抄録
Methods for the determination of six preservatives used in solid, semi-solid, and liquid foods were examined. Extraction procedures were divided into four steps : Step 1 : Extraction of preservatives from food with organic solvent. Step 2 : Separation of the preservatives from fatty substances by transfer of the former into an alkaline solution. Step 3 : Acidification of the alkaline layer with an acid followed by re-extraction of the acidic layer with an organic solvent. Step 4 : Concentration of organic solvent in vacuo and injection of an aliquot of the concentrate into an FID gas chromatograph. In Step 1, the homogenization and organic solvent extraction were carried out simultaneously in a Waring blender, since it had been confirmed that removal of protein and fat by use of suitable precipitant did affect the recovery of the preservatives. Ether was found to be suitable for the organic solvent of extraction. In Step 2, it became clear that the normality of the alkaline solution used must not be lower than 0.2. In order to avoid hydrolysis of p-hydroxybenzoates, 0.4 N potassium hydroxide solution in 50% methanol was finally chosen. In Step 3, the final pH of the solution must be brought to lower than 2 so that the preservatives may be successfully re-extracted with ether. In Step 4, the conditions for gas chromatography were as follows : Glass tube, 2 m in length, packed with 5% DEGS+1% H3PO4/Chromosorb W 60-80 mesh, column temp., 144° ; injection temp., 190° for sorbic acid, dehydroacetic acid, benzoic acid and salicylic acid ; glass tube, 1.5 m in length, packed with 3% SE-30/Chromosorb W 60-80 mesh, column temp., 180° ; injection temp. 230°for ethyl p-hydroxybenzoate and buthyl p-hydroxybenzoate. Recoveries were measured on Samsoe cheese, cream cheese, blue cheese, butter, wines, pickles, Korean ginseng extract, and honey, spiked at either 200 or 20 ppm of each preservative excluding SA. The recoveries at 200 ppm level ranged from 86.4 to 99.4%, while at 20 ppm level the recoveries were 84.0-95.1%. The minimum detection level of the 5 preservatives was 2 ppm.
