In vitro amylase hydrolysis of amylopectins from cereal starches based on molecular structure of amylopectins

Effect of solution on starch structure: New separation approach of amylopectin fraction from gelatinized native corn starch

The complete dissolution of starch without degradation are necessary prerequisites for starch fractionation to obtain amylose or amylopectin (AP). With the recent, continuous progress in finding efficient and eco-friendly starch-dissolving solutions, applying new solvents for starch fractionation is important. In this study, the effects of dimethyl sulfoxide (DMSO), NaOH, and CaCl2 solutions on starch structure and AP product parameters during starch fractionation were compared with respect to the starch deconstruction effect. This study proved that the CaCl2 solution could effectively dissolve corn starch (50 °C, solubility of 98.96 %), and promote the regeneration of starch into uniform and fine particles. Furthermore, the three solvents (DMSO, NaOH, and CaCl2) changed the crystal structure of corn starch, but they were all non-derivatizing solvents. The effect of the CaCl2 solution on the molecular structure of corn starch was the least significant of the three solvents. Finally, the extraction rate of AP from the CaCl2 solution reached 69.45 %. In conclusion, this study presents a novel and effective method for AP extraction.

Effect of Starch Primers on the Fine Structure of Enzymatically Synthesized Glycogen-like Glucan

Glycogen-like glucan (GnG) is a unique hyperbranched polysaccharide nanoparticle which is drawing increasing attention due to its biodegradability and abundant short branches that can be functionalized. Because starch and GnG are both composed of glucose residues and have similar glucosidic bonds, GnG could be fabricated by sucrose phosphorylase, α-glucan phosphorylase, and branching enzymes from starch primers and sucrose. In this study, high-amylose starch, normal starch, and waxy corn starch were used as primers to synthesize GnG, and their impact on the fine structure of GnG was investigated. Structural analysis indicated that with increasing content of amylopectin in the starch primer, the proportion of short chains in GnG decreased, and the degree of β-amylolysis and α-amylolysis was enhanced. Amylose in the primer contributed to a compact and homogeneous structure of GnG, while amylopectin triggered the formation of branch points with a more open distribution. These findings provide a new strategy for regulating the fine structure of GnG.

In vitro starch digestibility of buckwheat cultivars in comparison to wheat: The key role of starch molecular structure

The objective of this study was to compare the in vitro digestibility of different buckwheat and wheat starch cultivars and establish the relationship between digestibility and structure of buckwheat starch. Structure of starches were analyzed with size exclusion chromatography and fluorophore-assisted capillary electrophoresis. Results showed that the amylose content of Tartary buckwheat starch (TBS) and common buckwheat starch (CBS) was 3-4% lower than that of wheat starch. However, no significant difference in the digestibility was found between them. The fast digestion rate coefficient of TBS was negatively correlated with the amount of long amylopectin chains (24 < DP ≤ 36), and the total digested starch percentage of CBS was negatively correlated with the amount of medium-long amylopectin chains (13 < DP ≤ 24). This suggests that the digestibility of fully gelatinized starch had no association with the botanical sources but may be more influenced by starch structure.

Comparison of functional properties of porous starches produced with different enzyme combinations

To obtain porous starch granules with higher absorption capacities, three types of enzyme combinations were adopted to modify wheat and maize starches: (1) sequential α-amylase (AA) → glucoamylase (GA); (2) sequential branching enzyme (BE) → GA; and (3) sequential AA→BE→GA. The results indicated that AA→BE→GA treatment had a most optimal influence on porous starches. Compared to AA→GA and BE→GA, the mesopores in wheat starch granules treated with AA→BE→GA decreased by 52.82 and 48.70%, respectively. Conversely, the macropores increased by 216.68 and 138.18%, respectively. While for maize starch, the percentages of mesopores and macropores hardly changed after three enzyme combinations. Comparing the three enzyme treatments showed that pore volume (0.005 and 0.007 cm³/g) and pore size (36.35 and 26.54 nm) were largest in the AA→BE→GA treated wheat and maize starches, respectively. Compared to the AA→GA and BE→GA, the adsorption capacities for oil, dye and heavy metal ions, wheat starch treated with AA→BE→GA increased by 46.61 and 242.33%, and 44.52 and 134.41%, and 28.83 and 271.72%, respectively. Correspondingly, that of maize starch increased by 29.71 and 133.29%, and 42.92 and 79.93%, and 28.16 and 161.43%, respectively. These results may provide a new and valuable enzyme combination for optimising porous starch granules with higher absorption capacities.

Low molecular weight alkaline thermostable α-amylase from Geobacillus sp. nov

Industrial demands for enzymes that are stable in a broad range of conditions are increasing. Such enzymes, one of which is α-amylase, could be produced by extremophiles. This study reports a thermostable α-amylase produced by a newly isolated Geobacillus sp. nov. from a geothermal area. The phylogenetic analysis of the 16S rRNA gene showed that the isolate formed a separate branch with 95% homology to Geobacillus sp. After precipitation using ammonium sulphate followed by ion-exchange chromatography, the enzyme produced a specific activity of 25.1 (U/mg) with a purity of 6.5-fold of the crude extract. The molecular weight of the enzyme was approximately 12.2 kDa. The optimum activity was observed at 75 °C and pH 8. The activity increased in the presence of Ba²⁺ and Fe²⁺ but decreased in the presence of K⁺ and Mg²⁺. Ca²⁺ and Mn²⁺ increased the activity slightly. The activity completely diminished with the addition of Cu²⁺. EDTA and PMSF also sharply reduced enzyme activity. Although the stability was moderate, the low molecular weight could be an important feature for its future applications.