Effect of physico-chemical conditions and operating parameters on flux and retention of different components in ultrafiltration and nanofiltration fractionation of sweet whey

Butylina Svetlana Effect of physico-chemical conditions and operating parameters on flux and retention of different components in ultrafiltration and nanofiltration fractionation of sweet whey Lappeenranta 2007 126 p. Acta Universitatis Lappeenrantaensis 268 Diss. Lappeenranta University of Technology ISBN 978-952-214-378-5 ISSN 1456-4491 ISBN 978-952-214-379-2 (PDF) In this thesis the effect of physico-chemical conditions and operating parameters on the fractionation of sweet whey was studied. In the beginning of the thesis the environmental impact of whey and the routes of its utilisation including the treatment with membranes were reviewed. The experimental part is divided into two main sections considering ultrafiltration and nanofiltration steps of sweet whey fractionation. The selection of ultrafiltration membrane was made using the molar mass cut-off value determined with single polyethylene glycol solutions under conditions providing low concentration polarisation. The critical flux concept was used for protein concentration by ultrafiltration of sweet whey because whey solution contains proteins, which are well-known as fouling agents. Sieving characteristics of different whey components have been studied. Peptide fractions of whey ultrafiltration permeates were characterised by using size exclusion chromatography and MALDI-TOF mass spectrometry. The average pore sizes of nanofiltration membranes were characterised using solutions of neutral solutes. The zeta potentials of the studied nanofiltration membranes were evaluated from streaming potential measurements. Model solutions of amino acids were applied to study the role of pore size and charge of the membranes in separation. The retention of amino acids was affected by pH and by the ionic strength of the solution, as well as by intermolecular interactions. Whey ultrafiltration permeates containing low molar mass peptides, lactose and salts were tested in nanofiltration at acidic and alkaline pH. The nanofiltration of whey ultrafiltration permeates was found to be more feasible at alkaline pH, where the irreversible fouling decreased and the permeate flux was higher. At this pH the selectivity of lactose separation from peptides was increased, compared to that at acidic pH.