Analysis of underivatized amino acids in protein hydrolysates for cosmetic application by capillary electrophoresis

Abstract

AbstractIn this work, the use of two chromophores, 3,5‐dinitrobenzoate and phthalate, and the additives α‐cyclodextrin and methanol was investigated with the goal of developing three electrolyte systems for the capillary electrophoretic analysis of free underivatized amino acids in commercially available protein hydrolysates of diverse origin: keratin, silk fiber, milk, soybean, fish tissue, and cattle leather. Sixteen amino acids could be effectively separated by two distinct methods. Several amino acids were identified in the studied hydrolysates and confirmed by spiking techniques. As expected, those products which originated from acidic hydrolysis were richer in free amino acids than those which originated from enzymatic hydrolysis. The quantitative determination of Asp, Glu, Cys, Ser, and Pro in Queratan, a keratin hydrolysate, was also performed and some method validation parameters were established. The coefficient of variation for migration time was better than 1% for all amino acids except Asp, Leu, Lys, and Pro. Overall, peak height repeatability was slightly better than peak area. Calibration curves based on peak heights present a good fit, with coefficients of correlation better than 0.99. The LOD for the amino acids identified in Queratan ranged from 1.0 to 7.0 mg L–1.