Use of glycoside hydrolase family 8 xylanases in baking

Advances in the understanding of the production, modification and applications of xylanases in the food industry

Xylanases have broad applications in the food industry to decompose the complex carbohydrate xylan. This is applicable to enhance juice clarity, improve dough softness, or reduce beer turbidity. It can also be used to produce prebiotics and increase the nutritional value in foodstuff. However, the low yield and poor stability of most natural xylanases hinders their further applications. Therefore, it is imperative to explore higher-quality xylanases to address the potential challenges that appear in the food industry and to comprehensively improve the production, modification, and utilization of xylanases. Xylanases, due to their various sources, exhibit diverse characteristics that affect production and activity. Most fungi are suitable for solid-state fermentation to produce xylanases, but in liquid fermentation, microbial metabolism is more vigorous, resulting in higher yield. Fungi produce higher xylanase activity, but bacterial xylanases perform better than fungal ones under certain extreme conditions (high temperature, extreme pH). Gene and protein engineering technology helps to improve the production efficiency of xylanases and enhances their thermal stability and catalytic properties.

Combined strategies for improving the heterologous expression of a novel xylanase from Fusarium oxysporum Fo47 in Pichia pastoris

Xylanase, an enzyme capable of hydrolyzing non-starch polysaccharides found in grain structures like wheat, has been found to improve the organizational structure of dough and thus increase its volume. In our past work, one promising xylanase FXYL derived from Fusarium oxysporum Fo47 and first expressed 779.64 U/mL activity in P. pastoris. It has shown significant potential in improving the quality of whole wheat bread, making it become a candidate for development as a new flour improver. After optimization of expression elements and gene dose, the xylanase activity of FXYL strain carrying three-copies reached 4240.92 U/mL in P. pastoris. In addition, 12 factors associated with the three stages of protein expression pathway were co-expressed individually in order in three-copies strain, and the translation factor Pab1 co-expression increased FXYL activity to 8893.53 U/mL. Nevertheless, combining the most effective or synergistic factors from three stages did not exhibit better results than co-expressing them alone. To further evaluate the industrial potential, the xylanase activity and protein concentration reached 81184.51 U/mL and 11.8 g/L in a 5 L fed-batch fermenter. These engineering strategies improved the expression of xylanase FXYL by more than 104-fold, providing valuable insights for the cost-effective industrial application of FXYL in the baking field.

From freezing to functioning: cellular strategies of cold-adapted bacteria for surviving in extreme environments

The ability of cold-adapted bacteria to survive in extreme cold and diverse temperatures is due to their unique attributes like cell membrane stability, up-regulation of peptidoglycan biosynthesis, increased production of extracellular polymeric substances, and expansion of membrane pigment. Various cold-adapted proteins, including ice-nucleating proteins (INPs), antifreeze proteins (AFPs), cold shock proteins (Csps), and cold-acclimated proteins (CAPs), help the bacteria to survive in these environments. To sustain cells from extreme cold conditions and maintain stability in temperature fluctuations, survival strategies at the molecular level and their mechanism play significant roles in adaptations in cryospheric conditions. Furthermore, cold shock domains present in the multifunctional cold shock proteins play crucial roles in their adaptation strategies. The considerable contribution of lipopeptides, osmolytes, and membrane pigments plays an integral part in their survival in extreme environments. This review summarizes the evolutionary history of cold-adapted bacteria and their molecular and cellular adaptation strategies to thrive in harsh cold environments. It also discusses the importance of carotenoids produced, lipid composition, cryoprotectants, proteins, and chaperones related to this adaptation. Furthermore, the functions and mechanisms of adaptations within the cell are discussed briefly. One can utilize and explore their potential in various biotechnology applications and their evolutionary journey by knowing the inherent mechanism of their molecular and cellular adaptation to cold climatic conditions. This review will help all branches of the life science community understand the basic microbiology of psychrophiles and their hidden prospect in life science research.

An insight into microbial sources, classification, and industrial applications of xylanases: A rapid review

Endo 1,4-β-d-xylanases (EC3.2.1.8) are one of the key lignocellulose hydrolyzing enzymes. Xylan, which is present in copious amounts on earth, forms the primary substrate of endo-xylanases, which can unchain the constituent monosaccharides linked via β-1,4-glycosidic bonds from the xylan backbone. Researchers have shown keen interest in the xylanases belonging to glycoside hydrolase families 10 and 11, whereas those placed in other glycoside hydrolase families are yet to be investigated. Various microbes such as bacteria and fungi harbor these enzymes for the metabolism of their lignocellulose fibers. These microbes can be used as miniature biofactories of xylanase enzymes for a plethora of environmentally benign applications in pulp and paper industry, biofuel production, and for improving the quality of food in bread baking and fruit juice industry. This review highlights the potential of microbes in production of xylanase for industrial biotechnology.

Endo-1,4-β-xylanase-containing glycoside hydrolase families: Characteristics, singularities and similarities

Endo-1,4-β-xylanases (EC 3.2.1.8) are O-glycoside hydrolases that cleave the internal β-1,4-D-xylosidic linkages of the complex plant polysaccharide xylan. They are produced by a vast array of organisms where they play critical roles in xylan saccharification and plant cell wall hydrolysis. They are also important industrial biocatalysts with widespread application. A large and ever growing number of xylanases with wildly different properties and functionalites are known and a better understanding of these would enable a more effective use in various applications. The Carbohydrate-Active enZYmes database (CAZy), which classifies evolutionarily related proteins into a glycoside hydrolase family-subfamily organisational scheme has proven powerful in understanding these enzymes. Nevertheless, ambiguity currently exists as to the number of glycoside hydrolase families and subfamilies harbouring catalytic domains with true endoxylanase activity and as to the specific characteristics of each of these families/subfamilies. This review seeks to clarify this, identifying 9 glycoside hydrolase families containing enzymes with endo-1,4-β-xylanase activity and discussing their properties, similarities, differences and biotechnological perspectives. In particular, substrate specificities and hydrolysis patterns and the structural determinants of these are detailed, with taxonomic aspects of source organisms being also presented. Shortcomings in current knowledge and research areas that require further clarification are highlighted and suggestions for future directions provided. This review seeks to motivate further research on these enzymes and especially of the lesser known endo-1,4-β-xylanase containing families. A better understanding of these enzymes will serve as a foundation for the knowledge-based development of process-fitted endo-1,4-β-xylanases and will accelerate their development for use with even the most recalcitrant of substrates in the biobased industries of the future.

A novel cold-active GH8 xylanase from cellulolytic myxobacterium and its application in food industry

Although xylanase have a wide range of applications, cold-active xylanases have received less attention. In this study, a novel glycoside hydrolase family 8 (GH8) xylanase from Sorangium cellulosum with high activity at low temperatures was identified. The recombinant xylanase (XynSc8) was most active at 50 °C, demonstrating 20% of its maximum activity and strict substrate specificity towards beechwood and corncob xylan at 4 °C with V_max values of 968.65 and 1521.13 μmol/mg/min, respectively. Mesophilic XynSc8 was active at a broad range of pH and hydrolyzed beechwood and corncob xylan into xylooligosaccharides (XOS) with degree of polymerization greater than 3. Moreover, incorporation of XynSc8 (0.05-0.2 mg/kg flour) provided remarkable improvement (28-30%) in bread specific volume and textural characteristics of bread compared to commercial xylanase. This is the first report on a novel cold-adapted GH8 xylanase from myxobacteria, suggesting that XynSc8 may be a promising candidate suitable for bread making.

Xylo-Oligosaccharide Utilization by Engineered Saccharomyces cerevisiae to Produce Ethanol

The engineering of xylo-oligosaccharide-consuming Saccharomyces cerevisiae strains is a promising approach for more effective utilization of lignocellulosic biomass and the development of economic industrial fermentation processes. Extending the sugar consumption range without catabolite repression by including the metabolism of oligomers instead of only monomers would significantly improve second-generation ethanol production This review focuses on different aspects of the action mechanisms of xylan-degrading enzymes from bacteria and fungi, and their insertion in S. cerevisiae strains to obtain microbial cell factories able of consume these complex sugars and convert them to ethanol. Emphasis is given to different strategies for ethanol production from both extracellular and intracellular xylo-oligosaccharide utilization by S. cerevisiae strains. The suitability of S. cerevisiae for ethanol production combined with its genetic tractability indicates that it can play an important role in xylan bioconversion through the heterologous expression of xylanases from other microorganisms.

Extremophilic Prokaryotic Endoxylanases: Diversity, Applicability, and Molecular Insights

Extremophilic endoxylanases grabbed attention in recent years due to their applicability under harsh conditions of several industrial processes. Thermophilic, alkaliphilic, and acidophilic endoxylanases found their employability in bio-bleaching of paper pulp, bioconversion of lignocellulosic biomass into xylooligosaccharides, bioethanol production, and improving the nutritious value of bread and other bakery products. Xylanases obtained from extremophilic bacteria and archaea are considered better than fungal sources for several reasons. For example, enzymatic activity under broad pH and temperature range, low molecular weight, cellulase-free activity, and longer stability under extreme conditions of prokaryotic derived xylanases make them a good choice. In addition, a short life span, easy cultivation/harvesting methods, higher yield, and rapid DNA manipulations of bacterial and archaeal cells further reduces the overall cost of the product. This review focuses on the diversity of prokaryotic endoxylanases, their characteristics, and their functional attributes. Besides, the molecular mechanisms of their extreme behavior have also been presented here.

Egyptian chia seeds (Salvia hispanica L.) during germination: Upgrading of phenolic profile, antioxidant, antibacterial properties and relevant enzymes activities

Little studies on chia sprouts were not deeply address the polyphenols profiles and their functional properties during long period of germination. This study aims to evaluate the impact of germination process on the phenolic profile, antioxidant and antibacterial properties and relevant enzymes activities of Egyptian chia seeds. The total phenolic and flavonoid contents of chia sprouts increased several times during ten days of germination and maximized on 7-day sprouts (6.4 and 11.5 folds, respectively). In HPLC analysis, seventeen phenolic compounds were detected on 7-day sprouts compared to fifteen in dry seeds, where two new phenolic compounds (p-coumaric acid and kaempferol) were detected. The concentrations of all the identified phenolic compounds increased several folds (1.8-27) on 7-day sprouts. The total antioxidant activity increased 10, 17, and 29 folds on 7-day sprouts using DPPH, ABTS and PMC antioxidant methods, respectively compared to the dry seeds. Both antioxidant and carbohydrate-cleaving enzymes increased in chia sprouts and correlated with their phenolic content and antioxidant activity. The phenolic content of 7-day sprouts showed a potent antibacterial activity against some human enteric pathogenic bacteria including Escherichia coli O157-H7, Salmonella typhi, Pseudomonas aeruginosa and Staphylococcus aureus with lower MIC values compared to the raw seeds.

Molecular profiling of microbial community structure and their CAZymes via metagenomics, from Tsomgo lake in the Eastern Himalayas

The present study is the first of its kind which is focused on Tsomgo lake, a high-altitude lake, located in the Eastern Himalayas of Sikkim. To get a major insight into the bacterial diversity, the shotgun sequencing was carried out in Illumina platform. Our results showed that both the samples TLSS1 (soil) and TLSW1 (water), had Proteobacteria as the most abundant taxa. Cluster of Orthologous group (COG) functional category of TLSS1 has 1,46,965 predicted functions. Cluster of Orthologous Group (COG) functional category of TLSW1 has 1,34,773 predicted functions. Kyoto Encyclopedia of Gene and Genomes (KEGG) functional category of TLSS1 has 1,76,825 predicted functions, most of the sequence fall in metabolism followed by Environmental information processing function. (KEGG) functional category of TLSW1 has 1,62,696 predicted functions and it follows the same pattern as TLSS1. Our studies also provide insight into the presence of distribution of different carbohydrate-active enzymes (CAZymes) present in Tsomgo lake. We have found that in case of both the samples TLSW1 and TLSS1, GlycosylTransferases were active followed by GlycosylHydrolase. The result found, represents for the first time very important findings related to the microbial diversity and the abundance of CAZymes in Tsomgo lake one of the pristine high-altitude lakes in Sikkim.

ADJUSTING FLOUR QUALITY BY ENZYMES: CURRENT STATE, PROBLEM ANALYSIS, FUTURE DEVELOPMENT PROSPECTS

The article overviews the issue of wheat flour modification by enzymes. The role of enzymes in the dough formation process is considered. Modern ways of providing the desired dough parameters for flour products in conditions of Ukraine are shown. Recommendations and suggested directions for further research are given. Flour is a complex multicomponent product and have to correspond with a number of requirements for its composition and properties. Different conditions of grain cultivation and storage result in significant deviations of its quality indicators when it comes to flour mills. The modification of flour going through adding several technological additives, in particular by enzyme products. The action of enzymes to a large extent allows to adjust the properties of the dough and of flour end-products. In addition, enzymes further affect the nutritional values of flour, which makes it possible for the flour production to use low-quality grain, while maintaining the planned quality indicators of flour. The functional properties of flour fractions obtained on different technological passages depend on the content of various anatomical parts of the grain from which they derived from. Particle size, starch damage, protein content, fat content, ash content and intensity of enzyme activity vary significantly depending on the type of grinding equipment. All this gives reason for recommending the introduction of enzymes not while manufacturing bakery end-products but still at the stage of flour production. The damage to the grain with a corn bug, grain germination in Ukraine puts grain-processing plants the task of assessing the activity of own grain enzyme systems. Indirectly, this can be estimated using the gluten deformation index and the grain Falling Number. But the estimation of enzyme systems by such methods does not allow precisely to calculate the amount and composition of enzyme products necessary to achieve maximum effect when adjusting flour properties. The issue of removing anti-nutrient factors in flour, which is largely inhibitors of the action of both their own grain enzyme systems and additionally introduced enzyme preparations, is also relevant.

Efficient expression and secretion of endo-1,4-β-xylanase from Penicillium citrinum in non-conventional yeast Yarrowia lipolytica directed by the native and the preproLIP2 signal peptides

Filamentous fungi are the most common industrial xylanase producers. In this study, the xynA gene encoding xylanase A of Penicilium citrinum was successfully synthesized and expressed in Yarrowia lipolytica under the control of the strong constitutive TEF promoter. Native and preproLIP2 secretion signals were used for comparison of the expression and secretion level. The recombinant xylanase was produced as a soluble protein, and the total activity production reached 11 and 52 times higher than the level of activity produced by the fungus P. citrinum native strain, respectively. Maximum activity was observed with the preproLIP2 secretion signal at 180 U/mL. Post translational glycosylation affected the molecular mass of the recombinant xylanase, resulting in an apparent molecular weight larger than 60 kDa, whereas after deglycosylation, the recombinant XynA displayed a molecular mass of 20 kDa. The deglycosylated xylanase was purified by ion exchange chromatography and reached 185-fold of purification. The enzyme was optimally active at 55 °C and pH 5 and stable over a broad pH range (3-9). It retained more than 80% of the original activity after 24 h. It conserved around 80% of the original activity after pre-incubation at 40 °C for 6 h. With birchwood xylan as substrate, the enzyme showed a K_m of 5.2 mg/mL, and k_cat of 245 per s. The high level of secretion and the stability over a wide range of pH and at moderate temperatures of the re-XynA could be useful for variety of biotechnological applications.

Psychrophilic lifestyles: mechanisms of adaptation and biotechnological tools

Cold-adapted microorganisms inhabiting permanently low-temperature environments were initially just a biological curiosity but have emerged as rich sources of numerous valuable tools for application in a broad spectrum of innovative technologies. To overcome the multiple challenges inherent to life in their cold habitats, these microorganisms have developed a diverse array of highly sophisticated synergistic adaptations at all levels within their cells: from cell envelope and enzyme adaptation, to cryoprotectant and chaperone production, and novel metabolic capabilities. Basic research has provided valuable insights into how these microorganisms can thrive in their challenging habitat conditions and into the mechanisms of action of the various adaptive features employed, and such insights have served as a foundation for the knowledge-based development of numerous novel biotechnological tools. In this review, we describe the current knowledge of the adaptation strategies of cold-adapted microorganisms and the biotechnological perspectives and commercial tools emerging from this knowledge. Adaptive features and, where possible, applications, in relation to membrane fatty acids, membrane pigments, the cell wall peptidoglycan layer, the lipopolysaccharide component of the outer cell membrane, compatible solutes, antifreeze and ice-nucleating proteins, extracellular polymeric substances, biosurfactants, chaperones, storage materials such as polyhydroxyalkanoates and cyanophycins and metabolic adjustments are presented and discussed.

Alkaline Active Hemicellulases

Xylan and mannan are the two most abundant hemicelluloses, and enzymes that modify these polysaccharides are prominent hemicellulases with immense biotechnological importance. Among these enzymes, xylanases and mannanases which play the vital role in the hydrolysis of xylan and mannan, respectively, attracted a great deal of interest. These hemicellulases have got applications in food, feed, bioethanol, pulp and paper, chemical, and beverage producing industries as well as in biorefineries and environmental biotechnology. The great majority of the enzymes used in these applications are optimally active in mildly acidic to neutral range. However, in recent years, alkaline active enzymes have also become increasingly important. This is mainly due to some benefits of utilizing alkaline active hemicellulases over that of neutral or acid active enzymes. One of the advantages is that the alkaline active enzymes are most suitable to applications that require high pH such as Kraft pulp delignification, detergent formulation, and cotton bioscouring. The other benefit is related to the better solubility of hemicelluloses at high pH. Since the efficiency of enzymatic hydrolysis is often positively correlated to substrate solubility, the hydrolysis of hemicelluloses can be more efficient if performed at high pH. High pH hydrolysis requires the use of alkaline active enzymes. Moreover, alkaline extraction is the most common hemicellulose extraction method, and direct hydrolysis of the alkali-extracted hemicellulose could be of great interest in the valorization of hemicellulose. Direct hydrolysis avoids the time-consuming extensive washing, and neutralization processes required if non-alkaline active enzymes are opted to be used. Furthermore, most alkaline active enzymes are relatively active in a wide range of pH, and at least some of them are significantly or even optimally active in slightly acidic to neutral pH range. Such enzymes can be eligible for non-alkaline applications such as in feed, food, and beverage industries.This chapter largely focuses on the most important alkaline active hemicellulases, endo-β-1,4-xylanases and β-mannanases. It summarizes the relevant catalytic properties, structural features, as well as the real and potential applications of these remarkable hemicellulases in textile, paper and pulp, detergent, feed, food, and prebiotic producing industries. In addition, the chapter depicts the role of these extremozymes in valorization of hemicelluloses to platform chemicals and alike in biorefineries. It also reviews hemicelluloses and discusses their biotechnological importance.

Distinguishing the differences in β-glycosylceramidase folds, dynamics, and actions informs therapeutic uses

Glycosyl hydrolases (GHs) are carbohydrate-active enzymes that hydrolyze a specific β-glycosidic bond in glycoconjugate substrates; β-glucosidases degrade glucosylceramide, a ubiquitous glycosphingolipid. GHs are grouped into structurally similar families that themselves can be grouped into clans. GH1, GH5, and GH30 glycosidases belong to clan A hydrolases with a catalytic (β/α)8 TIM barrel domain, whereas GH116 belongs to clan O with a catalytic (α/α)6 domain. In humans, GH abnormalities underlie metabolic diseases. The lysosomal enzyme glucocerebrosidase (family GH30), deficient in Gaucher disease and implicated in Parkinson disease etiology, and the cytosol-facing membrane-bound glucosylceramidase (family GH116) remove the terminal glucose from the ceramide lipid moiety. Here, we compare enzyme differences in fold, action, dynamics, and catalytic domain stabilization by binding site occupancy. We also explore other glycosidases with reported glycosylceramidase activity, including human cytosolic β-glucosidase, intestinal lactase-phlorizin hydrolase, and lysosomal galactosylceramidase. Last, we describe the successful translation of research to practice: recombinant glycosidases and glucosylceramide metabolism modulators are approved drug products (enzyme replacement therapies). Activity-based probes now facilitate the diagnosis of enzyme deficiency and screening for compounds that interact with the catalytic pocket of glycosidases. Future research may deepen the understanding of the functional variety of these enzymes and their therapeutic potential.

A type D ferulic acid esterase from Streptomyces werraensis affects the volume of wheat dough pastries

A type D ferulic acid esterase (FAE) was identified in the culture supernatant of Streptomyces werraensis, purified, sequenced, and heterologously produced in E. coli BL21(DE3)Star by co-expressing chaperones groES-groEL (69 U L^-1). The unique enzyme with a mass of about 48 kDa showed no similarity to other FAEs, and only moderate homology (78.5%) to a Streptomycete β-xylosidase. The purified reSwFAED exhibited a temperature optimum of 40 °C, a pH optimum in the range from pH seven to eight and a clear preference for bulky natural substrates, such as 5-O-trans-feruloyl-L-arabinofuranose (FA) and β-D-xylopyranosyl-(1→2)-5-O-trans-feruloyl-L-arabinofuranose (FAX), compared to the synthetic standard substrate methyl ferulate. Treatment of wheat dough with as little as 0.03 U or 0.3 U kg^-1 reSwFAED activity resulted in a significant increase of the bun volume (8.0 or 9.7%, resp.) after baking when combined with polysaccharide-degrading enzymes from Aspergillus. For the first time, the long-standing, but rarely proven positive effect of a FAE in baking was confirmed.

High copy and stable expression of the xylanase XynHB in Saccharomyces cerevisiae by rDNA-mediated integration

Xylanase is a widely-used additive in baking industry for enhancing dough and bread quality. Several xylanases used in baking industry were expressed in different systems, but their expression in antibiotic free vector system is highly essential and safe. In the present study, an alternative rDNA-mediated technology was developed to increase the copy number of target gene by integrating it into Saccharomyces cerevisiae genome. A xylanase-encoding gene xynHB from Bacillus sp. was cloned into pHBM367H and integrated into S. cerevisiae genome through rDNA-mediated recombination. Exogenous XynHB expressed by recombinant S. cerevisiae strain A13 exhibited higher degradation activity towards xylan than other transformants. The real-time PCR analysis on A13 genome revealed the presence of 13.64 copies of xynHB gene. Though no antibiotics have been used, the genetic stability and the xylanase activity of xynHB remained stable up to 1,011 generations of cultivation. S. cerevisiae strain A13 expressing xylanase reduced the required kneading time and increased the height and diameter of the dough size, which would be safe and effective in baking industry as no antibiotics-resistance risk. The new effective rDNA-mediated technology without using antibiotics here provides a way to clone other food related industrial enzymes for applications.

Novel substrates for the automated and manual assay of endo-1,4-β-xylanase

endo-1,4-β-Xylanase (EC 3.2.1.8) is employed across a broad range of industries including animal feed, brewing, baking, biofuels, detergents and pulp (paper). Despite its importance, a rapid, reliable, reproducible, automatable assay for this enzyme that is based on the use of a chemically defined substrate has not been described to date. Reported herein is a new enzyme coupled assay procedure, termed the XylX6 assay, that employs a novel substrate, namely 4,6-O-(3-ketobutylidene)-4-nitrophenyl-β-4⁵-O-glucosyl-xylopentaoside. The development of the substrate and associated assay is discussed here and the relationship between the activity values obtained with the XylX6 assay versus traditional reducing sugar assays and its specificity and reproducibility were thoroughly investigated.

The Effects of Amyloglucosidase, Glucose Oxidase and Hemicellulase Utilization on the Rheological Behaviour of Dough and Quality Characteristics of Bread

Wheat flour, whole wheat flour, 25 and 50 % rye flour substituted wheat flour blends, 15 and 30 % wheat bran substituted wheat flour blends were supplemented with amyloglucosidase (at 0.000875 and 0.001 %), glucose oxidase (at 0.0003 and 0.001 %) and hemicellulase (at 0.001 and 0.005 %). The effects of enzymes on the extensographic properties of dough and quality characteristics of bread (specific volume, baking loss percentage and final moisture content) were studied. The interaction between type of flour/blend, type of enzyme and dosage of enzyme affected resistance to extension, extensibility and ratio of resistance to extensibility of doughs significantly. The interactions between type of flour/blend, type of enzyme and dosage of enzyme affected specific volume, baking loss percentage and final moisture content of breads significantly. The findings in this study indicated that enzymes can exhibit unexpected effects on dough and bread properties depending on type of flour and dosage of enzyme.

Bacterial xylanases: biology to biotechnology

In this review, a comprehensive discussion exclusively on bacterial xylanases; their gene organization; different factors and conditions affecting enzyme yield and activity; and their commercial application have been deliberated in the light of recent research findings and extensive information mining. Improved understanding of biological properties and genetics of bacterial xylanase will enable exploitation of these enzymes for many more ingenious biotechnological and industrial applications.

Thermoresistant xylanases from Trichoderma stromaticum: Application in bread making and manufacturing xylo-oligosaccharides

The enzymes Xyl1 and Xyl2 from T. stromaticum were purified and identified by mass spectrometry (MALDI-TOF/MS). Xyl1 contained three proteins with similarity to xylanase family 10, 62 and anarabinofuranosidase of the Trichoderma genus and Xyl2 contained a protein with similarity to endo-1,4-β-xylanase. High xylanase activity was found at 50°C for Xyl1 and 60°C for Xyl2 and pH 5.0 for both, retaining more than 80% of activities for one hour at 60°C and pH 5-8. Ag²⁺ and β-mercaptoethanol increased while SDS and EDTA inhibited the xylanase activity of both Xyl1 and Xyl2 extracts. The Km and V_max values for purified Xyl2 were 9.6mg/mL and 28.57μmol/min/mg, respectively. In application tests, both Xyl1 and Xyl2 were effective in degrading beechwood xylan to produce xylo-oligosaccharides. In baking, adding Xyl1 increased the softness and volume of wheat bread and whole grain bread, qualities increasingly desired by consumers in this segment.

Extremozymes from Marine Actinobacteria

Marine microorganisms that have the possibility to survive in diverse conditions such as extreme temperature, pH, pressure, and salinity are known as extremophiles. They produce biocatalysts so named as extremozymes that are active and stable at extreme conditions. These enzymes have numerous industrial applications due to its distinct properties. Till now, only a fraction of microorganisms on Earth have been exploited for screening of extremozymes. Novel techniques used for the cultivation and production of extremophiles, as well as cloning and overexpression of their genes in various expression systems, will pave the way to use these enzymes for chemical, food, pharmaceutical, and other industrial applications.

Discovering novel enzymes by functional screening of plurigenomic libraries from alga-associated Flavobacteriia and Gammaproteobacteria

Alga-associated microorganisms, in the context of their numerous interactions with the host and the complexity of the marine environment, are known to produce diverse hydrolytic enzymes with original biochemistry. We recently isolated several macroalgal-polysaccharide-degrading bacteria from the surface of the brown alga Ascophyllum nodosum. These active isolates belong to two classes: the Flavobacteriia and the Gammaproteobacteria. In the present study, we constructed two "plurigenomic" (with multiple bacterial genomes) libraries with the 5 most interesting isolates (regarding their phylogeny and their enzymatic activities) of each class (Fv and Gm libraries). Both libraries were screened for diverse hydrolytic activities. Five activities, out of the 48 previously identified in the natural polysaccharolytic isolates, were recovered by functional screening: a xylanase (GmXyl7), a beta-glucosidase (GmBg1), an esterase (GmEst7) and two iota-carrageenases (Fvi2.5 and Gmi1.3). We discuss here the potential role of the used host-cell, the average DNA insert-sizes and the used restriction enzymes on the divergent screening yields obtained for both libraries and get deeper inside the "great screen anomaly". Interestingly, the discovered esterase probably stands for a novel family of homoserine o-acetyltransferase-like-esterases, while the two iota-carrageenases represent new members of the poorly known GH82 family (containing only 19 proteins since its description in 2000). These original results demonstrate the efficiency of our uncommon "plurigenomic" library approach and the underexplored potential of alga-associated cultivable microbiota for the identification of novel and algal-specific enzymes.

Determination of the optimum mixture of transglutaminase, l-ascorbic acid and xylanase for the quality and consumer acceptability of bread using response surface methodology

The optimum levels of transglutaminase (TGase), l-ascorbic acid (l-AA), and xylanase (Xyl) were determined using response surface methodology to improve quality and consumer acceptability of bread made with wheat flour. A Box-Behnken design with three independent variables (TGase, l-AA, and Xyl) and three levels was used to develop models for the different responses (peak time, mixing tolerance, extensibility, resistance, specific volume, hardness, and consumer acceptability). Overall, l-AA and Xyl improved dough and bread properties, whereas the addition of TGase positively affected to texture and overall acceptability by consumer test. The optimal formulation for dough and bread properties and consumer acceptability were identified and the optimal value was 0.36 g/100 g TGase, 0.026 g/100 g Xyl, and 0.005 g/100 g l-AA. The results demonstrate that the addition of optimum amounts of TGase, Xyl, and l-AA improves the baking quality of the flour by enhancing dough properties and increase the consumer acceptability of the bread.

Improved Expression and Characterization of a Multidomain Xylanase from Thermoanaerobacterium aotearoense SCUT27 in Bacillus subtilis

A xylanase gene was cloned and characterized from Thermoanerobacterium aotearoense SCUT27, which was attested to consist of a signal peptide, one glycoside hydrolase family 10 domain, four carbohydrate binding modules, and three surface layer homology domains. The change of expression host from Escherichia coli to Bacillus subtilis resulted in a 4.1-fold increase of specific activity for the truncated XynAΔSLH. Five different versions of secretion signals in B. subtilis indicated that it was preferably routed via a Sec-dependent pathway. Purified XynAΔSLH showed a high activity of 379.8 U/mg on beechwood xylan. XynAΔSLH was optimally active at 80 °C, pH 6.5. Thin layer chromatography results showed that xylobiose and the presumed methylglucuronoxylotriose (MeGlcAXyl3) were the main products liberated from beechwood xylan catalyzed by the recombinant xylanase. All of the results suggest that XynAΔSLH is a suitable candidate for generating xylooligosaccharides from cellulosic materials for industrial uses.

Marine extremophiles: a source of hydrolases for biotechnological applications

The marine environment covers almost three quarters of the planet and is where evolution took its first steps. Extremophile microorganisms are found in several extreme marine environments, such as hydrothermal vents, hot springs, salty lakes and deep-sea floors. The ability of these microorganisms to support extremes of temperature, salinity and pressure demonstrates their great potential for biotechnological processes. Hydrolases including amylases, cellulases, peptidases and lipases from hyperthermophiles, psychrophiles, halophiles and piezophiles have been investigated for these reasons. Extremozymes are adapted to work in harsh physical-chemical conditions and their use in various industrial applications such as the biofuel, pharmaceutical, fine chemicals and food industries has increased. The understanding of the specific factors that confer the ability to withstand extreme habitats on such enzymes has become a priority for their biotechnological use. The most studied marine extremophiles are prokaryotes and in this review, we present the most studied archaea and bacteria extremophiles and their hydrolases, and discuss their use for industrial applications.

Distinct roles for carbohydrate-binding modules of glycoside hydrolase 10 (GH10) and GH11 xylanases from Caldicellulosiruptor sp. strain F32 in thermostability and catalytic efficiency

Xylanases are crucial for lignocellulosic biomass deconstruction and generally contain noncatalytic carbohydrate-binding modules (CBMs) accessing recalcitrant polymers. Understanding how multimodular enzymes assemble can benefit protein engineering by aiming at accommodating various environmental conditions. Two multimodular xylanases, XynA and XynB, which belong to glycoside hydrolase families 11 (GH11) and GH10, respectively, have been identified from Caldicellulosiruptor sp. strain F32. In this study, both xylanases and their truncated mutants were overexpressed in Escherichia coli, purified, and characterized. GH11 XynATM1 lacking CBM exhibited a considerable improvement in specific activity (215.8 U nmol(-1) versus 94.7 U nmol(-1)) and thermal stability (half-life of 48 h versus 5.5 h at 75°C) compared with those of XynA. However, GH10 XynB showed higher enzyme activity and thermostability than its truncated mutant without CBM. Site-directed mutagenesis of N-terminal amino acids resulted in a mutant, XynATM1-M, with 50% residual activity improvement at 75°C for 48 h, revealing that the disordered region influenced protein thermostability negatively. The thermal stability of both xylanases and their truncated mutants were consistent with their melting temperature (Tm), which was determined by using differential scanning calorimetry. Through homology modeling and cross-linking analysis, we demonstrated that for XynB, the resistance against thermoinactivation generally was enhanced through improving both domain properties and interdomain interactions, whereas for XynA, no interdomain interactions were observed. Optimized intramolecular interactions can accelerate thermostability, which provided microbes a powerful evolutionary strategy to assemble catalysts that are adapted to various ecological conditions.

Developing a xylanase XYNZG from Plectosphaerella cucumerina for baking by heterologously expressed in Kluyveromyces lactis

Background

Xylanase can replace chemical additives to improve the volume and sensory properties of bread in the baking. Suitable baking xylanase with improved yield will promote the application of xylanase in baking industry. The xylanase XYNZG from the Plectosphaerella cucumerina has been previously characterized by heterologous expression in Pichia pastoris. However, P. pastoris is not a suitable host for xylanase to be used in the baking process since P. pastoris does not have GRAS (Generally Regarded As Safe) status and requires large methanol supplement during the fermentation in most conditions, which is not allowed to be used in the food industry. Kluyveromyces lactis, as another yeast expression host, has a GRAS status, which has been successfully used in food and feed applications. No previous work has been reported concerning the heterologous expression of xylanase gene xynZG in K. lactis with an aim for application in baking.

Results

The xylanase gene xynZG from the P. cucumerina was heterologously expressed in K. lactis. The recombinant protein XYNZG in K. lactis presented an approximately 19 kDa band on SDS-PAGE and zymograms analysis. Transformant with the highest halo on the plate containing the RBB-xylan (Remazol Brilliant Blue-xylan) was selected for the flask fermentation in different media. The results indicated that the highest activity of 115 U/ml at 72 h was obtained with the YLPU medium. The mass spectrometry analysis suggested that the hydrolytic products of xylan by XYNZG were mainly xylobiose and xylotriose. The results of baking trials indicated that the addition of XYNZG could reduce the kneading time of dough, increase the volume of bread, improve the texture, and have more positive effects on the sensory properties of bread.

Conclusions

Xylanase XYNZG is successfully expressed in K. lactis, which exhibits the highest activity among the published reports of the xylanase expression in K. lactis. The recombinant XYNZG can be used to improve the volume and sensory properties of bread. Therefore, the expression yield of recombinant XYNZG can be further improved through engineered strain containing high copy numbers of the XYNZG, and optimized fermentation condition, making bread-baking application possible.

Bread Staling: Updating the View

Staling of bread is cause of significant product waste in the world. We reviewed the literature of the last 10 y with the aim to give an up-to-date overview on processing/storage parameters, antistaling ingredients, sourdough technology, and measurement methods of the staling phenomenon. Many researchers have been focusing their interest on the selection of ingredients able to retard staling, mainly hydrocolloids, waxy wheat flours (WWF), and enzymes, but different efforts have been made to understand the molecular basis of bread staling with the help of various measurement methods. Results obtained confirm the central role of amylopectin retrogradation and water redistribution within the different polymers in determining bread staling, but highlighted also the importance of other flour constituents, such as proteins and nonstarch polysaccharides. Data obtained with thermal, spectroscopy, nuclear magnetic resonance, X-ray crystallography, and colorimetry analysis have pointed out the need to encourage the use of one or more of these techniques in order to better understand the mechanisms of staling. Results so far obtained have provided new insight on bread staling, but the phenomenon has not been fully elucidated so far.

Novel Cold-Adapted Esterase MHlip from an Antarctic Soil Metagenome

An Antarctic soil metagenomic library was screened for lipolytic enzymes and allowed for the isolation of a new cytosolic esterase from the a/b hydrolase family 6, named MHlip. This enzyme is related to hypothetical genes coding esterases, aryl-esterases and peroxydases, among others. MHlip was produced, purified and its activity was determined. The substrate profile of MHlip reveals a high specificity for short p-nitrophenyl-esters. The apparent optimal activity of MHlip was measured for p-nitrophenyl-acetate, at 33 °C, in the pH range of 6-9. The MHlip thermal unfolding was investigated by spectrophotometric methods, highlighting a transition (Tm) at 50 °C. The biochemical characterization of this enzyme showed its adaptation to cold temperatures, even when it did not present evident signatures associated with cold-adapted proteins. Thus, MHlip adaptation to cold probably results from many discrete structural modifications, allowing the protein to remain active at low temperatures. Functional metagenomics is a powerful approach to isolate new enzymes with tailored biophysical properties (e.g., cold adaptation). In addition, beside the ever growing amount of sequenced DNA, the functional characterization of new catalysts derived from environment is still required, especially for poorly characterized protein families like α/b hydrolases.

Psychrophilic enzymes: from folding to function and biotechnology

Psychrophiles thriving permanently at near-zero temperatures synthesize cold-active enzymes to sustain their cell cycle. Genome sequences, proteomic, and transcriptomic studies suggest various adaptive features to maintain adequate translation and proper protein folding under cold conditions. Most psychrophilic enzymes optimize a high activity at low temperature at the expense of substrate affinity, therefore reducing the free energy barrier of the transition state. Furthermore, a weak temperature dependence of activity ensures moderate reduction of the catalytic activity in the cold. In these naturally evolved enzymes, the optimization to low temperature activity is reached via destabilization of the structures bearing the active site or by destabilization of the whole molecule. This involves a reduction in the number and strength of all types of weak interactions or the disappearance of stability factors, resulting in improved dynamics of active site residues in the cold. These enzymes are already used in many biotechnological applications requiring high activity at mild temperatures or fast heat-inactivation rate. Several open questions in the field are also highlighted.

Molecular characterization of a cold-active recombinant xylanase from Flavobacterium johnsoniae and its applicability in xylan hydrolysis

A novel xylanase gene, xyn10A, was cloned from Flavobacterium johsoniae, overexpressed in a flavobacterial expression system, the recombinant enzyme purified by Ni-affinity chromatography, and enzyme structure and activity analyzed. Xyn10A was found to be a modular xylanase with an Fn3 accessory domain on its N-terminal and a catalytic region on the C-terminal. The optimum pH and temperature for Xyn10A was 8.0 and 30 °C, but Xyn10A retained 50% activity at 4 °C, indicating that Xyn10A is a cold-active xylanase. A Fn3-deletion xylanase had relative activity ca. 3.6-fold lower than the wild-type, indicating that Fn3 promotes xylanase activity. The Fn3 region also contributed to stability of the enzyme at elevated temperatures. However, Fn3 did not bind this xylanase to insoluble substrates. The enzyme hydrolyzed xylo-oligosaccharides into xylobiose, and xylose with xylobiose as the main product, confirming that Xyn10A is a strict endo-β-1,4-xylanase. Xyn10A also hydrolyzed birchwood and beechwood xylan to yield mainly xylose, xylobiose and xylotriose.

Influence of xylanase addition on the characteristics of loaf bread prepared with white flour or whole grain wheat flour

The aim of this study was to verify the influence of the addition of the enzyme xylanase (four concentrations: 0, 4, 8, and 12 g.100 kg-1 flour) on the characteristics of loaf bread made with white wheat flour or whole grain wheat flour. Breads made from white flour and added with xylanase had higher specific volumes than those of the control sample (no enzyme); however, the specific volume did not differ significantly (p < 0.05) among the breads with different enzyme concentrations. All formulations made from whole grain wheat flour and added with xylanase also had specific volumes significantly higher than those of the control sample, and the highest value was found for the 8 g xylanase.100 kg-1 flour formulation. With respect to moisture content, the formulations with different enzyme concentrations showed small significant differences when compared to the control samples. In general, breads made with the addition of 8 g enzyme.100 kg-1 flour had the lowest firmness values, thus presenting the best technological characteristics.

Optimization to low temperature activity in psychrophilic enzymes

Psychrophiles, i.e., organisms thriving permanently at near-zero temperatures, synthesize cold-active enzymes to sustain their cell cycle. These enzymes are already used in many biotechnological applications requiring high activity at mild temperatures or fast heat-inactivation rate. Most psychrophilic enzymes optimize a high activity at low temperature at the expense of substrate affinity, therefore reducing the free energy barrier of the transition state. Furthermore, a weak temperature dependence of activity ensures moderate reduction of the catalytic activity in the cold. In these naturally evolved enzymes, the optimization to low temperature activity is reached via destabilization of the structures bearing the active site or by destabilization of the whole molecule. This involves a reduction in the number and strength of all types of weak interactions or the disappearance of stability factors, resulting in improved dynamics of active site residues in the cold. Considering the subtle structural adjustments required for low temperature activity, directed evolution appears to be the most suitable methodology to engineer cold activity in biological catalysts.

Treatment of bran containing bread by baking enzymes; effect on the growth of probiotic bacteria on soluble dietary fiber extract in vitro

Different ways of treating bran by baking enzymes prior to dough making and the baking process were used to increase the amount of water-soluble dietary fiber (DF) in wheat bread with added bran. Soluble DF was extracted from the bread with water and separated from the digestible material with gastrointestinal tract enzymes and by solvent precipitation. The baking enzyme mixtures tested (xylanase and glucanase/cellulase, with and without lipase) increased the amounts of soluble arabinoxylan and protein resistant to digestion. The isolated fiber was used as a growth substrate for 11 probiotic and intestinal Bifidobacterium strains, for commensal strains of Bacteroides fragilis and Escherichia coli, and for potential intestinal pathogenic strains of E. coli O157:H7, Salmonella typhimurium, and Clostridium perfringens. Fermentation analyses indicated that the tested strains had varying capacity to grow in the presence of the extracted fiber. Of the tested probiotic strains B. longum species generally showed the highest ability to utilize the fiber extracts, although the potential pathogens tested also showed an ability to grow on these fiber extracts. In sum, the enzymes used to improve the baking process for high-fiber bread can also be used to produce in situ soluble fiber material, which in turn can exert prebiotic effects on certain potentially beneficial microbes.

Function and biotechnology of extremophilic enzymes in low water activity

Enzymes from extremophilic microorganisms usually catalyze chemical reactions in non-standard conditions. Such conditions promote aggregation, precipitation, and denaturation, reducing the activity of most non-extremophilic enzymes, frequently due to the absence of sufficient hydration. Some extremophilic enzymes maintain a tight hydration shell and remain active in solution even when liquid water is limiting, e.g. in the presence of high ionic concentrations, or at cold temperature when water is close to the freezing point. Extremophilic enzymes are able to compete for hydration via alterations especially to their surface through greater surface charges and increased molecular motion. These properties have enabled some extremophilic enzymes to function in the presence of non-aqueous organic solvents, with potential for design of useful catalysts. In this review, we summarize the current state of knowledge of extremophilic enzymes functioning in high salinity and cold temperatures, focusing on their strategy for function at low water activity. We discuss how the understanding of extremophilic enzyme function is leading to the design of a new generation of enzyme catalysts and their applications to biotechnology.

Benefits of β-xylanase for wheat biomass conversion to bioethanol

BACKGROUND

The efficiency of bioethanol production from wheat biomass is related to the quality of end products as well as to safety criteria of co-products such as distiller's dried grains with solubles (DDGS). The inclusion of a new biocatalyst for non-starch polysaccharide degradation in fermentation processes could be one of the solutions. The objective of this study was to evaluate the influence of β-xylanases in combination with traditional amylolytic enzymes on the efficiency of bioethanol production and DON detoxification during fermentation of Fusarium-contaminated wheat biomass with high concentration of deoxynivalenol (DON; 3.95 mg kg(-1)).

RESULTS

The results showed that the negative effect of Fusarium spp. on yield and quality of bioethanol could be eliminated by the application of Trichoderma reesei xylanase in combination with amylolytic enzymes. This technological solution allowed to increase the concentration of ethanol in the fermented wort by 35.3% and to improve the quality of bioethanol by decreasing the concentrations of methanol, methyl acetate, isoamyl and isobutyl alcohols. Mass balance calculations showed that DDGS was the main source of DON contamination, comprising 74% of toxin found in wheat biomass. By using new enzyme combination for wheat biomass saccharification, a higher level of detoxification (41%) of DON was achieved during the fermentation process.

CONCLUSION

The addition of Trichoderma reesei xylanase played a positive role in bioethanol production from Fusarium-contaminated wheat biomass, indicating that the yeast-growing medium was enriched during the enzymatic treatment.

GH11 xylanases: Structure/function/properties relationships and applications

For technical, environmental and economical reasons, industrial demands for process-fitted enzymes have evolved drastically in the last decade. Therefore, continuous efforts are made in order to get insights into enzyme structure/function relationships to create improved biocatalysts. Xylanases are hemicellulolytic enzymes, which are responsible for the degradation of the heteroxylans constituting the lignocellulosic plant cell wall. Due to their variety, xylanases have been classified in glycoside hydrolase families GH5, GH8, GH10, GH11, GH30 and GH43 in the CAZy database. In this review, we focus on GH11 family, which is one of the best characterized GH families with bacterial and fungal members considered as true xylanases compared to the other families because of their high substrate specificity. Based on an exhaustive analysis of the sequences and 3D structures available so far, in relation with biochemical properties, we assess biochemical aspects of GH11 xylanases: structure, catalytic machinery, focus on their "thumb" loop of major importance in catalytic efficiency and substrate selectivity, inhibition, stability to pH and temperature. GH11 xylanases have for a long time been used as biotechnological tools in various industrial applications and represent in addition promising candidates for future other uses.

Use of psychrophilic xylanases provides insight into the xylanase functionality in bread making

The bread-improving potential of three psychrophilic xylanases from Pseudoalteromonas haloplanktis TAH3A (XPH), Flavobacterium sp. MSY-2 (rXFH), and unknown bacterial origin (rXyn8) was compared to that of the mesophilic xylanases from Bacillus subtilis (XBS) and Aspergillus aculeatus (XAA). XPH, rXFH, and rXyn8 increased specific bread volumes up to 28%, 18%, and 18%, respectively, while XBS and XAA gave increases of 23% and 12%, respectively. This could be related to their substrate hydrolysis behavior. Xylanases with a high capacity to solubilize water-unextractable arabinoxylan (WU-AX) during mixing, such as XBS and XPH, increased bread volume more than xylanases that mainly solubilized WU-AX during fermentation, such as rXFH, rXyn8, and XAA. Irrespective of their intrinsic bread-improving potential, the dosages needed to increase bread volume to a similar extent were much lower for psychrophilic than for mesophilic xylanases. The xylanase efficiency mainly depended on the enzyme's temperature activity profile and its inhibition sensitivity.