Microstructure and properties of bitter vetch (Vicia ervilia) protein films reinforced by microbial transglutaminase

• Proteins from Vicia ervilia (VE) seeds are effective transglutaminase (TG) substrates.
• We studied the effect of TG addition to VE protein-based film forming solution.
• Protein crosslinks produced by TG affect film microstructure examined by AFM and SEM.
• TG improves film mechanical features and increases its gas barrier properties.
• No changes in film water vapor permeability were observed in TG-containing films.

Calcium-independent Streptoverticillium sp. transglutaminase was positively tested to prepare new crosslinked biomaterials by using bitter vetch (Vicia ervilia) seed proteins as effective acyl donor and acceptor substrates of the enzyme. Film morphology was evaluated by both atomic force microscopy and scanning electron microscopy. The surface of films prepared in the presence of transglutaminase appeared more compact and smoother than those prepared in the absence of enzyme. Mathematical analysis of surface roughness indicated that the values derived were significantly higher in the films obtained in the absence of enzyme (Rq = 84.4 ± 1.5 nm) compared to the ones prepared in its presence (Rq = 41.1 ± 1.2 nm). Moreover, film cross-sections showed the presence of several discontinuous zones in the control films, absent in those prepared with transglutaminase that, on the contrary, showed a very homogeneous structure. Enzymatically polymerized films exhibited a markedly decreased oxygen (700-fold) and carbon dioxide (50-fold) permeability, with respect to the control ones, as well as significantly different mechanical properties being increased their resistance and stiffness. On the basis of these features, a possible application of enzymatically crosslinked bitter vetch protein films as coatings of different food products is suggested.

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