Properties of high-crystalline rice amylodextrins prepared in acid-alcohol media as fat replacers

Rice starch isolated from a Korean variety (Ilpumbyo) was hydrolyzed in acidic alcohol solutions to prepare granular rice amylodextrins. Relative crystallinity, thermal properties, and average degree of polymerization (DP) of the amylodextrins were investigated. Degree of hydrolysis and DP decreased as the alcohol concentration increased (70-99%) at the same acid concentration (2 or 4% HCl). In 99% ethanol medium, rice starch was more selectively hydrolyzed in the amorphous regions of starch granule than it was in 70% ethanol medium. A chains (DP 10-12) and B₁ chains (DP 20-24) of amylopectin were predominant in the dextrin prepared in 4% HCl, 99% ethanol solution, whereas the larger chains were more prevalent in 4% HCl, 70% ethanol. Rice amylodextrin showed higher crystallinity than native rice starch retaining the typical A-type X-ray diffraction, except the amylodextrin prepared in 70% alcohol, which transformed to the V-pattern. Melting enthalpy and onset temperature of rice amylodextrins measured by differential scanning calorimetry were lower than those of native starch, indicating that less energy was associated with crystal melting. When the rice amylodextrin replaced a portion of oil in the formulation of a mayonnaise-like emulsion, emulsion viscosity, stability, and oil droplet distribution were evaluated. Emulsions prepared with this rice amylodextrins had small and uniform oil droplets and displayed high emulsion viscosity and good stability, showing a good possibility for the amylodextrins to be used as fat replacers.