[Validation of Method for Nitrite Determination in Foods].

In general, nitrite in food is extracted under slightly alkaline conditions, deproteinized, and analyzed by a colorimetric method using color development by diazotization. However, depending on the sample, the sample solution may become cloudy and difficult to filter by the deproteinization treatment of the analytical method. Recently, an improved analytical method that solves these problems has been reported. Therefore, a validation study was performed on the improved analytical method was performed. The concentrations of sodium nitrite added to cod roe, fish sausage, and ham, which were not labeled with sodium nitrite, were set at the upper limits of the standards for use. We set the target values of 70-120% for trueness, less than 15% for intralaboratory reproducibility, and less than intralaboratory reproducibility for repeatability. As a result, the target values were met for the three samples verified: 88-92% for trueness, 2.0-3.0% for repeatability, and 3.2-4.3% for intralaboratory reproducibility. In addition, an interlaboratory study was conducted by eight institutes on the improved analytical method for nitrite. At each institution, sodium nitrite was added to the same three samples as in the validation study, at concentrations equivalent to twice the lower limit of quantification and the upper limit of the standards for use and analyzed in triplicate. The estimated trueness from the obtained analyses ranged from 82 to 95%, the repeatability ranged from 2.3 to 5.8%, and the inter-room reproducibility ranged from 3.5 to 11%. Thus, the improved analytical method could be useful for determining nitrite in foods.

[Improvement of Nitrite Analysis Method in Food Products].

The conventional analysis method has problems with extraction efficiency, operability, and reproducibility. In this study, we attempted to solve these problems and improve the analytical method to obtain sufficient extraction efficiency and good operability and accuracy. The conventional method was able to get sufficient extraction in dried meat products, where the extraction efficiency of the conventional method was low, by increasing the concentration of sodium hydroxide solution at the time of homogenization. Suction filtration after adding the defoaming agent was added allowed for accurate volume adjustment. The turbidity of the extract caused by insufficient addition of zinc acetate solution was removed by increasing the amount of zinc acetate solution that was added. Turbidity caused by starch was removed by adding pancreatin. The RSD of the quantitative values was improved by adding sodium hydroxide solution and 80-90℃ water and immediately homogenizing. Furthermore, by changing the dilution factor of the extract solution in the colorimetric method, the inhibition of coloration by reducing substances was suppressed, and more accurate quantitative values could be obtained than with the conventional method. The recovery rate was 78.5-105% (RSD 0.7-5.8%), which was a good result. This method was considered to be a useful analytical method that can contribute to improving the inspection accuracy of nitrite ion analysis.

[Analysis of Acidic Tar Dyes in High-Protein Foods: Achievement of Improved Recoveries and Shortened Operation Time by Loading Sample Extract onto Polyamide Columns at pH 8.5].

The recoveries of xanthene dyes in the analysis of acidic tar-dyes in high-protein foods were improved by loading them onto polyamide columns at pH 8.5, instead of using the conventional pH 3-4 solution. The experimental scale was reduced to approximately half that of the conventional method. Furthermore, instead of eliminating the organic solvent in the extract by evaporation, the extract was diluted with water prior to PA column cleanup in order to reduce the ratio of organic solvent so that acidic tar-dyes would be better retained on the column. The above two procedures shortened the operation time and allowed for a simpler protocol. With this method, the recoveries of erythrosine, phloxine, and rose bengal from salted cod roe were 82, 88, and 74%, respectively. The recovery percentages were greatly improved compared to those achieved by conventional column loading at pH 3.5 (26, 44, and 18%, respectively). The recoveries of azo-dyes (Amaranth, New Coccine, Allura Red AC, Tartrazine, Sunset Yellow FCF) were also improved from 41-66 to 79-99%.

Analyses of Acidic Tar Dyes in High-Protein Foods and Examination of Extraction and Clean-Up Methods for Various Foods.

Extraction and clean-up methods were examined for the analysis of acidic tar dyes in various high-protein foods. 1% Aqueous ammonia followed by ethanol, 1% aqueous ammonia-ethanol (1 : 1) mixture, and 1% aqueous ammonia-tetrahydrofuran (1 : 1) mixture were used in sequence for boiled fish paste (kamaboko), pounded fish cake (hanpen), and sausage. The sausage extract was centrifuged at low temperature to solidify and remove the contained fat. Salted cod roe with red pepper was extracted twice with 1% aqueous ammonia-ethanol (1 : 1) mixture, followed by extraction with 1% aqueous ammonia-tetrahydrofuran (1 : 1) mixture. A divinylbenzene-N-vinylpyrrolidone copolymer column was used for the clean-up of xanthen dyes. In the case of clogging-prone samples, the same type of large-particle-size column was used. A polyamide column was used for clean-up of the other dyes. When each dye was added at 5 µg/g in the foods, recoveries from kamaboko, hanpen, and sausage ranged from 76 to 102%, and the average recovery from the two types of salted cold roe with red pepper ranged from 45 to 98%.