Influence of supramolecular forces on the linear viscoelasticity of gluten

Abstract

Stress relaxation behavior of hydrated gluten networks was investigated by means of rheometry combined with μ-computed tomography (μ-CT) imaging. Stress relaxation behavior was followed over a wide temperature range (0-70°C). Modulation of intermolecular bonds was achieved with urea or ascorbic acid in an effort to elucidate the presiding intermolecular interactions over gluten network relaxation. Master curves of viscoelasticity were constructed, and relaxation spectra were computed revealing three relaxation regimes for all samples. Relaxation commences with a welldefined short-time regime where Rouse-like modes dominate, followed by a power law region displaying continuous relaxation concluding in a terminal zone. In the latter zone, poroelastic relaxation due to water migration in the nanoporous structure of the network also contributes to the stress relief in the material. Hydrogen bonding between adjacent protein chains was identified as the determinant force that influences the relaxation of the networks. Changes in intermolecular interactions also resulted in changes in microstructure of the material that was also linked to the relaxation behavior of the networks.

The Impact of Water Content and Mixing Time on the Linear and Non-Linear Rheology of Wheat Flour Dough

“…Yet, the compliance curves did not show any significant deviations from Hibberd's principle over the entire course of the creep and recovery phases for both the strong Bilux doughánd the weak Bison dough. It is important to note, however, that even with creep tests, probing the longest time scales in dough is not straightforward, because of aging effects that will continuously change the physicochemical and viscoelastic properties of the material [53]. We already mentioned [43] that a creep time of 30 min is not sufficient to reach the steady-state flow regime.…”

The Interplay Between the Main Flour Constituents in the Rheological Behaviour of Wheat Flour Dough

“…This time dependency is believed to stem from several factors such as enzymatic reactions ongoing in the flour, a continuous evolution in flour component interactions and the relaxation of the stresses induced during mixing, shaping and loading in the rheometer (Létang et al 1999). To eliminate the contribution of the latter, dough should be allowed sufficient resting time before starting the rheological experiments (Kontogiorgos et al 2016). It is, however, difficult to determine what a sufficient resting time would be, as the other physico-chemical factors will still induce time dependency.…”

“…The ability of the gluten network to incorporate compounds that contained either free thiol groups (Villegas et al 1963) or disulfide bonds (Jones and Carnegie 1971) indicates that SH/SS interchange reactions do indeed occur in dough. On the contrary, the second school of thought suggests that the continuity of the gluten network also strongly depends on hydrogen bonds, hydrophobic interactions, and chain entanglements (Jekle and Becker 2015;Kontogiorgos et al 2016). The primary function of the SS cross-links would then be to hold the (unbranched) polypeptide chains together within each glutenin molecule (Bloksma 1990).…”

Linear viscoelasticity of gluten: Decoupling of relaxation mechanisms

“…Temperature-induced conformational changes further complicate the landscape with additional formation of intermolecular β-sheets by loss of α-helices or interchange of disulfide linkages on heating (Georget and Belton, 2006). The cooperation of supramolecular forces, temperature and time on gluten viscoelasticity have been recently put under rheological scrutiny revealing that the importance of hydrogen bonding precedes over disulfide cross links (Kontogiorgos et al, 2016). Additionally, in the mesoporous structure of gluten,…”

“…It is evident from the above discussion that water levels would play critical role in the viscoelasticity of gluten networks and other similar hydrated biopolymer systems due to chain conformational changes and water resettling within the pores of the structures. In our previous investigations, we have focused on the influence of protein composition (Kontogiorgos and Dahunsi, 2014) and supramolecular forces (Kontogiorgos et al, 2016) on the relaxation dynamics of model gluten networks focusing, however, at one hydration level. The aims of the present investigation are to build on our previous findings and by using gluten as model system to explore the influence of hydration and decouple the mechanisms that contribute to the relaxation dynamics in hydrated gluten.…”