Water activity, pH and density of aqueous amino acids solutions.

The water activity, pH and density of some aqueous amino acid solutions were determined at 25 degrees C in three different types of solvents. Previous published experimental data on water activity and solubility of amino acids in aqueous solutions were used together with data from this work to test the applicability of a group contribution model. The activity coefficients were estimated by the UNIFAC-Larsen model combined with the Debye-Hückel equation, taking also into account the partial dissociation phenomena of species in solution. Interaction energies between the charged species Na(+) and Cl(-) and the specific groups of amino acids (COOH and NH(2)) were adjusted using experimental solubility data.

Partitioning of whey proteins, bovine serum albumin and porcine insulin in aqueous two-phase systems.

Partitioning of the proteins from cheese whey, bovine serum albumin and porcine insulin were analysed using aqueous two-phase systems (ATPS) prepared with PEG-phosphate, PEG-citrate and PEG-maltodextrin (MD). Proteins were quantified through one of the following methods: FPLC, Bradford and spectrophotometry at 280 nm. Results showed that whey proteins partitioned unevenly on the phases of the systems used, with alpha-lactoalbumin (alpha-La) concentrated in the upper phase and beta-lactoglobulin (beta-Lg) in the lower. Albumin in PEG-MD systems concentrated in the MD-rich lower phase. Porcine insulin showed great affinity with the PEG-rich phase, its partition coefficient was always over 10 and increases with PEG molecular mass.

Performance of a Graesser contactor in the continuous extraction of whey proteins: mixing, mass transfer and efficiency.

The performance of a Graesser Raining Bucket Contactor in an extraction using aqueous two-phase systems was characterized by axial mixing coefficients and counter current mass transfer for whey protein purification. The influence of rotor speed, phase ratio and phase velocity on the salt phase axial mixing coefficients was determined applying a dispersion model to the residence time distribution experiments. When dissolving whey powder in the salt-rich phase of the system, alpha-lactalbumin was extracted to the polyethylene-glycol-rich phase, whereas beta-lactoglobulin predominantly remained in the bottom phase, making the process suitable for removal of the major allergen beta-lactoglobulin. The mass transfer in the phase system was determined from the steady state data of alpha-lactalbumin extraction. On the basis of a diffusion model, the efficiency of the counter current extraction under different process conditions was calculated from results of the mass transfer experiments.