The “ghosting effect” on gas chromatography using column with polyester and phosphoric acid as the liquid phase refers to the appearence of peaks with same retention time as free acids previously injected when shorter chain fatty acids or water were injected. This ghosting effect was caused by the absorption occurs on the nonvolatile residues in the flashheater, on the column and connection tubes and on the glass wool plugs. Such ghosting effects on gas chromatographic analysis are likely to cause low detector response and false peaks, as a result, they may sometimes invalidate either qualitative or quantitative analysis by gas chromatography. These effects can be eliminated by using phosphoric acid column packing prepared with silanized supports, glass wool plugs treated with phosphoric acid and on column injection with glass column at the direct analysis of food preservatives such as sorbic acid, dehydroacetic acid and benzoic acid.
A procedure for qualitative analysis of 2- (2-furyl) -3- (5-nitro-2-furyl) -acrylamide (FNFA) in foods is presented. F-NFA is extracted from food with benzene and the extract is applied to column chromatography using silica gel to remove substances that interfere with the separation of F-NFA from nitrofurazone and nitrofurylacrylamide on thin-layer plates. F-NFA is, hereby, separated from both of the chemicals by thin-layer chromatography using silica gel.
The method described herein consists of (1) extraction of 2- (2-furyl) -3- (5-nitro-2-furyl) -acrylamide (F-NFA) with benzene from food, (2) separation of F-NFA from nitrofurazone and nitrofurylacrylamide on a silica gel chromatographic column and (3) determination of the separated F-NFA by ultraviolet spectroscopy at 380mμ. The analysis can be applied to the determination of F-NFA in either fish meals or Soybean curd.
A method for the detection of food preservatives (benzoic acid, salicylic acid, methyl, ethyl, propyl and butyl esters of p-hydroxybenzoic acid, sorbic acid and dehydroacetic acid) is described. The food preservatives can be isolated from a food by steam distillation and further purified by extraction procedures of the distillate. The food preservatives are then separated by thin-layer chromatography on polyamide with the following solvent systems, (a) n-hexane·acetic acid (20: 0.7), (b) benzene·acetic acid (20: 0.5), (c) benzene·methyl alcohol·acetic acid (20: 0.2: 0.5) and (d) benzene·methyl alcohol·acetic acid (20: 0.5: 0.3). The solvent system (a) is suitable for the separation of dehydroacetic acid, benzoic acid and sorbic acid, (b) for the separation of the others except dehydroacetic acid, (c) for the separation of the esters of p-hydroxybenzoic acid and (d) for the separation of the esters in the presence of salicylic acid. And the thin-layer chromatography is also applied to the separation of p-hydroxybenzoic acid.
Separatory identification of coloring agents for use in margarine was carried out by thin-layer chromatography; The coloring agents herein mean β-carotene, Yellow AB and OB, Annatto, Turmeric and Riboflavin tetrabutyrate. 1) Solvent extraction method, with repeated recrystallization using dry ice, seemed suitable as a method for extraction of the coloring agents from margarine. Column chromatography was not suitable. 2) The best solvent for development in thin-layer chromatograghy was a mixture of n-hexane, acetone and ethanol in the ratio of 20: 6: 1. This solvent mixture did not show any difference by changes of temperature above 15°C. 3) Even a minute amount of the coloring matter can be detected on the developed plate by use of a color developer and by fluorescence test.
Modified EC medium designated as SMEC medium was devised for the determination of Eseherichia coli from various kinds of food. Successful results were obtained on using SMEC medium in differentiating E. coli from coliform bacteria group. The composition and making procedure of the SMEC medium were described as follows: Bacto-tryptose 20g Lactose 5g Sodium chloride 5g K2HPO4 2g KH2PO4 6.325g Sodium lauryl sulfate 0.25g Bile salt No. 2 0.5g Streptomycin (SM) 10mg (10μg/ml) 0.2% BCP 16ml (0.032g) Distilled water 1000ml Adjust to pH 6.2 Dispense 10ml of liquid medium in Durham fermentation tube, and sterilized by Koch's steam sterilizer at 100°C for 60min and incubate at 44.5±0.1°C for 24 hours. SMEC medium produced gas may be considered to show a positive result for E. coli. Among food-borne EC groups, positive strains by EC test were utilized to test the detectability of the same strains by SMEC medium. Results of the test were as follows: 100% in E. coli I, 92.7% in E. coli II, 27.2% in Citrobacter freundii, 15.9% in Klebsiella aerogenes and 23.5% in irregular type, respectively. SMEC medium promoted the growth of Escherichia coli type, but was significantly suppressive against other coliform group showing positive EC test.
Hydrolysis of sodium carboxymethylstarch (Na-CMS) with human saliva was studied. Na-CMS with high degree of substitution (H.D.S. -CMS) and Na-CMS with low degree of substitution (L.D.S. -cMS) were used for the study and potato starch was refered to them. The experiments were carried out concerning determination of reducing sugar as glucose and remaining Na-CNS and measurement of shift of the absorption maximum of the color of hydrolyzed product with iodine. The hydrolysis of L.D.S. -CMS was larger than H.D.S. -CMS, but less than starch in all cases. The result was seemed to be caused by carboxymethyl group.