Solid-state fermentation: A technique with a high upcycling potential

Sustainability in the food industry is a concept that is gaining increasing interest due to the environmental situation we are experiencing. An important part of any food process subject to sustainable improvements are its residues or byproducts. When applying such strategies, it is crucial to differentiate between valorization and upcycling. Both concepts integrate perfectly within the framework of a circular bioeconomy, but the latter alone allows the use of the byproduct within the food industry. One way to valorize or upcycle a byproduct is through solid-state fermentation (SSF). This technology allows us to valorize and upcycle byproducts using microorganisms, with minimal water addition and minimal energy expenditure. In the field of valorization, the strategy lies in using precision fermentation to produce compounds of interest such as ethanol, biostimulants and biopesticides. In the field of upcycling, SSF enables us to: (1) extract components of interest, such as phenolic compounds or oligosaccharides, (2) modify the nutritional composition of the byproduct, as by producing polyunsaturated fatty acids from saturated and monounsaturated fatty acids, and (3) achieve 100% recycling of the byproduct, or total upcycling, as with the production of seed flours. Despite its benefits, however, SSF presents significant challenges, especially in industrial scale-up. Precise control of process conditions, such as temperature and humidity, is critical to optimize microbial growth and metabolite production. Ongoing research in SSF technology is vital to overcome these obstacles and to unlock the full potential of SSF in the upcycling of food industryby-products. SSF is a fundamental pillar of a future in which biotechnology will be key in efficient resource management and in minimizing the environmental impact of the food industry.