Multiscale structure and precipitation mechanism of debranched starch precipitated by different alcohols.

Alcohol solution is a cheap, simple, and effective precipitating solvent frequently used for separating debranched starch (DBS), yet little is known about the precipitation mechanism of DBS by different alcohols. This study precipitated DBS from pullulanase-hydrolyzed starch using ethanol, n-butanol, and isopentanol. The multiscale structures of DBS were characterized, including chain length, single/double helix, and crystalline. The chain conformation and precipitation mechanism of DBS in different alcohols was investigated using molecular dynamics (MD) simulation. DBS precipitated by n-butanol contained the largest proportion of short chain (DP6-24, 83.2 %), the highest V-type crystallinity (21.1 %), and the largest single-helix content (24.7 %). A single helix conformation of DBS chain was determined in alcohols, where alcohol molecules entered the helix cavity. Intra/inter-molecular hydrogen bonds stabilized the helix, with a large number of hydrogen bonds leading to strong molecular interaction and stable helical structure. The solvent accessible surface area of DBS chain decreased by 7.88-19.32 % in alcohols, and the radial distribution function revealed that the first solvent layer of DBS chain at 0.29 nm was closely related to hydrogen bonding. This study provides a basis for the choice of precipitation solvent for preparing DBS with different chain lengths and physicochemical properties.