Effect of domestic cooking methods on protein digestibility and mineral bioaccessibility of wild harvested adult edible insects

Wild harvested edible insects are characterised by high protein and mineral contents with potential to contribute substantially to nutrition security. However, nutritional content is only beneficial when proteins are digestible and minerals bioaccessible. This study determined the effects of domestic processing on protein digestibility and mineral bioaccessibility of two wild harvested insect species: Eulepida mashona (beetle) and Henicus whellani (cricket). Samples of both insects were subjected to boiling, roasting, or combined boiling and roasting, imitating the way insects are traditionally prepared in Zimbabwe. Moreover, they were in vitro digested according to INFOGEST protocol. Boiling of both insects resulted in loss of protein as it leached into the boiling water. The raw insects had a higher protein in vitro digestibility than the boiled and roasted insects, and the maximal decrease in protein digestibility was around 25% for twice boiling of the beetles and for boiled and roasted crickets. For both insect species, boiling resulted in non-significant loss of iron and zinc. Iron was the least bioaccessible mineral in both insects, based on the concentrations of soluble mineral measured by ICP-AES. However, beetles had a much higher iron bioaccessibility (30.7%) as compared to crickets (8.11%). Interestingly, boiling resulted in about 50% decrease in iron and zinc bioaccessibility in both species while roasting did not. The reduced protein digestibility and mineral accessibility with processing can be explained by protein modification and interactions of minerals with other food components, such as chitin and phytochemicals. Because of the reduction in protein digestibility and mineral accessibility during boiling, roasting should be favoured over boiling and in any case short boiling time is recommended.