Modification of tapioca starch granule surfaces on soluble fiber formation

Abstract

Enzyme hydrolysis, acid hydrolysis and acid hydrolysis combined with ball milling, which was used after acid pretreatment, were applied to modify granular surface of tapioca starch in order to study an efficient method to produce soluble fiber. Microscopic and specific surface area evidence indicated the different mechanisms of each modification method. The enzyme hydrolysis influenced starch granules with various characteristics: medium-size holes, sponge-like erosion, internal cracks and single holes extending into the granule interior. Using acid hydrolysis, starch granules were lost their smoothness with the external corrosion. The small particles and maximum of specific surface area (6.55 m²/cm³) were obtained from the combination of acid hydrolysis and ball milling. Soluble fiber formation was achieved by using pyroconversion reaction. The pyroconversion treatment of amyloglucosidase treated starch for 6 h gave the highest total dietary fiber (TDF) content (64.58% w/w db) and high solubility (85.43%).  The extensive modification of acid hydrolysis combined with ball milling before pyroconversion provided low value of solubility (23.40%) and TDF content (12.30%).  The extensive modification did not improve the solubility and promote the formation of soluble fiber.