An intercomparison of methods involving 18 European laboratories was organized to assess the state-of-the-art of vitamin determination in foods. Each laboratory received identical samples of dry food reference material (homogeneous powders, milk powder, pork muscle and haricot vert beans), which have recently been certified for major dietary components and elements. Each laboratory was requested to perform the analyses by its own routine methods. The results for water-soluble vitamins are reported. The reproducibility for the determination of vitamin B1 in milk powder, pork muscle and haricot vert beans with high-performance liquid chromatography (HPLC), fluorimetric and microbiological methods was good, with the relative standard deviation of reproducibility (RSDReprod) ranging from 11 to 18%. Differences between laboratories for the determination of the vitamin B2 content of milk powder, pork muscle and haricot vert beans determined using HPLC and microbiological methods were very high, with RSDReprod ranging from 28 to 74%. The extraction and hydrolysis procedures were probably the most important sources of variation. For vitamin B6 various HPLC and microbiological methods were used. The variation in the results for vitamin B6 was high, except in milk powder. The RSDReprod ranged from 18 to 51%. A major part of this variability was due to differences in the extraction and hydrolysis procedures and problems with the identification of the vitamin B6 vitamers by HPLC. Variation in the results for niacin obtained with the microbiological methods in milk powder, pork muscle and haricot vert beans, was small; RSDReprod = 9-15%.(ABSTRACT TRUNCATED AT 250 WORDS)
Several ring tests have been organized by the International Organisation for Standardization (ISO) and the Measurement and Testing Programme (BCR) for improving glucosinolate methods. Finally, HPLC of desulphoglucosinolates is recommended by ISO, the European Committee for Standardization (CEN), and the European Commission (EC) as the official method. X-ray fluorescence has also become particularly common for fast analysis. After checking stability of intact glucosinolates in whole rapeseeds, the BCR has three reference materials (CRM 366, CRM 190, CRM 367) available, certified for their total glucosinolate and sulphur contents. Currently, the Measurement and Testing Programme is supporting a research project concerning the stability of desulphoglucosinolates and intact glucosinolates extracts. At the present time, best results are observed with lyophilized extracts sealed in brown glass ampoules and stored at -18 degrees C.
An intercomparison of methods involving 18 European laboratories was organized to assess the state-of-the-art of vitamin determination in foods. Each laboratory received identical samples of dry food reference material (homogeneous powders, milk powder, pork muscle and haricot vert beans), which were recently certified for major dietary components and elements. Each laboratory was requested to perform the analyses by its own methods. Results for fat-soluble vitamins are reported. All participants isolated the fat-soluble vitamins by alkaline saponification. For retinol, only high-performance liquid chromatography (HPLC), reversed- or normal-phase, was applied, with both ultraviolet (UV) and fluorescence detection. Results in milk powder showed a relative standard deviation of reproducibility (RSDReprod) of only 10%. Carotene was determined by HPLC (reversed- and normal-phase) and with open-column chromatography at atmospheric pressure. For beta-carotene results in milk powder agreed very well; the RSDReprod was 14%. The values reported for haricot vert beans showed poor agreement; the RSDReprod was 52%. A major part of this variability was due to differences in methodological principles. The results for alpha-tocopherol in milk powder and haricot vert beans agreed very well, with RSDSReprod of 16 and 15%, respectively. Only HPLC (reversed- and normal-phase) with UV and fluorescence detection was applied.
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