title: Molecular structure of citric acid cross-linked starch films.
abstract: The effect of citric acid (CA) on starch films has been examined. A new method to detect cross-linking of starch by CA in solution-cast films by molecular weight measurements is described. Furthermore, we managed to distinguished between free, mono- and di-esterified CA and quantify di-ester content within starch films by using a modification in the method of complexometric titration with copper(II)-sulfate. Cross-linking of starch by CA occurred at low temperature, 70°C, which we assumed is so far the lowest temperature reported where cross-linking reaction occurred. This is essential for starch coating applications within paper industry since no high temperatures for curing will be required. However, curing at 150°C and high CA concentrations, 30 pph, increased cross-linking reaction. Furthermore, the physical properties like water solubility, gel content and glass transition temperature, were highly reflected by changes in the molecular structure i.e. cross-linking and hydrolysis, as well as CA content and curing temperature.
authors.affiliation: Department of Food Science, Uppsala BioCenter, Swedish University of Agricultural Sciences, Box 7051, SE-75007 Uppsala, Sweden. carolin.menzel@slu.se
authors.forename: Carolin
authors.initials: C
authors.lastname: Menzel
authors.forename: Erik
authors.initials: E
authors.lastname: Olsson
authors.forename: Tomás S
authors.initials: TS
authors.lastname: Plivelic
authors.forename: Roger
authors.initials: R
authors.lastname: Andersson
authors.forename: Caisa
authors.initials: C
authors.lastname: Johansson
authors.forename: Ramune
authors.initials: R
authors.lastname: Kuktaite
authors.forename: Lars
authors.initials: L
authors.lastname: Järnström
authors.forename: Kristine
authors.initials: K
authors.lastname: Koch
mesh_terms: D000687:Amylopectin / Q000737:chemistry*; D000688:Amylose / Q000737:chemistry*; D019343:Citric Acid / Q000737:chemistry*; D019327:Copper Sulfate / Q000737:chemistry; D003432:Cross-Linking Reagents / Q000737:chemistry; D015394:Molecular Structure; D008970:Molecular Weight; D012995:Solubility; D013696:Temperature; D014867:Water / Q000737:chemistry
chemical_list: D003432:Cross-Linking Reagents; D014867:Water; D019343:Citric Acid; D000688:Amylose; D000687:Amylopectin; D019327:Copper Sulfate