Analysis of molecular structure of starch citrate obtained by a well-stablished method

• Only diester is produced upon starch esterification with citric acid.
• Only dextrins undergo ester linking.
• No crosslinking occurs between molecules of amylopectin.

Nuclear magnetic resonance spectroscopy (NMR) and high-performance size exclusion chromatography (HPSEC) were applied to investigate the molecular structure of starch citrate produced under various conditions. Native potato starch and retrograded starch (produced by freezing and defrosting of native potato starch in the concentration of 10 g of starch per 100 g of solution) were roasted at 100 °C with citric acid applied at doses of 10 or 20 g per 100 g starch. The NMR analyses of the produced starch citrates demonstrated that retrograded starch was characterized by greater susceptibility to esterification than the native starch, and that only starch esters were produced upon esterification conducted under the applied experimental conditions. The molecular mass (Mw) distribution profiles of diesters and products after basic de-esterification as well as the molecular mass balance enabled concluding that intermolecular crosslinking occurred between dextrins (produced during acidic hydrolysis) that were linking with each other or were attaching to high-molecular amylopectin. The study excluded explicitly the formation of crosslinks between high-molecular fractions of starch.