Characterization of free aromatic amino acids and estimation of exposition rate of phenylalanine in casein hydrolysates by second derivative spectrophotometry.

In this work, the second derivative spectrophotometry (SDS), a fast, simple and relatively low-cost method,-was used to characterize aromatic amino acids at two pH values (7 and 13) and to evaluate the exposition rate of Phe in casein hydrolysates prepared with papain. The results indicate that at 37 degrees C, pH 7.5 and an enzyme:substrate ratio of 4:100, for hydrolyzing casein by papain, the highest Phe exposition was observed. Therefore these are the most appropriate conditions for Phe removal and preparation of supplements for phenylketonurics. The use of SDS at pH 13.0 gives a good resolution of Tyr and Trp peaks. A similarity among SDS spectra of aromatic amino acids and protein hydrolysates, was also observed.