Summary -The preparation of peptide fractions from case in hydrolysates can be achieved by the use of ultrafiltration for the removal of the enzyme from the reaction mixture and/or to obtain specifie fractions of peptides. However, the ultrafiltration of case in hydrolysates is subjected to severe fouling phenomena which affect both the flux decline and the rejection properties of the membrane. Polysulfone membrane material used in previous work showed specifie rejection properties towards charged or hydroxylated amino acids. Polysulfone and polyethersulfone fiat sheet membranes were selected for their distinctive surface properties. The ultrafiltration of a tryptic hydrolysate from sodium caseinate was studied and physico-chemical variables were introduced, namely, pH of the hydrolysate (pH 6, 8, 10) and addition of a calcium sequestrant (EDTA 20 mmol 1-1 ). Flux decline measurements, total nitrogen rejection, molecular mass distribution profile, and amino acid composition of the permeates were determined. Although the polyethersulfone membranes showed greater permeability to water (+ 15%) at 25°C th an polysulfone, no distinctive effect of membrane material was observed in the permeation flux (1 h-1 m-2 ) during ultrafiltration of the hydrolysates. The rejection coefficients were similar for both materials. It was observed that the pH and the excess of EDT A had a much stronger effect th an the mate rial on the rejection properties (nitrogen, peptides, amino acids) and the flux decline. The two materials seemed to exhibit different surface reactivity towards charged molecules.
-Polysulfone (PSI) ultrafiltration membranes can be used for the fractionation of casein hydrolysates. However, the major Iimiting 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 specifie 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 EDT A, followed by acidic and basic desorption of adsorbed material. Membranes of 50 kDa (MM CO) 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-Ii ne RP-HPLC/mass spectrometer. The modification of physico-chemical conditions (pHIEDT A) 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 attractive or repulsive interactions with the rrfembrane. Thus, the peptides were c1assified in three groups according to these characteristics: 1) hydrophobie peptides presenting high affinity with the membrane (a.~1.25); II) peptides presenting no specificity between total hydrolysate and membrane (0.75 < a. < 1.25), and III) peptides excluded from the membrane (0.75~a.) which were classified as acidic, neutral, and basic peptides. © Inra/Elsevier, Paris.polysulfone / adsorption / casein peptide / identification / mass spectrometry * Correspondence and reprints. E-mail: Yves.Pouliot@aln.ulaval.ca 634 L. Gourley et al. Résumé -Identificationde peptides caséiques interagissant avec les membranes ultrafiltrantes de polysulfone. Les membranes d'ultrafiltration de polysulfone (PSt) peuvent être utilisées pour le fractionnement d'hydrolysais caséiques. Cependant, cette application est limitée par la chute importante des flux de perméation observée durant la filtration. Des études préliminaires ont démon-tré que des interactions peptide-membrane pouvaient affecter la chute du flux de perméation et les propriétés de rejet du PSf. Une étude complémentaire montrait que l'adsorption statique d'un hydrolysat de caséine modifie les paramètres énergétiques de la surface membranaire. Des travaux sur l'adsorption statique ont donc été menés afin d'identifier les peptides adsorbés pouvant initier l'encrassement des membranes de PSf. L'adsorption a été effectuée sous les conditions physicochimiques suivantes: pH 6,0, 8,0 et 10,0, avec ou sans l'ajout d'EDTA, suivi d'une désorption acide et basique du matériel adsorbé. Des membranes de 50 kDa ont été choisies de façon à minimiser l'...
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