Pressure-induced changes in the structure of corn starches with different amylose content

Hylon VII and waxy corn starch-water suspensions (30%) were subjected to high pressure treatment at 650 MPa for 3, 6 and 9 min. Cross-polarisation/magic angle spinning (CP/MAS) 13C NMR, X-ray, HPLC, optical microscopy (LM) and scanning electron microscopy (SEM) were used to monitoring physico-chemical changes in the structure and microstructure of starch preparations. The NMR spectra of pressurised starches showed a displacement of the chemical shift associated to C1 atoms as well as changes in peak intensities for C1, C4 and C6 after 9 min of treatment. The treatment of starch suspension with high pressure resulted also in a significant decrease in degree of crystallinity (DC) along with time of treatment and, in the case of waxy corn starch resulted in complete loss of crystallinity already after 3 min of treatment. The profile of the molecular weight distribution of waxy corn starch pressurised for 6 and 9 min differed significantly from the one obtained for native starch. The microscopy analysis showed that the pressurisation of waxy corn after 3 min lead to formation of gel structure.