Preparation and properties of enzyme-modified cassava starch-zinc complexes.

Starch-zinc complexes were synthesized by reaction of enzyme-modified starch with zinc acetate. The effect of reaction parameters such as hydrolysis rate, reaction temperature, reaction time, pH value, and concentration of zinc acetate on the zinc content and zinc conversion rate was studied. The zinc content and conversion rate of the product prepared under optimal conditions were 100.24 mg/g and 87.06%, respectively. The results of scanning electron microscopy (SEM) demonstrated that the obtained starch-zinc complexes displayed a porous appearance. The results of Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and (13)C cross-polarization/magic-angle spinning nuclear magnetic resonance ((13)C CP/MAS NMR) showed that zinc was mainly coordinated to the oxygen atoms of the glucose unit 6-CH2OH. The formation of starch-zinc complexes was also indirectly confirmed by the results of conductivity measurements. Thermal properties of the complexes were influenced by the zincatation process. This study revealed that nonallergenic starch might be used effectively as a carrier of zinc for zinc supplementation purpose.