EFFECT OF HYDROLYSIS TIME ON THE DETERMINATION OF THE AMINO-ACID-COMPOSITION OF DIET, ILEAL DIGESTA, AND FECES SAMPLES AND ON THE DETERMINATION OF DIETARY AMINO-ACID DIGESTIBILITY COEFFICIENTS

A study was undertaken to determine the effect of hydrolysis time during amino acid analysis on individual amino acid yields from samples of a mixed diet, pig ileal digesta, and feces. Representative feed, digesta, and feces samples were hydrolyzed in duplicate in 6 M HCl in sealed evacuated tubes for 16, 24, 48, and 72 h, respectively, and then analyzed for their yields of alanine, arginine, aspartate, glutamate, glycine, histidine, isoleucine, leucine, lysine, phenylalanine, proline, serine, threonine, tyrosine, and valine. There was a significant (P < 0.05) curvilinear effect of hydrolysis time on the yields of all amino acids except tyrosine. The changes in isoleucine, lysine, and serine yields with hydrolysis time were parallel for the three types of samples, but for the other amino acids (except tyrosine) there were significant (P < 0.05) hydrolysis time-source interactions. This would introduce error into the calculation of amino acid digestibility coefficients if samples were only hydrolyzed for a standard time. To minimize the error due to incomplete hydrolysis or partial loss of amino acids, correction factors for each type of sample were calculated and can be applied to other samples.