Effects of post-harvesting practices on heavy metal levels of mopane caterpillar (Gonimbrasia belina) products and associated risk assessment

Abstract

Mopane caterpillars (Gonimbrasia belina) are one of the most consumed edible insects in Southern Africa, and they contribute nutritional benefits to human health. However, their contribution to the food and nutritional security can be hindered by food safety concerns due to heavy metal contamination associated with harvesting, processing and poor post-harvest practices. This study investigated the effectiveness of post-harvest practices (degutting, charcoal roasting and sun drying, boiling, frying and open pan roasting) in reducing the heavy metal contaminants (cadmium (Cd), mercury (Hg), lead (Pb), nickel (Ni), aluminium (Al), zinc (Zn), copper (Cu) and iron (Fe)) in mopane caterpillar sourced from Gwanda district in Zimbabwe. The post-harvest practice categories used in this study included: unprocessed (ungutted and naturally degutted samples), processed (manually degutted, and charcoal roasted and sun-dried), and cooked (boiled and salted; boiled, salted and roasted, and boiled, salted and fried) samples. An atomic absorption spectrometry (AAS) was used for quantification of metals and the values detected were used to assess health risks to consumers using a quantitative risk assessment calculation method. The unprocessed and manually degutted samples showed higher levels Cd and traces of Pb, while charcoal roasting and sun drying resulted in elevated levels of Al, Zn, Cu and Fe. Hg and Ni were not detected in any of the unprocessed, processed or cooked samples. Cooking processes resulted in reduction of the concentrations of detected metals to levels within the permissible values. The health risk assessment disclosed noncarcinogenic risks based on the high hazard index (HI) values (HI > 1) in unprocessed, processed, boiled and salted, and boiled, salted and roasted samples, indicating that caution should be taken. The overall findings from the study shows that by cooking mopane caterpillars through boiling and frying, health risks associated with heavy metal contamination can be reduced.