Toxin production by C. botulinurn type E was studied in cod, whiting, and flounder filets packaged in air-permeable film, vacuum packages and packages flushed with Nz or CO2 during storage at 8'; 12") or 26'C. Cod and whiting filets were flushed with CO2 and stored continuously at 4'C or cycled between 4" or 8' and 26°C. Cod and whiting fillets were flushed with gas mixtures and stored at 8'C or 26'C. Flounder deteriorated rapidly and was rejected by sensory evaluation prior to toxin detection during vacuum or modified atmosphere storage at 12"C and 8'C but after toxin detection at 26°C. Toxin was present either prior to or simultaneously with sensory rejection of cod and whiting fillets for all vacuum or modified atmosphere treatments and temperature regimens.
Selenium was determined by cathodic stripping voltammetry in a 1 mol l-1 HCl acid solution containing added CuII. In this medium, selenium was preconcentrated on the hanging mercury drop electrode and stripped cathodically in differential-pulse mode. After a deposition period of 1 min, 0.2 ng ml-1 of selenium could be detected. The method was applied to the analysis of food supplements. Total selenium was determined after digestion of the sample with HNO3-HClO4 and reduction to the electroactive SeIV by heating with HCl. Inorganic selenium (i.e., selenite and selenate) was similarly determined after extraction with dilute sodium hydroxide solution and clean-up on activated carbon. Representative over-the-counter preparations have been analysed.
An improved technique has been developed for determination of sulfites in food by differential pulse polarography. A Teflon™ sleeve is fitted to the dropping mercury electrode capillary so that SO2 is purged from the sample and simultaneously detected at peak potential. Bound sulfite in the sample is released at room temperature by addition of base in the absence of oxygen. For some foods, the prepared sample was passed through a Sep-Pak C-18 cartridge to remove naturally occurring sulfur compounds so that only added sulfite is measured. The level of detection was approximately 1 μg S02/g. Results agreed with those obtained by the optimized Monier- Williams method for a variety of foods.
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