Twelve laboratories collaboratively studied a liquid chromatographic method for determination of quinic, malic, and citric acids in cranberry juice cocktail and apple juice. Samples are passed through a disposable silica cartridge, filtered, and directly injected into the chromatograph. The mobile phase is 0.2M KH2PO4 (pH 2.4). Two reverse phase columns are used, with UV detection at 214 nm. Six samples of cranberry juice cocktail and 6 samples of apple juice were sent to each collaborator. Repeatability and reproducibility coefficients of variation ranged from 1.2 to 7.6% and from 2.9 to 14.7%, respectively, for quinic, malic, and citric acid levels above 0.10%. The precision of the method is satisfactory. The method has been adopted official first action.
Achloroform-methanol extraction method (complete extraction of fat in 3 min) for determining fat in processed and prepared foods has been studied collaboratively. Fourteen collaborators reported single replicate fat results on 7 samples representative of various food types and 2 spiked samples by the proposed method. Each sample was accompanied by a blind duplicate. For statistical purposes, the blind duplicates were treated as paired observations, and there were 2 laboratory outliers. There was a 97.9% agreement among the results from the remaining 12 collaborators and the Associate Referee for the unfortified samples. Recoveries of 93.8 and 98.3% were obtained on fortified samples, based on results obtained from 11 collaborators. The statistical analysis of the results indicate (ranges for standard deviations were Sr = 0.083-0.528, Sb = 0.101-0.379, Sd = 8.130-0.631, for fat values ranging from 1.58 to 26.91%) that this method is adequate for quantitating the fat content in a wide variety of processed foods for nutritional labeling. The method has been adopted official first action.
SUMMARY
A method is described for the separation and quantitative determination in a variety of foods of the following 5′‐nucleotides; eytidine‐5′‐phosphate, adenosine‐5′‐phosphate, uridine‐5′‐phosphate, inosine‐5′‐phosphate, and guan‐osine‐5′‐phosphate. This procedure employs a Dowex 1 ion‐exchange resin in the formate form to adsorb and concentrate the nucleotides from an aqueous extract of the food sample. The nucleotides are separated and eluted in the order previously given by means of a gradient elution system, consisting of water—formic acid‐sodium formate. The method gives complete resolution of the 5′‐nucleotides from each other, but not from their corresponding 2′‐ and 3′‐forms. Therefore, following chromatographic separation, the 5′‐nucleotides are determined calorimetrically in the presence of the 2′‐ and 3′‐nncleotides by oxidation with periodate and reaction of the oxidation products with 2, 4‐dinitrophenylhydrazine.
They furnished the bacterial extract from E. coli, the crude bacterial extract, the lyophilized extract of E. coli, the preparation from yeast, and the two fungal preparations, respectively.
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