Structure of branching enzyme- and amylomaltase modified starch produced from well-defined amylose to amylopectin substrates

Abstract

Highlights •Enzyme modification of starch systems with well-defined amylose:amylopectin ratios provides detailed insight into the effects of substrate branching on enzymatic chain transfer • High amylose substrates produce high branching rates, high M w, short chains and low amylolytic digestion when treated with branching enzyme alone or in combination with amylomaltase.• Not only branching density but also molar mass of the glucan product restricts dietary degradation by steric hindrance towards human pancreatic α-amylase and α-glucosidases. AbstractThermostable branching enzyme (BE, EC 2.4.1.18) from Rhodothermus obamensis in combination with amylomaltase (AM, EC 2.4.1.25) from Thermus thermophilus was used to modify starch structure exploring potentials to extensively increase the number of branch points in starch. Amylose is an important constituent in starch and the effect of amylose on enzyme catalysis was investigated using amylose-only barley starch (AO) and waxy maize starch (WX) in well-defined ratios. All products were analysed for amylopectin chain length distribution, α-1,6 glucosidic linkages content, molar mass distribution and digestibility by using rat intestinal α-glucosidases. For each enzyme treatment series, increased AO content resulted in a higher rate of α-1,6 glucosidic linkage formation but as an effect of the very low initial branching of the AO, the final content of α-1,6 glucosidic linkages was slightly lower as compared to the high amylopectin substrates. However, an increase specifically in short chains was produced at high AO levels. The molar mass distribution for the enzyme treated samples was lower as compared with substrate WX and AO, indicating the presence of hydrolytic activity as well as cyclisation of the substrate. For all samples, increased amylose substrate showed decreased α-and β-amylolysis. Surprisingly, hydrolysis with rat intestinal α-glucosidases was higher with increasing α-1,6 glucosidic linkage content and decreasing M w indicating that steric hindrance towards the α-glucosidases was directed by the molar mass rather that the branching density of the glucan per se. Our data demonstrate that a higher amylose content in the substrate starch efficiently produces α-1,6 glucosidic linkages and that the present of amylose generates a higher M w and more resistant product than amylopectin. The combination of BEAMBE provided somewhat more resistant α-glucan products as compared to BE alone.

Barley Starch: Composition, Structure, Properties, and Modifications

“…The enzyme treatment increased the amount of short unit chains in “amylose‐only” starch and reduced the molecular size due to branching and degradation, respectively. The increased branching (α‐1,6 linkages) of starch led to increased resistance to amylolysis and the resistance was more pronounced for the treated “amylose‐only” starch (Sorndech and others ). Pullulanase treatment of barley flour also increased the RS content up to 1.3% (Harder and others ).…”

“…Various enzymatic modifications have been applied to increase the RS content (Kim and others , ; Harder and others ; Sorndech and others ), to produce malt (Patindo and others ; Chu and others ), and to study the influence of starch structure/type on starch degradation (You and Izydorczyk ; Naguleswaran and others , ).…”

“…The increased T p reflects the increased amount of unit chains of DP 13 to 36, which participated in the formation of new crystals. “Amylose‐only” and waxy starches were hydrolyzed by BE of Rhodothermus obamensis and amylomaltase of Thermus thermophilus to decrease their enzyme susceptibility (Sorndech and others ). The enzyme treatment increased the amount of short unit chains in “amylose‐only” starch and reduced the molecular size due to branching and degradation, respectively.…”

Slowly Digestible‐ and Non‐Digestible α‐Glucans: An Enzymatic Approach to Starch Modification and Nutritional Effects

“…3.2.1.2), maltogenic α‐amylase (MA, E.C. 3.2.1.133) derived from various microbial sources . The catalytic specificity of these enzymes is highly diverse and combinations of these, such as the combination of BE, MA, and TGase, producing SDMs from rice starch showed products with lower retrogradation as compared to the native rice starch substrate .…”

“…As a consequence, BE can be used as an anti‐staling agent added during dough preparation in industrial bread production . However, more importantly, BE has been reported for the production of highly branched α‐glucans which can be used as functional food ingredients to enhance their slowly digestible property . Hence, the catalytic mechanism of BE is important in many areas of starch processing.…”