Anti-digestion properties of amylosucrase modified waxy corn starch

The Influence of Starch Modification with Amylosucrase Treatment on Morphological Features

Amylosucrase (AS) is a starch-modifying enzyme from Neisseria polysaccharea used to produce low-glycemic starches such as slowly digestible starch (SDS) and resistant starch (RS). The morphology of native, control, and AS-modified waxy corn starches (230 and 460 U) was examined using a particle size analyzer and field-emission scanning electron microscopy (FE-SEM). AS modification of the starch elongated the glucose and resulted in higher SDS and RS contents. The mean particle sizes of the control, 230 U-AS-, and 460 U-AS-treated starches were 56.6 µm, 128.0 µm, and 176.5 μm, respectively. The surface of the 460 U-AS-treated starch was entirely porous and coral-like, while the 230 U-AS-treated starch had a partial dense and flat surface which did not react with AS. FE-SEM of the granule cross section confirmed that the center contained a dense and flat region without any evidence of AS reaction to either of the AS-treated starches. It was assumed that the particle size and porous and sponge-like particle features might be related to the SDS and RS fractions.

Amylopectin-Sodium Palmitate Complexes as Sustainable Nanohydrogels with Tunable Size and Fractal Dimensions

Starch-based nanohydrogels with polyelectrolyte characteristics may find unique applications. Herein, the branch chains of amylopectin (AP) were elongated to different extents by amylosucrase, followed by complexation with sodium palmitate (SP) to produce nanohydrogels. Modified AP (mAP) with a longer chain length displayed a better ability to complex with SP, and the mixtures exhibited nanosized particles with an average diameter ranging from 153.5 to 1049.8 nm. The gel strength of bulk nanohydrogels was dependent on the chain length of mAP and SP content, and their fractal dimension was between 1.82 and 2.45. The crystalline structure of native AP was altered from A- to B-type after chain elongation and, subsequently, to B + V-type after complexing with SP. Diffraction peaks of the complexes at 2θ of 7.5°, 12.9°, and 19.8° implied that the AP side chains formed left-handed single helices and the hydrophobic SP was entrapped in the helix cavity.

Tailoring Digestibility of Starches by Chain Elongation Using Amylosucrase from Neisseria polysaccharea via a Zipper Reaction Mode

Amylosucrase from Neisseria polysaccharea (NpAS) was applied to modify waxy corn starch (WCS) and irradiated WCS, whose attenuated digestibility was studied. Herein, the mobility of the reaction mixture did not affect the enzyme catalytic efficiency, and the reaction kinetics suggest that the enzyme elongated the starch chain via a zipper reaction mode. The A-type crystalline structure of native and irradiated WCS was changed to B type after NpAS treatment, and a longer chain length led to a further increase in the gelatinization temperature. Chain elongation increased the content of resistant starch (RS) from 22.3% (native WCS) to be as much as 64.4% for NpAS-modified WCS, accordingly decreasing the contents of both rapidly and slowly digestible starches. Pearson correlation analysis implies that the RS content of NpAS-modified starches was positively and negatively correlated to the proportion of intermediate chains [13 ≤ degree of polymerization (DP) ≤ 24] and short chains (DP ≤ 12), respectively.

Thermostable Amylosucrase from Calidithermus timidus DSM 17022: Insight into Its Characteristics and Tetrameric Conformation

Amylosucrase (EC 2.4.1.4, ASase), a typical carbohydrate-active enzyme, can catalyze 5 types of reactions and recognize more than 50 types of glycosyl acceptors. However, most ASases are unstable even at 50 °C, which limits their practical industrial applications. In this study, an extremely thermostable ASase was discovered from Calidithermus timidus DSM 17022 (CT-ASase) with an optimal activity temperature of 55 °C, half-life of 1.09 h at 70 °C, and melting temperature of 74.47 °C. The recombinant CT-ASase was characterized as the first tetrameric ASase, and a structure-based truncation mutation was conducted to confirm the effect of tetrameric conformation on its thermostability. In addition, α-1,4-glucan was found to be the predominant product of CT-ASase at pH 6.0-8.0 and 30-60 °C.