Partial branching enzyme treatment increases the low glycaemic property and α-1,6 branching ratio of maize starch

A study focusing on the distinct fine structure of starch in mealy and waxy potatoes

In this research, we examined the fine structure of starch in three mealy and three waxy potato varieties to understand their impact on potato texture. This research revealed significant variations in starch granule morphology, particle size, crystalline structure, molecular structure, and pasting properties between the different textures. Mealy potato starch granules appeared as rounded ovoid with inconsistent particle sizes (ranging from 35.9 to 41.8 μm), whereas waxy potato starch granules exhibited sharp polygonal shapes with consistent larger sizes (42.1-49.7 μm). While both types displayed a B-type crystalline morphology, the relative crystallinity of mealy potato starch (31.28%, 38.00% and 29.07%) is higher than that of waxy potato starch (27.38% 26.68% and 26.12%) as determined by X-ray diffraction. Additionally, the mealy potato starches had lower amylopectin content, degree of branching, short-chain amylopectin content, and molecular weight, but higher trough viscosity, final viscosity, and setback value than waxy potato starches. These differences in fine structure contributed significantly to the variations in texture between mealy and waxy potato starches, highlighting potential implications for breeding programs aimed at improving specific textural attributes for targeted application in the food industry.

Tailoring banana starch characteristics through combined preheating and branching enzyme approaches

Digestibility of starch, a notable raw bioresource, is affected by its granular form, structure, and processing conditions. This study aimed to investigate the effect of pre-heating temperatures (60-85 °C) and subsequent branching enzyme (BE) modification on green banana starch to modify its structural and functional properties. Pre-heating at 60-65 °C maintained granular integrity while enabling BE to increase α-1,6 linkages (5.2-8.4 %). At 70 °C, partial gelatinization facilitated greater BE access, resulting in amylose reduction (3.2 %) and maximum branch formation (10.4 %). Complete gelatinization at 75-85 °C eliminated Maltese crosses and maximized BE accessibility, producing amorphous structures with negligible amylose content (< 1.1 %). Both solubility and gel transmittance increased progressively with higher pre-heating temperatures, with completely gelatinized samples exhibiting the highest values. Chain-length distribution analysis revealed an increase in short chains (DP 6-12) with a concurrent decrease in longer chains across all the modified samples. In-vitro digestibility results demonstrated that BE-modified starches exhibited substantially increased slowly digestible and resistant starch content after cooking, particularly at higher temperatures. This approach offers a versatile strategy for producing banana starch ingredients with tailored structural, functional, and nutritional properties.

Effect of Modification by β-Amylase and α-Glucosidase on the Structural and Physicochemical Properties of Maize Starch

Single enzymatic modifications are limited to starch. Complex modification with synergistic amylases will improve starch properties more significantly. In this study, maize starch was compound modified by β-amylase and α-glucosidase. The structure and physicochemical properties of the corn starch were determined by scanning electron microscopy (SEM), X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance hydrogen spectroscopy (1HNMR), high-performance anion-exchange chromatography (HPAEC-PAD), differential scanning calorimetry (DSC) and Rapid Visco analyzer (RVA) to determine the changes in the structure and physicochemical properties of maize starch before and after the dual enzyme modification. The branching degree (4.95-7.10%) of maize starch was increased after bi-enzymatic modification, the amylose content (28.77-18.60%) was decreased, and the amylopectin content (70.79-81.71%) was elevated. The relative crystallinity (20.41-30.20%) and short-range ordered structure of the starch increased, and the dual enzyme modification led to a more compact structure. Dual enzyme-modified maize starch showed a decrease in long chains, an increase in short chains, and its degree of branching was elevated. Dual enzyme modification also affected the thermal stability, pasting, light transmittance (1.40-2.16%), solubility (20.15-13.76%), and swelling (33.97-45.79%) of maize starch. It can be concluded that the complex modification of maize starch by β-amylase and α-glucosidase significantly changed the amylose/amylopectin ratio of the starch and made its structure denser. These results can provide a theoretical basis for the enzymatic preparation of maize starch with different amylose/amylopectin ratios and the development and utilization of functional starches.

Effects of color protection and enzymatic hydrolysis on the microstructure, digestibility, solubility and swelling degree of chestnut flour

Chestnuts, despite their nutritional value, pose challenges in starch processing, digestion, and absorption. This study employed various color-fixing formulations and processing methods to simulate the in vitro digestion of both untreated and enzymatically hydrolyzed chestnut flour. Changes in starch properties, digestion characteristics, and estimated glycemic index (eGI) were analyzed to understand how enzymatic hydrolysis affects chestnut flour properties. The results showed that the browning of chestnut flour was the least when the mass ratio of vitamin C, citric acid, and EDTA-Na2 was 9:1:0.3. Following treatment with pullulanase and glucoamylase, the content of rapidly digestible starch decreased to 10 %, while the content of slowly digestible starch and resistant starch increased to 62 % and 27 %, respectively. The eGI value of chestnut flour after enzymatic hydrolysis increased to 61.85-65.14, the hydrolysis rate was 78.37 %-89.20 %, the water holding capacity was 5.3-8.6, the solubility was 51.33 %-58.33 %, and the swelling degree decreased to 2.21-3.33 mL/g.

Elucidation of the noncovalent interactions driving enzyme activity guides branching enzyme engineering for α-glucan modification

Branching enzymes (BEs) confer to α-glucans, the primary energy-storage reservoir in nature, a variety of features, like slow digestion. The full catalytic cycle of BEs can be divided in six steps, namely two covalent catalytic steps involving glycosylation and transglycosylation, and four noncatalytic steps involving substrate binding and transfers (SBTs). Despite the ever-growing wealth of biochemical and structural information on BEs, clear mechanistic insights into SBTs from an industrial-performance perspective are still missing. Here, we report a Rhodothermus profundi BE (RpBE) endowed with twice as much enzymatic activity as the Rhodothermus obamensis BE currently used in industry. Furthermore, we focus on the SBTs for RpBE by means of large-scale computations supported by experiment. Engineering of the crucial positions responsible for the initial substrate-binding step improves enzymatic activity significantly, while offering a possibility to customize product types. In addition, we show that the high-efficiency substrate-transfer steps preceding glycosylation and transglycosylation are the main reason for the remarkable enzymatic activity of RpBE, suggestive of engineering directions for the BE family.

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.

Improving the thermal stability and branching efficiency of Pyrococcus horikoshii OT3 glycogen branching enzyme

In practical applications, the gelatinisation temperature of starch is high. Most current glycogen branching enzymes (GBEs, EC 2.4.1.18) exhibit optimum activity at moderate or low temperatures and quickly lose their activity at higher temperatures, limiting the application of GBEs in starch modification. Therefore, we used the PROSS strategy combined with PDBePISA analysis of the dimer interface to further improve the heat resistance of hyperthermophilic bacteria Pyrococcus horikoshii OT3 GBE. The results showed that the melting temperature of mutant T508K increased by 3.1 °C compared to wild-type (WT), and the optimum reaction temperature increased by 10 °C for all mutants except V140I. WT almost completely lost its activity after incubation at 95 °C for 60 h, while all of the combined mutants maintained >40 % of their residual activity. Further, the content of the α-1,6 glycosidic bond of corn starch modified by H415W and V140I/H415W was approximately 2.68-fold and 1.92-fold higher than that of unmodified corn starch and corn starch modified by WT, respectively. Additionally, the glucan chains of DP < 13 were significantly increased in mutant modified corn starch. This method has potential for improving the thermal stability of GBE, which can be applied in starch branching in the food industry.

Designing a Specific Pretreatment on Corn Starch to Facilitate Enzymatic Rearrangement of Glycosidic Bonds for Efficiently Reducing Starch Digestibility

Bacterial 1,4-α-glucan branching enzymes (GBEs) provide a viable strategy for glycosidic bond rearrangement in starch and regulation of its digestion rate. However, the exponential increase in paste viscosity during starch gelatinization has a detrimental effect on the catalytic action of GBEs, thereby limiting productivity and product performance. Here, we designed an enzymatic treatment on corn starch granules by the GBE from Rhodothermus obamensis STB05 (Ro-GBE) prior to the glycosidic bond rearrangement of gelatinized starch catalyzed using the GBE from Geobacillus thermoglucosidans STB02 (Gt-GBE). Specifically, a moderate amount of Ro-GBE was required for the pretreatment stage. The dual GBE modification process enabled the treatment of more concentrated starch slurry (up to 20%, w/w) and effectively reduced starch digestibility. The resulting product contained a rapidly digestible starch fraction of 66.0%, which was 11.4% lower than that observed in the single Gt-GBE-modified product. The mechanistic investigation showed that the Ro-GBE treatment promoted swelling and gelatinization of starch granules, reduced starch paste viscosity, and increased the mobility of water molecules in the starch paste. It also created a preferable substrate for Gt-GBE. These changes improved the transglycosylation efficiency of Gt-GBE. These findings provide useful guidance for designing an efficient process to regulate starch digestibility.

Production of highly branched α-limit dextrins with enhanced slow digestibility by various glycogen-branching enzymes

α-Limit dextrins (α-LDx) are slowly digestible carbohydrates that attenuate postprandial glycemic response and trigger the secretion of satiety-related hormones. In this study, more highly branched α-LDx were enzymatically synthesized to enhance the slowly digestible property by various origins of glycogen branching enzyme (GBE), which catalyzes the transglycosylation to form α-1,6 branching points after cleaving α-1,4 linkages. Results showed that the proportion of branched α-LDx in starch molecules increased around 2.2-8.1 % compared to α-LDx from starch without GBE treatment as the ratio of α-1,6 linkages increased after different types of GBE treatments. Furthermore, the enzymatic increment of branching points enhanced the slowly digestible properties of α-LDx at the mammalian α-glucosidase level by 17.3-28.5 %, although the rates of glucose generation were different depending on the source of GBE treatment. Thus, the highly branched α-LDx with a higher amount of α-1,6 linkages and a higher molecular weight can be applied as a functional ingredient to deliver glucose throughout the entire small intestine without a glycemic spike which has the potential to control metabolic diseases such as obesity and type 2 diabetes.

Biosynthesis of maltodextrin-derived glucan dendrimer using microbial branching enzyme

Glucan dendrimers were developed with microbial branching enzyme (BE) treated maltodextrin. The molecular weight (M_w) of recombinant BE was 79.0 kDa, and its optimum activity was observed at pH 7.0 and 70 °C. BE converted different maltodextrins with dextrose equivalent value of 6 (MD6), 12 (MD12), or 19 (MD19) into the given glucan dendrimers, along with the marked increment of the molecular density (approximately 30-60 folds) and α-1,6 linkage percentage (up to 7.3-9.7%). Among three glucan dendrimers, the enzyme-treated MD12 showed a more homogeneous M_w distribution with the maximum M_w of 5.5 × 10⁶ g/mol, indicating that higher substrate catalytic specificity of BE for MD12 substrate. During transglycosylation with MD12 for 24 h, the shorter chains (degree of polymerization, DP < 13) increased from 73.9% to 83.0%, accompanying by a reduction of medium chains (DP13-24) and long chains (DP > 24). Moreover, the slowly digestible and resistant nutritional fractions were increased by 6.2% and 12.5%, respectively. The results suggested that the potentiality of BE structuring glucan dendrimer with tailor-made structure and functionality for industrial application.

Biomimetic synthesis of maltodextrin-derived dendritic nanoparticle and its structural characterizations

The maltodextrin-derived dendritic nanoparticle was fabricated using microbial branching enzyme and its structural characterizations were investigated. During biomimetic synthesis, molecular weight distribution of maltodextrin substrate with 6.8 × 10⁴ g/mol shifted to the narrower and uniform distribution region with the larger molecular weight up to 6.3 × 10⁶ g/mol (MD12). The enzyme-catalyzed product had the larger size, higher molecular density as well as higher percentage of α-1,6 linkage, accompanying by more chain accumulations of DP 6-12 and disappearance of DP > 24, suggesting the biosynthesized glucan dendrimer had a compact tighter branched structure. The interaction of molecular rotor CCVJ and local structure of dendrimer was monitored, displaying there was a higher intensity related with the numerous nano-pockets at the branch points of MD12. The maltodextrin-derived dendrimers had the single spherical particulate shape with the size range of 10-90 nm. The mathematical models were also established to reveal the chain structuring during enzymatic reaction. The above results showed that the biomimetic strategy for novel dendritic nanoparticle with controllable structure arising from branching enzyme treated maltodextrin, which would help to enlarge the panel of available dendrimer.

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.

Optimization of Corn Resistant Starch Preparation by Dual Enzymatic Modification Using Response Surface Methodology and Its Physicochemical Characterization

Corn starch was dually modified using thermostable α-amylase and pullulanase to prepare resistant starch (RS). The concentration of starch liquid, the amount of added thermostable α-amylase, the duration of enzymatic hydrolysis and the amount of added pullulanase were optimized using RSM to increase RS content of the treated sample. The optimum pretreatment conditions were 15% starch liquid, 3 U/g thermostable α-amylase, 35 min of enzymatic hydrolysis and 8 U/g pullulanase. The maximum RS content of 10.75% was obtained, and this value was significantly higher than that of native corn starch. The degree of polymerization (DP) of the enzyme-modified starch decreased compared with that of native starch. The scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) were performed to assess structural changes in native and pretreated starch. The effect of dual enzyme pretreatment on the structure and properties of corn starch was significant. Unlike the untreated one, the pretreated corn starch showed clear pores and cracks. Significant differences in RS contents and structural characterization between starch pretreated and untreated with dual enzymes demonstrated that the dual enzyme modification of corn was effective in enhancing RS contents.

The impact of gliadin and glutenin on the formation and structure of starch-lipid complexes

This study evaluated the influence of the main gluten fractions (gliadin and glutenin) on the physicochemical properties of binary wheat starch-Lauric acid (WS-LA) complexes during heat processing to explore the complex structure and digestion of WS-LA in the presence of gluten. Ternary WS-LA-glutenin complexes were prepared at different pH (5.2 and 7), whereas WS-LA-gliadin was prepared using ethanol, and their physicochemical properties were analyzed. We found that the addition of glutenin displayed a sharper and higher diffraction peak than samples without protein, which increased short-range order structure (low full width at half-maximum (FWHM) of the band at 480 cm^-1) and good thermal stability (melting peak appeared at a higher temperature); the opposite was shown for gliadin. Even though glutenin increased the resistant starch (RS) content than WS-LA, all samples prepared in 65% ethanol showed higher RS content than WS-LA-glutenin samples. These findings might improve our understanding of the relationship between gliadin/glutenin and binary complexes and provide a theoretical basis for preparing starch-based foods with a low glycemic index.

Effect of highly branched α-glucans synthesized by dual glycosyltransferases on the glucose release rate

Increasing α-1,6 linkages in starch molecules generates a large amount of α-limit dextrins (α-LDx) during α-amylolysis, which decelerate the release of glucose at the intestinal α-glucosidase level. This study synthesized highly branched α-glucans from sucrose using Neisseria polysaccharea amylosucrase and Rhodothermus obamensis glycogen branching enzyme to enhance those of slowly digestible property. The synthesized α-glucans (Mw: 1.7-4.9 × 10⁷ g mol^-1) were mainly composed of α-1,4 linkages and large proportions of α-1,6 linkages (7.5%-9.9%). After treating the enzymatically synthesized α-glucans with the human α-amylase, the quantity of branched α-LDx (36.2%-46.7%) observed was higher than that for amylopectin (26.8%) and oyster glycogen (29.1%). When the synthetic α-glucans were hydrolyzed by mammalin α-glucosidases, the glucose generation rate decreased because the amount of embedded branched α-LDx increased. Therefore, the macro-sized branched α-glucans with high α-LDx has the potential to be used as slowly digestible material to attenuate postprandial glycemic response.

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.

Structural and digestion properties of potato starch modified using an efficient starch branching enzyme AqGBE

Modified potato starch with slower digestion may aid the development of new starch derivatives with improved nutritional values, and strategies to increase nutritional fractions such as resistant starch (RS) are desired. In this study, a correspondence between starch structure and enzymatic resistance was provided based on the efficient branching enzyme AqGBE, and modified starches with different amylose content (Control, 100%; PS1, 90%; PS2, 72%; PS3, 32%; PS4, 18%) were prepared. Through SEM observation, NMR and X-ray diffraction analyses, we identified that an increased proportion of α-1,6-linked branches in potato starch changes its state of granule into large pieces with crystallinity. Molecular weight and chain-length distribution analysis showed a decrease of molecular weight (from 1.1 × 10⁶ to 1.1 × 10⁵ g/mol) without an obvious change of chain-length distribution in PS1, while PS2-4 exhibited an increased proportion of DP 6-12 with a stable molecular weight distribution, indicating a distinct model of structural modification by AqGBE. The enhancement of peak viscosity was related to increased hydrophobic interactions and pieces state of PS1, while the contents of SDS and RS in PS1 increased by 37.7 and 49.4%, respectively. Our result provides an alternative way to increase the RS content of potato starch by branching modification.

Two 1,4-α-glucan branching enzymes successively rearrange glycosidic bonds: A novel synergistic approach for reducing starch digestibility

Enzymatically rearranging α-1,4 and α-1,6 glycosidic bonds in starch is a green approach to regulating its digestibility. A two-step modification process successively catalyzed by 1,4-α-glucan branching enzymes (GBEs) from Rhodothermus obamensi STB05 (Ro-GBE) and Geobacillus thermoglucosidans STB02 (Gt-GBE) was investigated as a strategy to reduce the digestibility of corn starch. This dual GBE modification process caused a reduction of 25.8 % in rapidly digestible starch fraction in corn starch, which were more effective than single GBE-catalyzed modification with the same duration. Structural analysis indicated that the dual GBE modified product contained higher branching density, more abundant short branches, and shorter external chains than those in single GBE-modified product. These results demonstrated that a moderate Ro-GBE treatment prior to starch gelatinization caused several suitable alterations in starch molecules, which promoted the transglycosylation efficiency of the following Gt-GBE treatment. This dual GBE-catalyzed modification process offered an efficient strategy for regulating starch digestibility.

Long chains and crystallinity govern the enzymatic degradability of gelatinized starches from conventional and new sources

Slowly digestible starches have received interest due to their lower increase of postprandial blood glucose and insulin levels and, hence, modification of starches towards slower digestibility has commercial interest. However, chemical characteristics driving enzymatic (digestive) degradation are not fully unraveled. The digestion properties of starches have been linked to their crystalline type, chain length distribution, amylose content or degree of branching, but content and length of relatively long side-chains in amylopectin has not been paid attention to. Therefore, this research focusses on the unique content and length of amylopectin side-chains from conventional and new starch sources (potato, corn, pea, and tulip) correlated to the enzymatic digestion. The rate of hydrolysis was found to be correlated with the crystalline type of starch, as previously suggested, however, the complete hydrolysis of all starches, independent of the crystalline type and source, was shown to be governed by the content of longer amylopectin chains.

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.

Rheological and technological characterization of red rice modified starch and jaboticaba peel powder mixtures

Properties of modified starch and its interaction with functional raw materials are of great interest to the food industry. Thus, this study aimed to evaluate the rheological and technological characterization of starches modified by the action of the enzymes α-amylase and amyloglucosidase and their mixtures with jaboticaba peel powder. The parameters of firmness, gumminess, and final viscosity of starches paste increased, and the tendency to setback was reduced with the addition of jaboticaba peel powder. Starches and mixtures presented shear-thinning behavior. The addition of jaboticaba peel powder to starches increased water, oil, and milk absorption capacity, while syneresis remained stable over the storage period. The addition of jaboticaba peel powder had a positive effect on native and modified starches' rheological and technological properties, qualifying it as an alternative for developing new functional food products.

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.

Comparison of the Structural Properties and Nutritional Fraction of Corn Starch Treated with Thermophilic GH13 and GH57 α-Glucan Branching Enzymes

Two thermophilic 1,4-α-glucan branching enzymes (GBEs), CbGBE from Caldicellulosiruptor bescii and PhGBE from Pyrococcus horikoshii, which belong to the glycoside hydrolase family 13 and 57 respectively, were cloned and expressed in Escherichia coli. Two GBEs were identified to have α-1,6 branching activity against various substrates, but substrate specificity was distinct. Starch was modified by two GBEs and their in vitro digestibility and structural properties were investigated. Short-branched A chains with a degree of polymerization (DP) of 6–12 increased with CbGBE-modified starch, increasing the proportion of slow digestible and resistant starch (RS) fractions. PhGBE-modified starch resulted in an increase in the RS fraction only by a slight increase in part of A chains (DP, 6–9). Compared to the proportion of control not treated with GBE, the proportion of α-1,6 linkages in CbGBE- and PhGBE-modified starch increased by 3.1 and 1.6 times. ¹³C cross polarization/magic angle sample spinning (CP/MAS) NMR and XRD pattern analysis described that GBE-modified starches reconstructed double helices but not the crystalline structure. Taken together, CbGBE and PhGBE showed distinct branching activities, resulting in different α-1,6 branching ratios and chain length distribution, and double helices amount of starch, ultimately affecting starch digestibility. Therefore, these GBEs can be used to produce customized starches with controlled digestion rates.

Physicochemical Properties of Starches in Proso (Non-Waxy and Waxy) and Foxtail Millets (Non-Waxy and Waxy)

Proso and foxtail millets are widely cultivated due to their excellent resistance to biotic and abiotic stresses and high nutritional value. Starch is the most important component of millet kernels. Starches with different amylose contents have different physicochemical properties. In this study, starches in proso (non-waxy and waxy) and foxtail millets (non-waxy and waxy) were isolated and investigated. All the starch granules had regular polygonal round shapes and exhibited typical “Maltese crosses”. These four starches all showed bimodal size distribution. The waxy proso and foxtail millets had higher weight-average molar mass and branching degree and lower average chain length of amylopectin. These four starches all presented A-type crystallinity; however, the relative crystallinity of waxy proso and foxtail millets was higher. The two waxy millets had higher onset temperature, peak temperature, conclusion temperature, and gelatinization enthalpy. However, the two non-waxy millets had higher setback viscosity, peak time, and pasting temperature. The significantly different physicochemical properties of waxy and non-waxy millet starches resulted in their different functional properties.

Met349 Mutations Enhance the Activity of 1,4-α-Glucan Branching Enzyme from Geobacillus thermoglucosidans STB02

1,4-α-Glucan branching enzyme (GBE, EC 2.4.1.18) is used to increase the number of α-1,6 branch points in starch and glycogen. On the basis of a multiple sequence alignment of the GBEs from a variety of bacteria, residue 349 (Geobacillus thermoglucosidans STB02 numbering) in region III is generally methionine in bacteria with higher identity, while it is threonine or serine in bacteria with lower identity. Four mutants (M349T, M349S, M349H, and M349Y) were constructed by site-directed mutagenesis and characterized. M349T and M349S showed 24.5% and 21.1% increases in specific activity compared with that of wild-type GBE, respectively. In addition, M349T and M349S displayed 24.2% and 17.6% enhancements in the α-1,6-glycosidic linkage ratio of potato starch samples, respectively. However, M349Y displayed a significant reduction in activity. Moreover, the mutations at M349 have a negligible effect on substrate specificity. Thus, M349T and M349S are more suitable for industrial applications than wild-type GBE.