Evaluation of the dietary protein using an optimized HPLC method

Abstract

Protein quality is determined by the type and concentration of the essential amino acids and by their bioavailability. Hence, the content of dietary essential amino acids from a protein or mixture of proteins is a factor which determines the feeding quality of the protein. The purpose of the study was to evaluate the quality of the protein from a high protein raw ingredient (corn gluten) using a chromatographic method (HPLC) under optimized experimental conditions. In this study, we used pre-column derivatization, separation by high-performance liquid chromatography (HPLC) and UV detection. The optimized method was used to determine the amino acids from high-protein raw ingredients commonly used in animal feeding (corn gluten, 61%CP). A set of 6 amino acids analyses has been performed in 6 different days, each sample being prepared in double. For characterization of data strings we used quality parameters: average, standard deviation, standard error, confidence level, precision, accuracy. For verifying the Gaussian shape of the strings we used the Kernel Density. For identifying and rejecting the outliers from the data strings we used the Q test. The very low values of the accuracy for several amino acids (glutamic acid, threonine, alanine, valine, phenylalanine, isoleucine, leucine) determined us to introduce the dilution stage (1:2) for the hydrolysed samples. The method can be considered as repeatable (precision in different days) and accurate (evaluation by tracing yields) for all the determined amino acids.