Analysis of a preferential action of alfa-amylase from B. licheniformis towards amorphous regions of starch

M.L. FORESTI; M.P. WILLIAMS; R. MARTINEZ-GARCÍA; A. VAZQUEZ

CARBOHYDRATE POLYMERS

ELSEVIER SCI LTD

Lugar: Amsterdam; Año: 2014 vol. 102 p. 80 - 87

0144-8617

Waxy maize starch was subjected to -amylase (Bacillus licheniformis) hydrolysis in buffered medium todetermine the evolution of reaction in quantitative terms and also in terms of the morphology and crystallinityof the partially hydrolyzed starch granules. Gathered data allowed studying the pattern of actionof this -amylase over waxy maize starch granules, with particular focus on a preferential hydrolysis ofthe amorphous regions of starch. Results showed that waxy maize starch hydrolysis followed a two-stagekinetic profile with an initial stage characterized by high reaction rate, followed by a slower second stage.The change of hydrolysis rate occurred at approximately 6 h of reaction, a time for which X-ray diffractiondata quantitatively analyzed by three different techniques showed a maximum of crystallinity inpartially hydrolyzed granules. Scanning electron microscopy images illustrated the action of -amylaseswhich implied the exoerosion of the granules surface, the entry of -amylases into the granules throughradial channels, their endoerosion towards the granule exterior, and their fragmentation. Fragmentationof waxy maize starch granules revealed internal layered structures of starch which were interpreted ashydrolyzed/non-hydrolyzed growth rings. Under the conditions chosen, kinetic, electron microscopy andX-ray data all gave evidence of a preferential action of -amylase from Bacillus licheniformis towards theless ordered regions of waxy maize starch. Results showed that, provided the proper hydrolysis time ischosen, starch granules with increased crystallinity can be obtained by a pure enzymatic treatment.