Microbial transglutaminase and its application in the food industry. A review

Microbial transglutaminase alters the immunogenic potential and cross-reactivity of horse and cow milk proteins

Horse milk is a valuable raw material and a very attractive alternative for scientific research to address the issue of cow milk (CM) allergy due to its protein profile. A decrease in immunoreactive properties can be achieved by thermal, enzymatic, and hydrolytic processing. Therefore, the aim of this study was to explore the possibility of reducing the immunoreactivity of horse milk proteins by microbial transglutaminase (TG) polymerization. To determine how TG linking alters immunoreactivity under simulated digestion of the examined milk, analyses were performed before, during, and after digestion. The dose-dependent (1, 10, and 100 U) effects of microbial TG on horse and cow milk were analyzed. A consecutive 3-stage digestion was simulated with salivary, gastric, and intestinal fluids. The effects of digestion were analyzed by SDS-PAGE, particle size analysis, and size-exclusion chromatography. Immunoreactivity was assessed using competitive ELISA (β-lactoglobulin and α-casein) and immunodot (sera from 7 patients aged 3 to 13 years who are allergic to CM proteins). Horse milk contained almost half of the amount of total proteins in CM. The dose 1 U/g of total milk protein changed the immunoreactivity of both cow and horse milk. With increasing TG doses, α-casein immunoreactivity increased, and β-lactoglobulin decreased. After total digestion, horse milk was characterized by 2.4-fold lower average IgE and 4.8-fold lower IgG reactivity than CM. We found that TG alters the IgE and IgG reactivity of CM after in vitro digestion. Horse milk was less reactive to IgE and IgG than was CM, with animal and patient sera. The effect of TG on immunoreactivity depends on enzyme quantity and milk protein type. The diet based on modified horse milk proteins could be an alternative for some patients with CM protein allergy; however, confirmation through clinical trials is needed.

Elevated Levels of 1,25-Dihydroxyvitamin D in Plasma as a Missing Risk Factor for Celiac Disease

The prevalence of celiac disease (CD) has increased significantly in some developed countries in recent decades. Potential risk factors that have been considered in the literature do not appear to provide a convincing explanation for this increase. This has led some researchers to hypothesize that there is a "missing environmental factor" that increases the risk of CD. Based on evidence from the literature, the author proposes that elevation in plasma levels of 1,25-dihydroxyvitamin D [1,25(OH)₂D] is a missing risk factor for CD, and relatedly that significant oral vitamin D exposure is a "missing environmental factor" for CD. First, elevated plasma levels of 1,25(OH)₂D are common in CD, especially in the newly diagnosed. Second, nine distinct conditions that increase plasma levels of 1,25(OH)₂D are either associated with CD or have indications of such an association in the literature. Third, a retrospective study shows that sustained oral vitamin D supplementation in infancy is associated with increased CD risk, and other studies on comorbid conditions support this association. Fourth, large doses of oral vitamin D upregulate many of the same cytokines, chemokines, and toll-like receptors that are upregulated in CD. Fifth, epidemiological evidence, such as the timing of the inception of a CD "epidemic" in Sweden, the increased prevalence of CD in Finland and the United States in recent decades, the unusually low prevalence of CD in Germany, and the differential in prevalence between Finnish Karelians and Russian Karelians, may all be explained by oral vitamin D exposure increasing CD risk. The same is true of some seemingly contradictory results in the literature on the effects of breastfeeding on CD risk. If future research validates this hypothesis, adjustments to oral vitamin D consumption among those who have genetic susceptibility may decrease the risk of CD in these individuals.

Transglutaminases: part I-origins, sources, and biotechnological characteristics

The transglutaminases form a large family of intracellular and extracellular enzymes that catalyze cross-links between protein molecules. Transglutaminases crosslinking properties are widely applied to various industrial processes, to improve the firmness, viscosity, elasticity, and water-holding capacity of products in the food and pharmaceutical industries. However, the extremely high costs of obtaining transglutaminases from animal sources have prompted scientists to search for new sources of these enzymes. Therefore, research has been focused on producing transglutaminases by microorganisms, which may present wider scope of use, based on enzyme-specific characteristics. In this review, we present an overview of the literature addressing the origins, types, reactions, and general characterizations of this important enzyme family. A second review will deal with transglutaminases applications in the area of food industry, medicine, pharmaceuticals and biomaterials, as well as applications in the textile and leather industries.

Application of Transglutaminase in Developing Cassava-based Wet Noodle for Quality and Shelf Life Improvement: A Review

Characteristic of cassava flour is relatively similar to wheat flour. Cassava flour has the potential to substitute 70-80% of wheat flour as the main ingredient for wet noodle production. Unfortunately, cassava flour has no gluten and lower protein content than wheat flour, which is important for the characteristic of a wet noodle. Therefore, transglutaminase (MTGase) is often applied in non-gluten products to improve its texture. This enzyme catalyzes the reaction between lysine and glutamine to form isopeptide cross-links. Moreover, the addition of MTGase to cassava-based wet noodle improves its texture and color. In addition, this effect gives better palatability for wet noodle. This enzyme can increase the shelf life of wet noodles and safe for our health. The present study demonstrates with patent and literature data the potential of MTGase in noodles based on cassava flour.

Continuous phase regulation of MoSe2 from 2H to 1T for the optimization of peroxidase-like catalysis

Simultaneous and synergistic modulation of the crystal phase and disorder in MoSe₂ to dramatically enhance their peroxidase-like activity.

State-of-the-art strategies and applied perspectives of enzyme biocatalysis in food sector - current status and future trends

With the recent progress in biotechnology, a wide variety of novel enzymes with unique physicochemical properties and diverse applications has been introduced, and new application list continues to extend in the future. Enzymes obtained from microorganisms, including bacteria, fungi, yeast are widely applied in numerous food formulations for intensifying their texture and taste. Owing to several desirable characteristics such as easy, cost-efficient and stable production, microbial-derived enzymes are preferred source in contrast to animals or plants. Enzymatic processes have a considerable impact in controlling the characteristics such as (1) physiochemical properties, (2) rheological functionalities, (3) facile process as compared to the chemical-based processing, (4) no or minimal consumption of harsh chemicals, (5) overall cost-effective ratio, (6) sensory and flavor qualities, and (7) intensifying the stability, shelf life and overall quality of the product, etc. in the food industry. Also, enzyme-catalyzed processing has also been designed for new food applications such as extraction of bioactive compounds, nutrient-rich and texture improved foods production, and eliminating food safety hazards. Herein, we reviewed recent applications of food-processing enzymes and highlighted promising technologies to diversify their application range in food industries. Immobilization technology enabled biocatalysts to be used cost-effectively due to reusability with negligible or no activity loss. Integrated progress in novel enzyme discovery, and recombinant DNA technology, as well as protein engineering and bioprocess engineering strategies, are believed to rapidly propagate biocatalysis at industrial-scale food processing or green and sustainable chemical manufacturing.

Review transglutaminases: part II-industrial applications in food, biotechnology, textiles and leather products

Because of their protein cross-linking properties, transglutaminases are widely used in several industrial processes, including the food and pharmaceutical industries. Transglutaminases obtained from animal tissues and organs, the first sources of this enzyme, are being replaced by microbial sources, which are cheaper and easier to produce and purify. Since the discovery of microbial transglutaminase (mTGase), the enzyme has been produced for industrial applications by traditional fermentation process using the bacterium Streptomyces mobaraensis. Several studies have been carried out in this field to increase the enzyme industrial productivity. Researches on gene expression encoding transglutaminase biosynthesis were performed in Streptomyces lividans, Escherichia coli, Corynebacterium glutamicum, Yarrowia lipolytica, and Pichia pastoris. In the first part of this review, we presented an overview of the literature on the origins, types, mediated reactions, and general characterizations of these important enzymes, as well as the studies on recombinant microbial transglutaminases. In this second part, we focus on the application versatility of mTGase in three broad areas: food, pharmacological, and biotechnological industries. The use of mTGase is presented for several food groups, showing possibilities of applications and challenges to further improve the quality of the end-products. Some applications in the textile and leather industries are also reviewed, as well as special applications in the PEGylation reaction, in the production of antibody drug conjugates, and in regenerative medicine.

Efficacy and Safety of Transglutaminase-Induced Corneal Stiffening in Rabbits

Purpose

To evaluate the biomechanical efficacy and safety of in vivo microbial transglutaminase (Tgases)-induced corneal crosslinking in a rabbit model.

Methods

A total of 34 white New Zealand rabbits were divided into two groups, a biochemistry group and a photochemistry group. The right eye of every rabbit was treated and left eyes served as negative controls. In the biochemistry group, a 1 U/mL solution of crosslinking agent microbial Tgases (Tgases CXL) was applied to the corneal surface, while in the photochemistry group, clinical ultraviolet A-riboflavin crosslinking (UVA/RF CXL) was used. Efficacy and safety evaluated on the 14th day after the procedures. Twelve pairs of corneal strips were harvested from the eyes of 12 euthanized rabbits in every group, and uniaxial tensile tests were performed to evaluate ex vivo biomechanical effects. The CXL-treated eye to its corresponding untreated eye ratio of tangent modulus were calculated. Another five pairs of corneal button were excised from euthanized animals in every group for corneal stroma and endothelium staining to evaluate changes in keratocyte distribution and endothelial cell damage.

Results

In tensile tests, tangent modulus was statistically higher in the Tgases CXL groups under 1.0 MPa (26.59 ± 4.54 vs. 21.47 ± 4.72 MPa, P = 0.04) and 1.5 MPa (29.75 ± 5.01 vs. 20.47 ± 6.63 MPa, P = 0.00). The tangent modulus ratio of Tgases group (1.72 ± 1.0 vs. 1.05 ± 0.22, P = 0.04) was significantly higher than that of UVA/RF under 1.5-MPa stress. The distribution of keratocytes in the corneal stroma and the morphologies of endothelial cells were similar in Tgases CXL-treated and untreated corneas. However, in the UVA/RF CXL group, keratocytes in the anterior half of stromal thickness were lost, and clear endothelial cell apoptosis was observed.

Conclusions

Tgases-CXL effectively stiffened the cornea and caused no damage to the endothelium and keratocytes in the cornea. This crosslinking method could be useful as a next-generation treatment for corneal ectasia and could replace CXL of photochemistry.

Translational Relevance

These findings may give a new hope to biomechanically compromised corneal disease due to mechanical forces, such as corneal ectasia and keratoconus. A next-generation treatment to these corneal diseases due to mechanical forces may be designed based on the new findings.

Extracellular production of active-form Streptomyces mobaraensis transglutaminase in Bacillus subtilis

Transglutaminase (TG) from Streptomyces mobaraensis has been widely used in the food industry. It is secreted naturally as an inactive zymogen, which is then activated by the removal of the N-terminal pro-peptide. In this study, the mtg gene from S. mobaraensis was expressed in a food-grade strain of bacterium, Bacillus subtilis. When its native signal peptide was replaced by signal peptide SacB (SP_sacB) and the pro-peptide was replaced by that derived from S. hygroscopicus, an extracellular activity of 16.1 U/mg was observed. A modified Saccharomyces cerevisiae vacuolar ATPase subunit (VMA) intein was introduced into the zymogen to simplify its activation process by controlling temperature. When the cleavage site in the C-terminal of VMA was placed between the pro-peptide and core domain, the activation process was carried out at 18 °C. Promoter replacement further increased the enzymatic activity. Finally, the extracellular enzymatic activity reached 2.6 U/mg under the control of the constitutive promoter P_yvyD. This is the first report on the extracellular production of active-form Streptomyces TG in B. subtilis without splicing with the cleavage enzyme.

Molecular insights into the mechanism of substrate recognition of Streptomyces transglutaminases

The microbial TGase from Streptomyces mobaraensis has used in various food industries. However, the detailed substrate specificities of TGases from the Streptomyces species toward the natural peptides remains to be unclear. In this study, we conducted the comparison of two different TGases from Streptomyces mobaranensis (SMTG) and Streptomyces cinnamoneus (SCTG). To clarify the region associated with the characteristics of enzymes, we constructed a chimeric enzyme of CM, of which is consisted of N-terminal half of SCTG and C-terminal half of SMTG. To reveal the differences in the substrate specificity between SCTG and SMTG toward natural peptides, we investigated the time dependence of TGase activity on the productivity of cross-linking peptide with tryptic casein and lysine by using LC-MS. We identified two peptides of "VLPVPQK" and "AVPYPQR" as substrates for both of the TGases.

Optimization of microencapsulation conditions of transglutaminase by freeze drying

Transglutaminase (TG), which is an important enzyme for food processing, can enhance the firmness, viscosity and water binding capacity of food products by catalyzing the cross-linking reaction of proteins. Since preservation of the enzyme activity is essential, the production of microencapsulated powder form of TG can be a great challenge to maintain its initial activity. In this study, TG was microencapsulated using a freeze drying technique and the effects of homogenization conditions and coating material ratios on the enzyme activity were investigated using D-optimal combined design. Mannitol, gum arabic and casein were chosen as coating materials and different homogenization times (1-5 min) and homogenization rates (11,200-20,000 rpm) were applied. The optimum conditions which ensure the maximum enzyme activity have been determined as 11,200 rpm of homogenization rate, 1.27 min of homogenization time, and in addition a mixture of mannitol, gum arabic and casein with ratios 38.2, 40.2, and 21.6%, respectively. Most of the activity loss occurred in the homogenization stage and the coating materials preserved enzyme activity during freeze drying. At the optimum point, the remaining activity of the microencapsulated TG was 93% while that of the crude (without coating materials) TG was 64% at the same drying conditions. Moreover, the effects of the microencapsulation conditions on the physical properties of powder such as moisture content, color, particle, bulk and tapped densities, porosity and flowability were determined.

Genipin-Aided Protein Cross-linking to Modify Structural and Rheological Properties of Emulsion-Filled Hempseed Protein Hydrogels

Genipin, a natural electrophilic cross-linker, was applied (5, 10, 20, and 30 mM) to modify hempseed protein isolate (HPI). Genipin treatments resulted in general losses of total sulfhydryls (up to 2.9 nmol/mg) and free amines (up to 77.3 nmol/mg). Surface hydrophobicity decreased by nearly 90% with 30 mM genipin, corresponding to similar tryptophan fluorescence quenching. The genipin treatment converted HPI into highly cross-linked polymers. Hydrogels formed with such polymers when also incorporated with hemp oil emulsions exhibited substantially enhanced gelling ability: up to 3.3- and 2.6-fold increases, respectively, in gel strength and gel elasticity over genipin-untreated protein. The genipin-modified composite gels also exhibited superior water-holding capacity. Microstructural analysis revealed a compact gel network filled with protein-coated oil globules that interacted intimately with the protein matrix when treated with genipin. Such gels remained readily digestible. Hence, genipin-treated hemp protein hydrogels show promise as functional food components.

Microbial transglutaminase for biotechnological and biomedical engineering

Research on bacterial transglutaminase dates back to 1989, when the enzyme has been isolated from Streptomyces mobaraensis. Initially discovered during an extensive screening campaign to reduce costs in food manufacturing, it quickly appeared as a robust and versatile tool for biotechnological and pharmaceutical applications due to its excellent activity and simple handling. While pioneering attempts to make use of its extraordinary cross-linking ability resulted in heterogeneous polymers, currently it is applied to site-specifically ligate diverse biomolecules yielding precisely modified hybrid constructs comprising two or more components. This review covers the extensive and rapidly growing field of microbial transglutaminase-mediated bioconjugation with the focus on pharmaceutical research. In addition, engineering of the enzyme by directed evolution and rational design is highlighted. Moreover, cumbersome drawbacks of this technique mainly caused by the enzyme's substrate indiscrimination are discussed as well as the ways to bypass these limitations.

E40, a novel microbial protease efficiently detoxifying gluten proteins, for the dietary management of gluten intolerance

Gluten proteins are the causative agent of Celiac Disease (CD), a life-long food intolerance characterized by an autoimmune enteropathy. Inadvertent gluten exposure is frequent even in celiac patients complying with a gluten-free diet, and the supplementation of exogenous gluten-digestive enzymes (glutenases) is indeed a promising approach to reduce the risk of dietary gluten boost. Here we describe Endopeptidase 40, a novel glutenase discovered as secreted protein from the soil actinomycete Actinoallomurus A8, and its recombinant active form produced by Streptomyces lividans TK24. E40 is resistant to pepsin and trypsin, and active in the acidic pH range 3 to 6. E40 efficiently degrades the most immunogenic 33-mer as well as the whole gliadin proteins, as demonstrated by SDS-PAGE, HPLC, LC-MS/MS, and ELISA. T lymphocytes from duodenal biopsies of celiac patients showed a strongly reduced or absent release of IFN-γ when exposed to gluten digested with E40. Data in gastrointestinal simulated conditions suggest that no toxic peptides are freed during gluten digestion by E40 into the stomach to enter the small intestine, thus counteracting the intestinal inflammatory cascade to occur in CD patients. E40 is proposed as a novel candidate in Oral Enzymatic Therapy for the dietary management of gluten toxicity.

Effect of microbial transglutaminase cross-linking on the quality characteristics and potential allergenicity of tofu

Microbial transglutaminase (MTGase) has been developed as a new tofu coagulant in recent years due to its good hydrophilicity, high catalytic activity, and strong thermal stability. This study aimed to investigate the effect of MTGase on the physicochemical properties and immunoreactivity of tofu relative to conventional coagulants [brine and glucono-δ-lactone (GDL)]. Structural changes of the MTGase cross-linked soymilk protein were characterized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), circular dichroism (CD) spectroscopy, ultraviolet (UV) absorption spectroscopy, and fluorescence spectroscopy. The IgE-binding capacity of MTGase cross-linked proteins was tested by enzyme-linked immunosorbent assay (ELISA). The physicochemical properties, quality characteristics, and surface microstructures of five different types of tofu were determined by the Kjeldahl nitrogen method, texture analysis, and scanning electron microscopy (SEM). The digestibility of tofu was evaluated in vitro by simulated gastrointestinal (GIS) digestion. A cell sensitization experiment was performed in vitro to evaluate the capability of tofu digestion products to induce the release of bioactive mediators from human basophil leukemia (KU812) cells. Results indicated that MTGase significantly changed the advanced structure of the soymilk protein. Compared with tofu without MTGase, the composite coagulant tofu containing MTGase exhibited better quality. MTGase improved the water-holding capacity (WHC) of the internal mesh structure and increased the yield of tofu. The digestion products of the composite coagulant tofu, especially the GDL plus MTGase tofu, induced KU812 cells to release fewer bioactive mediators compared with those of MTGase-free tofu. MTGase can not only improve the quality of conventional coagulant tofu but also reduce the potential allergenicity of tofu to a certain extent.

The Secretion of Streptomyces monbaraensis Transglutaminase From Lactococcus lactis and Immobilization on Porous Magnetic Nanoparticles

Microbial transglutaminase (MTG) from Streptomyces mobaraensis is an important enzyme widely applied in food processing for the improvement of protein properties by catalyzing the cross-linking of proteins. In this work we aimed at improving the production and enabling an easy and efficient purification process from culture supernatants. Thus, recombinant vectors, with either a constitutive promoter (P_p5) or an inducible promoter (P_nisA), controlling the expression of the MTG gene fused to the signal peptide of Usp45 (SP_usp45) were constructed and then expressed in Lactococcus lactis. After purification, 43.5 ± 0.4 mg/L mature MTG-6His was obtained. It displayed 27.6 ± 0.5 U/mg enzymatic activity cross-linking soy protein isolate effectively. The purified mature MTG was immobilized with magnetic porous Fe₃O₄ nanoparticles, which improved its activity up to 29.1 ± 0.4 U/mg. The immobilized MTG maintained 67.2% of the initial activity after being recycled for 10 times. The high production and secretion of functional S. mobaraensis MTG from L. lactis and the magnetic immobilized MTG-6His onto Fe₃O₄ nanoparticles reported in this study would have potential industrial applications.

Expression of Zea mays transglutaminase in Pichia pastoris under different promoters and its impact on properties of acidified milk protein concentrate gel

BACKGROUND

Transglutaminase (TGase) catalyzes post-translational modification of proteins by γ-glutamyl-ϵ-lysine chain links, covalent conjugation of polyamines, and deamidation. Zea mays TGase (TGZ) is a plant TGase with potential application prospects in the food industry. In this study, two promoter types, P_FLD1 and P_TEF1 , were compared to improve the expression of TGZ, and the cross-linking effect of recombinant TGZ on the properties of acid-induced milk protein concentrate (MPC) gel was assessed.

RESULTS

A higher expression of TGZ was obtained under the induction of P_FLD1 with a production of 635 U L^-1 . After purification using chromatography, TGZ activity was 0.4 U mg^-1 . The results indicated that TGZ treatment has effectively improved the textural properties of MPC gel at strength level and water-holding capacity. Optimal texture of MPC gel was achieved after TGZ treatment using 2 U g^-1 TGZ for 2 h at 35 °C and pH 7.

CONCLUSION

Comparative analysis of the promoters has greatly contributed to the production of TGZ in the industrial field. Furthermore, the modification of MPC gel texture by TGZ indicated that this recombinant enzyme has a practical value in dairy product, especially in yoghurt industry. © 2019 Society of Chemical Industry.

Improved the expression level of active transglutaminase by directional increasing copy of mtg gene in Pichia pastoris

Background

The microbial transglutaminase (MTG) is inactive when only the mature sequence is expressed in Pichia pastoris. Although co-expression of MTG and its N-terminal pro-peptide can obtain the active MTG, the enzyme activity was still low. One of the basic steps for strain improvement is to ensure a sufficient level of transcription of the heterologous gene, based on promoter strength and gene copy number. To date, high-copy-number recombinants of P. pastoris are achievable only by cloning of gene concatemers, so methods for rapid and reliable multicopy strains are therefore desirable.

Results

The coexpression strains harboring different copies mtg were obtained successfully by stepwise increasing Zeocin concentration based on the rDNA sequence of P. pastoris. The genome of coexpression strains with the highest enzyme activity was analyzed by real-time fluorescence quantitative PCR, and three copies of mtg gene (mtg-3c) was calculated according to the standard curve of gap and mtg genes (gap is regarded as the single-copy reference gene). The maximum enzyme activity of mtg-3c was up to 1.41 U/mL after being inducted for 72 h in 1 L flask under optimal culture conditions, and two protein bands were observed at the expected molecular weights (40 kDa and 5 kDa) by Western blot. Furthermore, among the strains detected, compared with mtg-2c, mtg-6c or mtg-8c, mtg-3c is the highest expression level and enzyme activity, implying that mtg-3c is the most suitable for co-expression pro-peptide and MTG.

Conclusions

This study provides an effective strategy for improving the expression level of active MTG by directional increasing of mtg copies in P. pastoris.

Electronic supplementary material

The online version of this article (10.1186/s12896-019-0542-6) contains supplementary material, which is available to authorized users.

A comparative analysis of catalytic activity and stability of microbial transglutaminase in controlled denaturing conditions

Microbial transglutaminases (MTGs) catalyzes the formation of Gln-Lys isopeptide bonds and are widely used for the cross-linking of proteins and peptides in food and in biotechnological applications for bioconjugation reactions. In view of its practical utility, a comparative study of the catalytic activity and stability of the enzyme in a wide range of denaturing conditions has been performed through Circular Dichroism (CD), fluorescence and activity assays performed with model substrates. In agreement with previous results, we show that MTG has a significant structural and functional tolerance to pH changes, whereas the enzyme stability and activity decrease in presence of increasing amounts of denaturing agents, such as urea and guanidinium chloride (GdnHCl). Noteworthy, the activity of MTG in denaturing conditions differs markedly from that in pseudo-physiological settings, shifting unexpectedly toward higher substrate specificity. Also, the use of controlled amounts of denaturing agents (1.0-1.5 M urea) largely improves yields and purity of the final products of 10-15% and 25-30%, respectively. These findings widen the range of applicability of the MTG-mediated biocatalysis for industrial and biotechnological purposes.

Expression of recombinant transglutaminase gene in Pichia pastoris and its uses in restructured meat products

Transglutaminase is an effective enzyme that catalyzes the crosslinking of various meats, improves meat product quality, and is widely used in the meat industry. In this study, microbial transglutaminase (MTG) was expressed successfully in Pichia pastoris strain GS115, and the enzyme activity was approximately 0.70 U/ml. The recombinant MTG expressed in P. pastoris was used in the investigation of restructured pork and crosslinking of soy protein isolate (SPI) and chicken myofibrillar protein (MP). Results showed that the hardness, chewiness, and F1 of the restructured pork increased, and the adhesiveness decreased after MTG treatment, However, high temperature had greater effect on the texture of restructured pork after MTG treatment than that of the control. MTG can crosslink SPI component acidic subunits, subunits of β-conglycinin and MP component myosin heavy chain, and actin. MTG, as a food additive, can be successfully heterologously expressed, and the recombinant MTG has potential application in restructured meat products.

Immunoreactivity of Gluten-Sensitized Sera Toward Wheat, Rice, Corn, and Amaranth Flour Proteins Treated With Microbial Transglutaminase

The aim of this study was to analyze the effects of microbial transglutaminase (mTG) on the immunoreactivity of wheat and gluten-free cereals flours to the sera of patients with celiac disease (CD) and non-celiac gluten sensitivity (NCGS). Both doughs and sourdoughs, the latter prepared by a two-step fermentation with Lactobacillus sanfranciscensis and Candida milleri, were studied. In order to evaluate the IgG-binding capacity toward the proteins of the studied flours, total protein as well as protein fractions enriched in albumins/globulins, prolamins and glutelins, were analyzed by SDS-PAGE and enzyme-linked immunosorbent assay (ELISA). Results showed that while mTG modified both gluten and gluten-free flour by increasing the amount of cross-linked proteins, it did not affect the serum's immune-recognition. In fact, no significant differences were observed in the immunoreactivity of sera from CD and NCGS patients toward wheat and gluten-free protein extracts after enzyme treatment, nor did this biotechnological treatment affect the immunoreactivity of control samples or the sera of healthy patients. These results suggest that mTG may be used as a tool to create innovative gluten and gluten-free products with improved structural properties, without increasing the immune-reactivity toward proteins present either in doughs or in sourdoughs.

3D printing of meat

Three-dimensional printing (3DP) process stands as a developing technology for food manufacturing, which offers the opportunity to design novel food products with improved nutritional value and sensorial profile. This review analyses the potential applications of 3DP technology for meat processing and the elemental aspects affecting the printability and post-processing feasibility of 3D printed meat products. The combination of nutritionally balanced ingredients and novel internal structures may be schemed into a multi-material 3D model that meets special individual needs, such as chewing and swallowing difficulties. Furthermore, a temperature-controlled extruder-type 3D printer built with multi-head system is suggested to suit the required conditions for meat safety and rheological requirements.

Bioengineering of microbial transglutaminase for biomedical applications

Microbial transglutaminase (mTGase) is commonly known in the food industry as meat glue due to its incredible ability to "glue" meat proteins together. Aside from being widely exploited in the meat processing industries, mTGase is also widely applied in other food and textile industries by catalysing the formation of isopeptide bonds between peptides or protein substrates. The advancement of technology has opened up new avenues for mTGase in the field of biomedical engineering. Efforts have been made to study the structural properties of mTGase in order to gain an in-depth understanding of the structure-function relationship. This review highlights the developments in mTGase engineering together with its role in biomedical applications including biomaterial fabrication for tissue engineering and biotherapeutics.

The Collagen Suprafamily: From Biosynthesis to Advanced Biomaterial Development

Collagen is the oldest and most abundant extracellular matrix protein that has found many applications in food, cosmetic, pharmaceutical, and biomedical industries. First, an overview of the family of collagens and their respective structures, conformation, and biosynthesis is provided. The advances and shortfalls of various collagen preparations (e.g., mammalian/marine extracted collagen, cell-produced collagens, recombinant collagens, and collagen-like peptides) and crosslinking technologies (e.g., chemical, physical, and biological) are then critically discussed. Subsequently, an array of structural, thermal, mechanical, biochemical, and biological assays is examined, which are developed to analyze and characterize collagenous structures. Lastly, a comprehensive review is provided on how advances in engineering, chemistry, and biology have enabled the development of bioactive, 3D structures (e.g., tissue grafts, biomaterials, cell-assembled tissue equivalents) that closely imitate native supramolecular assemblies and have the capacity to deliver in a localized and sustained manner viable cell populations and/or bioactive/therapeutic molecules. Clearly, collagens have a long history in both evolution and biotechnology and continue to offer both challenges and exciting opportunities in regenerative medicine as nature's biomaterial of choice.

Efficient Production of Homogeneous Lysine-Based Antibody Conjugates Using Microbial Transglutaminase

Random conjugation of chemical linkers to endogenous lysines or cysteines within an antibody yields a heterogeneous mixture of conjugates with various drug-to-antibody ratios. One approach for generating homogeneous antibody conjugates utilizes enzymatic transfer of payloads onto a specific glycan or amino acid residue. Microbial transglutaminase (MTG) is an enzyme that catalyzes the formation of a stable isopeptide bond between a glutamine and a lysine. We have previously identified and reported several sites throughout the antibody structure where an engineered lysine is sufficient for transfer of a glutamine-based substrate onto the antibody. Whereas other enzymatic transfer strategies typically require significant antibody engineering to either modify the N-glycans or introduce a multi-amino acid enzyme recognition site, the lower contextual specificity of MTG for lysines allows just a single lysine point mutation in an antibody to be efficiently transamidated. Here we describe the molecular positioning of these single engineered lysine residues and the conjugation conditions for producing homogeneous antibody conjugates exemplified using azido- and auristatin F-based acyl donor substrates.

Microbial transglutaminase: A new potential player in celiac disease

Microbial transglutaminase is heavily used in the food processing industries to improve food qualities. Being a protein's glue, by cross-linking it creates neoepitope complexes that are immunogenic and potentially pathogenic in celiac disease. Despite low sequence identity, it imitates functionally its family member, the endogenous tissue transglutaminase, which is the autoantigen of celiac disease. The present comprehensive review highlights the enzyme characteristics, endogenous and exogenous intestinal sources, its cross-talks with gluten and gliadin, its immunogenicity and potential pathogenicity and risks for the gluten induced conditions. If substantiated, it might represent a new environmental inducer of celiac disease. The present findings might affect nutritional product labeling, processed food additive policies and consumer health education.

Recent, non-classical, approaches to antibody lysine modification

This review will discuss recent development in the bioconjugation of lysine residues on antibodies. As several chemoselective reagents have already been developed for modifying amine groups, recent strategies now tend to aim at being site-specific. Four general methods have been listed: kinetically controlled, template-directed or enzymatic strategies as well as the use of chemically programmed antibodies.

Preparation and Characterization of Bioplastics from Grass Pea Flour Cast in the Presence of Microbial Transglutaminase

The aim of this work was to prepare bioplastics, from renewable and biodegradable molecules, to be used as edible films. In particular, grass pea (Lathyrus sativus L.) flour was used as biopolymer source, the proteins of which were structurally modified by means of microbial transglutaminase, an enzyme able to catalyze isopeptide bonds between glutamines and lysines. We analyzed, by means of Zeta-potential, the flour suspension with the aim to determine which pH is more stable for the production of film-forming solutions. The bioplastics were produced by casting and they were characterized according to several technological properties. Optical analysis demonstrated that films cast in the presence of the microbial enzyme are more transparent compared to the untreated ones. Moreover, the visualization by scanning electron microscopy demonstrated that the enzyme-modified films possessed a more compact and homogeneous structure. Furthermore, the presence of microbial transglutaminase allowed to obtain film more mechanically resistant. Finally, digestion experiments under physiological conditions performed in order to obtain information useful for applying these novel biomaterials as carriers in the industrial field, indicated that the enzyme-treated coatings might allow the delivery of bioactive molecules in the gastro-intestinal tract.

Cross-Talk Between Gluten, Intestinal Microbiota and Intestinal Mucosa in Celiac Disease: Recent Advances and Basis of Autoimmunity

Celiac disease (CD) is an autoimmune disorder of the small intestine, caused by gluten induced inflammation in some individuals susceptible to genetic and environmental influences. To date, pathophysiology of CD in relation to intestinal microbiota is not known well. This review relies on contribution of intestinal microbiome and oral microbiome in pathogenesis of CD based on their interactions with gluten, thereby highlighting the role of upper gastrointestinal microbiota. It has been hypothesized that CD might be triggered by additive effects of immunotoxic gluten peptides and intestinal dysbiosis (microbial imbalance) in the people with or without genetic susceptibilities, where antibiotics may be deriving dysbiotic agents. In contrast to the intestinal dysbiosis, genetic factors even seem secondary in disease outcome thus suggesting the importance of interaction between microbes and dietary factors in immune regulation at intestinal mucosa. Moreover, association of imbalanced counts of some commensal microbes in intestine of CD patients suggests the scope for probiotic therapies. Lactobacilli and specific intestinal and oral bacteria are potent source of gluten degrading enzymes (glutenases) that may contribute to commercialization of a novel glutenase therapy. In this review, we shall discuss advantages and disadvantages of food based therapies along with probiotic therapies where probiotic therapies are expected to emerge as the safest biotherapies among other in-process therapies. In addition, this review emphasizes on differential targets of probiotics that make them suitable to manage CD as along with glutenase activity, they also exhibit immunomodulatory and intestinal microbiome modulatory properties.

Acid-Induced Gelation of Caseins Glycated with Lactose: Impact of Maillard Reaction-Based Glycoconjugation and Protein Cross-Linking

During food processing or storage, milk proteins can react with reducing sugars via the Maillard reaction (glycation), which may alter their techno-functional properties. The aim of this study was to investigate the relationship between molecular changes of casein occurring during different stages of the Maillard reaction and its acid-induced gelling properties. Therefore, sodium caseinate was heated in a dry state at 60 °C in the presence of lactose and analyzed for structural modifications by determining Amadori compounds (glycoconjugation) indirectly as furosine, the total lysine modification, and the extent of protein cross-linking. For techno-functional characterization, acid-induced gels were prepared by the addition of glucono-δ-lactone and evaluated by measuring pH kinetics during gel formation, gel strength, and water holding capacity. The time to reach pH 4.6 during the gelation process was significantly delayed with increasing extent of the Maillard reaction. Glycation with lactose also led to a significant increase in gel strength and water holding capacity. The increase in gel stability was rather independent from the amount of sugars covalently bound to the proteins during the early phase of the Maillard reaction but strongly correlated to the degree of protein polymerization. Small- and medium-sized casein oligomers, formed during advanced stages of the Maillard reaction, contributed considerably to the formation of stronger gels with higher water holding capacity, whereas a sharp increase in the relative amount of the polymer fraction observed during prolonged cross-linking processes caused a spontaneous destabilization of the gel network. Knowledge about structure-function relationships on a molecular level can provide useful information to control food texture by raw material quality.