Effects of Streptococcus thermophilus GtfB enzyme on dough rheology, bread quality and starch digestibility

Structural and property characterization of low-molecular-weight novel reuterans synthesized from pea starch by Limosilactobacillus reuteri N1 GtfB with 4,6-α-glucanotransferase II activity

Promising novel α-glucanotransferases with starch-converting activity have recently emerged from the CAZy GH70 GtfB subfamily. In this study, we thoroughly investigated and elucidated the impact of the newly characterized 4,6-α-glucanotransferase II Limosilactobacillus reuteri N1 GtfB (LrN1 GtfB), which was capable of synthesizing linear (α1 → 6) and branched (α1 → 4,6) linkages, on the fine structure, rheology, and retrogradation properties of pea starch (PS). The results revealed that as the reaction time increased, the total (α1 → 6) linkages in linear chains and branching points of PS increased from 5.6 % to 18.7 %, the molecular weight decreased from 7.3 × 106 g/mol to 7.4 × 104 g/mol, and the percentage of short chains (DP ≤ 12) increased from 47.4 % to 92.7 %, thereby producing low-molecular-weight, short-clustered novel reuterans with new (α1 → 6) linkages in both linear chains and branches. Additionally, LrN1 GtfB-modified PS exhibited lower storage/loss modulus and weaker creep property, indicating a significant attenuation of the strength and rigidity of the modified gel structure. Moreover, products derived from pea starch and LrN1 GtfB exhibited notably low retrogradation properties. These findings provide insights into the potential application of GtfB-type α-glucanotransferases in starch-based products, thereby producing unique-structured α-glucans with versatile properties from starch.

Acceptor Subsite Mutants of Limosilactobacillus fermentum NCC 2970 GtfB 4,3-α-Glucanotransferase Regulate the Ratio of (α1 → 3)/(α1 → 6) Linkages in Biosynthesized α-Glucans

Limosilactobacillus fermentum NCC 2970 GtfB (Lf2970 GtfB) is the only characterized 4,3-α-glucanotransferase (4,3-α-GTase) in the glycoside hydrolase (GH) 70 family belonging to the GtfB subfamily. However, the mechanism for its (α1 → 3) linkage formation remains unclear, and the structural determinants of its linkage specificity remain to be explored. Here, sequence alignment and structural comparison were conducted to identify key amino acids that may be critical for linkage specificity. Five residues of Lf2970 GtfB (D991, G1028, A1398, T1400, and E1405), located at donor and acceptor subsites, were selected for mutation. Product structure analysis revealed that D991 and G1028, located near the acceptor binding subsites, played crucial roles in linkage formation. Besides native (α1 → 4) and (α1 → 3) linkages, mutants G1028R and D991N showed 8 and 10% (α1 → 6) linkage increases compared to 1% for wild-type in products. Additionally, molecular docking studies demonstrated that the orientation of acceptor binding in G1028R and D991N mutants was favorable for (α1 → 6) linkage synthesis. However, the mutation at positions A1398, T1400, and E1405 indicated that the donor subsites contribute less to the linkage specificity. These results shed light on the structural determinants of linkage specificity of 4,3-α-GTase Lf2970 GtfB and provided insights into the structure-function relationship of family GH70.

Recent advances in enzymatic modification techniques to improve the quality of flour-based fried foods

Flour-based fried foods are among the most commonly consumed foods worldwide. However, the sensory attributes and nutritional value of fried foods are inconsistent and unstable. Therefore, the creation of fried foods with desirable sensory attributes and good nutritional value remains a major challenge for the development of the fried food industry. The quality of flour-based fried foods can sometimes be improved by physical methods and the addition of chemical modifiers. However, enzyme modification is widely accepted by consumers due to its unique advantages of specificity, mild processing conditions and high safety. Therefore, it is important to elucidate the effects of enzyme treatments on the sensory attributes (color, flavor and texture), oil absorption and digestibility of flour-based fried foods. This paper reviews recent research progress in utilizing enzyme modification to improve the quality of flour-based fried foods. This paper begins with the effects of common enzymes on the physicochemical properties (rheological property, retrogradation property and specific volume) of dough. Based on the analysis of the mechanism of formation of sensory attributes and nutritional properties, it focuses on the application of amylase, protease, transglutaminase, and lipase in the regulation of sensory attributes and nutritional properties of flour-based fried foods.

Identification of a novel starch-converting GtfB enzyme from the Fructilactobacillus sanfranciscensis TMW11304 to reduce the viscoelasticity and retrogradation of tapioca starch

Starch-converting α-glucanotransferases are efficient enzymatic toolkits for the biosynthesis of diverse α-glucans, which hold vast application potential in the food industry. In this work, we identified a novel GtfB protein from Fructilactobacillus sanfranciscensis TMW11304 (FsTMW11304 GtfB) in NCBI. Although this enzyme was highly conserved in motifs I-IV with those isomalto-maltopolysaccharides (IMMPs)-producing GtfB α-glucanotransferases, it possessed distinct deletions and mutations in two crucial loops shaping the active site. Hence, unlike those GtfB enzymes, FsTMW11304 GtfB not only exhibited excellent 4,6-α-glucanotransferase activity on amylose to generate atypically low-molecular-weight IMMPs with consecutive linear (α1 → 6) linkages up to 48 %, but also held good capability towards branched substrates. Besides, compared with the control, the treatment by FsTMW11304 GtfB reduced the storage/loss modulus of granular and gelatinized tapioca starches (TS) by 12.0 %/17.9 % and 91.4 %/82.9 %, respectively, indicating that the rigidity of the gel structure was attenuated to different degrees in the two reaction systems. Furthermore, the setback viscosity observed in the gelatinized TS modified by FsTMW11304 GtfB was only 5 % of that observed in the control group, suggesting the short-term anti-retrogradation property has been substantially improved. Thus, FsTMW11304 GtfB represents a meaningful addition to the α-glucanotransferases in GH70 family, which expands the repertoire of diverse α-glucans synthesized from starch and facilitates the understanding of the structure-function relationship of the GtfB α-glucanotransferases.

Insights into the Structure-Function Relationship of GH70 GtfB α-Glucanotransferases from the Crystal Structure and Molecular Dynamic Simulation of a Newly Characterized Limosilactobacillus reuteri N1 GtfB Enzyme

α-Glucanotransferases of the CAZy family GH70 convert starch-derived donors to industrially important α-glucans. Here, we describe characteristics of a novel GtfB-type 4,6-α-glucanotransferase of high enzyme activity (60.8 U mg-1) from Limosilactobacillus reuteri N1 (LrN1 GtfB), which produces surprisingly large quantities of soluble protein in heterologous expression (173 mg pure protein per L of culture) and synthesizes the reuteran-like α-glucan with (α1 → 6) linkages in linear chains and branch points. Protein structural analysis of LrN1 GtfB revealed the potential crucial residues at subsites -2∼+2, particularly H265, Y214, and R302, in the active center as well as previously unidentified surface binding sites. Furthermore, molecular dynamic simulations have provided unprecedented insights into linkage specificity hallmarks of the enzyme. Therefore, LrN1 GtfB represents a potent enzymatic tool for starch conversion, and this study promotes our knowledge on the structure-function relationship of GH70 GtfB α-glucanotransferases, which might facilitate the production of tailored α-glucans by enzyme engineering in future.

Exploring a GtfB-Type 4,6-α-Glucanotransferase to Synthesize the (α1 → 6) Linkages in Linear Chain and Branching Points from Amylose and Enhance the Functional Property of Granular Corn Starches

Starch-converting α-glucanotransferases of glycoside hydrolase family 70 (GH70) are promising enzymatic tools for the production of diverse α-glucans with (potential) commercial applications in food and health and as biomaterials. In this study, a novel GtfB enzyme from Weissella confusa MBF8-1 was screened in the National Center for Biotechnology Information (NCBI) nonredundant protein database. The enzyme (named WcMBF8-1 GtfB) displayed high conservation in motifs I-IV with other GtfB enzymes but possessed unique variations in several substrate-binding residues. Structural characterizations of its α-glucan products revealed that WcMBF8-1 GtfB exhibited an atypical 4,6-α-glucanotransferase activity and was capable of catalyzing, by cleaving off (α1 → 4)-linkages in starch-like substrates and the synthesis of linear (α1 → 6) linkages and (α1 → 4,6) branching points. The product specificity enlarges the diversity of α-glucans and facilitates recognition of the determinants of the linkage specificity in GtfB enzymes. Furthermore, the contents of slowly digestible starch and resistant starch of granular corn starches, modified by WcMBF8-1 GtfB, increased by 6.7%, which suggested the potential value for the utilization of WcMBF8-1 GtfB to prepare "clean-label" starch ingredients with improved functional attributes.

The quest for the perfect loaf of sourdough bread continues: Novel developments for selection of sourdough starter cultures

Sourdough fermentation, one of the oldest unit operations in food production, is currently experiencing a revival in bread production at the household, artisanal, and the industrial level. The expanding use of sourdough fermentation in bread production and the adaptation of fermentation to large scale industrial bread production also necessitate the development of novel starter cultures. Developments in the last years also have expanded the tools that are used to assess the metabolic potential of specific strains, species or genera of the Lactobacillaceae and have identified multiple ecological and metabolic traits as clade-specific. This review aims to provide an overview on the clade-specific metabolic potential of members of the Lactobacillaceae for use in sourdough baking, and the impact of these clade-specific traits on bread quality. Emphasis is placed on carbohydrate metabolism, including the conversion of sucrose and starch to soluble polysaccharides, conversion of amino acids, and the metabolism of organic acids. The current state of knowledge to compose multi-strain starter cultures (synthetic microbial communities) that are suitable for back-slopping will also be discussed. Taken together, the communication outlines the current tools for selection of microbes for use in sourdough baking.

Maltogenic amylase: Its structure, molecular modification, and effects on starch and starch-based products

Maltogenic amylase (MAA) (EC3.2.1.133), a member of the glycoside hydrolase family 13 that mainly produces α-maltose, is widely used to extend the shelf life of bread as it softens bread, improves its elasticity, and preserves its flavor without affecting dough processing. Moreover, MAA is used as an improver in flour products. Despite its antiaging properties, the hydrolytic capacity and thermal stability of MAA can't meet the requirements of industrial application. However, genetic engineering techniques used for the molecular modification of MAA can alter its functional properties to meet application-specific requirements. This review briefly introduces the structure and functions of MAA, its application in starch modification, its effects on starch-based products, and its molecular modification to provide better insights for the application of genetically modified MAA in starch modification.

New plant-based fermented beverage made of baru nut enriched with probiotics and green banana: composition, physicochemical and sensory properties

This study aimed to evaluate the influence of potential functional ingredients-green banana starch, green banana pulp flour or whole green banana flour-on the composition, physicochemical and sensory properties of plant-based fermented beverages made of baru nuts. The incorporation of green banana-derived ingredients, especially the whole flour, increased protein (2.44-2.81 g/100 g), fibre (1.53-2.32 g/100 g), resistant starch (0.15-0.33 g/100 g) and ash (0.36-0.61 g/100 g) content in fermented beverages. The total phenolic content and antioxidant capacity were higher in beverages added with pulp or whole flour. The main polyphenols identified were catechin (0.75-4.97 mg/100 g), gallic acid (0.29-0.52 mg/100 g) and ferulic acid (0.17-0.64 mg/100 g). All beverages showed to be rich in unsaturated fatty acids (68%) as omega-3, omega-6, and conjugated linoleic acid. The incorporation of green banana in beverages enhanced the probiotic bacteria growth indicating the potential prebiotic effect of the unripe fruit. The sensory acceptance of fermented beverages was also improved after adding green banana. Overall, whole green banana flour stood out as the main factor that increased the nutritional value of baru nut fermented beverage. Green banana was used for the first time as a potential prebiotic ingredient in a plant-based beverage. This novel product represents a potential symbiotic non-dairy alternative that could offer health benefits to consumers.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-023-05781-5.

Probiotics in the Sourdough Bread Fermentation: Current Status

Sourdough fermentation is an ancient technique to ferment cereal flour that improves bread quality, bringing nutritional and health benefits. The fermented dough has a complex microbiome composed mainly of lactic acid bacteria and yeasts. During fermentation, the production of metabolites and chemical reactions occur, giving the product unique characteristics and a high sensory quality. Mastery of fermentation allows adjustment of gluten levels, delaying starch digestibility, and increasing the bio-accessibility of vitamins and minerals. This review focuses on the main steps of sourdough fermentation, the microorganisms involved, and advances in bread production with functional properties. The impact of probiotics on human health, the metabolites produced, and the main microbial enzymes used in the bakery industry are also discussed.

Characterization and Preliminary Application of a Novel Lipoxygenase from Enterovibrio norvegicus

Lipoxygenases have proven to be a potential biocatalyst for various industrial applications. However, low catalytic activity, low thermostability, and narrow range of pH stability largely limit its application. Here, a lipoxygenase (LOX) gene from Enterovibrio norvegicus DSM 15893 (EnLOX) was cloned and expressed in Escherichia coli BL21 (DE3). EnLOX showed the catalytic activity of 40.34 U mg-1 at 50 °C, pH 8.0. Notably, the enzyme showed superior thermostability, and wide pH range stability. EnLOX remained above 50% of its initial activity after heat treatment below 50 °C for 6 h, and its melting point temperature reached 78.7 °C. More than 70% of its activity was maintained after incubation at pH 5.0-9.5 and 4 °C for 10 h. In addition, EnLOX exhibited high substrate specificity towards linoleic acid, and its kinetic parameters of Vmax, Km, and Kcat values were 12.42 mmol min-1 mg-1, 3.49 μmol L-1, and 16.86 s-1, respectively. LC-MS/MS analysis indicated that EnLOX can be classified as 13-LOX, due to its ability to catalyze C18 polyunsaturated fatty acid to form 13-hydroxy fatty acid. Additionally, EnLOX could improve the farinograph characteristics and rheological properties of wheat dough. These results reveal the potential applications of EnLOX in the food industry.

Directed Mutation of Two Key Amino Acid Residues Alters the Product Structure of the New 4,6-α-Glucanotransferase from Bacillus sporothermodurans

4,6-α-Glucanotransferases (4,6-α-GTs) convert amylose V into two types of differently structured products: a linear product connected by continuous α,1 → 6 bonds, such as isomalto/malto-polysaccharide (IMMP), and a highly branched product connected by alternating α,1 → 4 and α,1 → 6 bonds, such as reuteran-like polysaccharide (RLP). The synthesis process of 4,6-α-GT products is unclear, and exploring this process is significant for producing dietary fibers with potential applications. This study identified and expressed Geobacillus sp. 12AMOR1 GtfD-ΔC and Bacillus sporothermodurans GtfC-ΔC. After characterizing their products through ¹H NMR and enzymatic fingerprinting, we found that GtfD-ΔC synthesized RLP with 29% α,1 → 6 bonds, and GtfC-ΔC synthesized IMMP with 71% α,1 → 6 bonds. The maltoheptaose incubation experiment showed different chain-length transfer patterns of two 4,6-α-GTs, GtfC-ΔC and GtfD-ΔC, transferring single and multiple glucose residues in each transglycosylation reaction, respectively. Site-directed mutagenesis confirmed that positions S345 and I347 influence the product structure of GtfC-ΔC, and the S345T/I347V mutation changed the GtfC-ΔC product to a linear product connected by alternating α,1 → 4 and α,1 → 6 bonds (pullulan-like polysaccharide) and altered the chain-length transfer pattern of GtfC-ΔC. We proposed that different chain-length transfer patterns between GtfD-ΔC and GtfC-ΔC may explain their differences in product structures. These findings are significant for obtaining the desired dietary fiber by engineering 4,6-α-GT.

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.

GtfC Enzyme of Geobacillus sp. 12AMOR1 Represents a Novel Thermostable Type of GH70 4,6-α-Glucanotransferase That Synthesizes a Linear Alternating (α1 → 6)/(α1 → 4) α-Glucan and Delays Bread Staling

Starch-acting α-glucanotransferase enzymes are of great interest for applications in the food industry. In previous work, we have characterized various 4,6- and 4,3-α-glucanotransferases of the glycosyl hydrolase (GH) family 70 (subfamily GtfB), synthesizing linear or branched α-glucans. Thus far, GtfB enzymes have only been identified in mesophilic Lactobacilli. Database searches showed that related GtfC enzymes occur in Gram-positive bacteria of the genera Exiguobacterium, Bacillus, and Geobacillus, adapted to growth at more extreme temperatures. Here, we report characteristics of the Geobacillus sp. 12AMOR1 GtfC enzyme, with an optimal reaction temperature of 60 °C and a melting temperature of 68 °C, allowing starch conversions at relatively high temperatures. This thermostable 4,6-α-glucanotransferase has a novel product specificity, cleaving off predominantly maltose units from amylose, attaching them with an (α1 → 6)-linkage to acceptor substrates. In fact, this GtfC represents a novel maltogenic α-amylase. Detailed structural characterization of its starch-derived α-glucan products revealed that it yielded a unique polymer with alternating (α1 → 6)/(α1 → 4)-linked glucose units but without branches. Notably, this Geobacillus sp. 12AMOR1 GtfC enzyme showed clear antistaling effects in bread bakery products.

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.

Biosynthesis and industrial applications of α-amylase: a review

Amylase is amongst the most indispensable enzymes that have a large number of applications in laboratories and industries. Mostly, α-amylase is synthesized from microbes such as bacteria, fungi and yeast. Due to the high demand for α-amylase, its synthesis can be enhanced using recombinant DNA technology, different fermentation methods, less expensive and good carbon and nitrogen sources, and optimizing the various parameters during fermentation, e.g., temperature, pH and fermentation duration. Various methods are used to measure the production and activity of synthesized α-amylase like iodine, DNS, NS and dextrinizing methods. The activity of crude α-amylase can be elevated to the maximum level by optimizing the temperature and pH. Some metals also interact with α-amylase and increase its activity like K⁺, Na⁺, Mg²⁺ and Ca²⁺. Some industries such as starch conversion, food, detergent, paper, textile industries and fuel alcohol production extensively utilize α-amylase for their various purposes.

Characterization of recombinant rice quiescin sulfhydryl oxidase and its improvement effect on wheat flour-processing quality

In this study, recombinant rice quiescin sulfhydryl oxidase (rQSOX) was expressed and characterized, and its performance in flour-processing quality was further evaluated. The purified rQSOX exhibited the highest sulfhydryl oxidation activity (1.96 IU/mg) using dithiothreitol as a substrate, accompanying the production of H₂O₂. The optimal temperature and pH were 60 °C and pH 8.0 for rQSOX catalyzing oxidation of dithiothreitol. And rQSOX retained 50% of its maximum activity after incubation at 80 °C for 1 h. Moreover, rQSOX supplementation improved the farinograph properties of dough, indicated by the increased dough stability time and decreased degree of softening, and enhanced viscoelastic properties of the dough. Addition of rQSOX (10 IU/g flour) provided remarkable improvement in specific volume (37%) and springiness (17%) of the steamed bread, and significantly reduced the hardness by half, which was attributed to the strengthened gluten network. The results provide an understanding for rQSOX using in flour-processing industry.

The effect of additives combination on rheological properties of dough and quality of bread with Agaricus bisporus powder

The bread with Agaricus bisporus powder has the defects of poor texture and taste, so it is necessary to optimize the appropriate additives in order to improve its quality. The purpose of this study was to evaluate improvement of the combination of vital wheat gluten, sucrose fatty acid esters and cellulase on the improved Agaricus bisporus powder bread (IABPB), with wheat bread (WB) and bread with Agaricus bisporus powder (ABPB) as control. The results of rheological properties indicated the dough samples improved with three improvers had higher solid-like behaviour than the control sample. The results of nutritional quality analysis showed that the protein and dietary fiber content of IABPB was higher than those of WB and ABPB, but the fat content was relatively low. In addition, the additives combination could effectively improve the baking quality of ABPB. Compared with ABPB without additives, the specific volume increased by 21.22%, the brightness of bread crumb increased by 8.75%, but the crumb hardness decreased by 32.57%. Furthermore, the study on texture property and water migration during the storage showed that the addition of three improvers could delay the aging of bread. Therefore, it was feasible to use additives combination as a special quality improver for ABPB, which could effectively improve its quality.

Dextran Aldehyde in Biocatalysis: More Than a Mere Immobilization System

Dextran aldehyde (dexOx), resulting from the periodate oxidative cleavage of 1,2-diol moiety inside dextran, is a polymer that is very useful in many areas, including as a macromolecular carrier for drug delivery and other biomedical applications. In particular, it has been widely used for chemical engineering of enzymes, with the aim of designing better biocatalysts that possess improved catalytic properties, making them more stable and/or active for different catalytic reactions. This polymer possesses a very flexible hydrophilic structure, which becomes inert after chemical reduction; therefore, dexOx comes to be highly versatile in a biocatalyst design. This paper presents an overview of the multiple applications of dexOx in applied biocatalysis, e.g., to modulate the adsorption of biomolecules on carrier surfaces in affinity chromatography and biosensors design, to serve as a spacer arm between a ligand and the support in biomacromolecule immobilization procedures or to generate artificial microenvironments around the enzyme molecules or to stabilize multimeric enzymes by intersubunit crosslinking, among many other applications.