Resistant Starch Derived from Extruded Corn Starch and Guar Gum as Affected by Acid and Surfactants: Structural Characterization

Abstract

Corn starches with and without guar gum [10% (w/w)] and 2% (w/w) of diacetyl tartaric acid ester of monoglyceride, sodium stearoyl-2-lactylate or citric acid, respectively, were extrusion-cooked in a twin-screw extruder at 18% moisture, 150 °C and 180 rpm screw speed. The content of resistant starch was determined by sequential enzymatic digestion. The formation of resistant starch in extruded corn starch was strongly affected by the addition of gum and the different food additives. X-ray diffraction of the extruded starches gave a V diffraction pattern indicating the effect of extrusion cooking and amylose-lipid complexes. Enzymatic digestion did not affect the V-structure, which could apparently be attributed to extrusion cooking. Similarly, differential scanning calorimetric thermograms indicated that all isolated resistant starches exhibited endothermic transitions between 71—178 °C signifying a complex formation between amylose and the emulsifiers and possibly the melting of amylose crystallites in the resistant starch. Purification of the isolated resistant starches by size exclusion-high performance liquid chromatography showed a dependence of molecular weight on the added additives. Results of differential scanning calorimetry and X-ray diffraction suggest that amylose-lipid complexes could also be involved in the formation of resistant starch in extruded cornstarch.