Macromolecular characteristics and fine structure of amylomaltase-treated cassava starch

Improving paste stabilities of cassava starch through molecular density after maltogenic amylase and transglucosidase

To improve paste stability of cassava starch, including acid resistance, high-temperature shear resistance and freeze-thaw stability, cassava starch was modified by sequential maltogenic amylase and transglucosidase to form an optimally denser structure, or branched density (12.76 %), molecular density (15.17 g/mol/nm3), and the proportions of short-branched chains (41.41 % of A chains and 44.01 % of B1 chains). Viscosity stability (88.52 %) of modified starch was higher than that (64.92 %) of native starch. After acidic treatment for 1 h, the viscosity of modified starch and native starch decreased by 56.53 % and 65.70 %, respectively. Compared to native starch, modified starch had lower water loss in freeze-thaw cycles and less viscosity reduction during high-temperature and high-shear processing. So, the appropriate molecular density and denser molecule structure enhanced paste stabilities of modified starch. The outcome expands the food and non-food applications of cassava starch.

Bioinformatics and functional selection of GH77 4-α-glucanotransferases for potato starch modification

4-α-glucanotransferases (4αGTs, EC 2.4.1.25) from glycoside hydrolase family 77 (GH77) catalyze chain elongation of starch amylopectin chains and can be utilized to structurally modify starch to tailor its gelation properties. The potential relationship between the structural design of 4αGTs and functional starch modification is unknown. Here, family GH77 was mined in silico for enzyme candidates based on sub-grouping guided by Conserved Unique Peptide Patterns (CUPP) bioinformatics categorization. From + 12,000 protein sequences a representative set of 27 4αGTs, representing four different domain architectures, different bacterial origins and diverse CUPP groups, was selected for heterologous expression and further study. Most of the enzymes catalyzed starch modification, but their efficacies varied substantially. Five of the 4αGTs were characterized in detail, and their action was compared to that of the industrial benchmark enzyme, Tt4αGT (CUPP 77_1.2), from Thermus thermophilus. Reaction optima of the five 4αGTs ranged from ∼40-60 °C and pH 7.3-9.0. Several were stable for a minimum 4 h at 70 °C. Domain architecture type A proteins, consisting only of a catalytic domain, had high thermal stability and high starch modification ability. All five novel 4αGTs (and Tt4αGT) induced enhanced gelling of potato starch. One, At4αGT from Azospirillum thermophilum (CUPP 77_2.4), displayed distinct starch modifying abilities, whereas T24αGT from Thermus sp. 2.9 (CUPP 77_1.2) modified the starch similarly to Tt4αGT, but slightly more effectively. T24αGT and At4αGT are thus interesting candidates for industrial starch modification. A model is proposed to explain the link between the 4αGT induced molecular modifications and macroscopic starch gelation.

Conformational Switch of the 250s Loop Enables the Efficient Transglycosylation in GH Family 77

Amylomaltases (AMs) play important roles in glycogen and maltose metabolism. However, the molecular mechanism is elusive. Here, we investigated the conformational dynamics of the 250s loop and catalytic mechanism of Thermus aquaticus TaAM using path-metadynamics and QM/MM MD simulations. The results demonstrate that the transition of the 250s loop from an open to closed conformation promotes polysaccharide sliding, leading to the ideal positioning of the acid/base. Furthermore, the conformational dynamics can also modulate the selectivity of hydrolysis and transglycosylation. The closed conformation of the 250s loop enables the tight packing of the active site for transglycosylation, reducing the energy penalty and efficiently preventing the penetration of water into the active site. Conversely, the partially closed conformation for hydrolysis results in a loosely packed active site, destabilizing the transition state. These computational findings guide mutation experiments and enable the identification of mutants with an improved disproportionation/hydrolysis ratio. The present mechanism is in line with experimental data, highlighting the critical role of conformational dynamics in regulating the catalytic reactivity of GHs.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2019-2020

This review is the tenth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2020. Also included are papers that describe methods appropriate to analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. The review is basically divided into three sections: (1) general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation, quantification and the use of arrays. (2) Applications to various structural types such as oligo- and polysaccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals, and (3) other areas such as medicine, industrial processes and glycan synthesis where MALDI is extensively used. Much of the material relating to applications is presented in tabular form. The reported work shows increasing use of incorporation of new techniques such as ion mobility and the enormous impact that MALDI imaging is having. MALDI, although invented nearly 40 years ago is still an ideal technique for carbohydrate analysis and advancements in the technique and range of applications show little sign of diminishing.

Enhancing gel strength of Thermoproteus uzoniensis 4-α-glucanotransferase modified starch by amylosucrase treatment

4-α-glucanotransferase is used to produce thermoreversible starch gels to alleviate limitations to use of starch gels in repetitively heat-processed foods. However, the gel strength was weakened after this enzyme modification. In the present study, treatment by amylosucrase (NpAS) of corn starch and sucrose was applied to retain the gel thermoreversibility and eliminate the shortcoming caused by 4-α-glucanotransferase (TuαGT). Changes in molecular structure, rheological and retrogradation properties of modified starch were investigated after NpAS and TuαGT sequential and one-pot treatment, respectively. The apparent amylose content was reduced and increased by sequential and one-pot treatments, respectively, compared to single TuαGT modification. Chain length profiles showed higher proportion of degree of polymerization (DP) ≥ 13 by sequential treatment, whereas DP 6-12 was higher after one-pot treatment. All modified starches had reduced molecular weight. G' and G" increased by dual enzyme compared to single TuαGT treatment having little effect on retrogradation. Interestingly, starch subjected to 3 h one-pot treatment caused G' and G" temperature curves to cross-over, improving thermoreversible properties. The results indicate that NpAS treatment compensated for loss of starch gel strength caused by TuαGT and offered possibility to provide a wider range of thermoreversible starches.

Preparation and structural properties of selenium modified heteropolysaccharide from the fruits of Akebia quinata and in vitro and in vivo antitumor activity

Cancer is a complex disease, and blocking tumor angiogenesis has become one of the most promising approaches in cancer therapy. Here, an exopoly heteropolysaccharide (AQP70-2B) was firstly isolated from Akebia quinata. Monosaccharide composition indicated that the AQP70-2B was composed of rhamnose, glucose, galactose, and arabinose. The backbone of AQP70-2B consisted of →1)-l-Araf, →3)-l-Araf-(1→, →5)-l-Araf-(1→, →3,5)-l-Araf-(1→, →2,5)-l-Araf-(1→, →4)-d-Glcp-(1→, →6)-d-Galp-(1→, and →1)-d-Rhap residues. Based on the close relationship between selenium and anti-tumor activity, AQP70-2B was modified with selenium to obtain selenized polysaccharide Se-AQP70-2B. Then, a series of methods for analysis and characterization, especially scanning electron microscopy coupled with energy dispersive spectrometry (SEM-EDS), indicated that Se-AQP70-2B was successfully synthesized. Furthermore, zebrafish xenografts and anti-angiogenesis experiments indicated that selenization could improve the antitumor activity by inhibiting tumor cell proliferation and migration and blocking angiogenesis.

Heterologous expression of 4α-glucanotransferase: overproduction and properties for industrial applications

4α-Glucanotransferase (4α-GTase) is unique in its ability to form cyclic oligosaccharides, some of which are of industrial importance. Generally, low amount of enzymes is produced by or isolated from their natural sources: animals, plants, and microorganisms. Heterologous expressions of these enzymes, in an attempt to increase their production for applicable uses, have been widely studied since 1980s; however, the expressions are mostly performed in the prokaryotic bacteria, mostly Escherichia coli. Site-directed mutagenesis has added more value to these expressed enzymes to display the desired properties beneficial for their applications. The search for further suitable properties for food application leads to an extended research in expression by another group of host organism, the generally-recognized as safe host including the Bacillus and the eukaryotic yeast systems. Herein, our review focuses on two types of 4α-GTase: the cyclodextrin glycosyltransferase and amylomaltase. The updated studies on the general structure and properties of the two enzymes with emphasis on heterologous expression, mutagenesis for property improvement, and their industrial applications are provided.

Structural factors governing starch digestion and glycemic responses and how they can be modified by enzymatic approaches: A review and a guide

Starch is the most abundant glycemic carbohydrate in the human diet. Consumption of starch-rich food products that elicit high glycemic responses has been linked to the occurrence of noncommunicable diseases such as cardiovascular disease and diabetes mellitus type II. Understanding the structural features that govern starch digestibility is a prerequisite for developing strategies to mitigate any negative health implications it may have. Here, we review the aspects of the fine molecular structure that in native, gelatinized, and gelled/retrograded starch directly impact its digestibility and thus human health. We next provide an informed guidance for lowering its digestibility by using specific enzymes tailoring its molecular and three-dimensional supramolecular structure. We finally discuss in vivo studies of the glycemic responses to enzymatically modified starches and relevant food applications. Overall, structure-digestibility relationships provide opportunities for targeted modification of starch during food production and improving the nutritional profile of starchy foods.

Green and clean modification of cassava starch - effects on composition, structure, properties and digestibility

There is a growing need for clean and green labeling of food products among consumers globally. Therefore, development of green modified starches, to boost functionality, palatability and health benefits while reducing the negative processing impacts on the environment and reinforcing consumer safety is in high demand. Starch modification started in mid-1500s due to the inherent limitations of native starch restricting its commercial applications, with chemical modification being most common. However, with the recent push for "chemical-free" labeling, methods of physical and enzymatic modification have gained immense popularity. These methods have been successfully used in numerous studies to alter the composition, structure, functionality and digestibility of starch and in this review, studies reported on green modification of cassava starch, one of the most common utilized starches, within the last ten years have been critically reviewed. Recent research has introduced starch as an abundant, natural substrate for producing resistant starches through biophysical technologies that act as dietary fiber in the human body. It is evident that different techniques and processing parameters result in varying degrees of modification impacting the techno-functionality and digestibility of the resultant starch. This can be exploited by researchers and industrialists in order to customize starch functionality in accordance with application.

Structural characteristics and in vitro and in vivo immunoregulatory properties of a gluco-arabinan from Angelica dahurica

A water-soluble polysaccharide identified here as ADP80-2 was acquired from Angelica dahurica. ADP80-2 was a gluco-arabinan composed of arabinose and a trace of glucose with a molecular weight of 9950 g/mol. The backbone of ADP80-2 comprised →5)-α-L-Araf-(1→, →3, 5)-α-L-Araf-(1→, →6)-α-D-Glcp-(1→, with a terminal branch α-L-Araf-(1 → residue. In terms of immunoregulatory activity, ADP80-2 can significantly promote the phagocytosis, the production of nitric oxide (NO), and the secretion of cytokines (IL-6, IL-1β, and TNF-α) of macrophage. In addition to the cellular immunomodulatory activities, the chemokines related to immunoregulation were significantly increased in the zebrafish model after treated with ADP80-2. These biological results indicated that ADP80-2 with immunomodulatory effects was expected to be useful for the development of new immunomodulatory agents. Simultaneously, the discovery of ADP80-2 further revealed the chemical composition of A. dahurica used as a traditional Chinese medicine and spice.

Use of Amylomaltase to Steer the Functional and Nutritional Properties of Wheat Starch

The fine molecular structure of starch governs its functionality and digestibility, and enzymatic approaches can be utilized to tailor its properties. The aim of this study was to investigate the in situ modification of starch by amylomaltase (AMM) from Thermus thermophilus in model starch systems subjected to hydrothermal treatments under standardized conditions and the relationship between molecular structure, rheological properties and in vitro digestibility. When low dosages of AMM were added to a wheat starch suspension prior to submitting it to a temperature-time profile in a Rapid Visco Analyzer, the increased peak viscosity observed was attributed to partial depolymerization of amylose, which facilitated starch swelling and viscosity development. At higher dosages, the effect was smaller. The low cold paste viscosity as a result of the activity of AMM reflected substantial amylose depolymerization. At the same time, amylopectin chains were substantially elongated. The longer amylopectin chains were positively correlated (R² = 0.96) with the melting enthalpies of retrograded starches, which, in turn, were negatively correlated with the extent (R² = 0.92) and rate (R² = 0.79) of in vitro digestion. It was concluded that AMM has the potential to be used to deliver novel starch functionalities and enhance its nutritional properties.

Structural properties and in vitro and in vivo immunomodulatory activity of an arabinofuranan from the fruits of Akebia quinata

In our continuous searching for natural active polysaccharides with immunomodulatory activity, an arabinofuranan (AQP70-3) was isolated and purified from the fruits of Akebia quinata (Houtt.) Decne. by using ion-exchange chromatography and gel permeation chromatography for the first time. AQP70-3 contained both α-l-Araf and β-l-Araf, and the absolute molecular weight was 1.06 × 10⁴ g/mol. The backbone of AQP70-3 comprised →5)-α-l-Araf-(1→, →3,5)-α-l-Araf-(1→, and →2,5)-α-l-Araf-(1→, with branches of →1)-β-l-Arafand →3)-α-l-Araf-(1→ residues. Biological assay suggested that AQP70-3 can stimulate phagocytic activity and promote the levels of nitric oxide (NO), interleukin (IL)-6, IL-1β, and tumor necrosis factor-α (TNF-α) of RAW264.7 cells. Furthermore, AQP70-3 was found to increase the production of reactive oxygen species (ROS) and NO in zebrafish embryo model.

Amylomaltase from Thermus filiformis: expression in Saccharomyces cerevisiae and its use in starch modification

AIM

To express amylomaltase from Thermus filiformis (TfAM) in a generally recognized as safe (GRAS) organism and to use the enzyme in starch modification.

METHODS AND RESULTS

TfAM was expressed in Saccharomyces cerevisiae, using 2% (w/v) galactose inducer under GAL1 promoter. The enzyme was thermostable with high disproportionation and cyclization activities. The main large-ring cyclodextrin (CD) products were CD24-CD29, with CD26 as maximum at all incubation times. TfAM was used to modify cassava and pea starches, the amylose content decreased 18% and 30%, respectively, when 5% (w/v) starch was treated with 0·5 U TfAM g-1 starch. The increase in short branched chain (DP, degree of polymerization, 1-5) and the broader chain length distribution pattern which extended to the longer chain (DP40) after TfAM treatment were observed. The thermal property was changed, with an increase in retrogradation of starch as suggested by a lower enthalpy.

CONCLUSIONS

TfAM was successfully expressed in S. cerevisiae and was used to make starches with new functionality.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report on the expression of AM in the GRAS yeast and the production of a modified starch gel from pea starch to improve the versatility of starch for food use.

Progress in research and applications of cassava flour and starch: a review

The cassava flours and starches have elicited great use in the food and non-food industry. The diversity in cassava genotypes accounts for differences in end-product properties, and would require characterization of cassava varieties for suitability of culinary and processing. This review showed that screening criteria of cassava cultivars end-user properties include proximate contents, amylose content, structural, swelling, gelatinization and pasting characteristics, including freeze-thaw stability properties of cassava-derived flours and starches. Literature shows that the physiochemical properties vary with genetic factors (i.e. genotype). In this review, the amylose content was found to be the main genetic trait for discriminating the cassava varieties for gelatinization and pasting processes including resistant starches. Moreover, cassava derived raw materials (flours and starches) were found to have various application in baking, edible film, syrup, glucose, alcohol, and soups production.