Level and position of substituents in cross-linked and hydroxypropylated sweet potato starches using nuclear magnetic resonance spectroscopy

摘要: Sweet potato starch was cross-linked using sodium trimetaphosphate and hydroxypropylated propylene oxide. The level position of phosphorus hydroxypropyl groups within sweet investigated by proton nuclear magnetic resonance spectroscopy ((31)P, (1)H NMR). cross-linking reaction produced monostarch monophosphate distarch in a molar ratio 1:1.03, indicating that only half the introduced resulted possible cross-link. One cross-link per approximately 2900 glucose residues found. Phosphorylation leading to mainly occurred at O-3 O-6 (ratio 1:1). It inferred majority cross-links formed were between two positioned different chains, while minor part may be same chain. Hydroxypropylation under alkaline conditions formation intra-molecular cross-links, subsequent hydroxypropylation following lowered both intra- inter-molecular cross-linking. Using NMR substitution determined 0.155-0.165. predominantly O-2 (61%), (21%) slightly higher than (17%). In dual modified starch, preceding procedure lower hydroxypropylation, where decreased more compared O-3.