Aqueous two-phase systems for the valorization of cheese whey

Abstract

The dairy industry, of great importance in Galicia, generates in cheese production high volumes of whey, a residue with high content in organic matter that presents an environmental problem. The main objective of this thesis is the valorization of cheese whey through the recovery of high added-value compounds (lactose and proteins) using aqueous two phase systems, a mild medium for the separation of proteins and other biomolecules. Polymers (polyethylene glycols of different molecular weights and poly(ethylene glycol-ran-propylene-glycol) monobutyl ether) and salts (sodium, potassium and ammonium sulfate, and potassium tartrate) were selected as phase-forming components due to their relative low cost and green character, in addition to their compatibility with the components of cheese whey. Liquid-liquid equilibrium data for these systems were determined at several temperatures and atmospheric pressure. The measurement of physical properties (density and refractive index) was used to determine compositions of equilibrium phases. All data were adequately correlated with empirical equations to facilitate their management. These systems were used to analyze the partitioning of -lactose, bovine serum albumin, -lactalbumin and -lactoglobulin between the aqueous phases. The influence of polymer molecular weight, type of salt and pH on the partitioning was analyzed. Aqueous two phase systems generated with polyethylene glycol 1500 and ammonium sulfate (298 K and pH=4) or polyethylene glycol 600 and potassium tartrate (293 K and natural pH) were found to be promising options for the separation of -lactose and proteins. Polyethylene glycol 300 and sodium sulfate (298 K and pH ranging from 4 to 5) was found promising for proteins’ fractionation. Several strategies based on these systems and ultrafiltration were designed to separate the main components of cheese whey. These strategies were assessed using first a synthetic whey formulated with the key solutes dissolved in distilled water, and later using a real cheese whey from a local cheese producer (Queizúar S.L.). The aqueous biphasic system formed with polyethylene glycol 600 and potassium tartrate allowed a very good separation of lactose and proteins. Fractionation of the proteins was not achieved. Further studies are encouraged.