Pollution-Reduced Kjeldahl Method for Crude Protein

Abstract

Pollution from the Kjeldahl method for crude protein has been reduced by substituting a low level of copper (0.04 g CuSO4) for the mercury (0.7 g HgO) specified in the AOAC official method, 2.049. Adjustments were made in the salt-acid ratio so the new system could handle hard-to-digest samples in a reasonable time. The new method was rugged for lysine. HCl. It is designed to be used for crude protein in feeds or similar Kjeldahl work. Precision and accuracy were equal to or better than that for the official method in a study of 17 samples analyzed in duplicate on 3 different days. The following samples were used in the study: lysine. HCl, tryptophan, NBS standards, urea, meals, mixed feeds, grains, and forage. The average per cent nitrogen found was 9.52 by the official method and 9.53 by the copper method. The average standard deviation was 0.038 by the official method and 0.033 by the copper method, giving the corresponding relative standard deviations of 0.40 and 0.35%.

Mulberry Ethanol Extract and Rutin Protect Alcohol-Damaged GES-1 Cells by Inhibiting the MAPK Pathway

“…The standard curve is made with glucose and the regression equation is y = 0.0041x−0.03 (R 2 = 0.9996), unit: mg/g. Protein: The protein content in MBE was determined by the Kjeldahl method [38] with a slight modification.…”

Organic elemental analysis

“…Fraisse and Schmidt (36) devised an automated system with a sample feeder and vertical reactor which does not require the operator's attention. Kjeldahl digestion using CuS04 (37,38) or Ti02 (39) in place of Hg was shown to be satisfactory. Colorimetric determination of ammonia by the indophenol reaction (40) was generally employed in the automated systems (41)(42)(43)(44).…”

Determination of tryptophan in feedstuffs: Comparison of two methods of hydrolysis prior to HPLC analysis

“…Their nitrogen content was determined by a Kjeldahl method (Rexroad and Cathey, 1976). Maltodextrins came from CPC (UK) Ltd, Manchester, UK.…”