ABSTRACT
Isoflavones are biologically active compounds occurring naturally in a variety of plants, with relatively high levels found in soybeans. Twelve laboratories participated in a collaborative study to determine the aglycon isoflavone content of 8 test samples of soy and foods containing soy. The analytical method for the determination of isoflavones incorporates a mild saponification step that reduces the number of analytes measured and permits quantitation versus commercially available, stable reference standards. Test samples were extracted at 65 degrees C with methanol-water (80 + 20), saponified with dilute sodium hydroxide solution, and analyzed by reversed-phase liquid chromatography with UV detection at 260 nm. Isoflavone results were reported as microg/aglycon/g or microg aglycon equivalents/g. The 8 test samples included 2 blind duplicates and 4 single test samples with total isoflavone concentrations ranging from approximately 50 to 3000 microg/g. Test samples of soy ingredients and products made with soy were distributed to collaborators with appropriate reference standards. Collaborators were asked to analyze test samples in duplicate on 2 separate days. The data were analyzed for individual isoflavone components, subtotals of daidzin-daidzein, glycitin-glycitein, and genistin-genistein, and total isoflavones. The relative standard deviation (RSD) for repeatability was 1.8-7.1%, and the RSD for reproducibility was 3.2-16.1% for total isoflavone values of 47-3099 microg/g.
Subject(s)
Chromatography, Liquid/methods , Food Analysis/methods , Glycine max/chemistry , Isoflavones/analysis , Chromatography, Liquid/standards , Chromatography, Liquid/statistics & numerical data , Food Analysis/standards , Food Analysis/statistics & numerical data , Genistein/analysis , Genistein/chemistry , Glucosides/analysis , Glucosides/chemistry , Isoflavones/chemistry , Isoflavones/standards , Laboratories , Molecular Structure , Reference StandardsABSTRACT
Seventeen test foods were each analyzed by four methods. Total lysine was measured by conventional amino acid analysis. Reactive lysine was measured with either fluorodinitrobenzene, o-phthalaldehyde or a differential dye-binding procedure. The results were then compared with another group's results from rat growth assays of the same samples for availably lysine. A sample of deliberately heat-damaged milk powder gave a rat assay value corresponding to 64% of its total lysine content; other values were all higher and on average 99% for 7 animal products, and 87% for 9 vegetable products. The correlation coefficient between the two sets of values was 0.95. The 'reactive lysine' procedures failed to give a better prediction of the rat values.
Subject(s)
Lysine/analysis , Animals , Coloring Agents , Dinitrofluorobenzene , Freeze Drying , In Vitro Techniques , Lysine/metabolism , Nutritive Value , Rats , Weight Gain , o-PhthalaldehydeABSTRACT
Samples of 4 foods, 1 animal feed, isolated soy protein, and beta-lactoglobulin were analyzed by 9 laboratories to determine concentrations of cysteine as cysteic acid, methionine as methionine sulfone, and tryptophan. Sulfur amino acids were determined by AOAC method 43.A08-43.A13 for food and feed ingredients, in which samples are oxidized with performic acid before protein hydrolysis with 6N HCl. Tryptophan was determined after protein hydrolysis with 4.2N NaOH. In both methods, free amino acids were separated by ion-exchange or reverse-phase chromatography. Each laboratory was provided with detailed methods and with sealed vials containing solutions of standards. Samples were analyzed in duplicate, and variation between laboratories was determined. Coefficients of variation between laboratories for the 6 samples ranged from 5.50 to 11.8% for methionine as methionine sulfoxide, 8.59 to 17.3% for cysteine as cysteic acid, and 3.87 to 16.1% for tryptophan. Amino acid recoveries were determined by analysis of beta-lactoglobulin and were based on expected levels of each amino acid obtained from amino acid sequence data. The mean recovery of cysteine was 97% with a range of 88-119%. For methionine, mean recovery was 98% (range 89-115%) and for tryptophan, 85% (range 59-102%). Method 43.A08-43.A13 for food and feed ingredients has been adopted official first action for determination of cysteine and methionine in processed foods. The alkaline hydrolysis method has been adopted official first action for determination of tryptophan in foods and food and feed ingredients.
Subject(s)
Amino Acids, Sulfur/analysis , Animal Feed/analysis , Food Analysis , Tryptophan/analysis , Chromatography , Chromatography, Ion Exchange , Cysteine/analysis , Hydrolysis , Indicators and Reagents , Methionine/analysisABSTRACT
A method for the determination of sulfamethazine at the 0.5 ppm level by high performance liquid chromatography (HPLC) has been shortened and simplified by use of a mini-column clean-up procedure. Fortified feed samples were extracted with acetonitrile, concentrated, and redissolved in the mobile phase. Sulfamethazine was separated from most extraneous material by a mini-column of C18/Porasil B and AX/Corasil, and analyzed by HPLC at 254 nm. Liquid standard solutions were used to fortify four formulated swine feeds and corn sample each at three levels, giving an average recovery of 98% and a relative standard deviation of 7.3%. Tests were run using 32 antibiotics and drugs to determine if they would interfere. Most of these substances were not eluted under the conditions used. Compounds which absorbed at the wavelength used did not interfere with the sulfamethazine peak.
