Protein Kjeldahl analysis

In order to chemically analyse a sample of com for its protein content, a rather complex analytical procedure (e.g. Kjeldahl analysis) is required, a slow and expensive process. In our example, the PCR/PLS group of methods replaces this procedure with a much faster spectroscopic analysis. First, a mathematical relationship is established from a calibration set, comprising a matrix of NIR-spectra of the collection of samples and the vector of... 

Protein dispersibility index Dry product is dispersed in water by blending, then centrifuged at 880 x g for I0 min Protein dispersibility index (%) = (% water-dispersible prolein/% total protein) x 100 Advantages Tested in a collaborative study and found to be reproducible between laboratories. Disadvantages Limited to soy products protein is determined by Kjeldahl analysis, which can be a lengthy procedure. AOCS Method B a 10-65 (AOCS, 1999) AACC Method 46-24 (AACC, 2000)... 

Fig. 12 gives an overview of the variables in the reactor model. In accordance with what was demonstrated by lacobucci et al. (18) it is assumed that the concentration of solubilized, permeable protein is equal on both sides of the membrane. This assumption is substantiated by the fact that the protein hydroly-zate consists mainly of smaller, soluble peptides and unconverted protein ( ). The concentration of accessible protein in the feed stream, SR, will be smaller than PR, as it is likely that a small, constant percentage of the protein is undegradable, in accordance with what was found by lacobucci et al. (18). This fraction counts as protein in a Kjeldahl analysis, but is otherwise consi-... 

Kjeldahl analysis of nitrogen-containing compounds, proteins, p. 287... 

Albumin and globulins can be analyzed by the same procedure as for total proteins after fractionation by salting out with either sodium sulfate or sodium sulfite. More detailed information may be required about the protein fractions (a, j8, 7 globulins), in which case starch gel electrophoresis can be used to separate the proteins. Micro-Kjeldahl analysis of proteins is used when highly accurate data are required the biuret method is accurate to about 4%. 

As soy protein denatures, it forms insoluble aggregates. Two methods, NSI and PDI, are broadly used to evaluate protein solubility/dispersibility in soy protein products. The PDI (AOCS Official Method Ba-10-65, 1993) rapid stir method uses a blender to disperse the sample, and the NSI (AOCS Official Method Ba 11-65, 1993) slow stir method uses a laboratory stirrer. In both methods, the protein or nitrogen leached into the liquid phase is compared with the total protein or nitrogen in the sample as determined by Kjeldahl analysis. The NSI method usually gives lower values and is related to PDI by the formula (Central Soya Company, 1988) ... 

Alkali-extracted proteins from simflower oil cake (89% proteins, Nx6.25) and wheat gluten (76.5% proteins, Nx5.7) were reacted with n-octanol in the presence of an acid catalyst. Temperature, reaction time and catalyst concentration were varied according to an experimental design to maximize the esterification yield. The latter was determined by alkaline hydrolysis and subsequent analysis by gas chromatography. The hydrolysis of the peptide chain was traced by the determination of the amount of free amino groups in esterified proteins using 2,4,6-trinitrobenzene-sulfonic acid (TNBS) assays. The solubility curves of modified proteins in water as a function of pH were obtained by Kjeldahl analysis to determine the composition of the soluble and insoluble parts. 

Quantitation. Various standard protein analytical methods can be nsed for quantitation of collagen. These include determination of the total nitrogen content by Kjeldahl analysis, followed by estimation of the collagen concentration... 

The hydrolysis of 0.06 M BAA by papain is a first-order reaction under the conditions of assay (100). Specific activity (Gi) is expressed as K (first-order rate constant calculated in decimal logarithms) per milligram of protein nitrogen per milliliter of reaction mixture. Protein nitrogen can be estimated by the turbidometric method of Btlcher (36). The nitrogen content of standard papain solutions is determined by micro-Kjeldahl analysis. 

The Kjeldahl method is not a rapid means of analysis but it does have the advantage of being absolute. It is a sobering thought that a batch of bread can be made in less time than it takes to check the protein content of the flour by Kjeldahl. 

The Kjeldahl total nitrogen determination method is not very sensitive, hut it suits well for analyzing insoluble samples without preceding disintegration. Automated Kjeldahl protein estimations are used especially in food analysis. 

Both the light scattering and infrared techniques are widely used, and there are many reports of the correlation between one of these methods and a reference method, usually Babcock or Gerber in the case of fat analysis and total nitrogen by Kjeldahl for proteins. One source of disparity between the various correlations has been the choice of a reference method. The realization that different methods for fat analysis measure different chemicals and thus can be expected to give different results has been slow in reaching the industry. 

Since late in the 19th century, the classical Kjeldahl method has been recognized and accepted universally as the authoritative method of analysis for determining the protein content in a wide variety of ingredients and finished products. As a result of technical innovations there are currently available and in use semiautomated or fully automated protein analysis systems that are based on the classical Kjeldahl procedure. 

The preparation time for a PER is extensive and involves several days for acquisition of rats and their acclimation before a feeding trial begins. Preparation of a consistent and uniform diet is not trivial. Adequate diet for each treatment for the course of the study should be prepared shortly in advance of the study. Testing of the diet involves chemical analysis for protein (i.e., Kjeldahl N takes several hours) and accurate determination of other diet constituents (e.g., ash, crude lipid, and dietary fiber) so that isocaloric diets can be formulated between treatment groups. These determinations take >1 day to complete. It is recommended that multiple samples from each diet be obtained for proximate analysis of diet before it is fed to ensure that each diet has the proper nitrogen content (and this is same between diet treatments) and that all diets are isocaloric. 

L9. Levin, B., and Oberholzer, V. G., Paper electrophoresis of serum proteins with micro Kjeldahl nitrogen analysis of the protein fractions A comparison with free electrophoresis and salt fractionation methods. Am. J. Clin. Pathol. 23, 205 (1953). 

In order to improve the state of health and growth of domestic animals, their diet must be well balanced, therefore basic feed often needs to be enriched with respect to trace and minor elements. Such additions are made on the basis of results of analysis of the raw material, e.g. hay. A hay powder reference material has been considered necessary as being complementary to the rye grass material described in section 6.3. The EC Directive 79/373/EEC prescribes the determination of the nutrients Ca, P and Mg S and N are also important elements since they are used as indicators of the availability of proteins finally the administration of iodine to growing animals requires that this element be carefully monitored. Consequently, the hay powder CRM 129 was certified for its contents of Ca, K, Mg, P, S, Zn, I, N and Kjeldahl-N [10,11]. 

Proteins and Amino Acids Total protein in food and feed samples is commonly determined by Kjeldahl (acid digestion/titration) or Dumas (pyrolysis) or elemental analysis.14 FIPLC can separate major proteins and furnish protein profiles and speciation information. HPLC can be used to further characterize specific proteins via peptide mapping and amino acid sequence analysis. HPLC modes used for protein include IEC, SEC, RPC, and affinity chromatography with typical UV detection at 215 nm or MS analysis. Details on protein separations are discussed in the life sciences section. 

Soxhlet for fat and micro-Kjeldahl for protein). The preparation of freeze-dried meat mixtures to serve as calibration standards was also described in this work [32]. The availability of such pre-analysed, reconstitutable, shelf-stable calibration standards would facilitate the implementation of FTIR methods in the meat processing industry, in a similar manner as has been reported for milk analysis [33,34]. 

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