Fibrillar -Lactoglobulin Gels: Part 3. Dynamic Mechanical Characterization of Solvent-Induced Systems

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• 作者：Walraj S. Gosal ; Allan H. Clark ; and Simon B Ross-Murphy
• 刊名：Biomacromolecules
• 出版年：2004
• 出版时间：November 2004
• 年：2004
• 卷：5
• 期：6
• 页码：2430 - 2438
• 全文大小：184K
• 年卷期：v.5,no.6(November 2004)
• ISSN：1526-4602

文摘

Oscillatory shear rheometry has been used to study the gelation of -lactoglobulin at ambient in 50% v/vtrifluoroethanol (TFE)/pH 7 aqueous buffer and in 50% v/v ethanol (EtOH)/water at pH 2. In contrast towhat was found on heating aqueous solutions at pH 2 (Part 2 of this series), a more expected "chemicalgelation"-like profile was found with modulus components G' and G' ' crossing over as the gels formed andthen with G' ' passing through a maximum. In addition, for the EtOH system, there was a significant modulusincrease at long time, suggestive of a more complex two-step aggregation scheme. Modulus-concentrationrelationships were obtained for both systems by extrapolating cure data to infinite time. For the TFE gels,this data was accurately described by classical branching theory, although it could also be approximated bya constant power-law relationship. Only the latter described the modulus-concentration data for the gelsin ethanol, but there were problems here of greater frequency dependence of the modulus values and muchless certain extrapolation. Gel times for the TFE systems showed higher power laws in the concentrationthan could be explained by the branching theory in its simplest form being similar, in this respect, to theheat-set systems at pH 2. Such power laws were harder to establish for the EtOH gels as for these there wasevidence of gel time divergence close to a critical concentration. Reduced G'/G'_inf versus t/t_gel data weredifficult to interpret for the gels in ethanol, but for the TFE system they were consistent with previousresults for the heat-set gels and approximated master curve superposition. The frequency and temperaturedependences of the final gel moduli were also studied. In general, the networks induced by alcohols appearedmore flexible than those obtained by heating.