Mineral composition of cultivation media affects mineral bioaccessibility of edible filamentous fungus Rhizopus oligosporus

The presence of antinutrients remains a major challenge for sustainable protein alternatives. Fungi-based protein, commonly referred to as mycoprotein, is free of phytates and can accumulate substantial amounts of minerals from its growth environment; however, these minerals may not be bioaccessible. We hypothesized that mineral concentrations in the fungal cultivation medium play a key role in determining the mineral bioaccessibility of fungal biomass. This study investigated how cultivation media concentrations of zinc (Zn), iron (Fe), phosphorus (P), and calcium (Ca) influence fungal mineral content and in vitro gastrointestinal accessibility using a full-factorial design and the INFOGEST in vitro digestion protocol. Fungal mineral content increased with higher concentrations of the corresponding minerals in the cultivation media. Media Zn and Fe concentrations exhibited a reciprocal positive interaction, with each enhancing uptake of the other. Low-P conditions further increased both Zn and Fe content. In addition, media phosphorus and calcium concentrations showed a positive interaction, resulting in increased P and Ca content in the fungal biomass. Fungal biomass mineral accessibility was strongly affected by media composition. Biomass cultivated in high-Zn media exhibited high zinc accessibility (19–44%), whereas low-Zn media produced biomass with antinutritional effects on zinc. Conversely, high-Fe media yielded biomass with iron bioaccessibility up to 25%, while low-Fe media produced biomass with Fe accessibility exceeding 100%, likely due to siderophore-mediated chelation. Overall, these findings indicate that cultivation media mineral composition affects mineral content and bioaccessibility in R. oligosporus fungal biomass, supporting its use as a sustainable iron and zinc source.