Abstract
Ethanol precipitation process for purification of branched dextrin (BD) in Nägeli amylodextrin from waxy rice starch was developed. Temperature and ethanol concentration for precipitation were main parameters affecting the recovery and purity of BD, and the purification condition at 4 °C and 10 % (v/v) ethanol in water was adopted. After four-time precipitation, the BD recovery was 34.6 %, whereas the purity improved from 78.5 % at the initial to 94.5 % at the four-time purified BD (BD4). BD4 mainly showed a chain length distribution between 18 to 35 with a mode length of 25, which shifted after enzymatic debranching with isoamylase to that between 9 and 20 with a mode length of 14. Each purified BD was solubilized in water, and each solution was mixed with methanol-water at 25 °C to a final methanol concentration of 16 M. The flakes of BD precipitated with 16 M methanol exhibited an A-type crystal structure by an X-ray diffraction analysis, and the speed generation of white flakes in 16 M methanol dramatically increased as the purification time increased. The effect of addition of highly branched cyclic dextrin (HBCD) or sodium tetraborate on BD aggregation in 16 M methanol was also investigated, where the former retarded aggregation but the latter had no effect on the velocity. Thus, the purified BD enables rapid characterization of aggregation of double helix structures of A-type crystal structure, and screening of compounds which could affect the phenomena for prediction of potentials in starch modification as well.