Built by Iron, changed by heat: Mineral bioaccessibility in iron-fortified and processed Hermetia illucens larvae

Black soldier fly larvae (BSFL) are a promising source of dietary minerals for food and feed. This study quantified the bioaccessibility of iron, calcium, zinc, and magnesium in BSFL reared on iron-fortified diets (269–7803 mg Fe/kg) and subjected to thermal processing. Iron fortification increased larval iron content and the number of naturally occurring iron nanoparticles (~45 nm), consistent with entoferritin-mediated storage. Although iron bioaccessibility decreased from ~50% to ~25% with fortification, the concentration of soluble iron released after in vitro digestion increased from 0.08 to 0.20 mg/mL, increasing total bioaccessible iron content. Thermal processing showed nutrient-specific effects: blanching reduced iron bioaccessibility, likely via entoferritin denaturation, but enhanced calcium and zinc bioaccessibility by disrupting mineral storage structures. Overall, these results demonstrate that iron-fortified BSFL can increase the absolute amount of bioaccessible iron despite reduced fractional bioaccessibility, underscoring their potential as a mineral-rich ingredient for food and feed. • Iron fortification raises iron nanoparticle content in BSF larvae. • Iron fortification does not change iron nanoparticle size in BSF larvae. • Entoferritin remains the main iron storage across all iron fortification levels. • Iron fortification increases digestible iron content. • Blanching lowers iron but greatly boosts calcium bioaccessibility.