Whey Protein Isolation Overview and Membrane Operations

Abstract

Fractionation and concentration of whey proteins from whey is one of the more successful industrial applications of ultrafiltration (UF). However, due to flux decline during operation, the practical limit for whey concentration by UF in modern plants is around 24 % total solids, with a protein to total solid ratio limit of ~0.72:1 (Mulvihill and Ennis 2003). Diafiltration is thus employed to achieve a higher protein to total solid ratio, ~0.80:1, with a total solid content of approximately 28 %. However, the efficiency of UF in whey processing is limited by several factors, the most significant of which are concentration polarization and membrane fouling (Rao 2002). Both factors adversely affect permeate flux, which may also be aggravated by protein–protein and membrane–protein interactions (Lipnizki 2005). These impacts however may be minimized by choosing suitable membrane material and configuration as well as the appropriate process conditions such as transmembrane pressure, feed velocity or recirculation rate, temperature, and composition including pretreatment of whey (Cheryan 1998). Opposing charge on the whey proteins and the membrane induces protein–membrane electrostatic attractions initiating protein adsorption on the membrane surface (Lipnizki 2005). This may result in the undesirable protein unfolding, denaturation, and aggregation especially at high-shear operations (Cheryan 1998). The polymeric polysulfone membrane has been the most widely used membrane in whey UFmainly due to its low cost, good thermal stability, and mechanical properties (Brans et al. 2004). The main problem with the use of the hydrophobic polysulfone membrane in the whey processing in comparison to ceramic or hydrophilic polymeric membranes is associated with greater attraction between the membrane surface and the proteins through the hydrophobic and electrostatically induced interactions resulting in severe fouling and flux retardation (Brans et al. 2004). Today ceramic membranes are gaining more attention because of their greater resistance against cleaning and disinfection. Due to abovementioned limitations, whey protein isolates are manufactured commercially by one of two fundamentally different processes – microfiltration followed by ultrafiltration or ion exchange (Neville et al. 2001). These two processes use completely different methods to isolate the valuable proteins that are present in low concentrations in cheese whey.