Charles R. Warner

Reactions of antioxidants in foods

The chemical transformations of BHT and BHA in the deep-fat frying of potatoes were studied. Approximately 80% of the BHT and its associated decomposition products was lost from the lard after six batches of french fries. This may have been due to steam distillation caused by the water boiled out of the potatoes. In contrast, 80% of the radiocarbon introduced as radiolabelled BHA was retained by the frying medium even after 12 batches of french fries. The concentration of intact BHA decreased to undetectable levels after four batches. Because of the complexity of the products formed in the heated fats, studies were undertaken on the thermolysis of a hydroperoxy derivative of BHT, 2,6-di-tert-butyl-4-hydroperoxy-4-methylcyclohexa-2,3-dienone++ + (HBHT). The product mixture, which was identified by mass spectrometry and gas chromatography-mass spectrometry, included BHT, 2,6-di-tert-butyl-4-hydroxy-4-methylcyclohexa-2,5-dienone and 3,5-di-tert-butyl-4-hydroxybenzaldehyde. Elemental compositions of other unidentified products were determined by high-resolution mass spectrometry.

Measurement of bromate in bottled water by high‐performance liquid chromatography with post‐column flow reactor detection

The objective of this work was to develop a reliable, rugged high-performance liquid chromatographic (HPLC) method for determination of trace levels of bromate (< 10 micrograms/l) in bottled water. HPLC separation was achieved by ion interaction chromatography using a C-18 reversed-phase column and a mobile phase consisting of methanol/water (20:80, v/v) with tetrabutylammonium acetate as the ion interaction reagent. A post-column reaction based on oxidation of o-dianisidine in acidic solution to a product detected at 500 nm provided selective measurement of the oxidants. The limit of detection and the limit of quantitation were 1 and 3 micrograms/l, respectively. Iodate, chlorite, and nitrite were chromatographically separated from bromate and measured by monitoring the post-column reaction. Chloride and chlorate at levels that might be found in bottled water did not interfere with the determination of bromate. Bromate was detected in bottled waters at concentrations up to 40 micrograms/l.

Alteration of phenolic antioxidants in heated vegetable oil

Studies were conducted to follow the fate of antioxidants in heated vegetable oil at temperatures approximating those of frying conditions. Samples of vegetable oils spiked with 0.02% [14C] BHA or 0.02% [14C] TBHQ were heated at ca. 180–190 C for 4.5 hr. It was found that 24 and 48% of the radioactivity added as BHA and TBHQ, respectively, remained in the oils. Normal-phase HPLC analyses revealed that 55% of the radiolabel in the heated BHA-oil and 95% in the heated TBHQ-oil were not eluted as parent substances. The as-yet unidentified alteration products in the heated oil appear to be less polar than the added antioxidants.

Residue determination of hydrazine in water by derivatization and gas chromatography

Abstract A method is described for the determination of hydrazine residue in water. Hydrazine is converted to the acetone azine, which is extracted with methylene chloride and determined by gas chromatography using a nitrogen/phosphorus detector. The limit of detection is 0.1 part per billion (10 9 ), and the recoveries ageraged 92% for water fortified with 0.1 to 10 parts per billion of hydrazine. The derivatization of trace levels of hydrazine with a large excess of acetone was compared in a predominantly aqueous system and a methanolic system. The derivatization proceeds quantitatively in 53 min in the methanolic system and in less than 2 m in in the aqueous system. Excellent yields of the azine were obtained at ppb levels.

Survey of sulphites determined in a variety of foods by the optimized Monier‐Williams method

A survey of sulphite levels in a variety of foods including dried fruit, dried mashed potatoes, shrimp, canned mushrooms and fruit juices has been conducted. The levels found ranged from 0 ppm in orange juice to 3722 ppm as sulphur dioxide in dried fruit. The foods were analysed by the optimized Monier-Williams procedure.

Determination of free and reversibly bound sulphite in foods by reverse‐phase, ion‐pairing high‐performance liquid chromatography

The reaction of sulphite with formaldehyde to form hydroxymethylsulphonate (HMS), which is very stable under the controlled conditions of this assay, was used as the first step in an analytical procedure to determine foodborne sulphite. The effect of mobile-phase pH on the stability of HMS during high-performance liquid chromatography was studied. It was found that on-column HMS dissociation to formaldehyde and bisulphite increased with the pH of the mobile phase; therefore the relatively low pH 4.7, at which the dissociation of HMS was approximately 2%, was selected for the analysis. In addition, the release of sulphite from its reversibly bound forms in wine and other foods was examined as a function of the pH of the extraction medium by following the appearance of HMS formed from the reaction of the freed sulphite with formaldehyde. The rate of dissociation of the reversibly bound sulphite was relatively slow at pH 3 but very rapid at pH 7. This difference in kinetics was exploited to develop a procedure to determine free and reversibly bound sulphite in food. The method was challenged by post-reagent spiking studies, i.e. adding the sulphite spike after the food has been blended with the sulphite-protective formaldehyde solution but before proceeding with the remainder of the assay. An average recovery of 100% with a standard deviation of 5.2% (n = 45) was realized at levels of 5, 10 and 20 ppm by weight as sulphur dioxide. Recovery of the sulphite added as the bisulphite addition product of acetaldehyde, a model compound for reversibly bound sulphite, was 95%.

Sulphite stabilization and high‐performance liquid chromatographic determination: A reference method for free and reversibly bound sulphite in food

A high-performance liquid chromatographic (HPLC) post-column reactor combination has been developed for the determination of sulphite (free and reversibly bound) in 15 different foods. The foods were treated with a pH 5.1 buffered aqueous 2% formaldehyde solution to convert the labile sulphite to the relatively stable hydroxymethylsulphonate. Reverse-phase ion-pairing HPLC with a post-column detector consisting of an initial reaction with KOH followed by colorimetric reaction with Ellmans reagent buffered at pH 6.3 were used for separation and quantitation. The photometric detector at 412 nm quantitated the strongly absorbing 3-carboxy-4-nitrothiophenolate anion, the product of the sulphite reaction with Ellmans reagent. The recovery at levels of 5-100 ppm as sulphur dioxide was greater than 90% by reverse isotope dilution assay. Repetitive analysis of a single grape juice extract containing 20 ppm SO2 showed a relative standard deviation of 2.2%.

A device which permits selective purging of the solvent and other components from a gas-liquid chromatographic column

Abstract A gas-liquid chromatographic column configuration is described which utilizes two auxiliary ports located approximately one-third of the column length from the column inlet. In the purge mode of operation, one port is pressurized while the other is open to vent. This permits selective purging of certain components of the sample mixture from the column. In the conventional mode of operation, both ports are effectively closed. The usefulness of this column configuration is demonstrated with the trimethylsilyl derivatives of 2- and 5-isosorbide mononitrates.

Br concentration as an indication of pre-baking bromation of bread products

Br concentration in bread for baked bread products was shown to be linearly proportional to the amount of Br added per kg of flour used to make the product. Br concentration in bread can be used to help identify those bread products with the greatest likelihood of containing bromate residues. Instrumental neutron activation analysis was used to determine Br in test portions of bread products from commercial bakeries, homemade bread, flour, and unbaked dough. High performance liquid chromatography was used to determine the bromate residue in selected test portions.

Post-column complexion technique for the spectrophotometric detection of poly(oxy-1,2-ethanediyl) oligomers in steric exclusion chromatography

Abstract A solid-phase complexation column (SPCC), which consists of ammonium cabaltothiocyanate (ACTC) adsorbed on a solid support, has been developed as part of a selective detection technique for molecules bearing one or more poly(oxy1,2-ethanediyl) oligomers (POEs). Due to the ion-dipole attraction between the ammonium ion and the negative dipoles of the polyether oxygen atoms, a quantity of ACTC is solubilized in the mobile phase as the POE-ACTC complex. The complexed ACTC is readily quantitated at 320 or 620 nm because of the strongly absorbing cobaltothiocyanate anion. The detection technique is approximately 100 times more sensitive than the differential refractive index detector for this class of compounds. This detector is used with steric exclusion chromatography on Sephadex LH-20 and μStyragel columns.