Journal - Association of Official Analytical Chemists最新文献

The use of the lipid globule stain to aid in differentiating the Bacillus cereus group (i.e., B. cereus, B. cereus var. mycoides, and B. thuringiensis) from other Bacillus species was investigated. Smears from colonies grown on suitable agar were made on precleaned slides, stained, and examined microscopically for characteristic deep blue lipid globules. The study included a total of 649 cultures of Bacillus species plus 143 incompletely characterized Bacillus isolates from food. Only B. cereus, B. cereus var. mycoides, B. thuringiensis, B. megaterium, and B. sphaericus were consistently positive for lipid globules, although at times, a few cells of B. aneurinolyticus and B. thiaminolyticus were also positive. The lipid globule stain procedure is of value in differentiating Bacillus species, especially when performed by an experienced analyst and used in conjunction with tests for cell and spore morphology.

A simple and precise method of detecting brominated vegetable oil (BVO) in soft drinks is described. After extraction of BVO using diethyl ether, the concentrated ethereal solution was treated with a small quantity of zinc dust to convert the organic bromide to inorganic form; the solution was subsequently treated with lead dioxide to liberate bromine. The bromine evolved was detected by means of fluorescein-impregnated filter paper strip that turns pink because eosin is formed. The test can detect as low as 10 ppm (2 mg/200 ml) of BVO under experimental conditions. Gas chromatography was carried out on sodium methoxide derivatives prepared from ether extract for quantitation.

Rehydratable dry-film plating methods for total coliforms and Escherichia coli in foods have been compared to the AOAC most probable number methods. Fourteen laboratories participated in the collaborative study. Three coliform and E. coli levels in 6 samples of 4 product types (flour, nuts, cheese, and beef with gravy) and in 3 samples of 2 product types (mushrooms and raw turkey) were tested in duplicate by the participants. The mean log counts for the 3 methods were comparable. In general, the repeatability and reproducibility variances of the plating methods were as good as or better than that of the MPN method. The method has been adopted official first action by AOAC.

The present paper describes an enzyme-linked immunoassay (ELISA) used in combination with thin-layer chromatography (TLC) and liquid chromatography (LC) for determination of fusarochromanone (TDP) mycotoxins in barley, wheat, and a Fusarium culture grown in rice and corn. The mycotoxins were first extracted from the sample with 100% methanol and subjected to TLC or LC without additional cleanup treatment. Individual fractions eluted from TLC or LC were acetylated, then analyzed by ELISA. Determinations of TDP toxins at levels as low as 0.1 and 0.5 ng were achieved by ELISA in combination with LC and TLC, respectively. The detection limit for TDP-1 in barley and wheat was about 20 ppb by ELISA alone as compared with a detection limit of 5 ppb by a combination of ELISA with either TLC or LC. Overall analytical recovery (% of added) of TDP-1 added to barley and wheat at 5, 10, and 20 ppb of TDP-1 was 106.9 +/- 15.3 and 113.2 +/- 11.6 by LC-ELISA and 108.8 +/- 9.1 and 110.4 +/- 4.9 by TLC-ELISA, respectively. Analysis of extracts obtained from Fusarium equiseti R6137 grown in corn and rice by the combination of TLC and ELISA revealed that diacetyl-TDP was also produced by this fungus in addition to TDP-1 and TDP-2. Comparable results were obtained when fungal extracts were subjected to ELISA, LC, and immunochromatography (i.e., combination of ELISA with either TLC or LC).