Fermentation: Principle, Types, Applications and Limitations

The process of fermentation has been a longstanding method of manufacturing employed since the inception of human civilization. The process of fermenting meats, wines, and milks has been documented for millennia, with the oldest documents tracing back to 6000 BC.

Principle of fermentation

Fermentation is the scientific process by which aerobic or anaerobic bacteria convert substrates enzymatically and develop under controlled conditions to produce meals, beverages, or other valuable compounds. Fermentation is facilitated by the inherent processes of microbiologies; metabolism, which guarantees the development and reproduction of microorganisms, is a fundamental attribute of natural microbial activities. Microbial metabolism encompasses the breakdown of substrates and the processes of growth, reproduction, aging, and death. It is accompanied by the synthesis and modification of various metabolites. Initially, microorganisms often generate signals upon seeing their surroundings to stimulate the production of proteins (enzymes), which are then released from the cell through sequential transport processes. Next, enzymes catalyze the conversion of substrates into essential nutrients such as amino acids, nucleotides, sugar, fatty acids, and vitamins necessary for the microorganism's growth. The proliferation of microbes and the buildup of metabolic products trigger the initiation of novel metabolic pathways, leading to the production of secondary metabolites including pigments, antibiotics, poisons, and hormones. Ultimately, when the environment undergoes changes that surpass the microbes' capacity to adjust, they promptly perish. Within laboratory settings, it is customary to quantify microbial growth curves, which depict the dynamic fluctuations in population as microorganisms proliferate and divide in novel and suitable habitats until their ultimate elimination. Fermentation is an intricate process; microorganisms possess highly robust regulatory mechanisms, and even slight variation in the surroundings can result in the synthesis of distinct compounds. The intended products can be achieved by regulating fermentation parameters, including strain filtration and transformation conditions, and by refinement of process parameters through fermentation modeling to produce products with minimal cost, maximum production, and optimal quality.

The relationship between fermentation and human life. (Feng R., et al., 2018)

Types of fermentation techniques

Submerged fermentation

It employs free-flowing liquid substrates, including molasses, maize steep liquor, and nutrient broths. Enzymes and bioactive compounds are secreted into the fermentation broth. The substrates are consumed at a rapid pace, necessitating consistent nutrient supplementation. This fermentation method is most appropriate for microorganisms, such as bacteria, that necessitate high moisture.

Advantages: Submerged fermentation is responsible for approximately 80% of the global citric acid production. This form of microorganism thrives in a carbon medium, such as glucose or sucrose. The primary benefits of submerged fermentation include a lower production cost, a higher yield, a reduced risk of contamination, and a lower labor cost.

Disadvantages: It is susceptible to contamination by Penicillia, other Asperigillius, yeasts, and lactic acid bacteria, has a large quantity of heat generation, is time-consuming, and requires a large area. Additionally, it is limited by the limited number of surface microorganisms.

Surface fermentation

It refers to fermentations when microorganisms proliferate on the surface of the fermentation medium. The fungus Aspergillus niger produces citric acid via surface fermentation, where it forms a dense floating mycelia mat on the surface of the organic medium. The procedure is conducted within the fermentation tanks, during which enormous trays are organized as shelves. Trays made of aluminum and steel are widely utilized. The steel trays exhibit a greater percentage recovery of citric acid in comparison to the other trays.

Advantages and disadvantages: Although this method is generally employed in small and medium size enterprises, it is not widely used in large scale applications because to its time-consuming nature, significant space requirements, risk of contamination, high heat generation throughout the process, and high production costs.

Solid state fermentation (SSF)

It is a technique of biological synthesis employed in several sectors such as food, pharmaceutical, cosmetic, fuel, and textile industries. These biomolecules are generally metabolites produced by microbes cultivated on a specialized solid substrate. During this fermentation process, microorganisms proliferate on the solid surface in the absence of flowing liquid. The necessary moisture for the process is present in the absorbed or complicated molten state within the solid matrix. Commonly used fermenters include Erlenmeyer conical flasks, glass incubators, trays, rotating and horizontal drum bioreactors, and packed bed column reactors.

Advantages: This fermentation process is seeing global expansion because of its ability to produce citric acid with sustainable and achievable results.

Disadvantages: Its limitations are difficulties in scale-up, difficult control of process parameters, such as pH, moisture, temperature, nutrients, etc., higher impurity products, thus higher recovery product costs.

Types of fermentation and their advantages and disadvantages. (Gopinadh R., et al., 2016)

Fermentation technology at BOC Sciences

• Aerobic Fermentation
• Anaerobic Fermentation
• Continuous Fermentation & Fed-Batch Fermentation
• Solid State Fermentation (SSF)
• Submerged Fermentation (SmF)
• Fermentation CDMO
• Downstream Process Optimization
• Upstream Process Optimization

Applications of fermentation

Fermentation has a wide range of uses in many sectors, including food and beverage manufacturing, biofuel research, and medicines. Within the food and beverage sector, fermentation plays a crucial role in the production of several essential commodities, including bread, yogurt, beer, wine, cheese, and pickled vegetables. Through the utilization of microbial fermentation procedures, producers not only augment the taste and consistency of these food products but also conserve them and, in certain instances, boost their nutritional content. In the case of fermented dairy products such as yogurt and cheese, the probiotic properties of lactic acid bacteria play a significant role in promoting gut health.

Fermented Foods and Beverages: In the process of manufacturing beer and wine, alcoholic fermentation plays a crucial role by introducing distinct flavor characteristics through the metabolic breakdown of sugars by yeasts. Fermented foods with high in probiotics have been associated with enhanced metabolism and decreased fat storage. These foods may boost general metabolic health, assist control appetite, enhance insulin sensitivity, and support a healthy balance of gut flora—all of which may benefit weight management efforts.

Biofuel generation: In the field of biofuel generation, fermentation is well recognized as a viable and environmentally friendly substitute for energy sources derived from fossil fuels. Ethanol, derived from yeast fermentation of carbohydrates, is extensively used as a biofuel or combined with gasoline to mitigate carbon oxide emissions. Furthermore, the process of butanol fermentation is increasingly being used as a biofuel because of the greater energy content of butanol in comparison to ethanol. These methods show potential for tackling energy deficiencies and mitigating environmental consequences by transforming agricultural waste and biomass into commercially viable fuels.

Pharmaceutical Production: The pharmaceutical sector extensively depends on microbial fermentation for the large-scale manufacturing of antibiotics, vitamins, and other medicinal chemicals. For instance, the process of fermentation in microorganisms such as Penicillium plays a crucial role in the synthesis of antibiotics like penicillin. Similarly, various microagencies are used in the synthesis of vitamin B12 and amino acids. In addition to its direct use in pharmaceutical manufacturing, fermentation also enables the advancement of vaccines and biopharmaceuticals, such as insulin and monoclonal antibodies.

Different probiotic CHM fermentation strategies and their characterization. (Zhang X., et al., 2023)

Applications of fermentation technology at BOC Sciences

• Fermentation in Pharmaceuticals
• Fermentation for Special Small Molecules
• Fermentation in Human Nutrition
• Fermentation in Animal Health
• Fermentation in Agriculture
• Fermentation for Pigments
• Fermentation for Feed Additives

Limitations of fermentation

Product inconsistency: Fermentation processes provide a broad range of results based on the microorganisms involved, environmental parameters such as temperature and pH, and the precise fermentation conditions. Even little alterations in these factors can cause major differences in the flavor, texture, and safety of fermented food. For example, in food and beverage fermentation, incorrect conditions may promote the growth of unwanted bacteria, resulting in product spoilage or health problems for customers.

Byproducts and contamination: While the primary purpose of fermentation is to generate ethanol, lactic acid, or other beneficial molecules, microbes frequently produce secondary metabolites that might have a detrimental impact on product quality or flavor. For example, in alcoholic fermentation, large quantities of fusel alcohols or acetaldehyde might result in off-flavors or harmful consequences in the finished beverage. Similarly, in industrial fermentation, waste byproducts may demand extra stages for removal or recycling, raising production costs and complexity.

Cost challenge: While fermentation is typically thought to be an energy-efficient process, some forms of fermentation, particularly those that need completely anaerobic or aerobic conditions, might necessitate large energy input. For example, in large-scale fermentation systems, maintaining ideal temperature, pressure, and oxygen levels may entail significant energy usage, especially in processes such as acetic acid fermentation, which requires regulated aeration.

References

1. Feng R., et al., Fermentation trip: amazing microbes, amazing metabolisms, Annals of microbiology, 2018, 68: 717-729.
2. Zhang X., et al., Research advances in probiotic fermentation of Chinese herbal medicines, iMeta, 2023, 2(2): e93.
3. Gopinadh R., et al., Recent Advancements in Eco-Friendly and Economically Available Substrates for the Production of Citric Acid, INDIAN JOURNAL OF ENVIRONMENTAL PROTECTION, 2016, 36(5): 393-407.