Writing in the journal Innovative Food Science and Emerging Technologies, lead author Christian Schafer explained the proteins from vegetables "represent a valuable alternative to animal proteins for the manufacture of texturised foodstuffs", but they remain an unexploited ingredient, "due to the poor gelling properties of the native proteins".
This is not the first report on using TGase to modify the functional properties of proteins. Indeed, previous studies have looked at the effect of this enzyme on casein, soy proteins, whey proteins, myosin, and globulin.
The researchers, from the Fraunhofer Institute for Process Engineering and Packaging, the Technical University Munich, and Hohenheim University, investigated the cross-linking of MTG (Activa, Ajinomoto) on two commercial vegetable proteins, one derived from soy (SPI, "Supro", DuPont) and one derived from pea (PPI, "Pisane," Cosucra).
Schafer and co-workers report that the transglutaminase enzyme substantially modified the vegetable protein and gel strengths were found to increase significantly during incubation with MTG. The soy gel strength was reported to have increased by 155 per cent, while pea protein gel strength increased by 300 per cent.
"Superior gel firmness of PPI samples may not exclusively be attributed to the higher concentration of pea protein (18 per cent), which exceeded that of the soy protein by four per cent," wrote the researchers. "It is more likely that different positions of lysine cross-links, generated in PPI, have a greater impact on gelation than in the case of SPI."
"MTG-induced formation of lysine cross-links significantly enhanced the gelation of pea and soy protein isolates in the food model used," concluded the researchers.
Currently there is only a limited selection of cross-linking enzymes on the market, with microbial transglutaminase (MTG) being the most widely used enzyme for modifying the structure of food.
Source: Innovative Food Science and Emerging Technologies (Elsevier)
Published on-line ahead of print, doi: 10.1016/j.ifset.2007.01.005
"Comparative study of gelation and cross-link formation during enzymatic texturisation of leguminous proteins"
Authors: C. Schafer, C. Zacherl, K.-H. Engel, S. Neidhart, R. Carle