Determination and evaluation of inorganic arsenic in liquid food samples
Ingestion of arsenic in contaminated food and water is the predominate pathway of arsenic exposure for humans. Arsenic exists in different chemical species in the environment, with arsenite (As(III)) being more acutely toxic than other forms found in food. This dissertation focuses on two aspects of arsenite contamination in liquid food by (i) the development of an inexpensive reporter-based living cell sensor technology for determination of arsenite concentration in liquid food samples with minimal are no sample preparation and (ii) the use of more cost prohibitive analytical techniques such as x-ray atomic fine structure spectroscopy and inductively coupled plasma-mass spectroscopy to develop a fundamental understanding of the role of the food matrix, storage, processing and/or digestion play in chemical speciation and quantification. Pseudomonas fluorescens 18HR, an arsenite-responsive bioluminescence reporter strain, was used in a sensor format to detect concentrations below the 10 ppb arsenite (EPA maximum contaminant level for arsenic in water) in skim milk samples and diluted pH adjusted orange juice. The reporter strain was found to be selective for arsenite compared to the less toxic arsenate. Arsenite chemistry and bioaccessibility was influenced by the food matrix, processing, and digestion. In simulated digestion studies, arsenite contaminated orange juice and coffee samples resulted in oxidation to arsenate (As (V)), while no conversion was observed in milk and water. In addition, samples from simulated digestion of arsenite-contaminated orange juice and coffee significantly decreased arsenic accumulation by Caco-2 cells, while digested samples from contaminate milk and water caused significant increases over undigested controls. Common preparation or processing steps were also examined to determine their effect on chemistry and bioaccessibility. In all tested liquid food matrices, arsenite was unaffected by storage and simulated pasteurization, but heating near 100ºC resulted in a chemical modification tentatively identified as the formation of sulfur containing compound, which also affected bioaccessibility. In summary, these results demonstrate that: (i) the food matrix affect arsenic chemistry during some processing steps and digestion, and (ii) living-cell sensors can be used to determine arsenite concentrations in complex matrices in a selective manner to help ensure a safe food supply.
Nivens, Purdue University.
Food Science|Analytical chemistry
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