Abstract
Commercial corn starch or degermed corn contains lipids and protein, and starch-lipid (or protein) complexes were formed during extrusion. The formation of starch and lipid (or protein) complexes was investigated using the complex index (CI) and differential scanning calorimetry (DSC) analysis. The CI of extrudates of a commercial corn starch/germ mixture (or gluten meal) showed that starch was complexed with lipid or protein, thus decreasing the iodine-binding capacity of amylose. The CI increased as the content of germ or gluten meal blending starch increased. Blends containing degermed corn and thermostable or mesophilic α-amylase were extruded. The CI of extrudates was higher than 55%; however, the starch-lipid complex was not stable and could be separated. The DSC analysis of the blending starch extrudate and palmitic acid showed that the enthalpy of the starch-palmitic acid complex was increased with increasing fatty acid content. Increased complex formation required more DSC heating, resulting in an enthalpy change of the endothermic peak rise, with the peak temperature higher than 100℃.
Highlights
Starch granules are composed of two types of alpha-glucan, namely amylose and amylopectin
Complex index analysis The complex index (CI) determines the degree of starch-lipid complex formation
The CI determines the degree of starch-lipid complex formation.The portion of the starch bound by lipid will not bind iodine, the absorbance is related to the portion of starch that is complexed to the iodine
Summary
Starch granules are composed of two types of alpha-glucan, namely amylose and amylopectin. Amylose is a relatively long, linear alpha-glucan containing around 99% (1→4)-α- and (1→6)-alpha-linkages, which is a left-hand helix stabilized by inter-helical hydrogen bonds (Richard et al, 2004). Amylose complexes with certain agents such as iodine, lipids, dimethylsulfoxide (DMSO), alcohols, flavour compounds, etc. The driving force for complex formation is presumably its hydrophobic nature and involves transferring the hydrophobic guest molecule from water to the less polar environment within the amylose helix. The most common types of corn granules contain 71% starch, more than 5% lipid, about 10% protein and 14% water. According to the mechanization of complex formation, the starch-lipid complex is formed during extrusion (De Pilli et al, 2008)
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