Adsorption of phenylalanine from casein hydrolysates.

The specific diet therapy for phenylalaninemies requires special hydrolysates of proteins where phenylalanine content is reduced to approx 0.53% of the amino acids present. In previous work, Amberlite XAD-4 resin was used to retain phenylalanine from an acid hydrolysate of casein. It was also observed that the adsorption isotherm of phenylalanine on the resin showed a convex pattern that allowed a frontal chromatography. In the present study, this technique was improved, aiming at the processing of larger hydrolysates volumes. This was achieved with the use of two sequential columns (50 x 1 cm), each containing 34 cm3 of the resin, and joined through a 1-cm long tygon, tube 1 mm diameter. This system was used to process 100 mL of casein acid hydrolysate containing 12 g of free amino acid and allowed the reduction of phenylalanine content from 4.39 to 0.14% of the total amino acids present, within 1 h. It was also observed that this technique could not be directly applied to enzymatic hydrolysates of casein unless they were especially produced for this purpose, which means that in this kind of hydrolysate, phenylalanine should be free or linked in small adsorptive peptides.