title: Iodine binding to explore the conformational state of internal chains of amylopectin.
abstract: Previous studies have found that the proportion of long chains of amylopectin correlates to its functional and nutritional properties. As a possible explanation of this correlation, the iodine binding property of amylopectin internal chains was investigated as an indirect evidence of their ability to form helices for intra- or inter-molecular interactions. Waxy and amylose-extender waxy corn starches were hydrolyzed by β-amylase for varying periods of time to incrementally remove the external chains, and the absorbance and the wavelength of maximum absorbance of iodine binding were examined. Experimental results suggest that iodine can bind with both external and internal chains; a significant amount of absorption comes from the latter, as stepwise removal of external chains only somewhat reduced absorption. Internal amylopectin chains, thus, were concluded to likely pre-exist in helical form, as opposed to a conformational change into helices facilitating iodine binding in the absence of external chains. Such internal chain helical structures possibly drive intermolecular interactions that would explain why amylopectin with high proportion of internal chains form harder gels, create pastes less prone to shear breakdown, and are more slowly digesting.
authors.affiliation: Whistler Center for Carbohydrate Research and Department of Food Science, Purdue University, 745, Agriculture Mall Drive, West Lafayette, IN 47907, USA.
authors.forename: Xinyu
authors.initials: X
authors.lastname: Shen
authors.forename: Eric
authors.initials: E
authors.lastname: Bertoft
authors.forename: Genyi
authors.initials: G
authors.lastname: Zhang
authors.forename: Bruce R
authors.initials: BR
authors.lastname: Hamaker
mesh_terms: D000687:Amylopectin / Q000737:chemistry*; D000688:Amylose / Q000737:chemistry; D002236:Carbohydrate Conformation; D007455:Iodine / Q000737:chemistry*; D014885:Waxes / Q000737:chemistry; D003313:Zea mays / Q000737:chemistry
chemical_list: D014885:Waxes; D000688:Amylose; D000687:Amylopectin; D007455:Iodine
keywords: Amylopectin; Internal chains; Iodine; β-Amylolysis