Fermentation Process, Advantages and Disadvantages

 

What is Fermentation?

Fermentation is the process of converting carbohydrate to alcohol or acid using yeast, bacteria, or a combination of the two. Some examples include:

·         All alcoholic beverages are derived from fermentation.

·         The conversion of corn into ethanol is an example of fermentation used in biotechnology (ethanol fuel).

Lactic acid ferments are important in producing foods with a longer shelf life (e.g., sauerkraut, pickles, and yogurt). The production of citric acid also involves fermentation. Excessive lactic acid fermenting bacteria can cause food spoilage. One such bacteria is Lactobacillus bulgaricus , which produces large amounts of lactic acid during the production of yogurt. Fermentation in biotechnology is used to make a variety of products, including:

·         Alcoholic beverages (beer and wine)

·         Foods with a longer shelf life (e.g., sauerkraut, pickles, and yogurt)

·         Citric acid

Process of Fermentation

The term fermentation is most commonly used in the contexts of brewing, winemaking, and microbiology to refer to the bulk growth of mold or yeast where cells are able to produce alcohol from sugar. However, the term can also be applied more generally across biological systems where larger molecules are produced through catabolism of smaller molecules. Due to these broadly applicable characteristics, the field is often considered as a branch of biotechnology.

 

Biotechnology has made it possible for humans to convert raw materials (for example, plant matter) into desired products (for example, ethanol). Fermentation processes have existed since ancient times and are closely related with emerging biotechnology which has led to an increase in yields even though initial costs may be higher. Today, nearly all commercial biotechnology involves fermentation.

 

 

 

"Manufacturers have always sought to control factors of a process so they can reduce costs and improve product quality. Fermentation processes provide several advantages over other types of chemical synthesis, including the ability to work with unstable substrates, tolerance for impurities in starting materials, and the generation of selective by-products." However, the disadvantages include: "low reaction rates and low yield. Moreover, fermentations can be sensitive to cell concentration and reactant ratios as well as environmental conditions such as pH and temperature...These limitations have been largely overcome through advancements in systems designed for high throughput screening (HTS) which allow researchers to develop optimal sets of parameters that maximize yields".

 

 

 

One example is genetically engineered yeast used to ferment xylose to ethanol. In this process, "Xylose isomerase catalyzes the hydrolysis of D-xylulose into xylitol and D-xylonolactone".

 

 

 

For decades, scientists have been cloning genes from one organism and inserting them into another. This technique, called genetic engineering, allows us to steer nature in directions we want it to go. One example is genetically engineered yeast used to ferment xylose to ethanol. In this process, a strain of genetically engineered yeast is able to convert sugars founds in wood chips or switchgrass into ethanol which can be used as an alternative fuel source for cars or electricity generators. First, enzymes must be added that break down the cellulose and hemicellulose. Then, another enzyme is added that breaks down the cellulose and xylose and other sugars into ethanol.

 

 

 

"However, it has been noted that most of the energy used for this process comes from breaking down carbohydrates such as glucose rather than xylose". In order to address this issue, "Xylose isomerase catalyzes the hydrolysis of D-xylulose into xylitol and D-xylonolactone. This creates a more favorable equilibrium that allows cells to convert more of the available xylose into ethanol".

 

 

 

Due to these broadly applicable characteristics, the field is often considered as a branch of biotechnology: fermentation processes provide several advantages over other types of chemical synthesis, including the ability to work with unstable substrates, tolerance for impurities in starting materials, and the generation of selective by-products. However, the disadvantages include: low reaction rates and low yield as well as sensitivity to environmental conditions such as pH and temperature. These limitations have been overcome through advancements in high throughput screening (HTS) which allow researchers to screen large numbers of parameters that maximize yields.

 

 

 

"The companies often change one or more growth medium components at a time so they can identify those factors that impact cell metabolism. The most common fermentation media consist of complex broths with undefined compositions...Typically these broths are composed primarily of carbohydrates like sugars or starch along with nitrogenous compounds such as ammonium salts, vitamins, amino acids...cellulose, and other carbohydrates like xylan.

 

 

The Industrial Fermentation

A major driving force in the industrial fermentation field is to reduce costs. One of the most common approaches used by manufacturers is to use less expensive reactors that are more easily scaled up or down as needed for production purposes. "Manufacturers have always sought to control factors of a process so they can reduce costs and improve product quality". The "fermentation processes provide several advantages" including utilization of unstable substrates, tolerance for impurities in starting materials, and the generation of selective by-products, however some disadvantages include low reaction rates and low yield as well as sensitivity to environmental conditions such as pH and temperature. These limitations been overcome through advancements in high throughput screening (HTS) which allows researchers to screen large numbers of parameters that can maximize yields.

 

 

 

One example is genetically engineered yeast used to ferment xylose to ethanol. In this process, enzymes must be added that break down the cellulose and hemicellulose. Then another enzyme is added that breaks down the cellulose and xylose and other sugars into ethanol along with a change in media components from glucose to xylose. Unfortunately, "it has been noted that most of the energy used for this process comes from breaking down carbohydrates such as glucose rather than xylose". In order to address this issue, a strain of genetically engineered yeast is able to convert sugars founds in wood chips or switchgrass into ethanol which can be used as a biofuel. "Xylose isomerase catalyzes the hydrolysis of D-xylulose into xylitol and D-xylonolactone. This creates a more favorable equilibrium that allows cells to convert more of the available xylose into ethanol".

 

 

Pros

The advantage of using different fermentation media components include: decreased costs, reduced environmental impact, and easier product purification. Examples of this are using cellulosic sugars instead of glucose or using waste products such as straw pulp for carbon sources. In addition to yeast genetic engineering, advanced modeling techniques have also been widely used in the fermentation industry. One example is multivariate analysis where process parameters are studied simultaneously by applying statistical procedures to control fermentations. In addition, mass spectrometers have been used to sample the fermentation process as it occurs and provide a visual representation of what is going on during metabolism. This has led to a better understanding of the dynamics of the yeast cell metabolism which leads to increased biomass yield with higher purity.

 

 

Cons

The disadvantage of using different fermentation media components include: decreased product output, instability in system performance, and increased costs for purification techniques that rely on chemical means. In addition, there has been an increase in non-productive byproducts that require further purification processes or must be disposed of altogether. In terms of genetic engineering, there are several drawbacks such as mutations may result from changes in substrate-binding sites which can lead to less efficient energy usage and lower yield. In addition, host cell resistance to antibiotics used in the process may result from over expression of antibiotic biosynthesis genes.

 

 

Final Verdict

In order to lower costs and increase fermenter capacity, a lot of research has been done on nutrient recycling for a steady supply during large-scale fermentation. One example is one study that improved nitrogen utilization by eliminating residual ammonia through nitrification and denitrification within the fermenter system rather than adding ammonium salts or another compound to maintain auxotrophy. In this case, "a 7-kg/day fed-batch production was achieved using 11% less carbon sources". In terms of energy usage, one study was able to cut down costs by reducing CO2 production through aerobic storage with appropriately designed reactors and optimization of both carbon and nitrogen sources.