The range of fermented ingredients is limited only by the imagination and physical laws of nature (and operating cost). From renewable sources of nutrition to sustainable biofuels, the future may be fermented. Jon M Hansen and Joe Pfeifer give an overview of the technology's promise
Fermentation is an anaerobic or aerobic process that utilises the cultivation of micro-organisms to produce products metabolically. Biochemically, fermentation is an anaerobic process, whereas industrial fermentations generally refer to both aerobic and anaerobic processes.
The use of anaerobic fermentation has existed for thousands of years starting with the production of beer in ancient Egypt and fermented foods in India. Some of the earliest industrial fermentations were for the production of penicillin during World War II. Today, physical conditions such as temperature, pH, pressure and dissolved oxygen are typically monitored and controlled in industrial fermentations. Other variables are often monitored or controlled, depending on the sensitivities of the organism and process. The fermentation conditions vary depending on the organism and product of interest.
Fermentation products can be broken down into several basic categories. These include but are not limited to primary metabolites, secondary metabolites, energy storage, enzymes and whole-cell technologies. A wide variety of commercial products are made from fermentation for use in industrial, food/beverage, pharmaceutical, nutritional-supplements, biofuels, cosmetic and animal-feed applications.
Industrial products include small molecules such as amino acids, organic acids (eg, lysine, acetic acid, citric acid), vitamins, and other short-chain organic compounds that have a wide range of commercial applications. Medium-size molecules, such as fatty acids, isoprenoid compounds and proteins/enzymes, are also made by fermentation. There are a number of large molecules such as biopolymers (eg, bioplastics, polysaccharides) that are made by fermentation. Intact whole-cell technologies include single-cell proteins such as animal feed and yeast extract, single-cell oils (such as Martek products), and probiotics. Furthermore, improved lot-to-lot consistency, fewer impurities such as pesticides and contaminants, and reduced cost are also possible from an optimized culture and fermentation process designed for specific products.
Fermentation development typically starts out using a wild-type organism or an organism that has been through classical strain improvement. This is often coupled with a bio-rational strain selection approach and/or high-throughput screening technologies. Genetically modified organisms may also be developed in an effort to achieve higher product yields, or to manufacture products that cannot be produced cost effectively by other means. The desired product either accumulates within the cell or is secreted into the fermentation broth. For certain applications, the intact cells of the microorganism are the desired product.
Large-scale industrial fermentation technology has been around for nearly 80 years. A typical industrial fermentor consists of a large cylindrical tank with a height of four to six times the tank diameter. The tank is mixed through the use of a mechanical agitator and/or a compressed-air supply. Fermentation inlet air is usually dried and filtered. Nutrients and water added to the fermentor are typically sterilised using steam or filtration. Fermentation exhaust air is usually condensed and/or filtered. The majority of industrial fermentations are done under hygienic or aseptic conditions to minimise the growth of contaminants. To facilitate this, the systems are usually constructed using stainless steel to minimise corrosion and equipment deterioration.
There are several different fermentation cultivation methods. Most cultivation processes are either batch, fed-batch or continuous. In a batch process, all of the required ingredients are added to the fermentation at the beginning of the process, along with the addition of the micro-organism. In a fed-batch process, the organism is fed one or more nutrients, such as carbon and/or nitrogen, during a portion of the fermentation, thus enabling control of these variables at an optimum level throughout the process. In a continuous fermentation process, nutrients are added and cells/product(s) are harvested in a continuous manner to maximise product output and minimise vessel downtime.
On-line and at-line fermentation monitoring has progressed from the basics of temperature, pH and dissolved oxygen to more advanced measurement and detection methods. These can include off-gas mass spectrometry, Fourier transform near infrared (FTNIR), HPLC, online enzymatic analysis, dissolved carbon dioxide, various online electrolytic measurements (sodium, potassium, ammonium, etc.), fluorescence-based detection of various compounds, viable cell sensors, vessel liquid, and foam levels. A wide array of off-line analyses is also employed depending on the culture, process and product.
With advancements in process automation and information technology, the capability to analyse large amounts of fermentation data to optimise processes is greatly enhanced. Improvements in instrumentation and control technologies, in addition to batch automation capabilities, have enabled further advances in fermentation technology.
Recently, improvements in genetic modeling, sequencing and characterisation have provided additional tools that could prove to have a significant effect on future discovery and development, especially when coupled with fermentation, downstream processing and strain-improvement efforts. Computational fluid dynamics and other modeling tools can provide a greater understanding of scale-up and lead to improved fermentor design.
The future of fermentation holds many different directions that are limited only by the imagination and physical laws of nature (and operating cost). Some examples of cost-effective future industrial fermentation may include meal-replacement technologies, various renewable sources of food/nutrition, cosmetics, industrial products that are currently petrochemically based, novel biofuels and any number of recently identified bioactive compounds.
Fermentation offers an environmentally sustainable, contaminant-free production alternative to current methods of harvesting these products that may otherwise deplete our natural resources and harm our environment.
Jon M Hansen and Joe Pfeifer are directors of fermentation sciences at Martek Biosciences.