# The Clean Label Concept: Novel Approaches in Gluten-Free Breadmaking
## 8 Prospective Gluten Substitutes with Clean Label Status
### Transglutaminase  
Enzymes are widely applicable as processing aids in the food industry. With some exceptions, they do not have E numbers. As typical proteins, enzymes are destroyed by the high temperatures during baking, so they are not listed on the product label. One enzyme that can be used in clean label baked goods is transglutaminase. Transglutaminase catalyzes acyl transfer reactions between the \(\gamma\)-carboxamide group of l-glutamine and primary amines. Research has demonstrated that transglutaminase not only affects the protein structure, but also the rheological and viscoelastic properties of dough, enhancing gluten strength. As a consequence, gas retention, dough stability as well as the volume and bread structure is being improved, moreover, the bread crumb is strengthened [70,71]. Transglutaminase has an impact on dough water absorption, viscoelastic behavior, and thermal stability. In a study by [PERSON] et al. [70], the water absorption of oat dough was found to decrease as the enzyme level increased. Protein cross-linking was observed, as well as the formation and stabilization of a network structure. The longer dough development time and increased stability indicate that the elasticity of the oat dough was strengthened by enzyme activity. [PERSON] et al. [71] reported similar results for wheat-based doughs. Transglutaminase increased dough resistance by about 60%, while decreasing extensibility by around 57%, so the dough was tougher but less pliable. It is interesting to note that with higher enzyme content, the loaf volume diminished rapidly, with a corresponding increase in its weight. This can be explained by the fact that when the dough consistency is too tight, dense air cells are not able to develop. As a consequence, a sufficient amount of gas is not trapped in cells and its expansion during baking is not possible. This leads to a smaller bread volume, which in turn slows the rate of water evaporation during baking. As a result, the overall loaf weight increase is being observed. [PERSON] et al. [72] examined the correlation between transglutaminase and three protein sources (soya flour, skimmed milk powder, egg powder) in gluten-free breads. No significant effects were seen in breads containing soya flour. However, in case of breads with skimmed milk powder and egg powders, the usage of transglutaminase led to formation of a stable protein network. [PERSON] et al. [73] investigated the effects of transglutaminase and three types of proteins (whey protein, sodium caseinate, soy protein isolate) on gluten-free rice breads prepared using non-waxy rice flour. Different effects of the simultaneous use of the enzyme and protein were noticed. In the case of crumb hardness, an improvement was observed, while in the case of springiness, no impact was detected. The protein and transglutaminase were involved in the formation of a network that retained carbon dioxide. As a consequence, the bread volume increased. The highest volume increase was observed for a combination of the enzyme with soy protein isolate and whey protein. There was no significant difference between the volumes of the prototypes with sodium caseinate and those of the samples with caseinate and transglutaminase. [PERSON] et al. [74] investigated the impact of transglutaminase on the properties of gluten-free formulations consisting of pregelatinized cassava starch, sorghum, and egg white. Increasing the storage time led to crumb cohesiveness, chewiness, and resilience reduction, whereas increasing the enzyme content had a positive impact on firmness and chewiness. However, increasing the enzyme concentration beyond a specific point did not induce any further fundamental alterations in the rheological quality of the batters and breads. [PERSON] et al. [75] investigated the impact of the mentioned above enzyme on various proteins such as albumin, globulin, and gluten derived from buckwheat flour. The enzyme was not fraction specific; all protein types were involved in network formation.