Characterization of a Novel Maltose-Forming α-Amylase from Lactobacillus plantarum subsp. plantarum ST-III

Characterization of β-glucosidase activity of a Lactiplantibacillus plantarum 6-phospho-β-glucosidase

β-Glucosidases are useful for hydrolysis of glycosidically-bound volatiles (GBV), thereby facilitating the release of aroma chemicals from the fruit matrices. In this study, 10 putative glycosyl hydrolases belonging to GH1 family from Lactiplantibacillus plantarum NCIM 2903 were cloned and recombinantly expressed. Interestingly, only one (LpBgl5) of the nine soluble proteins, previously characterized as a 6-phospho-β-glucosidase showed β-glucosidase activity which was further characterized. The enzyme had an optimum pH and temperature of 6 and 40°C, respectively, and was categorized as aryl-β-glucosidase due to its ability to hydrolyze different natural as well as synthetic glucosides except cellobiose. The enzyme exhibited functional activity across multiple substrates, with relative activity decreasing sequentially from β-xylosidase to β-glucosidase and finally β-mannosidase. The β-xylosidase and β-glucosidase activities of LpBgl5 were stimulated up to 300% and 700% in the presence of 4 M xylose and 4 M glucose, respectively. The enzyme could also hydrolyze GBV from mango. To our knowledge, this is the first recombinant β-glucosidase/β-xylosidase/β-mannosidase from L. plantarum to have potential for aroma enhancement in fruit products. KEY POINTS: • A recombinant β-glycosidase from Lactiplantibacillus plantarum was characterized. • The enzyme showed higher β-xylosidase activity than β-glucosidase activity. • The enzyme could also hydrolyze glycosidically bound volatiles from mango.

Postbiotics in the Bakery Products: Applications and Nutritional Values

In recent years, the consumption of postbiotics has gained significant attention due to their potential health benefits. However, their application in the bakery industry remains underutilized. This review focuses on recent advances in the use of postbiotics, specifically the metabolites of lactic acid bacteria, in bakery products. We provide a concise overview of the multifaceted benefits of postbiotics, including their role as natural antioxidants, antimicrobials, and preservatives, and their potential to enhance product quality, extend shelf-life, and contribute to consumer welfare. This review combines information from various sources to provide a comprehensive update on recent advances in the role of postbiotics in bakery products, subsequently discussing the concept of sourdough as a leavening agent and its role in improving the nutritional profile of bakery products. We highlighted the positive effects of postbiotics on bakery items, such as improved texture, flavor, and shelf life, as well as their potential to contribute to overall health through their antioxidant properties and their impact on gut health. Overall, this review emphasizes the promising potential of postbiotics to revolutionize the bakery industry and promote healthier and more sustainable food options. The integration of postbiotics into bakery products represents a promising frontier and offers innovative possibilities to increase product quality, reduce food waste, and improve consumer health. Further research into refining techniques to incorporate postbiotics into bakery products is essential for advancing the health benefits and eco-friendly nature of these vital food items.

Two newly established and mutually related subfamilies GH13_48 and GH13_49 of the α-amylase family GH13

Currently, the main α-amylase family GH13 has been divided into 47 subfamilies in CAZy, with new subfamilies regularly emerging. The present in silico study was performed to highlight the groups, represented by the maltogenic amylase from Thermotoga neapolitana and the α-amylase from Haloarcula japonica, which are worth of creating their own new GH13 subfamilies. This enlarges functional annotation and thus allows more precise prediction of the function of putative proteins. Interestingly, those two share certain sequence features, e.g. the highly conserved cysteine in the second conserved sequence region (CSR-II) directly preceding the catalytic nucleophile, or the well-preserved GQ character of the end of CSR-VII. On the other hand, the two groups bear also specific and highly conserved positions that distinguish them not only from each other but also from representatives of remaining GH13 subfamilies established so far. For the T. neapolitana maltogenic amylase group, it is the stretch of residues at the end of CSR-V highly conserved as L-[DN]. The H. japonica α-amylase group can be characterized by a highly conserved [WY]-[GA] sequence at the end of CSR-II. Other specific sequence features include an almost fully conserved aspartic acid located directly preceding the general acid/base in CSR-III or well-preserved glutamic acid in CSR-IV. The assumption that these two groups represent two mutually related, but simultaneously independent GH13 subfamilies has been supported by phylogenetic analysis as well as by comparison of tertiary structures. The main α-amylase family GH13 has thus been expanded by two novel subfamilies GH13_48 and GH13_49. KEY POINTS: • In silico analysis of two groups of family GH13 members with characterized representatives • Identification of certain common, but also some specific sequence features in seven CSRs • Creation of two novel subfamilies-GH13_48 and GH13_49 within the CAZy database.

Development of Fermented Rice Water to Improve the Quality of Garaetteok, a Traditional Korean Rice Cake

In the rice processing industry, wastewater is an inevitable by-product of rice washing. To increase the utilization of washed rice water (WRW), seven types of fermented washed rice water (FWRW) were prepared using lactic acid bacteria (LAB) and carbohydrate hydrolase. The total concentration of small maltooligosaccharides (MOSs) in the amyloglucosidase (AMG) treatment groups was about ten times higher than in the untreated groups. After 6 h of fermentation, six of the seven FWRW samples reached a pH of 4 due to the increased concentration of organic acids and could, therefore, be used as food acidity regulators. To confirm the applicability of FWRW, the traditional Korean rice cake garaetteok was prepared with FWRW and stored at 4 °C for 5 days. A texture profile analysis (TPA) revealed that the hardness of garaetteok treated with FWRW was significantly lower than that of untreated garaetteok following storage. Differential scanning calorimetry (DSC) showed that FWRW retarded the retrogradation of garaetteok during storage. The addition of FWRW using Lactobacillus reuteri with an AMG group was particularly effective for inhibiting microbial activity in garaetteok during storage. These results suggest that FWRW using AMG-added L. reuteri can be used as a novel food additive for improving the quality of traditional Korean starch foods and could also reduce the volume of waste WRW.

Activity-Based Screening of Soil Samples from Nyingchi, Tibet, for Amylase-Producing Bacteria and Other Multifunctional Enzyme Capacities

Despite the interest in Tibetan soil as a promising source of functional enzymes with potential biotechnological applications, few studies have considered the screening and identification of amylase producing bacteria from Tibetan soil. Amylase has many applications in the food and feed industries, textile and biofuel production, and biomedical engineering. The area of amylase with specific properties is attracting growing attention because of its better application to various industrial conditions. This study aims to screen and identify amylase-producing strains from soil samples collected in Nyingchi, Tibet, and then explore whether the bacterial isolates are superior for unique enzymes. In this paper, a total of 127 amylase producing bacteria were isolated by activity-based screening of six Tibetan soil samples. The 16S rRNA gene survey then identified four major phyla, namely, firmicutes, bacteroidetes, proteobacteria, and actinobacteria, which were differentiated into twelve genera with a dominance of Bacillus (67.72%), followed by Pseudomonas (8.66%). Microbial diversity analysis revealed that the amylase-producing bacterial community of the Kadinggou forest soil sample showed the best variety (the Simpson index was 0.69 and the Shannon index was 0.85). The amylase activity assay of the bacterial isolates showed a mean of 0.66 U/mL at 28°C and pH 5.2. Based on the effect of temperatures and pHs on amylase activity, several bacterial isolates can produce thermophilic (50°C), psychrophilic (10°C), acidophilic (pH 4.2), and alkaliphilic (pH 10.2) amylases. Furthermore, four bacterial isolates were screened for amylase, protease, and esterase activities, which indicated multifunctional enzyme capacities. The present study is expected to contribute to our understanding of Tibetan microbial resources and their potential for scientific research and industrial applications.

Characterization of a novel type of glycogen-degrading amylopullulanase from Lactobacillus crispatus

Glycogen is one of the major carbohydrates utilized by the human vaginal microbiota, which is commonly dominated by Lactobacillus, especially L. crispatus. An in silico analysis predicted that a type I pullulanase was involved in glycogen degradation in L. crispatus. The biochemical and genetic properties of the pullulanase still need to be determined. Here, we de novo identified the glycogen (Glg)-utilization enzyme (named GlgU) from L. crispatus through a biochemical assay. GlgU was optimally active at acidic pH, approximately 4.0 ~ 4.5, and was able to hydrolyze glycogen into low-molecular-weight malto-oligosaccharides. Actually, GlgU was a type II pullulanase (amylopullulanase) with just one catalytic domain that possessed substrate specificity toward both α-1,4 and α-1,6-glucosidic bonds. Phylogenetically, GlgU was obviously divergent from the known amylases and pullulanases (including amylopullulanases) in lactobacilli. In addition, we confirmed the catalytic activity of glgU in a nonglycogen-utilizing lactobacilli strain, demonstrating the essential role of glgU in glycogen metabolism. Overall, this study characterized a novel type of amylopullulanases, contributing to the knowledge of the glycogen utilization mechanism of the dominant species of human vaginal microbiota. KEY POINTS: • GlgU was a type II pullulanase, not a type I pullulanase predicted before. • GlgU was able to completely hydrolyze glycogen into malto-oligosaccharides. • GlgU played a key role in the metabolism of extracellular glycogen.

Identification and Characterization of a Novel Hyperthermostable Bifunctional Cellobiohydrolase- Xylanase Enzyme for Synergistic Effect With Commercial Cellulase on Pretreated Wheat Straw Degradation

The novel cellobiohydrolase gene ctcel7 was identified from Chaetomium thermophilum, and its recombinant protein CtCel7, a member of glycoside hydrolase family 7, was heterologously expressed in Pichia pastoris and biochemically characterized. Compared with commercial hydrolases, purified CtCel7 exhibited superior bifunctional cellobiohydrolase and xylanase activities against microcrystalline cellulose and xylan, respectively, under optimal conditions of 60°C and pH 4.0. Moreover, CtCel7 displayed remarkable thermostability with over 90% residual activity after heat (60°C) treatment for 180 min. CtCel7 was insensitive to most detected cations and reagents and preferentially cleaved the β-1,4-glycosidic bond to generate oligosaccharides through the continuous saccharification of lignocellulosic substrates, which are crucial for various practical applications. Notably, the hydrolysis effect of a commercial cellulase cocktail on pretreated wheat straw was substantively improved by its combination with CtCel7. Taken together, these excellent properties distinguish CtCel7 as a robust candidate for the biotechnological production of biofuels and biobased chemicals.

Characterization of novel α-galactosidase in glycohydrolase family 97 from Bacteroides thetaiotaomicron and its immobilization for industrial application

Bacteroides thetaiotaomicron (B. thetaiotaomicron), which resides in the human intestinal tract, has a number of carbohydrate enzymes, including glycoside hydrolase (GH) family 97. Only a few GH 97 enzymes have been characterized to date. In this study, a novel α-galactosidase (Bt_3294) was cloned from B. thetaiotaomicron, expressed in Escherichia coli, and purified using affinity chromatography. This novel enzyme showed optimal activity at 60 °C and pH 7.0. Enzyme activity was reduced by 94.4% and 95.7% in the presence of 5 mM Ca²⁺ and Fe²⁺, respectively. It is interesting that Bt_3294 specifically hydrolyzed shorter α-galactosyl oligosaccharides, such as melibiose and raffinose. The D-values of Bt_3294 at 40 °C and 50 °C were about 107 and 6 min, respectively. After immobilization of Bt_3294, the D-values at 40 °C and 50 °C were about 37.6 and 29.7 times higher than those of the free enzyme, respectively. As a practical application, the immobilized Bt_3294 was used to hydrolyze raffinose family oligosaccharides (RFOs) in soy milk, decreasing the RFOs by 98.9%.

Unravelling the diversity of glycoside hydrolase family 13 α-amylases from Lactobacillus plantarum WCFS1

Background

α-Amylases specifically catalyse the hydrolysis of the internal α-1, 4-glucosidic linkages of starch. Glycoside hydrolase (GH) family 13 is the main α-amylase family in the carbohydrate-active database. Lactobacillus plantarum WCFS1 possesses eleven proteins included in GH13 family. Among these, proteins annotated as maltose-forming α-amylase (Lp_0179) and maltogenic α-amylase (Lp_2757) were included.

Results

In this study, Lp_0179 and Lp_2757 L. plantarum α-amylases were structurally and biochemically characterized. Lp_2757 displayed structural features typical of GH13_20 subfamily which were absent in Lp_0179. Genes encoding Lp_0179 (Amy2) and Lp_2757 were cloned and overexpressed in Escherichia coli BL21(DE3). Purified proteins showed high hydrolytic activity on pNP-α-D-maltopyranoside, being the catalytic efficiency of Lp_0179 remarkably higher. In relation to the hydrolysis of starch-related carbohydrates, Lp_0179 only hydrolysed maltopentaose and dextrin, demonstrating that is an exotype glucan hydrolase. However, Lp_2757 was also able to hydrolyze cyclodextrins and other non-cyclic oligo- and polysaccharides, revealing a great preference towards α-1,4-linkages typical of maltogenic amylases.

Conclusions

The substrate range as well as the biochemical properties exhibited by Lp_2757 maltogenic α-amylase suggest that this enzyme could be a very promising enzyme for the hydrolysis of α-1,4 glycosidic linkages present in a broad number of starch-carbohydrates, as well as for the investigation of an hypothetical transglucosylation activity under appropriate reaction conditions.

Enzymatic Glucosylation of Salidroside from Starch by α-Amylase

α-Amylases are among the most important and widely used industrial enzymes for starch processing. In this work, an α-amylase from Bacillus subtilis XL8 was purified and found to possess both hydrolysis and transglycosylation activities. The optimal pH and temperature for starch hydrolysis were pH 5.0 and 70 °C, respectively. The enzyme could degrade soluble starch into beneficial malto-oligosaccharides ranging from dimer to hexamer. More importantly, it was able to catalyze α-glycosyl transfer from the soluble starch to salidroside, a medicinal plant-derived component with broad pharmacological properties. The transglycosylation reaction catalyzed by the enzyme generated six derivatives in a total high yield of 73.4% when incubating with 100 mg/mL soluble starch and 50 mM salidroside (pH 7.5) at 50 °C for 2 h. These derivatives were identified as α-1,4-glucosyl, maltosyl, maltotriosyl, maltotetraosyl, maltopentaosyl, and maltohexaosyl salidrosides, respectively. They were novel promising compounds that might integrate the bioactive functions of malto-oligosaccharides and salidroside.

Development of an Inducible Secretory Expression System in Bacillus licheniformis Based on an Engineered Xylose Operon

The xylose operon can be an efficient biological component for regulatory expression uses in Bacillus licheniformis. However, its characteristic susceptibility to carbon catabolite repression (CCR) makes its application inconvenient. In this study, plasmids harboring the wild-type operons from three Bacillus species were constructed and introduced into B. licheniformis. These plasmids ensured secretory expression of maltogenic α-amylase (BLMA) in B. licheniformis under strict regulation. The glucose-mediated CCR was then alleviated by engineering the xylose operon of the expression system. Evidence showed that mutations in the highly conserved nucleotides of the identified catabolite responsive element (cre) consensus sequence prevented association of the regulator CcpA with DNA, thus resulting in an increase in BLMA activity of up to 12-fold. Furthermore, features of this engineered system for inducible expression were investigated. Induction in mid-log phase using 10 g/L xylose at 37 °C was found to be beneficial for promoting the accumulation of recombinant product, and the maximum yield of BlmMA reached 715.4 U/mL. This study contributes to the industrial application of the generally recognized as safe (GRAS) workhorse B. licheniformis.

Improvement of enzymatic properties of Rhizopus oryzae α-amylase by site-saturation mutagenesis of histidine 286

Optimal pH and ideal functioning temperature for fungal α-amylase can greatly contribute to improving enzyme efficiency in maltose-forming ability. This work aimed to improve the enzymatic properties of Rhizopus oryzae α-amylase by site-saturation mutagenesis of histidine 286. The biochemical properties of selected mutant enzymes were modified to increase their enzymatic efficiencies compared to their wild-type counterparts. For instance, the optimum temperature of mutants H286 L, H286I, H286S and H286 T was increased from 50 °C to 55 °C, while a similar increase was observed for H286 P from 50 °C to 60 °C. The optimum pH of mutants H286 L, H286I and H286D shifted from 5.5 to 5.0, and the optimum pH of mutant H286E shifted from 5.5 to 4.5. The results obtained showed that the mutant H286I showed a 1.5-fold increase in half-life at 55 °C and the mutant H286E showed a 6.43-fold increase in half-life at a pH of 4.5. Furthermore, the ability to form maltose from soluble starch for mutants H286 L and H286 M was significantly improved under the optimum conditions determined in the study. The catalytic mechanism responsible for improved maltose-forming ability was confirmed through molecular docking simulations with maltotriose among wild-type and mutant enzymes. The mutants with improved enzymatic properties that were attained in this work may help in future computer-aided directed evolution of fungal α-amylase.

Development and Application of Cyclodextrin Hydrolyzing Mutant Enzyme Which Hydrolyzes β- and γ-CD Selectively

Cyclodextrins (CDs) are produced from starch by cyclodextrin glucanotransferase (CGTase), which has cyclization activity. Specifically, α-CD is an important biomolecule, as it is a molecular carrier and soluble dietary fiber used in the food industry. Upon inspection of the conserved regions of the glycoside hydrolase (GH) 13 family amylases, the amino acids K232 and H233 of CGTase were identified as playing an important role in enzyme reaction specificity. A novel CD hydrolyzing enzyme, cyclodextrin glycosyl transferase (CGTase)-alpha, was developed using site-directed mutagenesis at these positions. Action pattern analysis using various substrates revealed that CGTase-alpha was able to hydrolyze β- and γ-CD, but not α-CD. This selective CD hydrolyzing property was employed to purify α-CD from a CD mixture solution. The α-CD that remained after treatment with CGTase-alpha and exotype glucoamylase was purified using hydrophobic interaction chromatography with 99% purity.