Emerging Solid-State Fermentation in Functional Foods: Bioactive Compounds, Functionality, Sensory Quality, Microbiota Influence and Industrial Perspectives

Although solid-state fermentation (SSF) has long been used in food production in various traditional contexts, it is now emerging as a particularly promising strategy for the development of functional food ingredients from plant materials and agro-industrial side streams. This review examines recent advances in the application of SSF to enhance the nutritional, functional, sensory, and technological properties of food matrices. Current evidence indicates that SSF can increase the bioactive potential of plant-based substrates by promoting the release and biotransformation of phenolic compounds, while also improving antioxidant capacity, protein digestibility, and techno-functional performance. In addition, the process may support the formation of food-relevant metabolites, including vitamins, peptides, organic acids, and other secondary compounds, while reducing selected antinutritional, allergenic, and undesirable constituents. These compositional changes are often accompanied by modifications in aroma, volatile profiles, visual attributes, and, more recently, gut microbiota-related effects. Attention is given to the use of fungal-based processes for the valorization of cereals, legumes, fruit by-products, and other underutilized substrates. The review also addresses the growing industrial interest in SSF, especially in relation to mycelium-based foods, alternative proteins, functional ingredients, and feed applications. Despite its clear potential, the broader implementation of SSF will require further research and development to support its effective translation into food applications.