title: Level and position of substituents in cross-linked and hydroxypropylated sweet potato starches using nuclear magnetic resonance spectroscopy.
abstract: Sweet potato starch was cross-linked using sodium trimetaphosphate and hydroxypropylated using propylene oxide. The level and position of phosphorus and hydroxypropyl groups within cross-linked and hydroxypropylated sweet potato starch was investigated by phosphorus and proton nuclear magnetic resonance spectroscopy ((31)P, (1)H NMR). The cross-linking reaction produced monostarch monophosphate and distarch monophosphate in a molar ratio of 1:1.03, indicating that only half of the introduced phosphorus resulted in a possible cross-link. One cross-link per approximately 2900 glucose residues was found. Phosphorylation leading to monostarch monophosphate mainly occurred at O-3 and O-6 (ratio 1:1). It was inferred that the majority of the cross-links formed in distarch monophosphate were between two glucose residues positioned in different starch chains, while a minor part of the cross-links may be formed between two glucose residues within the same starch chain. Hydroxypropylation under alkaline conditions resulted in the formation of intra-molecular phosphorus cross-links, subsequent hydroxypropylation following cross-linking lowered both the level of intra- and inter-molecular cross-linking. Using (1)H NMR the molar substitution of hydroxypropylation was determined to be 0.155-0.165. The hydroxypropylation predominantly occurred at O-2 (61%), and the level of substitution at O-6 (21%) was slightly higher than that at O-3 (17%). In dual modified starch, the preceding cross-linking procedure resulted in a slightly lower level of hydroxypropylation, where the substitution at O-6 decreased more compared to the substitution at O-2 and O-3.
authors.affiliation: Wageningen University, Laboratory of Food Chemistry, P.O. Box 17, 6700 AA Wageningen, The Netherlands; Jiangnan University, School of Food Science and Technology, 214122 Wuxi, PR China.
authors.forename: Jianwei
authors.initials: J
authors.lastname: Zhao
authors.affiliation: AVEBE Food Innovation Centre, 9640 AA Veendam, The Netherlands.
authors.forename: Zhenghong
authors.initials: Z
authors.lastname: Chen
authors.affiliation: Jiangnan University, School of Food Science and Technology, 214122 Wuxi, PR China.
authors.forename: Zhengyu
authors.initials: Z
authors.lastname: Jin
authors.affiliation: Wageningen NMR Centre, P.O. Box 8128, 6700 ET Wageningen, The Netherlands.
authors.forename: Pieter
authors.initials: P
authors.lastname: de Waard
authors.affiliation: AVEBE Food Innovation Centre, 9640 AA Veendam, The Netherlands.
authors.forename: Piet
authors.initials: P
authors.lastname: Buwalda
authors.affiliation: Wageningen University, Laboratory of Food Chemistry, P.O. Box 17, 6700 AA Wageningen, The Netherlands.
authors.forename: Harry
authors.initials: H
authors.lastname: Gruppen
authors.affiliation: Wageningen University, Laboratory of Food Chemistry, P.O. Box 17, 6700 AA Wageningen, The Netherlands. Electronic address: Henk.Schols@wur.nl.
authors.forename: Henk A
authors.initials: HA
authors.lastname: Schols
mesh_terms: D003432:Cross-Linking Reagents / Q000737:chemistry*; D005947:Glucose / Q000737:chemistry; D027723:Ipomoea batatas / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D010758:Phosphorus / Q000032:analysis; D011522:Protons; D013213:Starch / Q000031:analogs & derivatives* / Q000737:chemistry
chemical_list: D003432:Cross-Linking Reagents; D011522:Protons; D010758:Phosphorus; D013213:Starch; C046042:2-hydroxypropyl starch; D005947:Glucose
keywords: Cross-linking; Hydroxypropylation; Proton and phosphorus NMR; Substituent distribution; Sweet potato starch