The Kjeldahl method was introduced in 1883 and consists of three main steps: sample digestion, distillation, and ammonia determination (titration being the primary method). The Kjeldahl method uses sulfuric acid, a variety of catalysts, and salts to convert organically bound nitrogen in samples to ammonium with its subsequent measurement (Saez-Plaza et al., 2013). Today, this method is universally accepted and used in tens of thousands of laboratories throughout the world for nitrogen analysis in a wide variety of materials, such as foods, beverages, agricultural products, environmental samples, chemicals, biochemicals, and pharmaceuticals. However, successful analysis requires proper sampling and sample handling, which depend on the type of material. The Kjeldahl method has been validated and standardized for total (crude) protein estimation for a wide variety of food matrices, indirectly determined by their nitrogen content, and is the reference method adopted by many international organizations. The Kj...

An Overview of the Kjeldahl Method of Nitrogen Determination. Part II. Sample Preparation, Working Scale, Instrumental Finish, and Quality Control

In 1883 Kjeldahl devised a method for the determination of nitrogen, which has become a classical measurement in analytical chemistry and has been used extensively over the past 130 years. In the original method, sulfuric acid alone was used as a digestion medium. The use of a catalyst in Kjeldahl digestion accelerates oxidation and completes the digestion to allow the subsequent determination of nitrogen. Mercury (its use being in decline because of environmental concerns), selenium, and copper are the catalysts of choice, though for certain applications titanium has found some usage. Short digestion times in association with maximum nitrogen recovery may be achieved by using a methodology based on experimental design and response surfaces, with microwave digestion processes, and with the aid of the couple sulfuric acid-hydrogen peroxide without catalyst. The quantification of distilled ammonia is generally achieved by titration; the ammonia is absorbed in an excess of boric acid, followed by titration w...

An Overview of the Kjeldahl Method of Nitrogen Determination. Part I. Early History, Chemistry of the Procedure, and Titrimetric Finish

The impact of salt and fat level variation on the physiochemical properties and sensory quality of pork breakfast sausages

Effect of varying salt and fat levels on the sensory and physiochemical quality of frankfurters.

Determination of volatile nitrosamines in meat products by microwave-assisted extraction and dispersive liquid-liquid microextraction coupled to gas chromatography-mass spectrometry.

A study was designed to compare the Kjel-Foss automated macro-Kjeldahl method and a block digestion-steam distillation method. The official AOAC Kjeldahl method was used as a reference procedure. Six products with a crude protein range of 10-30% were analyzed by 23 laboratories. Five laboratories analyzed the samples by the official AOAC method, 8 laboratories used the automated Kjel-Foss method, and 11 laboratories used the block digestion with steam distillation method. Standard deviations for each product and each method for both repeatability and reproducibility are given. The block digestion-steam distillation method has been adopted official first action.

Comparison of three methods for determination of crude protein in meat: collaborative study.

Nine laboratories participated in a collaborative study of a method for determining 6 nitrosamines, dimethylnitrosamine, diethylnitrosamine, dibutylnitrosamine, nitrosopiperidine, nitrosopyrrolidine, and nitrosomorpholine, in the 5-17 ppb range. The coefficients of variation for repeatability were 10.8, 8.5, 10.4, 8.5, 8.7, and 7.8% with corresponding coefficients of variation for reproducibility of 16.4, 12.0, 13.6, 10.8, 11.2, and 10.3% and recoveries of 89.6, 91.6, 84.7, 90.0, 89.6, and 88.1%, respectively. The method was adopted official first action.

Mineral oil vacuum distillation method for nitrosamines in fried bacon, with thermal energy analyzer: collaborative study.

A collaborative study was conducted on a titrimetric EDTA method for the determination of calcium in mechanically separated poultry and beef tissue. Six laboratories analyzed, as blind duplicates, 5 poultry samples and 5 beef samples. Calcium concentrations covered the levels from 0.04 to 0.82%. Pooled standard deviations were 0.0165 for repeatability, 0.0072 for bias, and 0.0225 for reproducibility. The method has been adopted official first action.

Titrimetric Determination of Calcium in Mechanically Separated Poultry and Beef: Collaborative Study

A rapid screening procedure for the detection of volatile N-nitrosamines in fried bacon has been developed for the regulatory monitoring of bacon. This procedure uses vacuum mineral oil distillation of an alkaline sample. The distillate is collected in a prewet trap immersed in liquid nitrogen. After thawing, the distillate is transferred to a separator. The trap is rinsed with methylene chloride which is then used to extract the nitrosamines. The methylene chloride is dried with Na2SO4 and concentrated. A gas-liquid chromatograph coupled to a thermal energy analyzer is used to identify and quantitate the nitrosamines. Recoveries of 7 volatile N-nitrosamines added to 25 g fried bacon at the 10 ppb level (microgram/kg) ranged from 78 to 92%.

Anthony J Malanoski

Papers

Comparison of three methods for determination of crude protein in meat: collaborative study.

Mineral oil vacuum distillation method for nitrosamines in fried bacon, with thermal energy analyzer: collaborative study.

Titrimetric Determination of Calcium in Mechanically Separated Poultry and Beef: Collaborative Study

Screening procedure for detection of volatile N-nitrosamines in cooked bacon by one-trap mineral oil vacuum distillation and thermal energy analyzer.

Diagnostic Data Evaluation. Part II. Collaborative Study Evaluation: Coefficient of Variation Considered To Be A Constant