Enzymatic synthesis and properties of highly branched rice starch amylose and amylopectin cluster

Stabilization mechanism of white kidney bean based milk through novel perspectives of endogenous starch

Plant-based milk (PBM) substitutes have attracted worldwide attention, but the development is restricted by poor stability and limited categories. White kidney bean (WKB) is one potential healthy material for PBM production. Here, we aimed to obtain optimal WKB cultivars first, and further investigated stabilization mechanism in aspect of its endogenous starch. Among the investigated cultivars, three cultivars were selected as the most suitable for producing WKB emulsions. Native starch of the stable cultivars exhibited higher pasting temperature, less peak, trough, and final viscosity. With enzymatic hydrolysis, starch of stable cultivars showed higher solubility index while less swelling power, and less short range order. The observations were further proved through microscopy observation and correlation analysis between starch properties and WKB milk stability attributes. These results contribute to understand molecular mechanism for improving WKB milk stability from perspective of endogenous starch, and provide valuable information for raw materials selection with typical starch characteristics.

Insight to starch retrogradation through fine structure models: A review

The retrogradation of starch is crucial for the texture and nutritional value of starchy foods products. There is mounting evidence highlighting the significant impact of starch's fine structures on starch retrogradation. Because of the complexity of starch fine structure, it is a formidable challenge to study the structure-property relationship of starch retrogradation. Several models have been proposed over the years to facilitate understanding of starch structure. In this review, from the perspective of starch models, the intricate structure-property relationship is sorted into the correlation between different types of structural parameters and starch retrogradation performance. Amylopectin B chains with DP 24-36 and DP ≥36 exhibit a higher tendency to form ordered crystalline structures, which promotes starch retrogradation. The chains with DP 6-12 mainly inhibit starch retrogradation. Based on the building block backbone model, a longer inter-block chain length (IB-CL) enhances the realignment and reordering of starch. The mathematical parameterization model reveals a positive correlation between amylopectin medium chains, amylose short chains, and amylose long chains with starch retrogradation. The review is structured according to starch models; this contributes to a clear and comprehensive elucidation of the structure-property relationship, thereby providing valuable references for the selection and utilization of starch.

Enzymatic Modification of Starch Using Recombinant Genes from Sorghum in Escherichia coli: Insights and Potential Applications

SBEIIb (Sobic.004G163700), SSSIIa (Sobic.010G093400), and GBSSI (Sobic.010G022600) genes that regulate starch synthesis in sorghum endosperm were transferred into Escherichia coli by transgenic technology. SBEIIb, SSSIIa, and GBSSI enzymes were separated and purified through a Ni column and analyzed by electrophoresis with molecular weights and activities of 91.57 84.57, and 66.89 kDa and 551 and 700 and 587 U/μL, respectively. Furthermore, they were applied to starch modification, yielding interesting findings: the A chain content increased from 25.79 to 89.55% for SBEIIb-treated waxy starch, while SSSIIa extended the A chain to form DPs of the B chain, with A chain content decreasing from 89.55 to 37.01%, whereas GBSSI was explicitly involved in the synthesis of B1 chain, with its content increasing from 9.59 to 48.45%. Modified starch was obtained, which could be accurately applied in various industries. For instance, we prepared a sample (containing 89.6% A chain content) with excellent antiaging and antidigestion properties through SBEIIb modification. Moreover, higher RS3 (34.25%) and SDS contents (15.75%) of starch were obtained through the joint modification of SBEIIb and SSSIIa. These findings provide valuable insights for developing sorghum starch synthesis-related enzymes and offer opportunities for improving starch properties through enzymatic approaches.

Mechanism of action of three different glycogen branching enzymes and their effect on bread quality

Bread staling adversely affects the quality of bread, but starch modification by enzymes can counteract this phenomenon. Glycogen branching enzymes (GBEs) used in this study were isolated from Deinococcus geothermalis (DgGBE), Escherichia coli (EcGBE), and Vibrio vulnificus (VvGBE). These enzymes were characterized and applied for starch dough modification to determine their role in improving bread quality. First, the branching patterns, activity on amylose and amylopectin, and thermostability of the GBEs were determined and compared. EcGBE and DgGBE exhibited better thermostable characteristics than VvGBE, and all GBEs exhibited preferential catalysis of amylopectin over amylose but different degrees. VvGBE and DgGBE produced a large number of short branches. Three GBEs degraded the starch granules and generated soluble polysaccharides. Moreover, the maltose was increased in the starch slurry but most significantly in the DgGBE treatment. Degradation of the starch granules by GBEs enhanced the maltose generation of internal amylases. When used in the bread-making process, DgGBE and VvGBE increased the dough and bread volume by 9 % and 17 %, respectively. The crumb firmness and retrogradation of the bread were decreased and delayed significantly more in the DgGBE bread. Consequently, this study can contribute to understanding the detailed roles of GBEs in the baking process.

Development and applications of enzymatic modified starch with high water solubility providing a continuous supply of glucose

Amylopectin clusters (APCs) are produced by cyclodextrin glucanotransferase (EC 2.4.1.19). Their solubility rate in aqueous solution was found to be 16.7 %. The weight-average molecular weight of APCs is ∼105 Da, as determined by multiangle laser light scattering analysis. Side chain length analysis indicated that the relative proportions of side chains with a degree of polymerization in the ranges of 2-8 and 25-50 decreased and increased, respectively, during preparation of APCs. In the exercise experiment, the blood glucose level of rats was higher in the APC-treated group than in the groups treated with commercial carbohydrate supplement (CCD) and glucose. In the forced swimming test, the swimming time in the APC and CCD groups increased by 22.6 % and 31.1 %, respectively, compared with the glucose administration group. The insulin levels were also similar between the APC and CCD groups. However, the glycogen levels in the liver and muscles of mice were significantly higher in the APC group than control group. These results suggest that APCs could potentially enhance endurance when added to sports drinks.

Deciphering the structural and functional characteristics of an innovative small cluster branched α-glucan produced by sequential enzymatic synthesis

Highly branched α-glucan (HBAG) proved to be a promising material as an osmotic agent in peritoneal dialysis solutions. However, high resistance of HBAG to amylolytic enzymes might be a potential drawback for peritoneal dialysis due to its high degree of branching (20-30 %). To address this issue, we designed a small-clustered α-glucan (SCAG) with a relatively low molecular weight (Mw) and limited branching. Structural characteristics revealed that SCAG was successfully synthesized by modifying waxy rice starch (WRS) using sequential maltogenic α-amylase (MA) and starch branching enzyme (BE). The Mw of SCAG was 1.40 × 10⁵ Da, and its (α1 → 6) bonds ratio was 8.93 %, which was below that of HBAG. A relatively short branch distribution was observed in SCAG (CL = 6.27). Short-range orderliness of WRS was reduced from 0.749 to 0.322 with the MABE incubation. Additionally, SCAG had an extremely low viscosity (~12 cP) and nearly no retrogradation. Although the resistance of SCAG to amylolytic enzymes was enhanced by 15.22 % compared with native WRS, the extent was significantly lower than that of HBAG in previous studies. These new findings demonstrate the potential of SCAG as a novel functional α-glucan in food and pharmaceutical applications.

Structural characterization of potato starch modified by a 4,6-α-glucanotransferase B from Lactobacillus reuteri E81

The recent reports have revealed that increase in amount of α-1,6 linkages by modification of potato starch with enzyme (glycosyltransferases) treatment gains slowly digestible properties to the starch; however, the formation of new α-1,6-glycosidic linkages diminish the thermal resistance of the starch granules. In this study, a putative GtfB-E81, (a 4,6-α-glucanotransferase-4,6-αGT) from L. reuteri E81 was firstly used to produce a short length of α-1,6 linkages. NMR results revealed that external short chains mostly comprised of 1-6 glucosyl units were newly produced in potato starch, and the α-1,6 linkage ratio was significantly increased from 2.9 % to 36.8 %, suggesting that this novel GtfB-E81 might have potentially an efficient transferase activity. In our study, native and GtfB-E81 modified starches showed fundamental similarities with respect to their molecular properties and treatment of native potato starch with GtfB-E81 did not remarkably change thermal stability of the potato starch, which seems to be very prominent for the food industry given the significantly decreased thermal stability results obtained for the enzyme modified starches reported in the literature. Therefore, the results of this study should open up emerging perspectives for regulating slowly digestible characteristics of potato starch in future studies without a significant change in the molecular, thermal, and crystallographic properties.

Starch Chemical Composition and Molecular Structure in Relation to Physicochemical Characteristics and Resistant Starch Content of Four Thai Commercial Rice Cultivars Differing in Pasting Properties

Variations in starch pasting properties, considered an alternative potential quality classification parameter for rice starches, are directly controlled by the diverse starch molecular composition and structural features. Here, the starch characteristics of four rice cultivars (i.e., RD57, RD29, KDML105, and RD6) differing in pasting properties were assessed, and their relationship was determined. The results revealed that protein and moisture contents and their crystalline type were similar among the four rice starches. However, their molecular compositions and structures (i.e., reducing sugar and amylose contents, amylopectin branch chain-length distributions, granule size and size distribution, and degree of crystallinity) significantly varied among different genotypes, which resulted in distinct swelling, solubility, gelatinization, retrogradation, and hydrolytic resistance properties. The swelling power and gelatinization enthalpy (∆H) were positively correlated with C-type granule and relative crystallinity, but were negatively correlated with amylose content, B-type granule and median particle size (d(0.5)). Conversely, the water solubility and resistant starch content negatively correlated with C-type granule, but positively correlated with amylose content, B-type granule, and d(0.5). The gelatinization onset temperature (To(g)), and retrogradation concluding temperatures (Tc(r)), enthalpy (∆H(r)), and percentage (R%) were positively impacted by the amount of protein, amylose, and B1 chains (DP 13-24), while they were negatively correlated with short A chains (DP 6-12). Collectively, the starch physicochemical and functional properties of these Thai rice starches are attributed to an interplay between compositional and structural features. These results provide decisive and crucial information on rice cultivars' suitability for consumption as cooked rice and for specific industrial applications.

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.

Comparative Proteomics Reveals the Difference in Root Cold Resistance between Vitis. riparia × V. labrusca and Cabernet Sauvignon in Response to Freezing Temperature

Grapevines, bearing fruit containing large amounts of bioactive metabolites that offer health benefits, are widely cultivated around the world. However, the cold damage incurred when grown outside in extremely low temperatures during the overwintering stage limits the expansion of production. Although the morphological, biochemical, and molecular levels in different Vitis species exposed to different temperatures have been investigated, differential expression of proteins in roots is still limited. Here, the roots of cold-resistant (Vitis. riparia × V. labrusca, T1) and cold-sensitive varieties (Cabernet Sauvignon, T3) at -4 °C, and also at -15 °C for the former (T2), were measured by iTRAQ-based proteomic analysis. Expression levels of genes encoding candidate proteins were validated by qRT-PCR, and the root activities during different treatments were determined using a triphenyl tetrazolium chloride method. The results show that the root activity of the cold-resistant variety was greater than that of the cold-sensitive variety, and it declined with the decrease in temperature. A total of 25 proteins were differentially co-expressed in T2 vs. T1 and T1 vs. T3, and these proteins were involved in stress response, bio-signaling, metabolism, energy, and translation. The relative expression levels of the 13 selected genes were consistent with their fold-change values of proteins. The signature translation patterns for the roots during spatio-temporal treatments of different varieties at different temperatures provide insight into the differential mechanisms of cold resistance of grapevine.

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.

Slowly digestible property of highly branched α-limit dextrins produced by 4,6-α-glucanotransferase from Streptococcus thermophilus evaluated in vitro and in vivo

Starch molecules are first degraded to slowly digestible α-limit dextrins (α-LDx) and rapidly hydrolyzable linear malto-oligosaccharides (LMOs) by salivary and pancreatic α-amylases. In this study, we designed a slowly digestible highly branched α-LDx with maximized α-1,6 linkages using 4,6-α-glucanotransferase (4,6-αGT), which creates a short length of α-1,4 side chains with increasing branching points. The results showed that a short length of external chains mainly composed of 1-8 glucosyl units was newly synthesized in different amylose contents of corn starches, and the α-1,6 linkage ratio of branched α-LDx after the chromatographical purification was significantly increased from 4.6% to 22.1%. Both in vitro and in vivo studies confirmed that enzymatically modified α-LDx had improved slowly digestible properties and extended glycemic responses. Therefore, 4,6-αGT treatment enhanced the slowly digestible properties of highly branched α-LDx and promises usefulness as a functional ingredient to attenuate postprandial glucose homeostasis.

Yield, Grain Quality, and Starch Physicochemical Properties of 2 Elite Thai Rice Cultivars Grown under Varying Production Systems and Soil Characteristics

Rice production systems and soil characteristics play a crucial role in determining its yield and grain quality. Two elite Thai rice cultivars, namely, KDML105 and RD6, were cultivated in two production systems with distinct soil characteristics, including net-house pot production and open-field production. Under open-field system, KDML105 and RD6 had greater panicle number, total grain weight, 100-grain weight, grain size, and dimension than those grown in the net-house. The amounts of reducing sugar and long amylopectin branch chains (DP 25–36) of the RD6 grains along with the amounts of long branch chains (DP 25–36 and DP ≥ 37), C-type starch granules, and average chain length of the KDML105 were substantially enhanced by the open-field cultivation. Contrastingly, the relative crystallinity of RD6 starch and the amounts of short branch chains (DP 6–12 and DP 13–24), B- and A-type granules, and median granule size of KDML105 starch were significantly suppressed. Consequently, the open-field-grown RD6 starch displayed significant changes in its gelatinization and retrogradation properties, whereas, certain retrogradation parameters and peak viscosity (PV) of KDML105 starches were differentially affected by the distinct cultivating conditions. This study demonstrated the influences of production systems and soil characteristics on the physicochemical properties of rice starches.

Development of Freeze-Thaw Stable Starch through Enzymatic Modification

The use of unmodified starch in frozen foods can cause extremely undesirable textural changes after the freeze-thaw process. In this study, using cyclodextrin glucanotransferase (CGTase) and branching enzymes, an amylopectin cluster with high freeze-thaw stability was produced, and was named CBAC. It was found to have a water solubility seven times higher, and a molecular weight 77 times lower, than corn starch. According to the results of a differential scanning calorimetry (DSC) analysis, dough containing 5% CBAC lost 19% less water than a control dough after three freeze-thaw cycles. During storage for 7 days at 4 °C, bread produced using CBAC-treated dough exhibited a 14% smaller retrogradation peak and 37% less hardness than a control dough, suggesting that CBAC could be a potential candidate for clean label starch, providing high-level food stability under repeated freeze-thaw conditions.

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.

Millet starch: A review

The demand for millets and their products is becoming popular globally due to their various health-promoting properties. The major constituent of the millet is its starch which contributes about 70% of total millet grain and decides the quality of millet-based food products. The application of starch for various purposes is dependent upon its physicochemical, structural, and functional properties. A native starch does not possess all the required properties for a specific use. However, product-specific properties can be achieved by modifying the structure of starches. Information deficit on millet starch has undermined its potential use in new food product design. The objective of this review is to examine the chemical composition, characterization, structural chemistry, digestibility, hydrolysis, and modification techniques of the millet starches. The review paper also discusses the various applications of native and modified starches in the food industry.

An Innovative Short-Clustered Maltodextrin as Starch Substitute for Ameliorating Postprandial Glucose Homeostasis

Dietary starch is usually associated with elevated postprandial glycemic response. This is a potential risk factor of type 2 diabetes. Here, a 1,4-α-glucan branching enzyme (GBE) was employed to reassemble α-1,4 and α-1,6 glycosidic bonds in starch molecules. Structural characterization showed that GBE-catalyzed molecular reassembly created an innovative short-clustered maltodextrin (SCMD), which showed a dense internal framework along with shortened external chains. Such short-clustered molecules obstructed digestive enzymes attack and displayed dramatically reduced digestibility. Therefore, SCMD was served as a dietary starch substitute to improve postprandial glucose homeostasis. A 22.3% decrease in glycemic peak was therefore detected in ICR mice following SCMD intake (10.7 mmol/L), compared with that in the control (13.8 mmol/L). Moreover, an attenuated insulin response (40.5% lower than that in control) to SCMD intake was regarded suitable for diabetes management. These novel discoveries demonstrate that enzymatically rebuilding starch molecules may be a meaningful strategy for diabetes management.

Structural and functional modification of kudzu starch using α-amylase and transglucosidase

The large agglomeration of starch paste in hot water, and fast retrogradation tendency and low transparency of starch gel restrict widespread application of kudzu starch. To improve the above defects, kudzu starch was modified with sequentially α-amylase (AA) and transglucosidase (TG), the latter for varying times. The results indicated that, compared to kudzu starch, amylose content and molecular weight of AA/TG-treated starches reduced by 20.07% and 69.50%, respectively. The proportion of A chain increased by 68.68%, whereas B1, B2 and B3 chains decreased by 14.28%, 48.29% and 23.44%, respectively. The degree of branching dramatically increased by 128.3%. After AA→TG treatment, the changes of starch structure enhanced the functional properties of kudzu starch. The solubility, paste clarity and gelatinization temperature increased, whereas the relative crystallinity, viscosity, storage and loss moduli decreased. Overall, the AA→TG modification would be desirable to improve the functional properties of kudzu starch to expand more large-scale application.

Highly branched corn starch: Preparation, encapsulation, and release of ascorbic acid

The aim of this study was to prepare a supporting carrier, namely highly branched corn starch (HBCS), and to investigate its encapsulation property with ascorbic acid (AA). High amylose corn starch was converted into HBCS via dual enzymatic modification by successively using α-amylase and glycogen branching enzyme. The results showed that the ratio of α-1, 6 linkage of HBCS increased by 1.93%, and a short-to-medium chain length distribution with a compact branched conformation was formed, which suggested HBCS could be a potential highly branched carrier. The HBCS-AA inclusion complex was formed as confirmed by differential scanning calorimetry. The release of AA conformed to the pseudo-Fickian diffusion mechanism and followed the first-order kinetics. Meanwhile, the photostability and thermostability of the embedded AA were moderately enhanced. These findings suggest that HBCS provides new insights into the preparation of wall materials and can be potentially used to deliver AA into food systems.

Digestion kinetics of low, intermediate and highly branched maltodextrins produced from gelatinized starches with various microbial glycogen branching enzymes

Twenty-four branched maltodextrins were synthesized from eight starches using three thermostable microbial glycogen branching enzymes. The maltodextrins have a degree of branching (DB) ranging from 5 % to 13 %. This range of products allows us to explore the effect of DB on the digestibility, which was quantified under conditions that mimic the digestion process in the small intestine. The rate and extent of digestibility were analyzed using the logarithm of the slope method, revealing that the branched maltodextrins consist of a rapidly and slowly digestible fraction. The amount of slowly digestible maltodextrin increases with an increasing DB. Surprisingly, above 10 % branching the fraction of slowly digestible maltodextrin remains constant. Nevertheless, the rate of digestion of the slowly digestible fraction was found to decline with increasing DB and shorter average internal chain length. These observations increase the understanding of the structural factors important for the digestion rate of branched maltodextrins.

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.

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.

Properties and applications of starch modifying enzymes for use in the baking industry

Enzyme technology has many potential applications in the baking industry because carbohydrate-active enzymes specifically react with carbohydrate components, such as starch, in complex food systems. Amylolytic enzymes are added to starch-based foods, such as baking products, to retain moisture more efficiently and to increase softness, freshness, and shelf life. The major reactions used to modify the structure of food starch include: (1) hydrolysis of α-1, 4 or α-1, 6 glycosidic linkages, (2) disproportionation by the transfer of glucan moieties, and (3) branching by formation of α-1, 6 glycosidic linkage. The catalytic reaction of a single enzyme or a mixture of more than two enzymes has been applied, generating novel starches, with chemical changes in the starch structure, in which the changes of molecular mass, branch chain length distribution, and the ratio of amylose to amylopectin may occur. These developments of enzyme technology highlight the potential to create various structured-starches for the food and baking industry.

Complex formation of a 4-α-glucanotransferase using starch as a biocatalyst for starch modification

A 4-α-glucanotransferases from Thermus thermophilus (TTαGT) possesses an extra substrate binding site, leading to facile purification of the intact enzyme using amylose as an insoluble binding matrix. Due to the cost of amylose and low recovery yield, starch was replaced for amylose as an alternative capturer in this study. Using gelatinized corn starch at pH 9 with 36-h incubation in the presence of 1 M ammonium sulfate increased the TTαGT-starch complex formation yield from 2 to 56%. In preparative-scale production, TTαGT produced in Bacillus subtilis was recovered by 42.1% with the same specific activity as that of purified TTαGT. Structural and rheological analyses of the enzymatically modified starches revealed that the starch complex exhibited catalytic performance comparable to soluble TTαGT, suggesting that the starch complex can be used as a biocatalyst for modified starch production without elution of the enzyme from the complex.

An extremely thermostable maltogenic amylase from Staphylothermus marinus: Bacillus expression of the gene and its application in genistin glycosylation

The most extremely thermostable maltogenic amylase (SMMA) from archaeon Staphylothermus marinus has many potential applications in food processing. To ensure safety of microbial origin, a recombinant plasmid containing the enzymic gene and a constitutive promoter AmyR2 was constructed, and then transformed into a GRAS microorganism Bacillus subtilis. The purified SMMA from the liquid cultures of Bacillus has a specific activity of 66.96U/mg, two times more than that from Escherichia coli. SMMA was further employed to catalyze the genistion glycosylation using γ-CD as both glucosyl donors and solubilizer. Glycosylated genistins with one to four additional α-glucosyls and a molar percentage of 69.87% in genistin reaction mixture were identified and quantified by HPLC-UV-MS. The glycosylated genistins at 0.2-1.2mM showed an enhanced DPPH free radical scavenging capacity. To our knowledge, this is the first report on the Bacillus expression of archaeal maltogenic amylase.

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.

Expression and characterization of thermostable glycogen branching enzyme from Geobacillus mahadia Geo-05

The glycogen branching enzyme (EC 2.4.1.18), which catalyses the formation of α-1,6-glycosidic branch points in glycogen structure, is often used to enhance the nutritional value and quality of food and beverages. In order to be applicable in industries, enzymes that are stable and active at high temperature are much desired. Using genome mining, the nucleotide sequence of the branching enzyme gene (glgB) was extracted from the Geobacillus mahadia Geo-05 genome sequence provided by the Malaysia Genome Institute. The size of the gene is 2013 bp, and the theoretical molecular weight of the protein is 78.43 kDa. The gene sequence was then used to predict the thermostability, function and the three dimensional structure of the enzyme. The gene was cloned and overexpressed in E. coli to verify the predicted result experimentally. The purified enzyme was used to study the effect of temperature and pH on enzyme activity and stability, and the inhibitory effect by metal ion on enzyme activity. This thermostable glycogen branching enzyme was found to be most active at 55 °C, and the half-life at 60 °C and 70 °C was 24 h and 5 h, respectively. From this research, a thermostable glycogen branching enzyme was successfully isolated from Geobacillus mahadia Geo-05 by genome mining together with molecular biology technique.