Fractionation of gliadin hydrolysates in water-ethanol by ultrafiltration with modified or unmodified membranes

Ultrafiltration was applied to the fractionation of neutral vs. charged pep tides of similar size. The peptides, produced from gliadins, a major fracti on of wheat storage proteins, were obtained by limited hydrolysis with alph a-chymotrypsin in water-ethanol 80/20 (v/v). Peptides, according to their e lution by RP-HPLC, were quasi neutral (repetitive peptides) irrespective of pH, or positively charged (nonrepetitive peptides) at pH below 5. The tran smission through the membranes of the nonrepetitive peptides was less (unti l sevenfold) than that of the repetitive ones, because of the role of elect rostatic repulsion involved in the retention of charged solutes. The differ ence of transmission was more efficient at acidic pH (3) and low ionic stre ngth with inorganic membranes and in a wider range of pH and ionic strength with membranes modified by coating of positively charged polymers (polyvin ylimidazole PVI, polyethyleneimine PEI). A continuous diafiltration process using an inorganic membrane of low molecular cut-off permitted the selecti ve enrichment of the retentate in nonrepetitive peptides (up to 80%) and of the permeate in repetitive peptides (up to 88%) from hydrolysate feed cont aining about 60/40% of repetitive and nonrepetitive peptides, respectively, with a diafiltration volume of 4. (C) 1999 John Wiley & Sons, Inc.