Preparation of nano-sized starch particles by complex formation with n-butanol

High amylose corn starch was dissolved in an aqueous dimethyl sulfoxide solution and allowed to form complexes by migrating gravimetrically into n-butanol layer through a membrane filter at 70 °C. The starch-butanol complex yielded V6I-type crystals with broad reflections at d-spacings of 0.657 and 0.446 nm under an X-ray diffractogram. The amylose, the average Mw of which was 2.69 × 10⁵ as determined by size-exclusion column chromatography, mostly contributed to complex formation. Platelets of an average length less than 100 nm, interspersed in amorphous matrices, were observed in the crude complex. By hydrolyzing the crude complex with α-amylase, amorphous matrices were removed and starch crystallites of 10-20 nm, showing a V6I X-ray diffraction pattern at d-spacings 1.187, 0.685, 0.448 and 0.394 nm, were obtained. The average chain length of starch residing in the crystalline complex was DP 9, indicating that single crystallite units consisted of approximately 1.5 helical turn of anhydroglucose chains.