Separation of gallic acid from Cornus officinalis and its interactions with corn starch.

D101 macroporous resin combined with high speed counter-current chromatography (D101 MR-HSCCC) was used to separate gallic acid (GA) from Cornus officinalis, and GA was added to starch-based products to improve food quality. The interaction and action mechanism of corn starch (CS) with GA were investigated for prediction and thereby controlling the structure and functions of starch-based foods. Results show that GA with 98.72% purity was successfully obtained using the D101 MR-HSCCC technique. HSCCC solvent system was composed of n-hexane-ethyl acetate-methanol-water (1:5:1:5, v/v/v/v). GA inhibited CS dissolution and improved CS swelling. Based on the particle size distribution, GA could enlarge the size of CS-GA complexes. FT-IR spectra exhibit that the interactions between CS and GA may comprise the intermolecular hydrogen bond and non-covalent bond. The results of XRD, LF-NMR and AFM show that the presence of GA could increase the relative crystallinity of CS, decrease the spin relaxation time (T) and change the surface morphology of CS via the modification of hydrogen bonds distribution. Finally, SEM analysis indicates that GA could change the microstructure of CS-GA complexes. These findings facilitate the development of CS-based products and utilization of CS.