Influence of molecular interactions on ultrafiltration of a bovine hemoglobin hydrolysate with an organic membrane

Inter-molecular interactions involved in the hydrolysate were studied in order to explain heme and peptide high retentions observed during the ultrafiltration of a bovine hemoglobin peptidic hydrolysate with a 10 kDa modified polyethersulfone membrane. Physico-chemical properties of the peptidic fractions of the retentate and of the permeate were characterized by UV/vis spectroscopy, SDS-PAGE electrophoresis, size-exclusion chromatography, reversed phase HPLC, hydrophobic interaction chromatography on hemin agarose, precipitation with sodium chloride and amino acid compositions. Two populations of peptides were revealed in the hydrolysate: one forming high-molecular weight hydrophobic associations retained by the membrane, and another more hydrophilic, giving no associations and freely passing through the membrane. Contrary to the peptides of the permeate, peptides retained by the membrane had a high affinity and a large binding capacity for the heme. Heme as polymers is mainly linked by hydrophobic interactions with peptide associations to form large heme–peptide aggregates. These results suggest that high rejections of heme and peptide, often reported in the literature, during ultrafiltration of hemoglobin hydrolysates, could be largely explained by these associations.