Ultrafiltration performance of spent brewer's yeast protein hydrolysate: Impact of pH and membrane material on fouling

This work investigated membrane selectivity and fouling after the dead-end ultrafiltration of protein hydrolysate from spent brewer's yeast, a high protein brewing by-product. Ultrafiltration (UF) experiments were carried out with regenerated cellulose (RC) and polyethersulfone (PES) membranes of 30 kDa molecular weight cut-off at different pH values (5 and 8). Higher peptide retention (60% of total solids and 83% of peptides) was achieved using PES and a feed pH of 5. Ribonucleic acids were successfully separated from the peptide-rich fraction. The protein hydrolysate at pH 8 showed less susceptibility to the adsorption of proteins and smaller resistance to mass transfer. Similarities in the zeta potential of membranes and feed solution suggested that foulants aggregated in the surface of membranes by weak physical adsorption. Peptides were confirmed by FT-IR analysis as the main foulants. Hydrophilic membranes and feed at pH 8 increased UF performance of spent brewer's yeast hydrolysate.