Abstract
The pasting behavior and changes in intermolecular forces were compared between microwave (MW)- and hydrothermal (hot water; HT)-treated chlorogenic acid/lotus seed starch (LS)/water mixtures, by rheological, spectroscopic and microscopic analysis. MW treatment directly heated polar molecules throughout the starch granules producing even heating, compared with HT treatment in which heat transfer was limited to conduction from the granule surface. MW treatment more rapidly disrupted the starch double helical structure and liberated many starch chains that formed larger amounts of a non-covalent inclusion complex with CA than HT treatment. In addition, MW treatment produced a coating of LS-CA complex on the starch granule surface which modified the pasting properties of the starch. The LS-CA complex had a denser structure than LS, which enhanced the thermal stability and crystalline water binding capacity of LS. The non-covalent complexes were stabilized by hydrogen bonding and electrostatic interactions between starch chains, hydrophobic interactions between the caffeic acid residue in CA to the starch chain hydrophobic helical cavity and attraction of the hydroxyl groups at the reducing end of the LS chains to the H+ on the CA (electrostatic interaction). Of these, hydrogen bonding and electrostatic interactions were the main intermolecular forces between LS chains. These findings contribute to clarification of the mechanism of action of polyphenols on the starch gelatinization process and will help to improve the formulation of functional starch products.
Published Version
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