title: Analysis of a preferential action of α-amylase from B. licheniformis towards amorphous regions of waxy maize starch.
abstract: Waxy maize starch was subjected to α-amylase (Bacillus licheniformis) hydrolysis in buffered medium to determine the evolution of reaction in quantitative terms and also in terms of the morphology and crystallinity of the partially hydrolyzed starch granules. Gathered data allowed studying the pattern of action of this α-amylase over waxy maize starch granules, with particular focus on a preferential hydrolysis of the amorphous regions of starch. Results showed that waxy maize starch hydrolysis followed a two-stage kinetic profile with an initial stage characterized by high reaction rate, followed by a slower second stage. The change of hydrolysis rate occurred at approximately 6h of reaction, a time for which X-ray diffraction data quantitatively analyzed by three different techniques showed a maximum of crystallinity in partially hydrolyzed granules. Scanning electron microscopy images illustrated the action of α-amylases which implied the exoerosion of the granules surface, the entry of α-amylases into the granules through radial channels, their endoerosion towards the granule exterior, and their fragmentation. Fragmentation of waxy maize starch granules revealed internal layered structures of starch which were interpreted as hydrolyzed/non-hydrolyzed growth rings. Under the conditions chosen, kinetic, electron microscopy and X-ray data all gave evidence of a preferential action of α-amylase from Bacillus licheniformis towards the less ordered regions of waxy maize starch. Results showed that, provided the proper hydrolysis time is chosen, starch granules with increased crystallinity can be obtained by a pure enzymatic treatment.
authors: Instituto de Tecnología en Polímeros y Nanotecnología (ITPN), Facultad de Ingeniería, Universidad de Buenos Aires, Capital Federal, Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina. Electronic address: mforesti@fi.uba.ar.
authors: María Laura
authors: ML
authors: Foresti
authors: Instituto de Tecnología en Polímeros y Nanotecnología (ITPN), Facultad de Ingeniería, Universidad de Buenos Aires, Capital Federal, Argentina.
authors: María del Pilar
authors: Mdel P
authors: Williams
authors: Instituto de Tecnología en Polímeros y Nanotecnología (ITPN), Facultad de Ingeniería, Universidad de Buenos Aires, Capital Federal, Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina.
authors: Ricardo
authors: R
authors: Martínez-García
authors: Instituto de Tecnología en Polímeros y Nanotecnología (ITPN), Facultad de Ingeniería, Universidad de Buenos Aires, Capital Federal, Argentina; Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Argentina.
authors: Analía
authors: A
authors: Vázquez
mesh_terms: D001407:Bacillus / Q000201:enzymology*; D007700:Kinetics; D008855:Microscopy, Electron, Scanning; D013213:Starch / Q000378:metabolism*; D014961:X-Ray Diffraction; D003313:Zea mays / Q000378:metabolism*; D000516:alpha-Amylases / Q000378:metabolism*
chemical_list: D013213:Starch; D000516:alpha-Amylases
keywords: Amorphous regions; Hydrolysis; Starch; α-Amylase