Food Technology, Bioengineering and Bioreactor

What is Bioengineering?

• Bioengineering, also known as biomedical engineering or biological engineering, is a multidisciplinary field that combines principles from biology, engineering, and other related disciplines. It involves the application of engineering principles and techniques to solve problems in the fields of biology, healthcare, and medicine.
• Bioengineering encompasses a wide range of areas, including medical device development, tissue engineering, genetic engineering, biomaterials, biomechanics, bioinformatics, and more. It involves the design, development, and implementation of technologies and systems that improve human health and enhance our understanding of biological processes.
• In the context of bioengineering, organisms, cells, and molecular analogs are manipulated and utilized to develop innovative solutions. This may involve the engineering of biological systems to produce pharmaceuticals, biofuels, or other valuable products. It can also involve the development of medical devices, prosthetics, and diagnostic tools that aid in disease diagnosis and treatment.
• One of the key challenges in bioengineering is the integration of biological systems with engineering principles. This includes understanding and optimizing processes such as oxygenation in aerobic fermentation or designing bioreactors that can support high-density cultures. Researchers and engineers in the field work to improve the efficiency, productivity, and safety of biological processes through innovative engineering solutions.
• Bioengineering has a wide range of applications in various industries, including healthcare, pharmaceuticals, agriculture, environmental science, and energy production. It plays a crucial role in advancing medical treatments, developing sustainable bio-based products, improving diagnostic techniques, and addressing global health challenges.
• Overall, bioengineering combines the principles of biology and engineering to develop innovative solutions that improve human health, enhance our understanding of biological systems, and contribute to the advancement of various industries. It is a dynamic and rapidly evolving field that holds great promise for the future of healthcare, technology, and scientific discovery.

Bioengineering and Bioreactor

• Bioengineering plays a crucial role in the design and optimization of bioreactors, which are essential tools for microbial cultivation and various biochemical processes. A bioreactor is a specialized vessel that provides an optimal environment for the growth of microorganisms and the production of desired products.
• Bioreactors come in various sizes and designs, ranging from small-scale laboratory fermenters to large-scale industrial systems. The choice of bioreactor depends on the specific requirements of the microorganism and the intended application. High-value and low-volume products often require more complex and aseptic conditions, while large-volume and low-value products may utilize simpler fermenters.
• Bioengineering takes into account the process requirements of the microorganism and designs the optimal fermentation system. Stainless steel fermenters, built by bioengineering companies, are commonly used for microbial cultivation, accommodating bacteria, archaea, yeast, and extremophiles. These fermenters can range in capacity from 30 to 50,000 liters, depending on the scale of production.
• The performance of a bioreactor is evaluated based on reaction rates, which quantify the rate of reactant consumption or product formation per unit of time. Reaction rates are expressed as the change in concentration of a substance (reactant or product) over a specified time interval. The units used are typically moles per liter per unit time (M/s, M/min, or M/h).
• Calculating the reaction rate involves considering the stoichiometry of the reaction. For example, in the fermentation of sucrose to ethanol and carbon dioxide, the reaction rate of ethanol formation is four times faster than the reaction rate of sucrose consumption, based on the coefficients in the balanced chemical equation. The change in concentration of sucrose is negative since it decreases with time, while the change in concentration of ethanol is positive as it increases. The reaction rate is often defined in terms of the reactant or product with the smallest coefficient in the balanced equation, which in this case is sucrose.
• In summary, bioengineering plays a vital role in the design and optimization of bioreactors, enabling the efficient cultivation of microorganisms and the production of desired products. By considering the specific requirements of the microorganisms and the desired biochemical processes, bioengineers create tailored bioreactor systems that maximize productivity and maintain optimal conditions for microbial growth and product formation.

Calculating the Reaction Rate

To calculate the reaction rate of the fermentation of sucrose to ethanol and carbon dioxide, we can use the balanced chemical equation and the stoichiometry of the reaction.

The balanced chemical equation for the fermentation of sucrose is: C12H22O11 (aq) + H2O (l) → 4C2H5OH (aq) + 4CO2 (g)

The general equation for reaction rate is: Rate = Δ[B] / Δt = -Δ[A] / Δt

In this case, we can express the reaction rate of ethanol formation as four times faster than the reaction rate of sucrose consumption, based on the coefficients in the balanced chemical equation:

Δ[C2H5OH] / Δt = -4Δ[sucrose] / Δt

Since the concentration of the reactant (sucrose) decreases with time, the value of Δ[sucrose] is negative. To express the rate of change of the sucrose concentration as a positive value, we insert a minus sign in front of Δ[sucrose] in the equation. Conversely, the concentration of ethanol increases with time, so its rate of change is automatically expressed as a positive value.

The reaction rate is often defined in terms of the reactant or product with the smallest coefficient in the balanced chemical equation. In this case, the smallest coefficient corresponds to sucrose. Therefore, the reaction rate can be expressed as follows:

Rate = -Δ[sucrose] / Δt = (1/4) * (Δ[C2H5OH] / Δt)

This equation indicates that the rate of change in sucrose concentration is one-fourth of the rate of change in ethanol concentration. It provides a relationship between the changes in concentrations of sucrose and ethanol during the fermentation process.

By calculating and analyzing the reaction rates, scientists and engineers can gain insights into the progress and efficiency of the fermentation process, allowing for better optimization and control of the reaction conditions.

Equilibrium

Equilibrium refers to a state in a chemical reaction where the rate of the forward reaction is equal to the rate of the reverse reaction. In other words, at equilibrium, the concentrations of the reactants and products no longer change over time. This does not mean that the reaction has stopped, but rather that the forward and reverse reactions are occurring at an equal and balanced rate.

Equilibrium is represented by the double arrows in chemical equations, indicating that the reaction can proceed in both the forward and reverse directions. The position of the equilibrium is determined by the relative concentrations of the reactants and products at a given set of conditions such as temperature, pressure, and concentration.

The concept of equilibrium is based on the principle of microscopic reversibility, which states that any chemical reaction that can occur in one direction can also occur in the reverse direction. As the forward reaction proceeds, the concentrations of the reactants decrease, and the concentrations of the products increase. Simultaneously, the reverse reaction occurs, converting some of the products back into reactants. Eventually, a point is reached where the rates of the forward and reverse reactions become equal, resulting in a state of dynamic equilibrium.

At equilibrium, the concentrations of the reactants and products remain constant, but it is important to note that the reactants and products are still present and interconverting. The equilibrium position can be influenced by changing the conditions such as altering temperature, pressure, or concentration. Le Chatelier’s principle describes how an equilibrium system responds to changes in these conditions by shifting the equilibrium to counteract the change.

Equilibrium is a fundamental concept in chemistry and plays a crucial role in understanding and predicting the behavior of chemical reactions. It allows scientists to study the extent of a reaction, determine reaction constants, and design chemical processes that are efficient and practical.

Effects on Temperature

• Temperature has a significant effect on chemical reactions, including fermentation processes. When the temperature is increased, the kinetic energy of molecules also increases. This results in more frequent and energetic collisions between the reacting molecules, leading to an increased number of successful collisions that surpass the activation energy barrier.
• In the context of fermentation, higher temperatures can accelerate the reaction rates. Fermentation is a metabolic process where microorganisms, such as yeast or bacteria, convert sugars into alcohol, acids, or gases. These reactions are catalyzed by enzymes produced by the microorganisms.
• Raising the temperature during fermentation can have several effects. Firstly, it increases the rate of enzymatic activity. Enzymes work more efficiently at higher temperatures, leading to faster conversion of substrates. This can enhance the overall fermentation process, allowing for quicker production of desired products.
• Secondly, increased temperature can promote the growth and activity of the microorganisms involved in fermentation. Many microorganisms thrive in specific temperature ranges, and providing optimal conditions within that range can accelerate their metabolic processes. This is particularly important for thermophilic microorganisms that prefer higher temperatures.
• However, it is crucial to note that the effect of temperature on fermentation is not universally beneficial. Excessive temperatures can denature enzymes and disrupt the structure and function of microorganisms, leading to reduced fermentation efficiency or even cell death. Therefore, it is essential to carefully control and monitor the temperature to ensure it remains within the optimal range for the specific fermentation process.
• In summary, temperature plays a vital role in fermentation by influencing the rates of enzymatic reactions and microbial growth. While higher temperatures can generally speed up fermentation, it is important to strike a balance and maintain an optimal temperature range to ensure the desired product is obtained efficiently and with high quality.

Effects on equilibrium

• Temperature has a significant impact on chemical reactions, including those involved in fermentation processes. The equilibrium of a chemical reaction can be influenced by changes in temperature.
• In the context of fermentation, the equilibrium refers to the balance between the forward and reverse reactions occurring during the conversion of substrates into desired products by microorganisms. Temperature affects this equilibrium by influencing the reaction rates and the stability of enzymes and microorganisms involved in the process.
• When the temperature is increased, the rate of the forward reaction generally increases. This is because higher temperatures provide more kinetic energy to the molecules, leading to more frequent and energetic collisions. As a result, the reaction proceeds more quickly in the forward direction, favoring the production of the desired products.
• Conversely, when the temperature is decreased, the rate of the reverse reaction tends to increase. Lower temperatures reduce the kinetic energy of molecules, slowing down the forward reaction. This can shift the equilibrium towards the reverse reaction, leading to a decrease in the concentration of the desired products.
• It is important to note that each fermentation process has an optimal temperature range for achieving the desired outcome. The ideal temperature range allows for efficient enzymatic activity and microbial growth, ensuring a balanced and successful fermentation. Deviating from this optimal temperature range can disrupt the equilibrium and affect the progress of the fermentation.
• In winemaking, for example, the temperature during fermentation is carefully controlled to maintain an optimal rate of fermentation. Lower temperatures can slow down the fermentation process, while excessively high temperatures can lead to the inactivation of enzymes and the death of yeast cells, resulting in a stuck fermentation.
• In summary, temperature has a direct influence on the equilibrium of fermentation reactions. By controlling and adjusting the temperature within the optimal range, winemakers and fermentation practitioners can ensure the desired direction and rate of the fermentation process, ultimately leading to the production of high-quality products.

Effect of oxygen

The presence of oxygen plays a crucial role in fermentation processes, particularly in aerobic fermentations where microorganisms require oxygen for their growth and metabolism. The effect of oxygen is primarily related to its transfer and uptake rates in the fermentor.

During fermentation, it is important to maintain an adequate level of dissolved oxygen concentration to meet the oxygen demands of the culture. The critical dissolved oxygen concentration refers to the minimum concentration required to support the metabolic activities of microorganisms. If the dissolved oxygen concentration falls below this critical level, it can negatively impact the growth and productivity of the culture.

To ensure a balanced oxygen supply and demand in the fermentor, the oxygen transfer rate of the system should match the oxygen uptake rate of the culture. This is typically achieved by controlling the operating conditions of the fermentation process, such as biomass concentration and the specific oxygen uptake rate.

The transfer of oxygen from gas bubbles to the cells is influenced by factors such as the oxygen transfer coefficient (kL), the gas-liquid interface area (a), and the saturated dissolved oxygen (C*) in the liquid. The oxygen transfer rate (OTR) can be quantified using the equation:

NO2 = kLa (C* – CL)

Where:

• NO2 represents the oxygen transfer rate with units of mgO2·l−1h−1
• kL is the oxygen transfer coefficient (cm·h−1)
• a refers to the gas-liquid interface area (cm2·cm−3)
• kLa represents the volumetric oxygen transfer coefficient (h−1)
• C* represents the saturated dissolved oxygen (mg·l−1)
• CL denotes the actual dissolved oxygen concentration (mg·l−1)

By controlling these factors, the fermentor can be optimized to provide an adequate supply of oxygen to the microorganisms, promoting their growth and metabolic activities. However, it is important to note that the effect of oxygen can vary depending on the type of fermentation, as anaerobic fermentations do not require or tolerate the presence of oxygen.

In summary, the presence and control of oxygen in fermentation processes are crucial for maintaining the optimal conditions for microbial growth and metabolism. By managing the dissolved oxygen concentration and its transfer rates, the fermentor can support the oxygen demands of the culture, leading to successful and efficient fermentation outcomes.

Influences on Fermentation

• During fermentation, various factors can influence the process and its outcomes. Some key influences on fermentation include temperature, pH, and the presence of certain compounds.
• Temperature: Fermentation generates heat as a byproduct, and if this heat is not properly dissipated, the temperature of the fermentation vessel can rise. It is estimated that for each drop of 1°B (degrees Brix), the temperature can increase by approximately 2.3°F. To regulate the temperature and prevent excessive heat buildup, cooling jackets are often used on fermentation tanks. Maintaining the appropriate temperature is crucial as it affects the growth rate and metabolic activity of the microorganisms involved.
• pH: The pH of the fermentation environment plays a significant role in microbial growth and fermentation outcomes. Yeast and bacteria, including spoilage microbes, tend to grow best at around a pH of 5.5. To prevent spoilage and maintain the desired microbial activity, it is recommended to keep the must (fermentation mixture) at a pH range of 2.9 to 3.6. Lower pH values can inhibit yeast growth and fermentation, while higher pH values may promote the growth of undesirable microorganisms.
• Sulfur Dioxide (SO2): SO2 is commonly used in winemaking as a preservative and antimicrobial agent. It has the ability to slow down the growth of various microbes and can even kill certain microorganisms. By adding 30 to 50 parts per million (PPM) of SO2 to the must, non-wine yeasts and lactobacillus, which can negatively impact fermentation, can be discouraged.
• These factors, temperature, pH, and the use of compounds like SO2, have a significant impact on the fermentation process. By carefully controlling and optimizing these parameters, winemakers can achieve desired fermentation outcomes, including the growth of specific microorganisms, the production of desired flavors and aromas, and the prevention of spoilage and off-flavors.

Heat Transfer in Fermentation

Heat transfer plays a crucial role in fermentation processes to ensure optimal temperature control and efficient operation of bioreactors. There are two main heat transfer applications involved in bioreactor operation:

1. In situ batch sterilization of liquid medium: This process involves heating the fermenter vessel containing the liquid medium using steam to achieve sterilization. The vessel is held at the sterilization temperature for a certain period, and then cooling water is used to bring the temperature back to normal operating conditions. This sterilization step helps eliminate any unwanted microorganisms before introducing the desired microbial culture.
2. Temperature control during reactor operation: The metabolic activity of cells during fermentation generates heat, and maintaining the appropriate temperature is crucial for the growth and productivity of the microorganisms. Various heat transfer configurations can be used in bioreactors:

• Jacketed vessel: This configuration involves a heat transfer jacket surrounding the vessel. It provides moderate heat transfer area but is less commonly used on an industrial scale due to limited efficiency.
• External coil: Similar to the jacketed vessel, an external coil can be used for heat transfer, but it also offers limited surface area and is less favored in large-scale applications.
• Internal coil: This configuration utilizes a coil inside the vessel, which can provide a relatively large heat transfer area. However, it may interfere with mixing and cleaning processes and can lead to the growth of cells on the coil surface.
• External heat exchanger: An external heat exchanger unit is independent of the reactor and offers excellent heat transfer capability. It is easy to scale up and provides efficient temperature control. However, it requires meeting sterility conditions, ensuring the cells can withstand shear forces, and maintaining a short residence time to prevent oxygen depletion in aerobic fermentations.

Different types of heat exchangers can be employed in bioprocesses, including double-pipe heat exchangers, shell and tube heat exchangers, plate heat exchangers (less commonly used due to the small temperature difference in bioprocesses), and spiral heat exchangers.

Efficient heat transfer in fermentation is crucial to maintain the desired temperature conditions for microbial growth and optimize the productivity of the bioprocess. The choice of heat transfer configuration depends on factors such as the scale of operation, mixing requirements, cleaning considerations, and the need for sterility and oxygen availability.

Mass transfer in Fermentation

Mass transfer plays a crucial role in fermentation processes, particularly in aerobic cultures where the transfer of gases, such as oxygen, is essential for microbial growth and metabolism. Here are some key points related to mass transfer in fermentation:

• Mass transfer occurs in mixtures where there are local concentration variations. For example, when a dye is dropped into water, mass transfer processes are responsible for the movement of dye molecules until equilibrium is established and the concentration becomes uniform.
• Mass is transferred from one place to another in a system when there is a concentration difference or gradient. In the context of fermentation, mass transfer involves the movement of gases, nutrients, and metabolites within the fermentation broth.
• In bioprocessing, gas-liquid mass transfer is of significant importance because many fermentation processes require oxygen. Oxygen needs to be transferred from the gas phase into the liquid medium and then onto the surfaces of microbial cells for utilization in metabolic reactions.
• The solubility of oxygen in the fermentation broth is typically low, making efficient gas-liquid mass transfer crucial for adequate oxygen supply. Enhancing gas-liquid mass transfer is a priority in aerobic cultures and fermentations to ensure sufficient oxygen availability for microbial growth and productivity.

Strategies to enhance gas-liquid mass transfer in fermentation include:

• Increasing the surface area available for mass transfer by using aeration systems that promote efficient gas dispersion within the liquid medium.
• Optimizing agitation and mixing conditions to enhance the contact between the gas and liquid phases, ensuring effective transfer of gases.
• Controlling the environmental conditions such as temperature, pressure, and gas flow rates to optimize mass transfer efficiency.
• Using specific equipment or designs such as spargers, bubble columns, or specialized bioreactors that facilitate gas-liquid mass transfer.

Efficient gas-liquid mass transfer is essential for providing microorganisms with sufficient oxygen and nutrients, as well as removing waste products, to support their growth and metabolic activities during fermentation processes. It is an important aspect to consider in the design and operation of bioreactors and other fermentation systems.

Applications of Bioengineering

Bioengineering, with its integration of natural sciences and engineering principles, has various applications in the field of biotechnology and fermentation. Here are some key applications of bioengineering:

1. Customized Fermenters: Bioengineering designs and constructs stainless steel fermenters tailored to the specific requirements of microbial cultivation. These fermenters can accommodate a wide range of microorganisms, including bacteria, archaea, yeast, and extremophiles, with capacities ranging from 30 to 50,000 liters.
2. Optimization of Process Parameters: Bioengineering considers critical factors such as oxygen supply, stirrer dimensioning, and heating and cooling circuits in order to create optimal conditions for challenging microbial cultures. Using expert knowledge and computational fluid dynamics (CFD) simulations, they can achieve high material transition coefficients (kLa values) and provide support for aeration strategies to ensure optimal oxygen supply.
3. Aeration and Oxygen Supply: Oxygen is a vital requirement for many fermentation processes. Bioengineering specializes in developing aeration strategies that ensure sufficient oxygen supply for microorganisms and their metabolic processes. Whether the process requires anaerobic conditions or high oxygen demand, Bioengineering can offer solutions tailored to specific needs.
4. Advanced System Features: Bioengineering integrates various system features to meet specific requirements. Dosage vessels for corrective agents such as acids, bases, and anti-foams are included in their fermentation systems, allowing for precise control of process parameters. Additionally, they prioritize short heating and cooling periods to minimize negative effects on culture media and process duration.
5. Diverse Application Areas: Bioengineering’s expertise spans a wide range of application areas in biotechnology and fermentation. They address challenges related to high foam development, bio-safety requirements, high metabolic heat, continuous fermentation, GMP (Good Manufacturing Practice) production, and high cell density, among others. Their goal is to provide innovative solutions tailored to specific issues faced by clients.

Through their experience and expertise, Bioengineering contributes to the advancement of bioprocesses by developing and implementing optimized solutions for fermentation and microbial cultivation. Their focus on customized systems and attention to critical process parameters make them a valuable partner in various bioengineering applications.

FAQ

References

1. 
   Chisti, Y. (2007). Biodiesel from microalgae. Biotechnology Advances, 25(3), 294-306.
2. Nielsen, J., & Keasling, J. D. (2016). Engineering cellular metabolism. Cell, 164(6), 1185-1197.
3. Rathore, A. S., & Kapoor, G. (2009). Bioreactors and bioprocessing for biopharmaceuticals: a practical guide. Wiley.
4. Sun, J., Wang, Q., & Jiang, Y. (2015). Bioreactor design for tissue engineering: a critical review. Journal of Bioscience and Bioengineering, 120(5), 541-549.
5. Singh, R., Kumar, M., Mittal, A., & Mehta, P. K. (2016). Microbial enzymes: Industrial progress in 21st century. 3 Biotech, 6(2), 174.
6. Liu, C. G., Xue, Z. W., & Bai, F. W. (2015). Impact of bioreactor engineering on CHO cell culture. Advances in Biochemical Engineering/Biotechnology, 150, 59-87.
7. Balan, V., & Dale, B. E. (2011). Advanced biofuels: prospects and challenges. Advances in Biochemical Engineering/Biotechnology, 122, 405-427.
8. Ghorai, S., & Kumar, A. (2021). Bioengineering strategies for sustainable food production: A review. Journal of Food Engineering, 303, 110592.
9. Lee, S. Y., & Kim, H. U. (2015). Systems strategies for developing industrial microbial strains. Nature Biotechnology, 33(10), 1061-1072.
10. Pandey, A., Soccol, C. R., & Soccol, V. T. (2020). Bioprocess engineering: principles and applications. Elsevier.