Formation and isolation of nanocrystal complexes between dextrins and n-butanol

Starch dextrins of different molecular sizes (DPn 311, 142 and 39) were prepared by hydrolyzing a high amylose maize starch in acidic alcohol solutions. The dextrins were dissolved in an aqueous dimethyl sulfoxide solution (90% DMSO), and then the solution was allowed to migrate down into n-butanol separated by a membrane filter. The complex was gradually formed between the dextrin and butanol, and precipitated in the butanol layer. The dextrin–butanol complex yielded V6-I type crystals with broad reflections (d-spacings 1.123, 0.657 and 0.429 nm) under X-ray diffractograms. Platelets of average length less than 100 nm, interspersed in amorphous matrices, were observed in complexes of DPn 311 and 142, but that of DPn 39 showed different morphology, and the formation of complexes was limited. By hydrolyzing the complex of DPn 311 with α-amylase, amorphous matrices were selectively removed, and crystallites of 23–72 nm showing a V6-I X-ray diffraction pattern were obtained. However, crystallites in complexes of DPn 142 and 39 were eroded by amylolysis, forming large aggregates.