Document Type : Research Paper
CeFEMA/Chemical Engineering Department, Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal
CeFEMA/Chemical Engineering Department, Instituto Superior Técnico, Universidade de Lisboa, Lisboa, Portugal; Instituto Superior de Engenharia de Lisboa, Instituto Politécnico de Lisboa, Lisboa, Portugal
Instituto Nacional de Investigação Agrária e Veterinária (INIAV), Oeiras, Portugal
The processing of cheese whey pre-concentrated by reverse osmosis is carried out through ultrafiltration in diafiltration mode to produce whey protein concentrates with lower lactose content to be incorporated in beverages. The initial cheese whey protein and lactose contents are 2.13g/100g and 13.22g/100g, respectively.
The commercial membranes, GR95PP, supplied by Alfa Laval, Denmark, were characterized in terms of a hydraulic permeability of 1.21 l/(h∙m^2∙bar) and a molecular weight cut-off of 7500 Dalton. The permeation tests were carried out in a plate and frame Lab-Unit 20 from Alfa Laval, Denmark, and a membrane surface area of 0.072 m2 was installed.
The ultrafiltration of cheese whey in total recirculation mode yielded two asymptotic variations of the permeate fluxes versus the transmembrane pressure. For operating pressures up to 12 bar the permeate flux increases linearly with the pressure. Then, with the increasing pressure, they deviate from linearity and reach a limiting flux of 8.79 l/(h∙m^2∙bar) at 30 bar. The slope of the asymptotic linear variation is 0.48 l/(h∙m^2∙bar). To have minimal effects of concentration polarization the operating pressure was set-up at 12 bar.
The optimization of ultrafiltration/diafiltration was carried out in terms of the volumetric concentration factors and the frequency of diavolumes addition. At a volumetric concentration factor of 1.32 the lactose content decreased from 13.22% to 5.7%.