Microbial transglutaminase

Transglutaminase (also known as mTG, microbial transglutaminase) is an enzyme widely known among manufacturers that is commonly used as a texturizing agent. Its has a feature of catalyzing the formation of covalent bonds between free amino groups of lysine and gamma-carboxamide groups of glutamine. A stable and heat-resistant network of protein molecules is produced as a result.

Due to this property, transglutaminase can be used in all areas of the food industry. Specifically in the dairy production, it is added to starter culture in order to obtain denser structures of a final product, to reduce syneresis as well as to minimize the discharge of proteins into whey. In meat industry this enzyme is used to cross-link pieces of raw meat, while retaining meat juice and additional moisture more efficiently.

In the European Union, the use of industrial enzymes is not yet regulated, and there is also no list of enzymes that would be recognized as safe and suitable for use. Even if in some countries, for example in France, transglutaminase is permitted for use, but it is limited to only one transglutaminase producer, which is Streptoverticillium mobaraense. Ajinomoto, a Japanese company that produces mTG, declared on its official website: “Until the positive list has been drawn up, food enzymes and food using food enzymes may be placed on the market and used in accordance with the existing national rules in the EU Members”. The company’s website has a section entitled: “Is there any legislation governing TG in EU?”

In the past, the safety of food enzymes was assessed by the European Scientific Committee on Food (SCF). In 2003, the SCF was replaced by EFSA (European Food Safety Authority), which now provides independent advice and information on current and potential food-related risks. Directive (EC) 1332/2008, which was enacted in January 2009, regulates the use of enzymes in the food industry in the European Union. Among other things, it aims to create a list of enzymes, the use of which in food industry will be permitted after EFSA assessment, European Commission approval and vote in the European Parliament. Manufacturers were asked to submit dossiers on their enzymes before March 2015. Ajinomoto submitted the dossier on transglutaminase from Streptoverticillium mobaraense (strain S-8112), and other companies sent their dossiers for two more strains (strain DSM40587, strain DSM 40587). In order to provide information and ensure transparency, the commission decided to publish applications for food enzymes with no access restrictions. If we look into the document: Food enzyme applications submitted to the Commission within the legal deadline (Version 4 Updated on 25 July 2016), we shall see that it contains only three applications for different strains. However, an article by the scientists Aaron Lerner and Torsten Matthias, where they count the producers used in the food industry to produce mTG, which are mentioned in the scientific literature, lists about 20 different strains. It is supposed that EFSA is currently conducting an enzyme assessment. Updated information on the progress of this assessment can be found on the organization’s website. A report on the website of the European Commission says that, due to the large number of dossiers received (more than 300 dossiers on all enzymes) and due to the fact that all applications must be evaluated and subsequently approved, it will take several years to prepare the EU list. 6 years have passed since then, but there are still no updates at the indicated link, there are also no studies proving the safety of the enzyme.

That being said, there are a number of articles, which are published in high-ranking journals, that raise questions about the negative effects of this enzyme on human health. For instance, we can mention the article “Transglutaminases in dysbiosis as potential environmental drivers of autoimmunity” Its authors Aaron Lerner and Torsten Matthias referred to a number of recent studies relating to the adverse effects of mTG on the human intestine. In one of their latest articles for 2020 published in MDPI (International Journal of Molecular Sciences), which is a pioneer in open access scientific publishing and has supported the academic communites since 1996, the authors say: “The mTG enzyme mediates cross-linked complexes, which are immunogenic in celiac patients. The enzyme enhances intestinal permeability, suppresses mechanical and immunological enteric protective barriers, stimulates luminal bacterial growth, and augments the uptake of gliadin peptide. mTG and gliadin molecules are co-transcytosed through the enterocytes and are deposited sub-epithelially“. Especially note the conclusion: “The enzyme-treated wheat products are immunoreactive in patients with celiac disease. It is hoped that the present review will encourage clinical, scientific and regulatory debates on mTG safety, to protect the public from the enzyme’s unwanted effects”.It is important to note in this context that the authors of the article Lerner and Matthias work at the German institute AESKU.KIPP, which initiates and coordinates international cooperation projects in the field of autoimmunity research (the body’s immune response against self antigens). The team of scientists calls for research on the safety of the enzyme and warns about the consequences of its use. Lerner and Matthias write: “This review summarizes the epidemiological, scientific, serological, and clinical proof for the use of mTG and its transamidated products as food additives, as well as their immunogenicity, and potential pathogenicity”.

There is sufficient basic knowledge to address the safety issues concerning mTG within a framework of an interdisciplinary approach. Protecting public health from the adverse effects of mTG should be of paramount importance. Speaking of potential pathogenic activity, the authors report: it stimulates bacterial growth; augments the uptake of gliadin; affects the quality of mucus; is absorbed by dendritic cells of mucous membrane; creates luminal stable isopeptide bonds; enhances intestinal permeability; is transported transepithelially; is deposited sub-epithelially; exerts antiphagocytic activity; induces the production of specific antibodies; produces immunogenic complexes; is allergenic. Due to the potential pathogenic activity of the mTG enzyme and its immunogenic complexes with gliadin, the authors urge global food safety authorities to review existing knowledge and consider the status of this actively used food additive. If research results are obtained, the findings made on their basis will change food labelling, food additive policies and regulatory control for food products, which will have a positive impact on consumer health.

A Spanish publication that appeared two years ago “Microbial transglutaminase: a review on current concerning aspects“, written by specialists from the Department of Animal and Food Science, Faculty of Veterinary, University of Barcelona (Universitat Autònoma de Barcelona) Ioana Darloman and Montserrat Mor-Mur Francesch, states the following: “Besides the aspect of consumer deception, possible health impairments for celiac disease patients and a potential risk of microbial contaminations, microbial transglutaminase is currently also discussed as an allergen. Several hypotheses have been proposed in regard to the health effects of residual transglutaminase or products and by-products of the enzyme, yet, at this point in time, more research on the mTGase effect on human health is needed in order to fully confirm or rebut most hypotheses. The arising interest for the enzyme has also created a large amount of speculation in the scientific community, leading to confusion in some cases. In the scientific community there has been published contradictory information, most of which is the result of attributing functions and characteristics of mammalian transglutaminase to microbial transglutaminase”. Further, the authors expressly claim: “In the past years there has been an arising debate regarding aspects such as consumer deception and the possible negative health effects of this enzyme in the human body, partially due to the lax legislation and lack of detection methods”.

In addition to this, according to the classification provided by companies in ECHA (European Chemicals Agency) and CLP notifications, mTG may cause symptoms of allergy, asthma or breathing difficulties if inhaled.

In 2019, XEMA Co.Ltd developed a method for measuring the mass fraction of microbial transglutaminase in food samples by enzyme immunoassay method using the mTG-EIA panel. The method is registered in the Federal Information Fund for Ensuring the Uniformity of Measurements and certified by the Federal State Unitary Enterprise The Ural Research Institute for Metrology (UNIIM); the method detects only microbial transglutaminase (mTG) antibodies, and not tissue transglutaminase (tTG) antibodies or something else, regardless of its activity level; the method can detect the enzyme in any food. There is also a quick test designed for consumers or product manufacturers.

Finally we shall give some brief concluding observations of the article: in Europe, transglutaminase has an undefined “gray” status; an EFSA request for a scientific risk assessment for the food enzyme transglutaminase from S. mobaraense (S-8112) has had a status “in progress” for six years; European scientists from different countries raise the question of the need for additional in-depth studies of the enzyme in many articles and works; European scientists conduct research and give evidence of the potential pathogenic properties of mTG; The enzyme can be found in any food products by using a registered enzyme immunoassay (EIA) method.