scholarly journals Enzymatic Determination of Lactose and Galactose in Foods: NMKL Collaborative Methods Performance Study

1997 ◽  
Vol 80 (3) ◽  
pp. 584-590 ◽  
Author(s):  
Antti Mustranta ◽  
Carola Östman ◽  
I Aminoff ◽  
P Baardseth ◽  
E Eklund ◽  
...  
Keyword(s):  
Milk Powder ◽  
Meat Products ◽  
Enzymatic Oxidation ◽  
Performance Study ◽  
Cereal Products ◽  
Enzymatic Determination ◽  
Relative Standard ◽  
Analytical Tools ◽  
Hydrolysis Of

Abstract Enzymes are widely used in food chemistry as analytical tools. An enzymatic method for determining lactose and galactose in foods was evaluated in an interlaboratory methods performance study by 12 laboratories in 4 countries. The method is based on enzymatic hydrolysis of lactose and enzymatic oxidation of the hydrolysis products. The exchange of the coenzyme in the second reaction is the basis of quantitation. The method may be used for various types of foods, such as liquid and solid milk products, meat products, cereal products, fats, dressings, sweets, chocolate, and foods for special dietary uses. It is also applicable to lactose-free foods but not to products in which lactose has been partially hydrolyzed enzymatically to glucose and galactose. Six commonly used foodstuffs with lactose concentrations ranging from 0.4 g/100 g to 40 g/100 g and galactose concentrations up to 0.7 g/100 g were analyzed: crisp rye bread, milk chocolate, sausage, cheese, margarine, and baby food containing milk powder. They were distributed to the 12 participants as 12 randomly numbered test samples, representing blind duplicates of the 6 materials. The relative standard deviations for reproducibility (RSDR) were between 2.3-11% for lactose and 6.8-50% for galactose.

Enzymatic Determination of Free Glutamic Acid in Dried Soups and in Minced Sausages: NMKL1 Collaborative Study

1991 ◽  
Vol 74 (6) ◽  
pp. 921-925 ◽  
Author(s):  
M Tapani Hattula ◽  
Harriet C Wallin ◽  
◽  
R Andersen ◽  
K Blomberg ◽  
...  
Keyword(s):  
Glutamic Acid ◽  
Collaborative Study ◽  
Meat Products ◽  
Visible Range ◽  
Enzymatic Method ◽  
Study Materials ◽  
Enzymatic Determination ◽  
Relative Standard ◽  
The Mean

Abstract An enzymatic method for the determination of free glutamic acid in meat products and dried soups was collaboratively studied in 11 laboratories. In the presence of the enzyme glutamate dehydrogenase, L-giutamic acid is oxidatively deaminated by nicotinamide adenine dinucleotide (NAD) to 2-oxoglutarate. In a reaction catalyzed by diaphorase, the NADH thus formed converts 2-(p-iodophenyl)-3-(p-nitrophenyl)-5-phenyltetrazolium chloride to a formazan, which is measured in the visible range at 492 nm. Fourteen samples (7 samples of minced sausage and 7 samples of dried cauliflower soup) with glutamate contents varying between 0.4 and 16 g/kg were included In the study. Materials were distributed to participants as blind duplicates and as split level pairs. The mean relative standard deviation (RSDR) for reproducibility for the dried soup material containing glutamate between 7 and 16 g/kg was 4.6%. RSDR values for samples of minced sausage containing glutamate at lower levels (0.4-1.3 g/kg) were between 12 and 16%.

Enzyme Immunoassay for Determination of Gluten in Foods: Collaborative Study

1991 ◽  
Vol 74 (2) ◽  
pp. 257-264 ◽  
Author(s):  
John H Skerritt ◽  
Amanda S Hill
Keyword(s):  
Enzyme Immunoassay ◽  
Collaborative Study ◽  
Wheat Gluten ◽  
Meat Products ◽  
Processed Meat ◽  
Cereal Products ◽  
Relative Standard ◽  
Cooked Meats ◽  
Wheat Flours

Abstract A collaborative study was performed In 15 laboratories to validate a monoclonal antibody-based enzyme Immunoassay (EIA) for determination of gluten in foods. The study Included 13 samples: maize starch, "gluten-free" baking mixes, wheat flours, cookies, cooked meats, and a soup. Gluten was present In these samples at either zero or 0.02 to 10% by weight, I.e., over almost 3 orders of magnitude. The mean assay values for the foods varied from 88 to 105% of the actual amounts. The assay was quantitative for cereal products and the soup with repeatability (RSDr, relative standard deviation) and reproducibility (RSDR) of 16-22% and 24-33%, respectively. The assay was semiquantitative for the processed meat products (RSDr 14 and 26% and RSDr 46 and 56%), probably because gluten was unevenly distributed In the small (1 g) samples that were analyzed. The ELISA method produced no false positive results, and false negatives obtained with tannin-containing foods could be avoided by use of a modified sample extractant. None of the collaborators reported problems In following the protocol. The method has been adopted official first action by AOAC for determination of wheat gluten in foods.

Enzymatic colorimetry of lecithin and sphingomyelin in aqueous solution.

1983 ◽  
Vol 29 (8) ◽  
pp. 1513-1517 ◽  
Author(s):  
M W McGowan ◽  
J D Artiss ◽  
B Zak
Keyword(s):  
Aqueous Solution ◽  
Hydrogen Peroxide ◽  
Amniotic Fluid ◽  
Enzymatic Reaction ◽  
Detergent Solution ◽  
Enzymatic Determination ◽  
Red Color ◽  
Hydrolysis Of ◽  
Zwitterionic Detergent

Abstract A procedure for the enzymatic determination of lecithin and sphingomyelin in aqueous solution is described. The phospholipids are first dissolved in chloroform:methanol (2:1 by vol), the solvent is evaporated, and the residue is redissolved in an aqueous zwitterionic detergent solution. The enzymatic reaction sequences of both assays involve hydrolysis of the phospholipids to produce choline, which is then oxidized to betaine, thus generating hydrogen peroxide. The hydrogen peroxide is subsequently utilized in the enzymatic coupling of 4-aminoantipyrine and sodium 2-hydroxy-3,5-dichlorobenzenesulfonate, an intensely red color being formed. The presence of a non-reacting phospholipid enhances the hydrolysis of the reacting phospholipid. Thus we added lecithin to the sphingomyelin standards and sphingomyelin to the lecithin standards. This precise procedure may be applicable to determination of lecithin and sphingomyelin in amniotic fluid.

Automated enzymatic determination of starch in meat products

1982 ◽  
Vol 174 (4) ◽  
pp. 274-277
Author(s):  
Nel Haagsma ◽  
Joost W. Melten ◽  
Betty G. M. Gortemaker
Keyword(s):  
Meat Products ◽  
Enzymatic Determination

Sulfuric Acid/Hydrogen Peroxide Digestion and Colorimetric Determination of Phosphorus in Meat and Meat Products: Collaborative Study

1991 ◽  
Vol 74 (1) ◽  
pp. 22-26 ◽  
Author(s):  
David K Christians ◽  
Thomas G Aspelund ◽  
Scott V Brayton ◽  
Larry L Roberts
Keyword(s):  
Hydrogen Peroxide ◽  
Sulfuric Acid ◽  
Collaborative Study ◽  
Meat Products ◽  
Colorimetric Determination ◽  
Pork Sausage ◽  
Relative Standard ◽  
Significant Difference ◽  
Standard Deviations

Abstract Seven laboratories participated In a collaborative study of a method for determination of phosphorus in meat and meat products. Samples are digested In sulfuric acid and hydrogen peroxide; digestion Is complete In approximately 10 mln. Phosphorus Is determined by colorimetric analysis of a dilute aliquot of the sample digest. The collaborators analyzed 3 sets of blind duplicate samples from each of 6 classes of meat (U.S. Department of Agriculture classifications): smoked ham, water-added ham, canned ham, pork sausage, cooked sausage, and hamburger. The calibration curve was linear over the range of standard solutions prepared (phosphorus levels from 0.05 to 1.00%); levels in the collaborative study samples ranged from 0.10 to 0.30%. Standard deviations for repeatability (sr) and reproducibility (sR) ranged from 0.004 to 0.012 and 0.007 to 0.014, respectively. Corresponding relative standard deviations (RSDr and RSDR, respectively) ranged from 1.70 to 7.28% and 3.50 to 9.87%. Six laboratories analyzed samples by both the proposed method and AOAC method 24.016 (14th Ed.). One laboratory reported results by the proposed method only. Statistical evaluations Indicated no significant difference between the 2 methods. The method has been adopted official first action by AOAC.

Fluorometric Determination of Selenium in Foods

1974 ◽  
Vol 57 (2) ◽  
pp. 368-372 ◽  
Author(s):  
Milan Ihnat
Keyword(s):  
Standard Deviation ◽  
Milk Powder ◽  
Skim Milk ◽  
Skim Milk Powder ◽  
Food Samples ◽  
Fluorometric Method ◽  
Fluorometric Determination ◽  
Relative Standard ◽  
The Mean

Abstract A fluorometric method using 2,3-diaminonaphthalene for estimating selenium has been evaluated with regard to its applicability to food samples. Charring of the sample during digestion appeared to result in losses of native and added selenium from some samples, so a modified wet digestion procedure was introduced. Digestion first in nitric acid followed by a mixture of nitric-perchloric-sulfuric acids substantially reduced the incidence of sample charring for a variety of foods. The mean apparent recovery of selenium added as selenite or selenate at 100 and 500 ng levels to 0.1 and 1.0 g corn cereal, skim milk powder, and meat and 0.1 g fish was 101.0%; the actual recovery of the same levels of selenium from standard solutions was 96.6%. For a variety of samples containing 5—750 ng native or added selenium, the standard deviation as 4.7 + 1.95 X 10-2W ng, where W = ng selenium in the sample taken for analysis. The relative standard deviation (RSD) as a function of selenium weight (ng) was 50% (10), 6.7% (100), 4.3% (200), 3.1% (400), 2.7% (600), and 2.5% (800). The detection limit (weight of selenium at which RSD = 50%) was 10 ng at a mean blank level of 25 ng.

scholarly journals Determination of Metals in Foods by Atomic Absorption Spectrometry after Dry Ashing: NMKL1 Collaborative Study

2000 ◽  
Vol 83 (5) ◽  
pp. 1204-1211 ◽  
Author(s):  
Lars Jorhem ◽  
G Afthan ◽  
G Cumont ◽  
H P Dypdahl ◽  
K Gadd ◽  
...  
Keyword(s):  
Standard Deviation ◽  
Atomic Absorption Spectrometry ◽  
Atomic Absorption ◽  
Collaborative Study ◽  
Milk Powder ◽  
Absorption Spectrometry ◽  
Relative Standard ◽  
Dry Ashing ◽  
Zinc Concentrations

Abstract A method for determination of lead, cadmium, zinc, copper, and iron in foods by atomic absorption spectrometry (AAS) after dry ashing at 450°C was collaboratively studied in 16 laboratories. The study was preceded by a practice round of familiarization samples and another round in which solutions were distributed and the metals were determined directly by AAS. The study included 5 different foods (liver paste, apple sauce, minced fish, wheat bran, and milk powder) and 2 simulated diets. A single analysis was carried out with each sample. Suitable sample combinations were used as split-level combinations for determination of the repeatability standard deviation. The reproducibility relative standard deviation for each of the elements ranged from 20 to 50% for lead concentrations of 0.040–0.25 mg/kg, from 12 to 352% for cadmium concentrations of 0.001–0.51 mg/kg, from 4 to 8% for zinc concentrations of 0.7–38 mg/kg, from 7 to 45% for copper concentrations of 0.51–45 mg /kg, and from 11 to 14% for iron concentrations of 4–216 mg/kg.

scholarly journals Determination of Total Phosphorus in Foods by Colorimetry: Summary of NMKL Collaborative Study

1996 ◽  
Vol 79 (6) ◽  
pp. 1408-1410 ◽  
Author(s):  
T Katrhna Pulliainen ◽  
Harriet C Wallin
Keyword(s):  
Total Phosphorus ◽  
Phosphorus Content ◽  
Collaborative Study ◽  
Colorimetric Method ◽  
Milk Powder ◽  
Molybdenum Blue ◽  
Relative Standard ◽  
Standard Deviations ◽  
Skimmed Milk Powder

Abstract A collaborative study was conducted to validate a spectrophotometric–colorimetric method for determining total phosphorus in foods. The sample was dry-ashed in the presence of zinc oxide, and total phosphorus content was measured colorimetrically as molybdenum blue. Twelve laboratories from the Nordic countries participated in the study. The test materials included potato flour, sausage, cold ham, infant formula powder, cheese, and skimmed milk powder. Participants received 12 randomly coded samples of 2 blind duplicates of each material. Phosphorus contents of materials varied between 0.076 and 0.96 g/100 g. Relative standard deviations for repeatability of the method varied from 1.1% for 0.96 g phosphorus/100 g to 5.4% for 0.29 g phosphorus/100 g. Relative standard deviations for reproducibility varied from 3.6% for 0.96 g phosphorus/100 g to 7.7% for 0.23 g phosphorus/100 g. The colorimetric method for determination of total phosphorus in foods has been adopted first action by AOAC INTERNATIONAL as an NMKUAOAC INTERNATIONAL method.

Liquid Chromatographic Determination of Unbound and Acetone-Soluble Bound Gossypol in Cottonseed Meals and Mixed Feeds

1992 ◽  
Vol 75 (5) ◽  
pp. 815-823
Author(s):  
Nickos A Botsoglou
Keyword(s):  
Chromatographic Determination ◽  
Gradient Elution ◽  
Liquid Chromatographic Method ◽  
Relative Standard ◽  
On Line ◽  
Liquid Chromatographic Determination ◽  
Mixed Feeds ◽  
Liquid Chromatographic ◽  
Hydrolysis Of

Abstract A liquid chromatographic method has been developed for the determination of unbound and acetone- soluble bound gossypol in cottonseed meals and mixed feeds at levels of 0.5 ppm. The method involves extraction with aqueous acetone in the presence of ascorbic acid, hydrolysis of the "soluble bound" forms with hydrochloric acid, partitioning into chloroform, and chromatographic separation on a 10 µm C18 column by step gradient elution using a methanol-water mobile phase acidified with phosphoric acid. With minor modifications, the method permitted discriminate determination of unbound gossypol and acetone-soluble hydrophilic and lipophilic forms of bound gossypol. The gossypol peak was characterized by on-line spectral scanning and absorbance rationing. Overall relative standard deviation was 6.7% and overall recovery was 98.1 ± 3.3%. When the method was applied to several cottonseed meal samples, results were inconsistent with those obtained by the official American Oil Chemists' Society method for "free" gossypol determination.

Reagent for the enzymatic determination of serum total cholesterol with improved lipolytic efficiency.

1983 ◽  
Vol 29 (6) ◽  
pp. 1075-1080 ◽  
Author(s):  
J Siedel ◽  
E O Hägele ◽  
J Ziegenhorn ◽  
A W Wahlefeld
Keyword(s):  
Total Cholesterol ◽  
Cholesterol Ester ◽  
High Performance ◽  
Serum Lipids ◽  
Serum Total Cholesterol ◽  
Enzymatic Determination ◽  
Layer Chromatography ◽  
Chloroform Methanol ◽  
Hydrolysis Of

Abstract We describe a sensitive method for quantifying the extent of cholesterol ester cleavage during enzymatic assay of total cholesterol in serum. Lipids are extracted from the assay mixture with chloroform/methanol (1/1 by vol), concentrated, then quantified by "high-performance" thin-layer chromatography. Although with conventional enzymatic reagents for determination of serum total cholesterol the hydrolysis of the cholesterol esters may be incomplete, a new enzymatic cholesterol reagent (Monotest Cholesterol, High Performance, Boehringer Mannheim) gives virtually complete cholesterol ester cleavage (i.e., greater than or equal to 99.5%). Use of this reagent with its improved lipolytic efficiency yields results for serum total cholesterol that are identical to those measured with a candidate reference procedure involving alkaline cholesterol ester saponification.

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