Analysis of Two Bentonites of Enological Interest before and after Commercial Activation by Solid Na2CO3

Abstract
Two natural calcium-rich bentonites used for the removal of wine proteins, originating from Greece and Turkey, were studied by X-ray diffraction, thermal analysis, and solid state NMR, before and after activation by solid Na2CO3. Exchange of Ca2+ by Na+ mainly occurs for cations located at the edge of layers and only weakly for interlayer cations. This Na2CO3 activation process leads to an increased efficiency in the adsorption process of bovine serum albumin (BSA) used as a model protein for both bentonites. A direct correlation is observed between the extent of Ca2+/Na+ exchange, the strength of adsorption of BSA, and the extent of unfolding of BSA backbone. Keywords: Bentonite; Na2CO3 activation; bovine serum albumin; X-ray diffraction; differential thermal analysis; thermogravimetry; NMR

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