Enzymatic modification of corn starch with 4-α-glucanotransferase results in increasing slow digestible and resistant starch

The Small Cycloamylose (CA15) Synthesizing Properties of 4-α-Glucanotransferase from Hyperthermophilic Archaeon Pyrobaculum arsenaticum with Its Distinct Disproportionation Activity

4-α-Glucanotransferase (4-α-GTase, EC 2.4.1.25) facilitates the transfer of α-1,4-linked glucan to another acceptor molecule. This enzyme is widely used during starch modification to produce unique materials, such as thermoreversible gel and cyclic glucan. Because most industrial processing of starch is conducted at elevated temperatures, hyperthermophilic enzymes have received considerable attention. However, only a few of the 4-α-GTases in the glycoside hydrolase family 77 have been isolated from hyperthermophilic archaea. Here, we report for the first time the cycloamylose-forming properties of an archaeal 4-α-GTase (ParGT) isolated from Pyrobaculum arsenaticum. ParGT exhibited optimal activity at pH 6.0 and 95 °C. In particular, ParGT can synthesize small cycloamyloses (CA15-18) with unique disproportionation patterns based on its low transglycosylation activity. Structural modeling with long-chain maltooligosaccharides revealed distinct amino acid residues at the acceptor and second acarbose-binding sites of ParGT. Mutations at Y322 and P231 at the acceptor binding site reduced the disproportionation activity for long-chain maltooligosaccharides, whereas E55 at the second acarbose-binding site influenced the cycloamylose size by affecting the positioning of the 460s loop. These findings provide valuable insights into the structural features and catalytic properties of hyperthermophilic archaeal 4-α-GTase, enabling future modifications of enzymes to improve their capacity to alter starch in diverse biotechnological processes.

Slowly hydrolyzable property of microbial dextrans at the small intestinal α-glucosidase levels leads to the modulated glycemic responses in the mouse model

Dextran-type α-glucans have been known as non-digestible ingredients that can be considered prebiotics to promote colon health. However, recent studies have revealed that various α-linked glucosyl units are hydrolyzed to glucose by small intestinal α-glucosidases. This study analyzed the structural characteristics of exopolysaccharides (EPSs) from Weissella species, and the hydrolysis properties at both in vitro/in vivo levels were investigated. Compared with a previous in vitro digestion model using fungal α-hydrolytic enzymes, dextrans, which mainly consist of α-1,6 linkages with small amounts of α-1,3 linked glucose units, were slowly hydrolyzed to glucose by mammalian mucosal α-glucosidases, resulting in attenuation of the initial glycemic response following administration of EPS samples to mice via oral gavage. The results of this study demonstrate the concept of dextran-type α-glucans as glycemic carbohydrates rather than dietary fibers or prebiotics. Slowly digestible dextrans can be applied as a functional ingredient to regulate postprandial glucose delivery throughout the gastrointestinal tract.

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.

Sequential starch modification by branching enzyme and 4-α-glucanotransferase improves retention of curcumin in starch-alginate beads

A new super-branched amylopectin with longer exterior chains was produced from normal maize starch by modification with branching enzyme followed by 4-α-glucanotransferase, and applied for co-entrapment of a curcumin-loaded emulsion in alginate beads. The network structure of the gel beads was obtained with Ca2+-cross-linked alginate and a modest load of retrograded starch. The dual enzyme modified starch contained more and longer α-1,6-linked branch chains than single enzyme modified and unmodified starches and showed superior resistance to digestive enzymes. Alginate beads with or without starch were of similar size (1.69-1.74 mm), but curcumin retention was improved 1.4-2.8-fold in the presence of different starches. Thus, subjecting the curcumin-loaded beads to in vitro simulated gastrointestinal digestion resulted in retention of 70, 43 and 22 % of the curcumin entrapped in the presence of modified, unmodified, or no starch, respectively. Molecular docking provided support for curcumin interacting with starch via hydrogen bonding, hydrophobic contacts and π-π stacking. The study highlights the potential of utilizing low concentration of dual-enzyme modified starch with alginate to create a versatile vehicle for controlled release and targeted delivery of bioactive compounds.

Designing starch derivatives with desired structures and functional properties via rearrangements of glycosidic linkages by starch-active transglycosylases

Modification of starch by transglycosylases from glycoside hydrolase families has attracted much attention recently; these enzymes can produce starch derivatives with novel properties, i.e. processability and functionality, employing highly efficient and safe methods. Starch-active transglycosylases cleave starches and transfer linear fragments to acceptors introducing α-1,4 and/or linear/branched α-1,6 glucosidic linkages, resulting in starch derivatives with excellent properties such as complexing and resistance to digestion characteristics, and also may be endowed with new properties such as thermo-reversible gel formation. This review summarizes the effects of variations in glycosidic linkage composition on structure and properties of modified starches. Starch-active transglycosylases are classified into 4 groups that form compounds: (1) in cyclic with α-1,4 glucosidic linkages, (2) with linear chains of α-1,4 glucosidic linkages, (3) with branched α-1,6 glucosidic linkages, and (4) with linear chains of α-1,6 glucosidic linkages. We discuss potential processability and functionality of starch derivatives with different linkage combinations and structures. The changes in properties caused by rearrangements of glycosidic linkages provide guidance for design of starch derivatives with desired structures and properties, which promotes the development of new starch products and starch processing for the food industry.

Biochemical characteristics and potential application of a thermostable starch branching enzyme from Bacillus licheniformis

Slowly digestible starch (SDS) has attracted increasing attention for its function of preventing metabolic diseases. Based on transglycosylation, starch branching enzymes (1,4-α-glucan branching enzymes, GBEs, EC 2.4.1.18) can be used to regulate the digestibility of starch. In this study, a GBE gene from Bacillus licheniformis (bl-GBE) was cloned, expressed, purified, and characterized. Sequence analysis and structural modeling showed that bl-GBE belong to the glycoside hydrolase 13 (GH13) family, with which its active site residues were conserved. The bl-GBE was highly active at 80 °C and a pH range of 7.5-9.0, and retained 90% of enzyme activity at 70 °C for 16 h. bl-GBE also showed high substrate specificity (80.88 U/mg) on potato starch. The stability and the changes of the secondary structure of bl-GBE at different temperature were determined by circular dichroism (CD) spectroscopy. The CD data showed a loss of 20% of the enzyme activity at high temperatures (80 °C), due to the decreased content of the α -helix in the secondary structure. Furthermore, potato starch treated with bl-GBE (300 U/g starch) showed remarkable increase in stability, solubility, and significant reduction viscosity. Meanwhile, the slowly digestible starch content of bl-GBE modified potato starch increased by 53.03% compared with native potato starch. Our results demonstrated the potential applications of thermophilic bl-GBE in food industries.

Structural Modifications and Strategies for Native Starch for Applications in Advanced Drug Delivery

Pharmaceutical excipients are compounds or substances other than API which are added to a dosage form, these excipients basically act as carriers, binders, bulk forming agents, colorants, and flavouring agents, and few excipients are even used to enhance the activity of active pharmaceutical ingredient (API) and various more properties. However, despite of these properties, there are problems with the synthetic excipients such as the possibility of causing toxicity, inflammation, autoimmune responses, lack of intrinsic bioactivity and biocompatibility, expensive procedures for synthesis, and water solubility. However, starch as an excipient can overcome all these problems in one go. It is inexpensive, there is no toxicity or immune response, and it is biocompatible in nature. It is very less used as an excipient because of its high digestibility and swelling index, high glycemic index, paste clarity, film-forming property, crystalline properties, etc. All these properties of starch can be altered by a few modification processes such as physical modification, genetic modification, and chemical modification, which can be used to reduce its digestibility and glycemic index of starch, improve its film-forming properties, and increase its paste clarity. Changes in some of the molecular bonds which improve its properties such as binding, crystalline structure, and retrogradation make starch perfect to be used as a pharmaceutical excipient. This research work provides the structural modifications of native starch which can be applicable in advanced drug delivery. The major contributions of the paper are advances in the modification of native starch molecules such as physically, chemically, enzymatically, and genetically traditional crop modification to yield a novel molecule with significant potential for use in the pharmaceutical industry for targeted drug delivery systems.

Preparation of Slowly Digested Corn Starch Using Branching Enzyme and Immobilized α-Amylase

The aim of this study was to modify the digestibility and structure of corn starch by treatment with compound enzymes. Corn starch was treated with two enzymes (α-amylase, which catalyzes hydrolysis, and branching enzyme, a transglycosidase that catalyzes branch formation), and the reaction was monitored by determining the content of slowly digestible starch in the reaction product. The fine structure and physical and chemical properties of enzyme-modified starch samples were analyzed using scanning electron microscopy, gel chromatography, and X-ray diffraction methods; modified starch has a high degree of branching, a high proportion of short-chain branched structures, and greatly improved solubility. The results show that the slow digestion performance of corn starch was significantly improved after hydrolysis by α-amylase for 4 h and treatment with branching enzyme for 6 h. These results show that enzymatic modification of corn starch can improve its slow digestibility properties.

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.

Production of Large-Ring Cyclodextrins by Amylomaltases

Amylomaltase is a well-known glucan transferase that can produce large ring cyclodextrins (LR-CDs) or so-called cycloamyloses via cyclization reaction. Amylomaltases have been found in several microorganisms and their optimum temperatures are generally around 60–70 °C for thermostable amylomaltases and 30–45 °C for the enzymes from mesophilic bacteria and plants. The optimum pHs for mesophilic amylomaltases are around pH 6.0–7.0, while the thermostable amylomaltases are generally active at more acidic conditions. Size of LR-CDs depends on the source of amylomaltases and the reaction conditions including pH, temperature, incubation time, and substrate. For example, in the case of amylomaltase from Corynebacterium glutamicum, LR-CD productions at alkaline pH or at a long incubation time favored products with a low degree of polymerization. In this review, we explore the synthesis of LR-CDs by amylomaltases, structural information of amylomaltases, as well as current applications of LR-CDs and amylomaltases.

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.

Starch granule size: Does it matter?

Nature has developed starch granules varying in size from less than 1 μm to more than 100 μm. The granule size is an important factor affecting the functional properties and the applicability of starch for food and non-food applications. Within the same botanical species, the range of starch granule size can be up to sevenfold. This review critically evaluated the biological and environmental factors affecting the size of starch granules, the methods for the separation of starch granules and the measurement of size distribution. Further, the structure at different length scales and properties of starch-based on the granule size is elucidated by specifying the typical applications of granules with varying sizes. An amylopectin cluster model showing the arrangement of amylopectin from inside toward the granule surface is proposed with the hypothesis that the steric hindrance for the growth of lamellar structure may limit the size of starch granules.

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.

Amylomaltases in Extremophilic Microorganisms

Amylomaltases (4-α-glucanotransferases, E.C. 2.4.1.25) are enzymes which can perform a double-step catalytic process, resulting in a transglycosylation reaction. They hydrolyse glucosidic bonds of α-1,4'-d-glucans and transfer the glucan portion with the newly available anomeric carbon to the 4'-position of an α-1,4'-d-glucan acceptor. The intramolecular reaction produces a cyclic α-1,4'-glucan. Amylomaltases can be found only in prokaryotes, where they are involved in glycogen degradation and maltose metabolism. These enzymes are being studied for possible biotechnological applications, such as the production of (i) sugar substitutes; (ii) cycloamyloses (molecules larger than cyclodextrins), which could potentially be useful as carriers and encapsulating agents for hydrophobic molecules and also as effective protein chaperons; and (iii) thermoreversible starch gels, which could be used as non-animal gelatin substitutes. Extremophilic prokaryotes have been investigated for the identification of amylomaltases to be used in the starch modifying processes, which require high temperatures or extreme conditions. The aim of this article is to present an updated overview of studies on amylomaltases from extremophilic Bacteria and Archaea, including data about their distribution, activity, potential industrial application and structure.

Potato starch modified by Streptococcus thermophilus GtfB enzyme has low viscoelastic and slowly digestible properties

Potato starch with high viscosity and digestibility cannot be added into some foods. To address this issue, a novel starch-acting enzyme 4,6-α-glucosyltransferase from Streptococcus thermophilus (StGtfB) was used. StGtfB decreased the iodine affinity and the molecular weight, but increased the degree of branching of starch at a mode quite different from glycogen 1,4-α-glucan branching enzyme (GBE). StGtfB at 5 U/g substrate mainly introduced DP 1-7 into amylose (AMY) or DP 1-12 branches into amylopectin (AMP), and increased the ratio of short- to long-branches from 0.32 to 2.22 or from 0.41 to 2.50. The DP 3 branch chain was the most abundant in both StGtfB-modified AMY and StGtfB-modified AMP. The DP < 6 branch chain contents in StGtfB-modified AMY were 42.68%, much higher than those of GBE-modified AMY. StGtfB significantly decreased viscoelasticity but still kept pseudoplasticity of starch. The modifications also slowed down the glucose generation rate of products at the mammalian mucosal α-glucosidase level. The slowly digestible fraction in potato starch increased from 34.29% to 53.22% using StGtfB of 5 U/g starch. This low viscoelastic and slowly digestible potato starch had great potential with respect to low and stable postprandial blood glucose.

Expression and characterization of 1,4-α-glucan branching enzyme from Microvirga sp. MC18 and its application in the preparation of slowly digestible starch

Nutraceuticals containing modified starch with increased content of slowly-digestible starch (SDS) may reduce the prevalence of obesity, diabetes and cardiovascular diseases due to its slow digestion rate. Enzymatic methods for the preparation of modified starch have attracted increasing attention because of their low environmental impact, safety and specificity. In this study, the efficient glucan branching enzyme McGBE from Microvirga sp. MC18 was identified, and its relevant properties as well as its potential for industrial starch modification were evaluated. The purified McGBE exhibited the highest specificity for potato starch, with a maximal specific activity of 791.21 U/mg. A time-dependent increase in the content of α-1,6 linkages from 3.0 to 6.0% was observed in McGBE-modified potato starch. The proportion of shorter chains (degree of polymerization, DP < 13) increased from 29.2 to 63.29% after McGBE treatment, accompanied by a reduction of the medium length chains (DP 13-24) from 52.30 to 35.99% and longer chains (DP > 25) from 18.51 to 0.72%. The reduction of the storage modulus (G') and retrogradation enthalpy (ΔHr) of potato starch with increasing treatment time demonstrated that McGBE could inhibit the short- and long-term retrogradation of starch. Under the optimal conditions, the SDS content of McGBE-modified potato starch increased by 65.8% compared to native potato starch. These results suggest that McGBE has great application potential for the preparation of modified starch with higher SDS content that is resistant to retrogradation.

Synergetic modification of waxy maize starch by dual-enzyme to lower the in vitro digestibility through modulating molecular structure and malto-oligosaccharide content

Cyclodextrinase (CDase) and cyclodextrin glucosyltransferase (CGTase) were synergistically used to provide a novel enzymatic method in lowing in vitro digestibility of waxy maize starch. The molecular structure, malto-oligosaccharide composition, and digestibility properties of the generated products were investigated. The molecular weight was reduced to 0.3 × 10⁵ g/mol and 0.2 × 10⁵ g/mol by simultaneous and sequential treatment with CDase and CGTase, while the highest proportion of chains with degree of polymerization (DP) < 13 was obtained by simultaneous treatment. The resistant starch contents were increased to 27.5% and 36.9% by simultaneous and sequential treatments respectively. Dual-enzyme treatment significantly promoted the content of malto-oligosaccharides (MOSs) by hydrolyzing cyclodextrins from CGTase with CDase. However, the replacement of cyclodextrins by MOSs did not obviously influence the digestibility of the products. The starch digestion kinetics further revealed the hydrolysis pattern of these two enzymes on the starch hydrolysate. It was proved that the starch digestibility could be lowered by modulating the molecular structure and beneficial MOSs content by this dual-enzyme treatment.

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.

Recombinant expression and characterization of the glycogen branching enzyme from Vibrio vulnificus and its application in starch modification

Resistant starch (RS) is helpful in controlling and preventing metabolic syndrome relevant diseases. However, the RS content of natural starch and modified starch produced by enzymatic method is generally low. To solve this problem, we selected the glycogen branching enzyme from Vibrio vulnificus (VvGBE) and investigated its application. Firstly, it was expressed in E. coli with the enzyme activity was 53.33 U/mL, and its optimum temperature and pH was 35 °C and 7.5, respectively. The half-life of VvGBE at 35 °C was 10 h, and the enzyme was most stable at pH 9.5. When we used the recombinant enzyme to treat corn starch, the content of RS increased by 19.41%, which was higher than that achieved with other enzymes. More specially, the conversion of slowly digestible starch to RS, which was only demonstrated in chemical modification, was accomplished. The fine structure of the modified starch was further investigated. Results showed that the number of short chains (DP < 13) increased to 90.58%, and the α-1,6 linkages ratio increased from 7.19% to 15.64%. The increase of short chains and α-1,6 linkages may contribute to high RS content. This study can provide a reference for the development of modified starch with lower digestibility.

Biofabrication, structure and characterization of an amylopectin-based cyclic glucan

A novel amylopectin-based cyclic architecture was fabricated, arising from microbial branching enzyme treated waxy rice starch. The recombinant enzyme had a molecular weight of 72.0 kDa, and exhibited optimum activity at pH 7.0 and 75 °C. During the cyclization reaction catalyzed by a branching enzyme, the molecular weight of amylopectin rapidly decreased for the initial 2 h, and then very slowly decreased, tapering off at approximately 1.8 × 105 g mol-1 at 12 h. The number of A-chain fractions greatly increased, whereas the percentage of B-chain fractions decreased after enzymatic modification, accompanied by more α-1, 6 linkage formation. The core ring structure as a glucoamylase-resistant fraction had a number-average degree of polymerization of 21, which was constructed by 19 glucose units linked with, 2 glucosyl stubs at the O-6-position of the cyclic glucan through α-1,4 and α-1,6 linkages. Similar to large-ring cyclodextrin with equal glucose units, this cyclic glucan had a cavity geometry with two-circular loops and short stubs in perpendicular planes. Moreover, this cyclic glucan could complex with iodine for the host-guest formation. These results revealed the potential application of the amylopectin-based cyclic glucan as a good delivery system to encapsulate and protect bioactive ingredients.

Reducing the glycemic impact of carbohydrates on foods and meals: Strategies for the food industry and consumers with special focus on Asia

Type 2 diabetes is increasingly prevalent in Asia, which can be attributed to a carbohydrate-rich diet, consisting of foods in the form of grains, for example, rice, or a food product made from flours or isolated starch, for example, noodles. Carbohydrates become a health issue when they are digested and absorbed rapidly (high glycemic index), and more so when they are consumed in large quantities (high glycemic load). The principal strategies of glycemic control should thus aim to reduce the amount of carbohydrate available for digestion, reduce the rate of digestion of the food, reduce the rate of glucose absorption, and increase the rate of glucose removal from blood. From a food perspective, the composition and structure of the food can be modified to reduce the amount of carbohydrates or alter starch digestibility and glucose absorption rates via using different food ingredients and processing methods. From a human perspective, eating behavior and food choices surrounding a meal can also affect glycemic response. This review therefore identifies actionable strategies and opportunities across foods and meals that can be considered by food manufacturers or consumers. They are (a) using alternative ingredients, (b) adding functional ingredients, and (c) changing processing methods and parameters for foods, and optimizing (a) eating behavior, (b) preloading or co-ingestion of other macronutrients, and (c) meal sequence and history. The effectiveness of a strategy would depend on consumer acceptance, compatibility of the strategy with an existing food product, and whether it is economically or technologically feasible. A combination of two or more strategies is recommended for greater effectiveness and flexibility.

The preparation, formation, fermentability, and applications of resistant starch

Resistant starch (RS) cannot be digested in the small intestine but can be fermented by microflora in the colon. To meet the demand for RS, effective methods and advanced equipment for preparing RS have emerged, but further development is needed. RS contents are affected by different prepared methods, starch source and certain nutrients such as protein, phenols, and hydrocolloids interacted with RS. As a beneficial fermentation substrate, RS modifies and stabilizes the intestinal flora to balance the intestinal environment and improve intestinal tract health and function. RS is also a kind of ingredient with potential physiological function, even better than that dietary fiber, but also in terms of providing various health benefits. RS has good food-processing characteristics as well and can thus be widely used in the food industry.

Efficient production of aggregation prone 4-α-glucanotransferase by combined use of molecular chaperones and chemical chaperones in Escherichia coli

In this study, a combined optimization strategy, based on co-expression of molecular chaperones and supplementation of osmolytes, was used to reduce the formation of inclusion bodies and enhance the expression of the soluble form of 4-α-glucanotransferase. The 4-α-glucanotransferase yield was enhanced by co-expression with pGro7 and supplementation of trimetlylamine oxide. Subsequently, the effects of process conditions (temperature, inducer concentration, and arabinose concentration) on cell growth and 4-α-glucanotransferase production were also investigated in shake flasks. In addition, a modified high-cell-density fermentation approach was proposed and applied in 3-L fermentor supplied with l-arabinose and trimetlylamine oxide, which achieved a dry cell weight of 65.92 g·L^-1. Through this cultivation approach at 28 °C, the activity of 4-α-glucanotransferase reached 332.5 U·g^-1 dry cell weight, which was 24.6-fold greater than the initial activity in shake flask cultivation. This combined strategy is expected to provide an efficient and economical approach to overproduction of aggregation prone proteins on a large scale.

Transglycosylation Properties of a Novel α-1,4-Glucanotransferase from Bacteroides thetaiotaomicron and Its Application in Developing an α-Glucosidase-Specific Inhibitor

In this study, α-glucanotransferase from Bacteroides thetaiotaomicron was expressed in Escherichia coli and characterized. Conserved amino-acid sequence alignment showed that Bacteroides thetaiotaomicron α-glucanotransferase (BtαGTase) belongs to the glycoside hydrolase family 77. The enzyme exhibited optimal catalytic activity at 60°C and pH 3.0. BtαGTase catalyzed transglycosylation reactions that produced only glycosyl or maltosyl transfer products, which are preferable for the generation of transglycosylated products with high yield. The 1-deoxynojirimycin (DNJ) glycosylation product G1-DNJ was generated using BtαGTase, and the inhibitory effect of G1-DNJ was analyzed. A kinetic study of inhibition revealed that G1-DNJ inhibited α-glucosidase to a greater extent than did DNJ but did not show any inhibitory effects towards α-amylase, suggesting that G1-DNJ is a potential candidate for the prevention of diabetes.

Synthesis of novel α-glucans with potential health benefits through controlled glucose release in the human gastrointestinal tract

The glycemic carbohydrates we consume are currently viewed in an unfavorable light in both the consumer and medical research worlds. In significant part, these carbohydrates, mainly starch and sucrose, are looked upon negatively due to their rapid and abrupt glucose delivery to the body which causes a high glycemic response. However, dietary carbohydrates which are digested and release glucose in a slow manner are recognized as providing health benefits. Slow digestion of glycemic carbohydrates can be caused by several factors, including food matrix effect which impedes α-amylase access to substrate, or partial inhibition by plant secondary metabolites such as phenolic compounds. Differences in digestion rate of these carbohydrates may also be due to their specific structures (e.g. variations in degree of branching and/or glycosidic linkages present). In recent years, much has been learned about the synthesis and digestion kinetics of novel α-glucans (i.e. small oligosaccharides or larger polysaccharides based on glucose units linked in different positions by α-bonds). It is the synthesis and digestion of such structures that is the subject of this review.