Determination of microbial transglutaminase in meat and meat products

The Frequently Used Industrial Food Process Additive, Microbial Transglutaminase: Boon or Bane

Microbial transglutaminase (mTG) is a frequently consumed processed food additive, and use of its cross-linked complexes is expanding rapidly. It was designated as a processing aid and was granted the generally recognized as safe (GRAS) classification decades ago, thus avoiding thorough assessment according to current criteria of toxicity and public health safety. In contrast to the manufacturer's declarations and claims, mTG and/or its transamidated complexes are proinflammatory, immunogenic, allergenic, pathogenic, and potentially toxic, hence raising concerns for public health. Being a member of the transglutaminase family and functionally imitating the tissue transglutaminase, mTG was recently identified as a potential inducer of celiac disease. Microbial transglutaminase and its docked complexes have numerous detrimental effects. Those harmful aspects are denied by the manufacturers, who claim the enzyme is deactivated when heated or by gastric acidity, and that its covalently linked isopeptide bonds are safe. The present narrative review describes the potential side effects of mTG, highlighting its thermostability and activity over a broad pH range, thus, challenging the manufacturers' and distributers' safety claims. The national food regulatory authorities and the scientific community are urged to reevaluate mTG's GRAS status, prioritizing public health protection against the possible risks associated with this enzyme and its health-damaging consequences.

The Potential Harmful Effects of Genetically Engineered Microorganisms (GEMs) on the Intestinal Microbiome and Public Health

Gut luminal dysbiosis and pathobiosis result in compositional and biodiversified alterations in the microbial and host co-metabolites. The primary mechanism of bacterial evolution is horizontal gene transfer (HGT), and the acquisition of new traits can be achieved through the exchange of mobile genetic elements (MGEs). Introducing genetically engineered microbes (GEMs) might break the harmonized balance in the intestinal compartment. The present objectives are: 1. To reveal the role played by the GEMs' horizontal gene transfers in changing the landscape of the enteric microbiome eubiosis 2. To expand on the potential detrimental effects of those changes on the human genome and health. A search of articles published in PubMed/MEDLINE, EMBASE, and Scielo from 2000 to August 2023 using appropriate MeSH entry terms was performed. The GEMs' horizontal gene exchanges might induce multiple human diseases. The new GEMs can change the long-term natural evolution of the enteric pro- or eukaryotic cell inhabitants. The worldwide regulatory authority's safety control of GEMs is not enough to protect public health. Viability, biocontainment, and many other aspects are only partially controlled and harmful consequences for public health should be avoided. It is important to remember that prevention is the most cost-effective strategy and primum non nocere should be the focus.

Transglutaminase in Foods and Biotechnology

Stabilization and reusability of enzyme transglutaminase (TGM) are important goals for the enzymatic process since immobilizing TGM plays an important role in different technologies and industries. TGM can be used in many applications. In the food industry, it plays a role as a protein-modifying enzyme, while, in biotechnology and pharmaceutical applications, it is used in mediated bioconjugation due to its extraordinary crosslinking ability. TGMs (EC 2.3.2.13) are enzymes that catalyze the formation of a covalent bond between a free amino group of protein-bound or peptide-bound lysine, which acts as an acyl acceptor, and the γ-carboxamide group of protein-bound or peptide-bound glutamine, which acts as an acyl donor. This results in the modification of proteins through either intramolecular or intermolecular crosslinking, which improves the use of the respective proteins significantly.

Role of Enzymatic Reactions in Meat Processing and Use of Emerging Technologies for Process Intensification

Meat processing involves different transformations in the animal muscle after slaughtering, which results in changes in tenderness, aroma and colour, determining the quality of the final meat product. Enzymatic glycolysis, proteolysis and lipolysis play a key role in the conversion of muscle into meat. The accurate control of enzymatic reactions in meat muscle is complicated due to the numerous influential factors, as well as its low reaction rate. Moreover, exogenous enzymes are also used in the meat industry to produce restructured products (transglutaminase), to obtain bioactive peptides (peptides with antioxidant, antihypertensive and gastrointestinal activity) and to promote meat tenderization (papain, bromelain, ficin, zingibain, cucumisin and actinidin). Emerging technologies, such as ultrasound (US), pulsed electric fields (PEF), moderate electric fields (MEF), high-pressure processing (HPP) or supercritical CO₂ (SC-CO₂), have been used to intensify enzymatic reactions in different food applications. This review aims to provide an overview of the enzymatic reactions taking place during the processing of meat products, how they could be intensified by using emerging technologies and envisage potential applications.

Microbial Transglutaminase Is a Very Frequently Used Food Additive and Is a Potential Inducer of Autoimmune/Neurodegenerative Diseases

Microbial transglutaminase (mTG) is a heavily used food additive and its industrial transamidated complexes usage is rising rapidly. It was classified as a processing aid and was granted the GRAS (generally recognized as safe) definition, thus escaping full and thorough toxic and safety evaluations. Despite the manufacturers claims, mTG or its cross-linked compounds are immunogenic, pathogenic, proinflammatory, allergenic and toxic, and pose a risk to public health. The enzyme is a member of the transglutaminase family and imitates the posttranslational modification of gluten, by the tissue transglutaminase, which is the autoantigen of celiac disease. The deamidated and transamidated gliadin peptides lose their tolerance and induce the gluten enteropathy. Microbial transglutaminase and its complexes increase intestinal permeability, suppresses enteric protective pathways, enhances microbial growth and gliadin peptide's epithelial uptake and can transcytose intra-enterocytically to face the sub-epithelial immune cells. The present review updates on the potentially detrimental side effects of mTG, aiming to interest the scientific community, induce food regulatory authorities' debates on its safety, and protect the public from the mTG unwanted effects.

The temperature and pH repertoire of the transglutaminase family is expanding

Transglutaminases (TGs) play important roles in the food industry, pharmacology, and biotechnology, but as protein cross‐linkers, their complexes are stable, resistant, immunogenic, and potentially pathogenic. Many TGs have been characterized, but they operate in narrow temperature and pH range limits. In a research article in this issue, Clemens Furnes and colleagues describe a novel cold‐adapted TG from Atlantic cod, which expands the operating boundaries to a lower temperature and a wider pH. In this accompanying commentary, we discuss how this TG opens new applications in cold environments and can be deactivated by heating. New sources of TGs should be explored in hot environments like hot springs, in order to increase the temperature and widen the pH ranges for human and industrial benefits.

Antibodies against neo-epitope of microbial and human transglutaminase complexes as biomarkers of childhood celiac disease

Tissue transglutaminase (tTG) and microbial transglutaminase (mTG) cross-link gliadins to form complexes that expose immunogenic neo-epitopes to produce tTG and mTG-neo-epitope antibodies. The aim of this study was to test the diagnostic performance of antibodies against non-complexed and complexed forms of transglutaminases, to correlate their activities to the intestinal damage and to explore age group dependency in celiac disease (CD). A total of 296 children with untreated CD and 215 non-celiac disease controls were checked by in-house enzyme-linked immunosorbent assays detecting immunoglobulin (Ig)A, IgG or combined detection of IgA and IgG (check) against tTG, AESKULISA® tTG New Generation (tTG-neo) and mTG-neo (RUO), IgA and IgG antibodies against deamidated gliadin peptide (DGP) and human IgA anti-endomysium antibodies (EMA) using AESKUSLIDES® EMA. Intestinal pathology was graded according the revised Marsh criteria, and age dependencies of the antibody activities were analysed. Using cut-offs estimated from receiver operating characteristic (ROC) curves, the highest area under curve (AUC) of the TG assays was 0·963 for tTG-neo check, followed by tTG check (0·962) when the diagnosis was based on enteric mucosal histology. tTG-neo check was the most effective to reflect the intestinal abnormalities in CD (r = 0·795, P < 0·0001). High levels of anti-mTG-neo IgG and anti-tTG-neo IgG appeared in the earlier age groups, as compared to anti-tTG IgG (P < 0·001). Considering antibody diagnostic performance based on AUC, enteric damage reflection and predictability at an early age, the anti-neo tTG check was the most effective diagnostic biomarker for pediatric CD. The mTG neo check might represent a new marker for CD screening, diagnosis and predictability.

Processed Food Additive Microbial Transglutaminase and Its Cross-Linked Gliadin Complexes Are Potential Public Health Concerns in Celiac Disease

Microbial transglutaminase (mTG) is a survival factor for microbes, but yeasts, fungi, and plants also produce transglutaminase. mTG is a cross-linker that is heavily consumed as a protein glue in multiple processed food industries. According to the manufacturers' claims, microbial transglutaminase and its cross-linked products are safe, i.e., nonallergenic, nonimmunogenic, and nonpathogenic. The regulatory authorities declare it as "generally recognized as safe" for public users. However, scientific observations are accumulating concerning its undesirable effects on human health. Functionally, mTG imitates its family member, tissue transglutaminase, which is the autoantigen of celiac disease. Both these transglutaminases mediate cross-linked complexes, which are immunogenic in celiac patients. The enzyme enhances intestinal permeability, suppresses mechanical (mucus) and immunological (anti phagocytic) enteric protective barriers, stimulates luminal bacterial growth, and augments the uptake of gliadin peptide. mTG and gliadin molecules are cotranscytosed through the enterocytes and deposited subepithelially. Moreover, mucosal dendritic cell surface transglutaminase induces gliadin endocytosis, and the enzyme-treated wheat products are immunoreactive in CD patients. The present review summarizes and updates the potentially detrimental effects of mTG, aiming to stimulate scientific and regulatory debates on its safety, to protect the public from the enzyme's unwanted effects.

Microbial transglutaminase should be considered as an environmental inducer of celiac disease

Due to the recent interest in food additives that can act as triggering factors in autoimmune diseases including celiac disease (CD), the present letter to the editor expands on the microbial transglutaminase (mTG). It is heavily consumed by a plethora of food processing industries as "glue of proteins" thus improving product's stability, texture and shelf life. However, more and more information is accumulated lately, questioning its safety. Its cross-linked gliadin complexes are immunogenic in CD. The enzyme increases gliadin uptake, is transported in a trans-epithelial way and deposited below the enterocyte's line, has anti- phagocytic activity, enhances intestinal permeability and creates luminal resistant isopeptide bonds. No doubt that mTG is beneficial to food industries but a caveat to public health is highly recommended.

Intracellular Localization of Microbial Transglutaminase and Its Influence on the Transport of Gliadin in Enterocytes

OBJECTIVE

Celiac disease (CD) is a systemic inflammatory disorder, characterized by the destruction of duodenal epithelium. The CD8 T cells involved are associated with cross-presentation. In addition to other factors, the rising prevalence of CD might be induced by microbial transglutaminase (mTG) an enzyme frequently used in food production that shares enzymatic and antigenic properties of tissue transglutaminase (TG2), the autoantigen in CD. We hypothesized that mTG and gliadin are transported into the endoplasmic reticulum (ER), indicating cross-presentation of both antigens.

METHODS

Apical incubation of duodenal biopsies from CD and control patients was performed with mTG alone or with mTG and simultaneously with Frazer's fraction. Evaluation was carried out by immunofluorescence and electron microscopy.

RESULTS

Approximately 6% to 9% of the intracellular mTG and gliadin were transported to the ER of enterocytes. RACE cells (Rapid uptake of Antigen into the Cytosol of Enterocytes) displayed an enhanced antigen uptake into a dilated ER. mTG strongly localized at the basolateral membrane and the lamina propria.

CONCLUSIONS

mTG and gliadin are transported to the ER of enterocytes and to a greater extent to the ER of RACE cells, suggesting cross-presentation of exogenous antigens. The strong localization of mTG at the basolateral membrane and the lamina propria may also indicate a potential antigenic interaction with cells of the immune system. Since mTG may not only been taken up with food stuffs but could also be released by bacteria within the intestinal microbiota, further investigations are needed regarding the role of mTG in CD pathogenesis.

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.

Microbial Transglutaminase Is Immunogenic and Potentially Pathogenic in Pediatric Celiac Disease

The enzyme microbial transglutaminase is heavily used in the food processing industries to ameliorate food qualities and elongate the products' shelf life. As a protein's glue, it cross-links gliadin peptides, creating neo-complexes that are immunogenic and potentially pathogenic to celiac disease communities. Even lacking sequence identity, it imitates functionally the endogenous tissue transglutaminase, known to be the autoantigen of celiac disease and representing an undisputable key player in celiac disease initiation and progress. The present review expend on the enzyme characteristics, exogenous intestinal sources, its cross-linking avidity to gluten or gliadin, turning naïve protein to immunogenic ones. Several observation on microbial transglutaminase cross linked complexes immunogenicity in celiac patients are reviewed and its pathogenicity is summarized. Warnings on its potential risks for the gluten dependent conditions are highlighted. When substantiated, it might represent a new environmental factor of celiac disease genesis. It is hoped that the presented knowledge will encourage further research to explore the mechanism and the pathogenic pathways taken by the gliadin cross linked enzyme in driving celiac disease.

A sensitive HPLC-MS/MS method for the simultaneous detection of microbial transglutaminase, and bovine and porcine fibrinogen/thrombin in restructured meat

A sensitive HPLC-MS/MS method for the simultaneous detection of microbial transglutaminase (TG) from Streptomyces mobaraensis, and bovine and porcine fibrinogen/thrombin in restructured meat was developed using tryptic marker peptides of TG (five markers), and bovine and porcine fibrinogen (six markers each). Meat binding experiments with beef and pork were performed using a technical TG mixture (Activa, Ajinomoto), and bovine and porcine plasmapowder FG (PPFG; Sonac B.V.). The method developed allows the simultaneous detection of the use of these cold-set binders in raw and heated samples. The peak areas of the fibrinogen marker peptides were increased by a factor of about 100, compared to blank values originating from the occurrence of residual blood in meat, using a concentration of 0.6% bovine and porcine PPFG. A differentiation between the use of blood plasma powder and PPFG using the ratios of fibrinogen to serotransferrin peptide peak areas seems to be possible.

Purification and biochemical characterization of a novel transglutaminase from Mythimna separata larvae (Noctuidae, Lepidoptera)

A novel transglutaminase (MsTGase) from Mythimna separata larvae was separated and purified; its biochemical property and enzymatic catalytic activities were investigated. MsTGase was obtained chromatographically by the precipitation of Sephadex G-100 gel and DEAE-Cellulose-52 ion-exchange column with 48-fold purification and a reproducible yield of approximately 12%. Molecular weight of the MsTGase was 63.5 KDa and its N-terminal amino acid sequence was GKIEEG-LVI. Michaelis constant of the MsTGase for the substrate N-CBZ-Gln-Gly was 12.83mM with a V_max of 7.99U/mL. Optimum conditions for MsTGase activity were at 42°C and pH7.5. The enzyme didn't possess metal ion at its catalytic active site; its activity could be significantly inhibited by Mg²⁺, but activated by Ca²⁺. Chlorpyrifos and spinosad showed a strong potential to increase MsTGase activity, supporting the view that MsTGase was a novel target. Moreover, the formation of intermolecular cross-links of casein and bovine serum albumin polymerized by MsTGase in the presence of DTT was observed. These findings pave the way for future studies on the physiological role of MsTGase and the potential impact of its regulation on MsTGase-associated pest management.

Production of dry-cured formed ham with different concentrations of microbial transglutaminase: Mass spectrometric analysis and sensory evaluation

Dry-cured formed hams were produced with different concentrations of microbial transglutaminase (TG; 0.05, 0.1, 0.2, 0.5, and 0.8% Activa PB) and glucono-delta-lactone as control. A sensory evaluation was performed during a 43-day storage to determine cohesion, cavities, and local separation of dry-cured formed ham. Rising TG concentrations resulted in a slight increase in the evaluation of all sensory parameters, whereas amounts of TG higher than 0.5% led to an only very minor improvement. Dry-cured formed ham samples were analyzed by a sensitive HPLC-MS/MS method for the detection of TG using five tryptic marker peptides. Even very small amounts of Activa PB (0.05%) were detectable unambiguously. A decrease of TG detectability during the storage time of dry-cured formed ham was not observed. Using four marker peptides, no false-positive or -negative results were obtained. The amounts of two marker peptides were calculated using isotope-labeled peptides. They showed high correlations to the amount of Activa PB (R²>0.995).

A sensitive high performance liquid chromatography-tandem mass spectrometry method for the detection of microbial transglutaminase in different types of restructured meat

A sensitive HPLC-MS/MS-method for the detection of microbial transglutaminase (TG) from Streptomyces mobaraensis in different types of restructured meat (pork, beef, chicken, and turkey) was developed using six tryptic marker peptides (8-11 amino acids). Meat binding experiments were performed with two technical TG mixtures with and without caseinate. After optimization of the conditions of extraction and tryptic digestion, restructured meat and blank values (total samples: 62) were analyzed in a raw and heated state. By investigation of samples pre-treated with oil marinade, emulsion marinade, seasoning salt as well as breadcrumbs, only very little effects of the type of pre-treatment on the detectability of TG were found. Using four marker peptides, no false-positive or false-negative results were obtained. The limit of detection (LOD) was about a factor of 10 below the recommended amount of transglutaminase for raw as well as heated restructured meat.

Colloidal Gold Probe-Based Immunochromatographic Strip Assay for the Rapid Detection of Microbial Transglutaminase in Frozen Surimi

Adding microbial transglutaminase (MTGase) to frozen surimi to enable the surimi to be sold as a higher-grade product at a higher price defrauds surimi product manufacturers and undercuts legitimate industry prices. Therefore, it is important to develop an accurate method of detecting the presence of MTGase in surimi. In this study, an immunochromatographic strip assay with a colloidal gold antibody probe was successfully developed and used to rapidly and qualitatively detect MTGase in surimi samples. The results were obtained in less than 10 min. The limit for the qualitative detection of MTGase using the immunochromatographic strip assay was identified as 1.0 μg/mL. The results of the immunochromatographic strip analysis of frozen surimi samples were verified by comparison with the results of a sandwich enzyme-linked immunosorbent assay. The colloidal gold probe-based immunochromatographic strip assay was thus found to be a rapid, economical, and user friendly method of detecting MTGase in surimi.

Possible association between celiac disease and bacterial transglutaminase in food processing: a hypothesis

The incidence of celiac disease is increasing worldwide, and human tissue transglutaminase has long been considered the autoantigen of celiac disease. Concomitantly, the food industry has introduced ingredients such as microbial transglutaminase, which acts as a food glue, thereby revolutionizing food qualities. Several observations have led to the hypothesis that microbial transglutaminase is a new environmental enhancer of celiac disease. First, microbial transglutaminase deamidates/transamidates glutens such as the endogenous human tissue transglutaminase. It is capable of crosslinking proteins and other macromolecules, thereby changing their antigenicity and resulting in an increased antigenic load presented to the immune system. Second, it increases the stability of protein against proteinases, thus diminishing foreign protein elimination. Infections and the crosslinked nutritional constituent gluten and microbial transglutaminase increase the permeability of the intestine, where microbial transglutaminases are necessary for bacterial survival. The resulting intestinal leakage allows more immunogenic foreign molecules to induce celiac disease. The increased use of microbial transglutaminase in food processing may promote celiac pathogenesis ex vivo, where deamidation/transamidation starts, possibly explaining the surge in incidence of celiac disease. If future research substantiates this hypothesis, the findings will affect food product labeling, food additive policies of the food industry, and consumer health education.

Changes in intestinal tight junction permeability associated with industrial food additives explain the rising incidence of autoimmune disease

The incidence of autoimmune diseases is increasing along with the expansion of industrial food processing and food additive consumption. The intestinal epithelial barrier, with its intercellular tight junction, controls the equilibrium between tolerance and immunity to non-self-antigens. As a result, particular attention is being placed on the role of tight junction dysfunction in the pathogenesis of AD. Tight junction leakage is enhanced by many luminal components, commonly used industrial food additives being some of them. Glucose, salt, emulsifiers, organic solvents, gluten, microbial transglutaminase, and nanoparticles are extensively and increasingly used by the food industry, claim the manufacturers, to improve the qualities of food. However, all of the aforementioned additives increase intestinal permeability by breaching the integrity of tight junction paracellular transfer. In fact, tight junction dysfunction is common in multiple autoimmune diseases and the central part played by the tight junction in autoimmune diseases pathogenesis is extensively described. It is hypothesized that commonly used industrial food additives abrogate human epithelial barrier function, thus, increasing intestinal permeability through the opened tight junction, resulting in entry of foreign immunogenic antigens and activation of the autoimmune cascade. Future research on food additives exposure-intestinal permeability-autoimmunity interplay will enhance our knowledge of the common mechanisms associated with autoimmune progression.