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.