By Dr. Colin Michie
Sausages vary. Their sensory powers fire up early morning hunger pangs with the smells and flavours of many cultures. Choices spoil us: What about a haggis, boudin blanc, hot dog, merguez, metworst, black pudding, fish or vegetarian? Many fillers are used to bind sausages, trapping their tasty juices and succulence. US regulations limit non-meat contents to 35% of a meat sausage. These binding molecules are central to much kitchen magic. Gluten or starches such as arrowroot or cornflour, gelatin and aspics, seaweed agar, carrageenan or alginates, perhaps fruit pectin can be used to thicken or change the texture of dishes.
The wonders of binders run from soup to nuts. Transglutaminases, nicknamed meat glues, are new kids on this block. In the last three decades, sausages have increasingly been held together using these enzymes. Transglutaminases knit amino acids together within their protein mixes, making them firmer and less fragile, trapping more water and facilitating slicing. Transglutaminases are used in the manufacture of pates and terrines, surimi fish paste and artificial crab meat. They are being used to develop new meat analogues.
The molecular capacities of transglutaminases mean chefs can create gastronomic novelties such as pastas and noodles with shrimp meats, or stabilised tasty foams. In processing meats and fish, transglutaminases allow lower salt levels in the final product. In dairy, lower fat contents become possible if milk proteins are cross-linked; ice cream can be made lighter and fluffier. In soya or bread doughs, protein cross-linking allows their products to have longer, safer shelf-lives. Processing with transglutaminases, weaving and knitting proteins has allowed the production of a wider variety of vegetarian and vegan foods, as well as the specific production of gluten-free products.
Transglutaminases are a family of enzymes found in most living creatures. Plants and fungi use them to help build structures and maintain these with cross-linked proteins. Humans have nine types. Many function inside cells; they are particularly common in the blood, liver and skin where they support cell and tissue growth, turnover and repair. One transglutaminase’s net-making is critical in cross-linking fibrin, toughening blood clots. If the clot is in a leg vein, for instance, this cross-linking prevents the clot breaking into emboli that could travel up the vein to damage the lungs and heart. These enzymes play roles in the construction of skin and hair, as well as being involved in controlling signalling cascades in the immune system, tackling invading pathogens.
In the 1980s, Japanese scientists identified soil bacteria that manufactured transglutaminases. This success for industrial biotechnology led to the microbial genes being integrated into microbes that could be cultured in vats, delivering larger amounts of purified enzyme, rather than isolating it from animal by-products.
Outside the food sector, transglutaminases are versatile assistant enzymes in tissue engineering. They can extend the lifespan of artificial collagen scaffolds, building and repairing tissue gaps following trauma or surgery – for instance, in the skull. Protein nets within these grafts, knitted in with transglutaminases, can stop bleeding and encourage blood vessel growth locally. Transglutaminases contribute to creating new drugs safely. They can add polyethylene glycol to therapeutic proteins to extend their lifespan in the blood circulation. Medications prepared in this way include those used to treat hepatitis C, or low white cell counts during chemotherapy. Binding drugs to specific antibodies so as to target them onto cancer cells is another application of these enzymes.
When processing wool, silk or leather transglutaminases “heal” damaged fibres, making them smoother and stronger, protecting them during processing and washing. In the cosmetics and beauty industries, transglutaminases are used in anti-ageing creams, hydrating serums, masks and hair treatments because they can work on surface proteins, increasing their water content, smoothing and moisturising them.
Our transglutaminases can become a target for our own immune systems, which then make antibodies to attack them. Autoantibodies to tissue transglutaminase are found in coeliac disease. Transglutaminases can act on peptides from gluten in the diet too, enabling them to be more inflammatory to individuals with certain tissue types. For these reasons, some researchers propose limiting the use of transglutaminases in food processing. They argue that these enzymes may be partly responsible for rising numbers of diagnoses of coeliac disease.
This is not a clearly defined position as there are many factors involved and patient numbers are uncertain. Further research on the risks or safety of transglutaminases in food processing is needed, along with raising awareness about these enzymes. Transglutaminases have varied national regulations governing their current uses. Since 1998, the FDA approved the use of microbial transglutaminases as “Generally regarded as safe” as an adjunct of food technologies.
Applications for transglutaminases are multiplying and diversifying. They are humanity’s latest glues, knitting their way into many areas of our daily lives.
Useful resources: pmc.ncbi.nlm.nih.gov/articles/PMC10419021 ~ cks.nice.org.uk/topics/coeliac-disease/diagnosis/asses. Dr. Colin Michie specializes in paediatrics, nutrition, and immunology. Michie has worked in the UK, southern Africa and Gaza as a paediatrician and educator and was the associate Academic Dean for the American University of the Caribbean Medical School in Sint Maarten.
