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Extraction efficiency of the wheat bran water-soluble proteins: a comparative study of two dyalisis methods
J. MERCADO-RUIZ (1), I. Torres-Cinco (1), R. Balandran-Quintana (1), J. Luna-Valdez (1), G. Chaquilla-Quilca (1) (1) Centro de Investigacion en Alimentacion y Desarrollo, A.C., Hermosillo Son., Mexico.

On a laboratory scale, the study of water-soluble proteins of wheat bran (WB) requires obtaining sufficient quantities of proteinaceous material, from which further purification can be carried out. The usual method of aqueous extraction involves membrane dialysis, which implies the use of large amounts of water, so it is desirable the search of alternatives. In this work, WB was subjected to aqueous extraction (1:10, w/v) and dialysis was performed into cellulose membranes (M1) or through a Sephadex-G75 column (M2); the latter explored as an alternative dialysis method. Both extractions were run at pH 8 because of a higher solubility of proteins at this pH. A third extraction (M3) was performed without adjustment of pH or dialysis, in order to compare the effect of these two variables on the extraction efficiency. The aqueous extracts were lyophilized, weighed and analyzed for protein content as well as subjected to SDS-PAGE for determining the MW profile. The efficiency of the methods was evaluated in terms of the yields of lyophilisate and protein. The lyophilisate yields (g/100 g WB) were 2.0, 1.0 and 6.0, whereas the protein yields (g/100 g lyophilisate) were 26, 6.4 and 7.0 for M1, M2 and M3, respectively. The pH resulting of mixing WB and water was 6.2, i.e. the pH at which M3 was run. The pH or the method of dyalisis had no effect on the type of recovered proteins, since nine bands were observed in all the SDS-PAGE gels, with MW ranging from 14.4 to 66.2 kDa. The high protein content in the lyophilisate from M1 suggests that the membrane dyalisis is the most effective method; however, the protein recovery in M2 and M3 were similar even when the yield of the M2 lyophilisate was 6-fold lower, so the dyalisis through Sephadex on a major scale would be an attractive alternative considering that the water consumption for M1 was 24-fold higher than for M2 or M3.