Identification of casein peptides interacting with polysulfone ultrafiltration membranes

Polysulfone (PSf) ultrafiltration membranes can be used for the fractionation of casein hydrolysates. However, the major limiting factor of this application remains the important permeation flux decline encountered during filtration. Previous studies showed that peptide-membrane interactions could affect both the flux decline and specific rejection properties of PSf. A complementary study showed that static adsorption of casein hydrolysate on PSf modifies the surface energy parameters of the membrane. Therefore, static adsorption experiments were conducted in order to identify the adsorbed peptides which would initiate fouling of PSf membranes. The adsorption was performed under different physico-chemical conditions, namely pH 6.0, 8.0, and 10.0, without or with addition of EDTA, followed by acidic and basic desorption of adsorbed material. Membranes of 50 kDa (MMCO) were chosen in order to minimize the effect of steric exclusion. The material collected from desorption experiments was referred to as adsorbed peptides and were analyzed by one-line RPHPLC/mass spectrometer. The modification of physico-chemical conditions (pH/EDTA) of the solution did not influence the adsorption profile of the peptides to a large extent. However, the balance size/hydrophobicity/charge of the peptides reflected more their adsorption behaviour in terms of am-active or repulsive interactions with the membrane. Thus, the peptides were classified in three groups according to these characteristics: I) hydrophobic peptides presenting high affinity with the membrane (alpha greater than or equal to 1.25); II) peptides presenting no specificity between total hydrolysate and membrane (0.75 < alpha < 1.25), and III) peptides excluded from the membrane (0.75 less than or equal to alpha) which were classified as acidic, neutral, and basic peptides. (C) Inra/Elsevier, Paris.