Quantitative estimation of the levels of some metal residues in fried rice sold in Adum and KNUST campus in Kumasi using instrumental neutron activation analysis.

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Food safety is an increasing important public health issue. Fried rice (also called “check-check”), a non indigenous dish which is becoming increasingly popular is perceived by a number of people as generally unsafe. This work sought to ascertain how safe fried rice meals sold in Kumasi is with regards to its metal residues. All samples analyzed were from Kumasi. Ten fried rice meal samples consisting of vegetables, chicken, sauce (shito) and fried rice from Adum, Ministries Area and KNUST campus have been analyzed for Fe, Zn, Al, As, Hg and Cd using instrumental neutron activation analysis (1NAA). The raw rice and cooked plain rice samples were also analyzed using the same technique. The intake values of Hg, Al and Zn (based on consumption of an average dry weight of 1 50g [dry weight equivalent] of a plate of fried rice) were lower than the Food and Nutrition Board (FNB, USA) and World Health Organization (WHO) Provisional Maximum Tolerable Intake (PMTI) values. For the other three elements, some Cd and As intake values were above the recommended limits, while all the intake values for Fe were above the WHO Recommended Daily Allowance (RDA). Generally, the intake for Hg was very low. The highest Hg intake was only 19.3% of the FNB PMTI value of 42.tg/day. The least Hg intake was 0.359μ/day. The range of Al intake was 2.64-39.44 mg Al/day which is 4.4%-65.7% of the WHO PMTI value of 60 mg/day. The intake values of Zn varied within the range 0.18-11.54 mg/day with 90% of the samples having Zn intake values lying close to the lower end of the range. The highest intake of Zn in the fried rice samples was 76.9% of the WHO RDA values of 15mg/day for an average 70kg male and 96.2% the WHO RDA values of 12mg for female. All the samples analysed had dry weight concentration of Fe in excess of the WHO RDA values of 10 mg/day for males and 15 mg/day for females. The intake values of Fe fell within the range 16.8-72.99 mg/day for 150g (dry mass) of fried rice. Only 40% of the samples had dry weight concentration of Cd below the WHO PMTI value (65 μg/day). The highest and the least intake of Cd for fried rice with average dry weight of 150g were 115.58 μg/day and 37.82 μg/day respectively. Ninety percent (90%) of the samples had dry weight concentration of As below the FNB PMTI value (120 μg/day). The range of As intake from consuming 150g (dry mass) of fried rice was 5.03 μg - 146.73 μg As/day. Generally, the fried rice component contributed significantly to the metallic contaminant of the dish while the contributions from the sauce were the least in most cases.
A Thesis submitted to the Department of Chemistry, Kwame Nkrumah University of Science and Technology, in partial fulfillment of the requirement for the award of the degree of Master of Science (Environmental Chemistry), 2006