Potentiodynamic Corrosion Evaluation and Heavy-Metal Contamination in Wet Grinding Machine processed Pepper and Maize media
Abstract
This work studied the corrosion of component parts of the wet-grinding machine (WGM), the workhorse of local food
processing for Nigerian families, with a view to quantifying the surreptitious food contamination through corrosion
of the machine’s metallic components. Potentiodynamic method was utilized for the quick capture of corrosion rates
before the onset of fermentation and its accompanying problematic pH swings. Corrosion of key machine
components was studied inside WGM-processed pepper and maize. Heavy-metal contamination of the
pepper/maize was investigated with Particle Induced X-Ray Emission (PIXE). Elemental composition of the machine’s
component parts was determined using Energy-Dispersive X-Ray Fluorescence (EDXRF). The maize medium was
found to be the more corrosive, with corrosion rates that ranges from 1.4481 mm/year (grinding stone) to 6.1838
mm/year (hopper). For the pepper medium, corrosion rate ranges from 0.057699 mm/year (shaft) to 0.37587
mm/year (grinding stone). The low corrosion rate observed in pepper medium may be due to its high concentration
of Vitamin C, which is well-known for inhibitory properties. The maize medium could not benefit from any inhibitory
effect of starch due to the presence of fibres which occludes the surface, filtering away the starch. WGM-processed
pepper/maize showed very high increases in concentration of heavy metals. Fe increased by 1100% and Mn by 64%
in WGM-processed pepper; Fe increased by 295% and Ti by 185% in the WGM-processed maize. EDXRF analysis of
the hopper, a non-wearing part, indicated the presence of Rb, also present in the WGM-processed pepper. This is an
indication that the contaminants likely originated from corrosion action and not wear.
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