Solid-state fermentation: forward-looking applications

Meeting the nutritional and energy needs of a growing world population whilst protecting the environment has become a major challenge. A process used for thousands of years, solid-substrate fermentation is one of the best solutions to rise to the challenge. 

Solid-state fermentation is a natural food-processing technique that was discovered by humans thousands of years ago. Used in Asia in the preparation of many fermented food products, such as tofu or sake, solid-state fermentation is used in other parts of the world in the making of specific types of cheese (e.g. blue veined) or bread, but also in the processing of coco beans to produce chocolate or coffee. 

Solid-state fermentation is a method that has long been known for extending the shelf-life of food products while improving their nutritional value. Today, many other applications rely on this natural process, especially to respond to environmental, energy and agricultural challenges.  


What is solid-state fermentation? 

Solid-state fermentation (SSF) is defined as a technique for growing microorganisms on solid, non-soluble materials in the absence or near absence of free water. The substrate or fermentation medium used for growing the microorganisms must meet their nutritional requirements. Filamentous fungi are the best type of microorganisms for solid-state fermentation, as this culture technique mimics their natural habitat. But bacteria can also be used, e.g. in composting, as well as yeast for ethanol or food production.  

A smaller impact on the environment 

One of the major advantages that SSF has over liquid or submerged fermentation is its low environmental footprint—a technique that perfectly illustrates the commitment of manufacturers to produce more naturally. “Producing spores by solid-state fermentation requires less water than in a liquid medium. This means that we generate less waste water and need less energy for drying, since the matrices we use for fermentation are agro-industrial wastes. Lastly, our matrices and additives are natural so we use very few chemical products”, explained Priscilla Poirier, Head of R&D at Metaspora, the production site of Agrauxine by Lesaffre specialised in the production of fungal biomass by SSF. 

The teams at Metaspora replicate natural solid-state fermentation in the best possible conditions—sterilised substrate, cleanroom, temperature control, etc.—and the spores that are obtained are of high quality and identical to naturally-occurring spores. 


A single process, a number of possibilities 

Metaspora’s core activity is the production of living microorganism biomass (mainly filamentous fungi) for biocontrol. It uses solid-state fermentation to produce stable biopesticides that are resistant to dryness for controlling plant pests and diseases. This market with a promising future is driven by the growing demand from farmers and consumers for ‘green’ alternatives to chemical pesticides, fungicides, and herbicides. Many governments are also supporting the trend, such as France with its successive ‘Ecophyto plans.  

“Today, our core production activity is biocontrol but we are also expanding our research and activities in other sectors such as animal health, nutraceuticals, cosmetics, etc.”, explained Pierre Grammare, Head of Metaspora. 

Solid-state fermentation is currently used in many applications, and the production of living microorganisms is only one of them. SSF can also be used to produce enzymes (cellulases, xylanases and proteases) or other molecules of interest. Here, the goal is to multiply a microorganism, e.g. one that is high in a particular enzyme, and then kill it to extract the enzyme. Solid-state fermentation makes possible the industrial production of enzymes for the textile, paper and food industry, detergent formulation, etc.  

Lastly, SSF can also be used to modify the substrate, e.g. to enhance the nutritional and functional properties of raw materials. Research* has shown that the total and digestible protein levels in rapeseed meal could be increased and reach equivalent levels to those found in soybean meal, the main source of protein in animal feed. 



A whole host of applications 

A wide range of industries have been using solid-state fermentation in the last twenty years and a lot of research is underway to find new applications.  

In animal health and nutrition, for instance, spores produced by SSF can be used as biocides, insecticides, and probiotics. There is ongoing research on the Agaricus blazei mushroom, which boasts a high beta-glucan content. If mixed with animal feed, it could reduce stress and improve farm animal immunity. Other studies are looking at adding some microorganisms to animal feed, so they can be released in pastures to control animal-parasitic nematodes (roundworms).  

Progress is still being made in the application of solid-state fermentation to the human food sector, which is driven in particular by the growing market for meat alternatives and vegan products. For example, steak substitutes made from mycelium—the root structure of mushrooms—with properties similar to animal fibres are now available.  

The future of the biofuel sector (biodiesel, bioethanol) will also see the development of substances produced from solid-state fermentation. This means that the use of low-cost substrates will significantly reduce the cost of production. 

There are many other applications such as bioremediation, i.e. a process that uses microorganisms to clean up polluted soils, as well as composting, methanation, direct air capture (a process of capturing carbon dioxide), the production of mushroom leather for the textile industry, packaging, or pest (insects) control services to private households. 


Identify market trends as early as possible 

Metaspora already produces microorganisms for a range of companies and is often contacted by businesses with innovative projects. According to Priscilla Poirier, while this is an advantage for the teams at Agrauxine, it will also benefit Lesaffre in the future.“It allows us to have a clear understanding of the market and identify trends as early as possible.” 

* Valorisation of rapeseed cake by solid state fermentation for application in animal feed – Thesis by Stéphanie SUTTER (2017) – Biotechnology pre-development platform, Welience (PPB) UMR Food and Microbiological Processes (UMR PAM). 

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