Glucansucrase (mutant) enzymes from Lactobacillus reuteri 180 efficiently transglucosylate Stevia component rebaudioside A, resulting in a superior taste

A Computational Approach to Understanding and Predicting the Edulcorant Profile of Glucosyl Steviol Glycosides

Understanding the edulcorant profile of synthetic glucosyl steviol glycosides (GSGs) and rare natural steviol glycosides (SGs) is challenging due to their numerous species and rareness. This study developed a computational model based on the interactions of SG molecules with human sweet and bitter taste receptors (hSTR/hBTR). The models demonstrated a high correlation between the cumulative interaction energies and the perceived sweetness of SGs (R2 = 0.97), elucidating the mechanism of the diverse sweetness of SGs. It also revealed that more (within three) glucose residues at the C-13 position of the SG molecule yield stronger sweetness and weaker bitterness. Furthermore, the computational prediction was consistently validated with the known sweetness of GSG and also aligned well with that of several natural mogrosides. Thus, this model possesses a potential to predict the sweetness of SGs, GSGs, and mogrosides, facilitating the application or targeted synthesis of GSGs with desired sensory profiles.

Selective synthesis of rebaudioside M2 through structure-guided engineering of glycosyltransferase UGT94D1

Rebaudioside M2 (Reb M2), a novel steviol glycoside derivative, has limited industrial applications due to its low synthetic yield and selectivity. Herein, we identify UGT94D1 as a selective glycosyltransferase for rebaudioside D (Reb D), leading to the production of a mono β-1,6-glycosylated derivative, Reb M2. A variant UGT94D1-F119I/D188P was developed through protein engineering. This mutant exhibited a 6.33-fold improvement in catalytic efficiency, and produced Reb M2 with 92% yield. Moreover, molecular dynamics simulations demonstrated that UGT94D1-F119I/D188P exhibited a shorter distance between the nucleophilic oxygen (OH6) of the substrate Reb D and uridine diphosphate glucose, along with an increased Ophosphate-C1-Oacceptor angle, thus improving the catalytic activity of the enzyme. Therefore, this study provides an efficient method for the selective synthesis of Reb M2 and paves the way for its applications in various fields.

Effects of aroma-taste interaction on the sensory attributes of rebaudiosides in soymilk and milk

BACKGROUND

Rebaudioside A (Reb-A) and rebaudioside M (Reb-M) are intense natural sweeteners but can also elicit bitterness and a bitter aftertaste. In this study, the effect of vanilla and chocolate flavorings on the sensory attributes of Reb-A and Reb-M applied to soymilk and milk was investigated to identify whether the addition of flavoring could enhance the sweetness via aroma-taste interactions.

RESULTS

Nine samples each of soymilk and milk were formulated by adding sucrose, Reb-A and Reb-M in three flavor conditions (no flavoring, vanilla, and chocolate). Descriptive analyses were conducted using nine panelists for the soymilk and eight panelists for the milk. Another descriptive analysis was conducted using the same samples with olfactory occlusion via the wearing of a nose clip to check whether the sweetness enhancement was due to olfactory input. The chocolate flavoring significantly enhanced the sweetness of Reb-A and Reb-M and reduced the bitterness, bitter aftertaste and astringency in both soymilk and milk. The vanilla flavoring was not as effective as the chocolate flavoring in enhancing sweetness. When the olfactory passage was closed with a nose clip, the sweetness enhancement and bitterness suppression were not detected in the samples.

CONCLUSION

The addition of chocolate flavoring could successfully improve the sensory profile of soymilk sweetened with Reb-A through aroma-taste interactions. © 2023 Society of Chemical Industry.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2017-2018

This review is the tenth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization mass spectrometry (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2018. Also included are papers that describe methods appropriate to glycan and glycoprotein analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, new methods, matrices, derivatization, MALDI imaging, fragmentation and the use of arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Most of the applications are presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. The reported work shows increasing use of combined new techniques such as ion mobility and highlights the impact that MALDI imaging is having across a range of diciplines. MALDI is still an ideal technique for carbohydrate analysis and advancements in the technique and the range of applications continue steady progress.

Highly efficient synthesis of mono-β-1,6-Glucosylated Rebaudioside A derivative catalyzed by glycosyltransferase YjiC

Steviol glycosides have attracted great interest because of their high levels of sweetness and safety, and absence of calories. Improvement of their sensory qualities via glycosylation modification by glycosyltransferase is a research hotspot. In this study, YjiC, a uridine diphosphate-dependent glycosyltransferase from Bacillus subtilis 168, was found with the ability to glycosylate rebaudioside A (Reb A) to produce a novel mono β-1, 6-glycosylated Reb A derivative rebaudioside L2 (Reb L2). It has an improved sweetness compared with Reb A. Next, a cascade reaction was established by combining YjiC with sucrose synthase AtSuSy from Arabidopsis thaliana for scale-up preparation of Reb L2. It shows that Reb L2 (30.94 mg/mL) could be efficiently synthesized with an excellent yield of 91.34% within 12 h. Therefore, this study provides a potential approach for the production and application of new steviol glycoside Reb L2, expanding the scope of steviol glycosides.

Sweetness profiles of glycosyl rebaudioside A and binary mixtures with sugar alcohols in aqueous solution and a lemonade model system

BACKGROUND

The demands for better-tasting alternative sweeteners have driven efforts to improve the sensory properties of rebaudioside A (Reb-A), such as glycosylation and blending with bulk sweeteners. This study attempted to (i) investigate the sensory profiles of a novel sweetener, glycosyl rebaudioside A (gReb-A), and its 1:1 mixtures with erythritol or maltitol, and (ii) compare between the sensory characteristics in an aqueous solution and lemonade.

RESULTS

The concentrations of the sweeteners were prepared to match the sweetness intensity of a 7% (w/v) sucrose solution using relative sweetness values determined using the two-alternative forced-choice test. Eight trained panelists identified sensory profiles of the sweeteners in an aqueous solution and lemonade using a descriptive analysis protocol. gReb-A had significantly less bitterness and lingering sweetness than Reb-A did, eliciting a sensory profile similar to that of sucrose. The mixture of gReb-A and erythritol was not sensorially differentiated from the sucrose in the aqueous solution. Blending with maltitol significantly enhanced the sweetness and suppressed the bitterness of gReb-A. gReb-A and its binary mixtures were perceived as more similar to sucrose in the lemonade than in solution.

CONCLUSION

This study suggests that glycosylation and blending with erythritol and maltitol gave a more sucrose-like sweetness profile in the aqueous solution and lemonade. The results of the study can be used to develop adequate sugar substitutes for acidic beverages. © 2021 Society of Chemical Industry.

Dynamic characteristics of sweetness and bitterness and their correlation with chemical structures for six steviol glycosides

Time-intensity (TI) dynamic sensory characterization was used to evaluate the temporal sweet and bitter perception of six commonly available steviol glycosides (Rubusoside, Stevioside, Rebaudioside C, Rebaudioside A, Rebaudioside D and Rebaudioside M). All parameters extracted from TI curves significantly varied among the six samples for both sweetness and bitterness. Compared to other compounds, Rebaudioside M and Rebaudioside D had faster onset of sweetness, quicker decay of aftertaste, and were nearly devoid of bitterness. Conversely, Rubusoside and Stevioside demonstrated an immediate distinct bitter taste and lingering aftertaste. Based on these results, a further investigation into the relationship between temporal properties and chemical structures was conducted. It was found that fewer glucosyl groups on C-19 would result in shorter time for initial stimulation and longer perception of bitterness, whereas more glucosyl groups on C-13 could trigger a faster increase and stronger intensity of sweetness. A shorter time to the peak for sweetness was obtained when the ratio of the number of glucosyl groups on C-13 to that on C-19 was lower, although there was no such effect on bitter taste. These relationships were explained by the adsorption and desorption of these compounds on the taste receptors. Higher numbers and larger sizes of substitutions at the C-19 position of steviol glycosides can increase their desorption percentages and lead to a quicker decay of sweetness. Meanwhile, compounds with fewer glucosyl groups, such as Rubusoside and Stevioside, presented lower desorption and thus longer bitter aftertaste. Overall, the addition of glucosyl groups would generate stronger sweetness and less bitterness if the substituent number on C-13 was closer to that on C-19. These findings conveyed insights into how to modify steviol glycosides to enhance their quality as sweeteners.

Enzymatic glucosylation of polyphenols using glucansucrases and branching sucrases of glycoside hydrolase family 70

Polyphenols exhibit various beneficial biological activities and represent very promising candidates as active compounds for food industry. However, the low solubility, poor stability and low bioavailability of polyphenols have severely limited their industrial applications. Enzymatic glycosylation is an effective way to improve the physicochemical properties of polyphenols. As efficient transglucosidases, glycoside hydrolase family 70 (GH70) glucansucrases naturally catalyze the synthesis of polysaccharides and oligosaccharides from sucrose. Notably, GH70 glucansucrases show broad acceptor substrate promiscuity and catalyze the glucosylation of a wide range of non-carbohydrate hydroxyl group-containing molecules, including benzenediol, phenolic acids, flavonoids and steviol glycosides. Branching sucrase enzymes, a newly established subfamily of GH70, are shown to possess a broader acceptor substrate binding pocket that acts efficiently for glucosylation of larger size polyphenols such as flavonoids. Here we present a comprehensive review of glucosylation of polyphenols using GH70 glucansucrase and branching sucrases. Their catalytic efficiency, the regioselectivity of glucosylation and the structure of generated products are described for these reactions. Moreover, enzyme engineering is effective for improving their catalytic efficiency and product specificity. The combined information provides novel insights on the glucosylation of polyphenols by GH70 glucansucrases and branching sucrases, and may promote their applications.

The role of metabolites of steviol glycosides and their glucosylated derivatives against diabetes-related metabolic disorders

Diabetes mellitus (DM), characterized by abnormal carbohydrate, lipid, and protein metabolism, is a metabolic disorder caused by a shortage of insulin secretion or decreased sensitivity of target cells to insulin. In addition to changes in lifestyle, a low-calorie diet is recommended to reduce the development of DM. Steviol glycosides (SGs), as natural sweeteners, have gained attention as sucrose alternatives because of their advantages of high sweetness and being low calorie. Most SGs with multiple bioactivities are beneficial to regulate physiological functions. Though SGs have been widely applied in food industry, there is little data on their glucosylated derivatives that are glucosylated steviol glycosides (GSGs). In this review, we have discussed the metabolic fate of GSGs in contrast to SGs, and the molecular mechanisms of glycoside metabolites against diabetes-related metabolic disorders are also summarized. SGs are generally extracted from the Stevia leaf, while GSGs are mainly manufactured using enzymes that transfer glucose units from a starch source to SGs. Results from this study suggest that SGs and GSGs share same bioactive metabolites, steviol and steviol glucuronide (SVG), which exhibit anti-hyperglycemic effects by activating glucose-induced insulin secretion to enhance pancreatic β-cell function. In addition, steviol and SVG have been found to ameliorate the inflammatory response, lipid imbalance, myocardial fibrosis and renal functions to modulate diabetes-related metabolic disorders. Therefore, both SGs and GSGs may be used as potential sucrose alternatives and/or pharmacological alternatives for preventing and treating metabolic disorders.

Bacterial α-Glucan and Branching Sucrases from GH70 Family: Discovery, Structure-Function Relationship Studies and Engineering

Glucansucrases and branching sucrases are classified in the family 70 of glycoside hydrolases. They are produced by lactic acid bacteria occupying very diverse ecological niches (soil, buccal cavity, sourdough, intestine, dairy products, etc.). Usually secreted by their producer organisms, they are involved in the synthesis of α-glucans from sucrose substrate. They contribute to cell protection while promoting adhesion and colonization of different biotopes. Dextran, an α-1,6 linked linear α-glucan, was the first microbial polysaccharide commercialized for medical applications. Advances in the discovery and characterization of these enzymes have remarkably enriched the available diversity with new catalysts. Research into their molecular mechanisms has highlighted important features governing their peculiarities thus opening up many opportunities for engineering these catalysts to provide new routes for the transformation of sucrose into value-added molecules. This article reviews these different aspects with the ambition to show how they constitute the basis for promising future developments.

Sweetness profiles of glycosylated rebaudioside A and its binary mixtures with allulose and maltitol

Rebaudioside A is a promising natural alternative sweetener but they produce increased bitterness, astringency, and unpleasant aftertastes. Glycosylation and blending with different sweeteners are known to improve the sensory characteristics of rebaudioside A. The present study was conducted to identify the relative sweetness and sensory profile of glycosyl rebaudioside A (g-reb A). The relative sweetness of g-reb A compared to 5% sucrose was determined using the two-alternative forced choice method. The sensory profiles of g-reb A and its mixtures with allulose and maltitol (1:1 ratio) were compared to those of rebaudioside A, rebaudioside D, rebaudioside M, sucralose, allulose, maltitol, and sucrose using descriptive analysis conducted by eight trained panelists. The relative sweetness of g-reb A was 155, which was lower than that of rebaudioside A. In addition, the bitter taste and aftertaste, astringency, and sweet onset of g-reb A were decreased compared to those of rebaudioside A.

Two-Step Enzymatic Conversion of Rebaudioside A into a Mono-α-1,4-Glucosylated Rebaudioside A Derivative

A new two-step enzymatic conversion process for the production of a novel mono-α-1,4-glucosylated rebaudioside A derivative (RA1G) was established via transglycosylation followed by hydrolyzation. In the transglycosylation reaction catalyzed by cyclodextrin glycosyltransferase, rebaudioside A (RA) was converted into glucosylated RA derivatives (RAGs), and the maximum conversion of 87.8% was obtained with the optimal conditions of 2 U/mL enzyme, 82.5 mg/mL β-cyclodextrin, and 82.5 mg/mL RA at 60 °C for 5 h. The obtained RAG solution was then directly used in hydrolyzation. Four amylases were screened for shortening the newly synthesized α-glucans of RAGs. A glucoamylase was found to produce RA1G as the single glucosylated product, and the maximum yield of 53.3% was achieved with the optimal conditions of adding 1.5 U/mL glucoamylase into RAG solution at 60 °C for 3 h. RA1G was identified as 13-[(2-O-β-D-glucopyranosyl-3-O-β-D-glucopyranosyl-β-D-glucopyranosyl) oxy] ent-kaur-16-en-19-oic acid-[(4-O-α-D-glucopyranosyl-β-D-glucopyranosyl) ester] by MS and NMR analysis and showed an improved sensory quality compared to RA.

Biocatalysis: Enzymatic Synthesis for Industrial Applications

Biocatalysis has found numerous applications in various fields as an alternative to chemical catalysis. The use of enzymes in organic synthesis, especially to make chiral compounds for pharmaceuticals as well for the flavors and fragrance industry, are the most prominent examples. In addition, biocatalysts are used on a large scale to make specialty and even bulk chemicals. This review intends to give illustrative examples in this field with a special focus on scalable chemical production using enzymes. It also discusses the opportunities and limitations of enzymatic syntheses using distinct examples and provides an outlook on emerging enzyme classes.

Natural and engineered transglycosylases: Green tools for the enzyme-based synthesis of glycoproducts

An increasing number of transglycosylase-based processes provide access to oligosaccharides or glycoconjugates, some of them reaching performance levels compatible with industrial developments. Nevertheless, the full potential of transglycosylases has not been explored because of the challenges in transforming a glycoside hydrolase into an efficient transglycosylase. Advances in studying enzyme structure/function relationships, screening enzyme activity, and generating synthetic libraries guided by computational protein design or machine learning methods should considerably accelerate the development of these catalysts. The time has now come for researchers to uncover their possibilities and learn how to design and precisely refine their activity to respond more rapidly to the growing demand for well-defined glycosidic structures.

Status of the application of exogenous enzyme technology for the development of natural plant resources

Exogenous enzymes are extraneous enzymes that are not intrinsic to the subject. The exogenous enzyme industry has been rapidly developing recently. Successful application of recombinant DNA amplification, high-efficiency expression, and immobilization technology to genetically engineered bacteria provides a rich source of enzymes. Amylase, cellulase, protease, pectinase, glycosidase, tannase, and polyphenol oxidase are among the most widely used such enzymes. Currently, the application of exogenous enzyme technology in the development of natural plant resources mainly focuses on improving the taste and flavor of the product, enriching the active ingredient contents, deriving and transforming the structure of a chosen compound, and enhancing the biological activity and utilization of the functional ingredient. In this review, we discuss the application status of exogenous enzyme technology for the development of natural plant resources using typical natural active ingredients from plant, such as resveratrol, steviosides, catechins, mogrosides, and ginsenosides, as examples, to provide basis for further exploitation and utilization of exogenous enzyme technology.

Enzymatic Synthesis of Glucosyl Rebaudioside A and its Characterization as a Sweetener

Rebaudioside A was modified via glucosylation by recombinant dextransucrase of Leuconostoc lactis EG001 in Escherichia coli BL21 (DE3), forming single O-α-D-glucosyl-(1″→6') rebaudioside A with yield of 86%. O-α-D-glucosyl-(1″→6') rebaudioside A was purified using HPLC and Diaion HP-20 and its properties were characterized for possible use as a food ingredient. Almost 98% of O-α-D-glucosyl-(1″→6') rebaudioside A was dissolved after 15 days of storage at room temperature, compared to only 11% for rebaudioside A. Compared to rebaudioside A, O-α-D-glucosyl-(1″→6') rebaudioside A showed similar or improved acidic or thermal stability in commercial drinks. Thus, O-α-D-glucosyl-(1″→6') rebaudioside A could be used as a highly pure and improved sweetener with high stability in commercial drinks. PRACTICAL APPLICATION: The proposed method can be used to generate glucosyl rebaudioside A by enzymatic glucosylation. Simple glucosyl rebaudioside A exhibited high acid/thermal stability and improved sweetener in commercialized drinks. This method can be applied to obtain high value-added bioactive compounds by enzymatic modification.

RQ3, A Natural Rebaudioside D Isomer, Was Obtained from Glucosylation of Rebaudioside A Catalyzed by the CGTase Toruzyme 3.0 L

In this study, a monoglucosyl rebaudioside A product was isolated from the mixture of glucosylated rebaudioside A obtained from the most reported and industrial used cyclodextrin glycosyl transferase, Toruzyme 3.0 L (CGTase, Toruzyme 3.0 L). The molecular structure of the monoglucosyl rebaudioside A was characterized using LC-MS/MS and methylation analysis combined with 1D and 2D NMR, indicating that it is 13-[(2-O-(3-α-O-D-glucopyranosyl)-β-D-glucopyranosyl-3-O-β-D-glucopyranosyl-β-D-glucopyranosyl)oxy] ent-kaur-16-en-19-oic acid β-D-glucopyranosyl ester (also known as RQ3, which naturally exists in Stevia extract as an isomer of rebaudioside D). This study may help to further understand the reaction mechanism of glucosylation of steviol glycoside assisted by Toruzyme 3.0 L in the aspect of molecule linkage pattern, and also benefit the application of the glucosylated rebaudiosides.

Enzymatic Synthesis and Characterization of a Novel α-1→6-Glucosyl Rebaudioside C Derivative Sweetener

Zero-calorie high-intensity sweeteners from natural sources perform very well in the market place. This has encouraged food scientists to continue the effort to search for novel natural ingredients to satisfy consumer demand. Rebaudioside C (reb C) is the third most prevalent steviol glycoside in the leaves of the Stevia rebaudiana Bertoni plant, but has limited applications in food and beverage products due to its low sweetness and high lingering bitterness compared to other major steviol glycosides, such as rebaudioside A (reb A). Here we present a new enzyme modification strategy to improve the taste profile of reb C by using Cargill's propriety enzyme and sucrose as a glucose donor. A novel α-1→6-glucosyl reb C derivative was produced and its structure was elucidated by mass spectrometry and NMR spectroscopy. Sensory analysis demonstrated that this new reb C derivative has improved sweetness, reduced bitterness, and enhanced solubility in water.

Mutational Analysis of the Role of the Glucansucrase Gtf180-ΔN Active Site Residues in Product and Linkage Specificity with Lactose as Acceptor Substrate

Glucansucrase Gtf180-ΔN from Lactobacillus reuteri uses lactose as acceptor substrate to synthesize five glucosylated lactose molecules (F1-F5) with a degree of polymerization (DP) of 3-4 (GL34) and with (α1→2)/(α1→3)/(α1→4) glycosidic linkages. Q1140/W1065/N1029 mutations significantly changed the GL34 product ratios. Q1140 mutations clearly decreased F3 3'-glc-lac with an (α1→3) linkage and increased F4 4',2-glc-lac with (α1→4)/(α1→2) linkages. Formation of F2 2-glc-lac with an (α1→2) linkage and F4 was negatively affected in most W1065 and N1029 mutants, respectively. Mutant N1029G synthesized four new products with additional (α1→3)-linked glucosyl moieties (2xDP4 and 2xDP5). Sucrose/lactose strongly reduced Gtf180-ΔN hydrolytic activity and increased transferase activity of Gtf180-ΔN and mutant N1029G, in comparison to activity with sucrose alone. N1029/W1065/Q1140 thus are key determinants of Gtf180-ΔN linkage and product specificity in the acceptor reaction with lactose. Mutagenesis of key residues in Gtf180-ΔN may allow synthesis of tailor-made mixtures of novel lactose-derived oligosaccharides with potential applications as prebiotic compounds in food/feed and in pharmacy/medicine.