Enzymatic biocatalysis processes on the semicrystalline and morphological order of native cassava starches (Manihot esculenta)

Abstract

Enzymatic biocatalysis has emerged as a green technology in starch modification with divergent results at the morphological level depending on the origin of the starch source. Therefore, various enzymatic biocatalysts were implemented to evaluate their effect on the morphological and semi-crystalline characteristics of native cassava starches. The degree of affinity of the biocatalysts and the conversion rate on native cassava starches were determined by kinetic parameters such as the Michaelis-Menten constant, whose results revealed the following order of affinity from highest to lowest: α-amylase, amyloglucosidase, pullulanase, and β-amylase. In addition, greater biocatalytic activity of α-amylase and β-amylase was evidenced on the amorphous zones of the polymer associated with the decrease in the amylose content and a significant increase in the degree of relative crystallinity. According to morphological analyses and XDR, the action of amyloglucosidase promoted exo-erosion phenomena and the appearance of lacerations on the granular surface of starch with the consequent decrease in the semicrystalline order. The pullulanase caused slightly eroded fragmented granules with greater biocatalytic activity on the crystalline lamellae, associated with a significant increase in the apparent amylose content. FTIR analysis in the 1,200-900 cm-1 region, corresponding to the starch fingerprint, allowed us to detect notable changes in the degree of molecular order after the enzymatic attack; this result was consistent with the degree of relative crystallinity estimated by X-ray diffraction. Likewise, the results allowed us to notice significant changes in the semi-crystalline order and morphological characteristics during the modification with α-amylase (AAM) and amyloglucosidase (AMG) associated with their greater affinity and preferential action on the amorphous structures located on the granular surface of native cassava starch.