Fungal fermentation: The blueprint for transforming industrial side streams and residues.

The escalating generation of industrial side streams and organic residues presents both a challenge and an opportunity for sustainable biotechnological solutions. Filamentous fungi, with their metabolic versatility and ability to secrete a wide spectrum of enzymes, have emerged as promising agents for transforming diverse waste substrates into high-value products within the biorefinery concept. This review explores the multifaceted applications of fungal fermentation (submerged, solid-state, and sequential) for valorizing agri-food, lignocellulosic, and marine residues into mycoproteins, enzymes, biochemicals, biomaterials, and agricultural applications. Emphasis is placed on the scalability, functional diversity, nutritional potential, and environmental relevance of fungal-derived products, particularly in addressing global protein demand, chemicals, materials and sustainable biomanufacturing. Furthermore, challenges, substrate heterogeneity, safety concerns, and emerging tools, such as AI and multi-omics, are discussed in the context of process optimization and regulatory acceptance. This paper highlights fungal fermentation as a pivotal biotechnology tool in advancing circular bioeconomy goals by contributing to sustainable food production, resource recovery, and the development of novel compounds of interest.