Effect of phosphorylation of the maize starch on thermal generation of stable and short-living radicals

Effect of hydrolysis, phosphorylation and treatment with high hydrostatic pressure on thermal generation of stable and short-living radicals in maize starch was studied by X-ray diffraction (XRD), electron paramagnetic resonance (EPR) spectroscopy, differential scanning calorim- etry and polarized light microscopy. Phosphorus was introduced into maize starch as mono- and distarch phosphates. XRD indicated localization of phosphate groups in amorphous part of the granule whereas calorimetric data suggested some cross-linking of the distarch phosphates. Stable and short-living radicals with unpaired electron localized at carbon atom were generated in all investigated samples in the temperature range commonly used for processing food. The number of detected short-living radicals, stabilized by a spin trap, is of two orders of magnitude greater than that of the stable radical species. Hydrolysis and phosphorylation strongly increase the number of stable radicals while pretreatment of the starch with high hydrostatic pressure diminishes their amount. The EPR spectra of stable radicals consist of two components, single line and another one with hyperfine structure, indicating interaction of unpaired electron with neighboring hydrogen atom. The EPR spectra of the spin trap adducts with short-living radicals contain three components from species differing in their dynamic properties depending on localization in zones of various degree of crystallinity.