DETERMINATION OF ALPHA-AMINO NITROGEN IN PEA PROTEIN HYDROLYSATES - ACOMPARISON OF 3 ANALYTICAL METHODS

Three spectrophotometric methods, using 2,4,6-trinitrobenzenesulphonic acid (TNBS), o-phthaldialdehyde (OPA) or ninhydrin, for the determina tion of alpha-amino nitrogen in pea protein isolates and hydrolysates were compared. The determined amounts of alpha-amino nitrogen differed greatly, depending on the method used. The TNBS and OPA methods produ ced comparable results, whereas the data obtained with the ninhydrin m ethod were only half of the TNBS or OPA values. Colour stability, reco very of the standard from the protein matrix and reproducibility of th e results were determined. The methods showed good accuracy (SE 1-3%) with recovery values of the standard (L-leucine) from the protein matr ix of 91, 111 and 75% for the OPA, ninhydrin and TNBS method, respecti vely. (C) 1998 Elsevier Science Ltd. All rights reserved.