Some applications come from a method to concentrate proteins

Abstract

All techniques usually used to assay proteins was not reliable in vegetable extract due to interferences with the components included in extracts like polyphenols, tanins, pectines, aromatics compounds. Absorbance at 280nm, Kjeldhal assay, Biuret and Lowry methods, Acid Bicinchonique technique and Bradford assay give the results depending on the composition of extract, on the presence or not of detergent and on the raw material (Marchal, 1995). Another difficulty in these extracts for the quantification of proteins comes from the large amount of water included in vegetable and the low concentration of proteins. Thus in red wines, proteins are usually not taken into account due to their low concentration (typically below 10 mgL-1) and to the presence of anthocyanis and polyphenols. Due to all these defects, alternative test should be developed. The perfect protein assay would exhibit the following characteristics: fast, easy to use, sensitive, accurate, precice and free from interferences. Futhermore this assay should be compatible with all substances commonly found in protein samples and at low concentration. Our purpose in this work is to combine the concentration of proteins by bentonite with separation electrophoretic 1D SDS Page and to examine some applications. First, wines were fined with 100g/hl of bentonite is largely sufficient to adsorbe all proteins (Paetzold and al.,1990). In these conditions, we observed at low concentrations of bentonite (under 20g/hl), the bentonite Electra® adsorbed only β glucanases and chitinases. Second after desorption by Laemmli buffer, proteins were separated by SDS-PAGE and quantified after coloration with Coomassie Blue R-250 by scanning coupled to the image analysis TotalLab software (Sauvage and al., 2010). The gels after destaining were scanned with a transmission scanner at 300 dpi to obtain a digitised image. The software compared the volume (area x intensity of each pixel) of each band to the volume of BSA band (included in standard file). Each band was characterized by the molecular weight and the quantity of proteins expressed in µg equivalent BSA. The sum of each band gave the total pool of proteins included in each sample. The standard deviation measured on 6 same sample on Chardonnay wine was 11%. The response was linear for each band up to 1µg/band. By this method we also got the relative composition of the majority of proteins. Last, but not least, proteins were desorbed from bentonite with buffer to denature proteins or only with a buffer to conserve the native form of proteins (like Tris buffer or NaCl solution). After this experimentation we checked if [1] Marchal R. Ph. Thesis, university of Reims, 1995.

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