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Biochemical Analysis and Rheological Properties of Gluten Modified by Transglutaminase

¹Unité de BIochimie et de Technologie des Protéines, INRA. ²Corresponding author. E-mail: larre@nantes.inra.fr ³Unité de Physicochimie des Macromolécules, Rue de la Géraudière, B.P. 71627, 44316 Nantes cedex 3, France.

A transglutaminase from Streptoverticillium sp. was used to create new covalent intermolecular cross-links between proteins in gluten. This modification induced drastic changes in its physicochemical properties as well as in its rheological behavior. To understand these changes, we characterized the gluten extractability in acetic acid and identified the proteins of supernatant and pellet by immunoblotting using antibodies specific for each prolamin class. The proportion of soluble proteins decreased drastically after transglutaminase treatment due to the formation of large insoluble polymers as shown by SDS-PAGE. Among the constitutive proteins of gluten, the high molecular weight glutenin subunits were the most affected in the transglutaminase reaction. The rheological behavior of gluten after 18 hr of incubation with transglutaminase was studied in shear by dynamic measurements over 10^-3 – 10¹ Hz frequency range and by creep and recovery tests. The behavior of treated glutens remained that of a transient network, but the viscoelastic response was shifted toward shorter times and the steady-state viscosity was greatly increased. The enzymatic treatment caused a considerable reinforcement of the network. The modified glutens were also less sensitive to thermal processing than unmodified glutens, as shown by a lower amplitude of variation of storage modulus G′ with temperature after enzymatic treatment.