Analytical methods for food-contact materials additives in olive oil simulant at sub-mg kg-1 level.

Methods of analysis for four additives (two antioxidants, IRGANOX 245 and 1035; an ultraviolet absorber, CHIMMASORB 81; and an optical brightening agent, UVITEX OB) in olive oil are reported. These additives have the potential to migrate from food-contact materials into the European Union fatty food simulant olive oil, which is the most difficult matrix for analysis. The additives were chosen because they differed in their chemically active groups, had different functions within the polymer, have low proposed specific migration limits and are commonly used in food-contact materials such as polystyrenes and polyolefins. The proposed analytical methods for the additives are simple, rapid, inexpensive and also broadly applicable to the aqueous food simulants. All methods were evaluated by constructing calibration curves, measurement of recovery and precision, and determining the limits of detection. Most of the methods involve direct injection of an olive oil solution for high-performance liquid chromatography analysis with ultraviolet-visible or fluorescence detection. The methods allowed establishment of additive stability and measurement of migration of the selected additives into olive oil at different time-temperature conditions used in migration studies into food simulants.

A nuclear magnetic resonance technique for determining hybridoma cell concentration in hollow fiber bioreactors.

We have developed a technique for determining cell concentration in a hollow fiber bioreactor based on 23Na nuclear magnetic resonance (NMR) spectroscopy. Cell concentrations determined with this method agreed closely with concentrations calculated from 31P NMR nucleoside triphosphate (NTP) measurements and oxygen consumption rate measurements. Oxygen transfer limitations, which can complicate cell mass determinations based on oxygen consumption rates, were shown to be negligible for the bioreactor used. Specific antibody production rates in hollow fiber culture, calculated from these cell number estimates, were similar to those found in suspension culture for this cell line.

Interactions of selenium and fluoride on growth, glycolysis and survival of Streptococcus mutans GS-5.

The effects of low concentrations (1.0 mmol/l of selenite and seleno-dl-cystine were tested alone, or in combination with NaF, on growth, glycolysis, and survival of Streptococcus mutans GS-5. In batch culture, both selenium-containing compounds (1.0 mmol/l) inhibited the growth rate and final cell yield by 92% or greater; glycolysis, however, was not affected. The observed bactericidal action of selenite at 0.1 mmol/l was pH-dependent. Fluoride reduced the killing effect of SeO3 in the culture medium and in a lactate-acetate buffer system at pH 6.5, 5.0 and 4.0. These data indicate that selenium-containing compounds exert an antibacterial action on cells of S. mutans in a manner which leaves glycolysis unaffected.

A comparison of three radiofrequency coils for NMR studies of conductive samples.

Three rf coil designs of equal volume (approximately 15 ml) were compared using conductive samples. Magnetic loss into the sample was the dominant noise source. At physiological conductivity the sensitivity of the horizontally aligned solenoid and loop-gap resonator was only 1.3 +/- 0.2 times that of the vertically aligned slotted tube resonator.