, Sulgen, Switzerland) at the end stage of the extruding chamber.…”