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.
Highlights
Starch is a complex carbohydrate composed of glucose units consisting of amylose and amylopectin [1,2] and is widely used in food production
The aims of this study were to evaluate and optimize the Extrusion-cooking process (ECP) conditions and to determine their effects on the physical and chemical changes in resistant starch (RS) formed from cornstarch
The RS content was 0.670 g/100 g, similar to the finding reported by Shi and Gao [34]
Summary
Starch is a complex carbohydrate composed of glucose units consisting of amylose and amylopectin [1,2] and is widely used in food production. Current market trends demand functional ingredients with health benefits, and starch transformed into resistant starch (RS) shows advantages in a diverse range of applications. RS has modified starch or starch fractions that are indigestible in the small intestine, so it is similar to dietary fiber and shows similar health benefits [3,4]. RS yields vary according to the hydrolysis process used; e.g., HCl (12%–25%) [8,9], lactic acid (2%–8%) [10], citrate (41%), and phosphate (25%–70%) [11,12]. Alternative hydrothermal processes performed at 110 ◦ C over three days yielded 12% RS [13] and up to 25% in an acidic environment [14,15,16,17]
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