Abdullah M Al Falih*
Department of Botany and Microbiology, College of Science, King Saud University, Saudi Arabia
*Corresponding author: Abdullah M Al-Falih, Department of Botany and Microbiology, College of Science, King Saud University, P.O. Box. 2455 Riyadh 11451 Saudi Arabia
Submission: September 29, 2021; Published: October 14, 2021
ISSN 2578-0336 Volume9 Issue2
The review has been extensively on the biological activities of yeast, focusing on the various uses of renewable feed stocks and their conversions into fuels and chemicals to cope with the increasing demand on sustainability issues around the world. Saccharomyces cerevisiae is the best studied eukaryote and a valuable tool for most aspects of basic research on eukaryotic organisms. S. cerevisiae is one of the most popular cell factories and has been successfully used in the modern biotechnology industry to produce a variety of substances such as ethanol, organic acids, amino acids, enzymes and therapeutic proteins. This review will focus on how to use different sustainable solutions to overcome the different environmental impacts on yeast. With a wide range of current developments and future prospects in yeast biotechnology explored and its applications and potentials discussed in general.
Keywords: Yeast, Fermentation, Biotechnology, Industry and Saccharomyces Cerevisiae
People have used yeasts and other microorganisms to produce many foods and drinks
since ancient times. Bread is a result of the microbial fermentation of the sugars to produce
carbon dioxide, which is released into the dough making the bread puffy. The human interest
and attempt to benefit from the activities of microorganisms dates back to prehistoric times,
but these activities were not used in industry until around the middle of the twentieth century
as a result of the cooperation that arose between microbiologists, engineers and capital owners
to develop industries based on the use of Microorganisms. Microbes are also essential in the
production of beer and wine, as the sugars are converted into alcohol. Microbial fermentation
is also a step during the chemical process of recycling waste. The raw materials used in the
industry vary and the most important of which are the following: corn steeper extract. barley,
cellulose, starch, grab, alcoholic products, soybean seeds, hydrocarbons and sucrose .
Figure 1 illustrates a general approach whereby metabolic engineering within a systems biology framework can play a vital role by using genetic modification to build the strain with the help of the metabolic model approach and further improve it by fermentation to obtain all growth materials as analysis of different omics will help further to obtain better insights for the model refinement.
Figure 1: A general metabolic engineering approach for different industrial productions (Nandy and Srivastava 2018).
Baker’s yeast has been used since ancient times since people knew bread and made it
an essential component of their food. Certain strains of Saccharomyces cerevisiae are now
used to improve the taste, consistency and texture of the dough. This yeast breaks down
(fermentation) the sugars, resulting in alcohol and CO2 bubbles that remain trapped in the
dough, which increases the size of the dough and inflates it. Usually, an amount of yeast is
added to the mixture of flour and water, an amount of salt and some sugar, then the dough
is left to ferment at a temperature of about 25 °C. During this period, the yeast breaks down the sugars in the dough into a mixture of alcohol and carbon
dioxide. Carbon dioxide gas in the bread, which gives the bread its
distinctive texture. Humans have resorted to the use of yeasts in
many matters, such as the production of antibiotics to treat diseases
caused by pathogenic microorganisms, as well as the production of
many important food or industrial materials such as bread, dairy
products, pickles, vitamins, enzymes, acids, proteins, fats and
steroid of vehicles, as happened with the Germans in World War II.
Baker’s yeast is simply beer yeast produced via a submerged fermentation process carried out in the presence of oxygen (Figure 2). Aerobic conditions favor yeast cell production, which is not of interest to ethanol producers, but is important when a large amount of cell mass must be produced.
Figure 2: Baker’s yeast production process.
Some sugars are directly available to the yeast, as the flour
itself contains about 2% of the available sugars in addition to the
sugars that are added, such as sucrose and cane sugar, and then
substituted for the sugars from wheat grain starch by two types
of enzymes, alpha-amylase and-amylase. Which is one of the basic
ingredients of the flour and is activated by water and the beta
amylase splits the starch from the ends into two units of glycose
to give maltose, which is a double sugar, and at the same time the alpha-amylase breaks down the long chain from the inside to
separate it into several short chains, giving the beta-amylase the
opportunity to act on it, resulting in a mixture of maltose and
glucose. Yeast converts glucose into alcohol and carbon dioxide.
Maltose is often fermented by yeast at the end of the fermentation
process when all other sugars are consumed. Disaccharides such
as sucrose and maltose are degraded by hydrolytic enzymes in the
cell into monosaccharides. Although some types of yeast can grow
on starch, they are less effective than other types that grow on
monosaccharides and disaccharides [2,3].
Although the main function of yeast is to increase the size of the dough, it has some other effects .
In the dry yeast manufactured by the old methods, a sugar solution must be added and kept at a temperature of 26-32 °C for 6-12 hours until the cells become active in number large enough to carry out the fermentation process. As for the yeast manufactured by modern methods, it can be used directly without the need for previous treatment.
It should be noted that the global production of baker’s yeast reaches more than two million tons annually, and it is present in several forms, including pressed yeast, active dry and instantaneous dry, and these pictures differ from each other in the degree of activity and the extent of stability .
In the European countries yeast biotechnology, a one million tonnes is produced annually, and about 30% of which is exported globally. The worled market’s annual growth rate was 8.8% from 2013 to 2018. S. cerevisiae has been an essential component of human life because of its extensive use in food and beverage fermentation industry in which it has a high commercial significance. A discussion on the contribution of S. cerevisiae in wine, bread and cocoa fermentations follows, highlighting approach such as the process of biochemical reactions that take place in the yeast cell and whose products determine the terminal products, the traits that strains should have in order to be successful starters and the potential of exploiting native strains in industry. In recent years, there is an alternative vinifications employing mixed yeast inocula of S. cerevisiae and non-Saccharomyces species as cultural fermenter starters. So several researchers and many biotechnological industries have turned to vinification processes involving fermentations with mixed yeast inocula. As non-Saccharomyces inocula have served member species of several genera as shown in Table 1, among them Candida, Debaryomyces Hanseniaspora, Issatchenkia, Metschnikowia, Pichia, Kluyveromyces/Lanchancea, Torulaspora, Wickerhamomyces. The mixed starters of these yeasts are applied in a co-, or sequential fashion and often in varying ratios of cell numbers.
Table 1: Mixed starter cultures of S. cerevisiae with non-Saccharomyces species leading to improved organoleptic traits .
Saccharomyces cerevisiae is widely applied in microbial
biotechnology production of chemicals, metabolites via genetic
manipulation which is relatively easy and experiences from its
wide use in the existing industrial fermentations that might
directly benefit the yeast S. cerevisiae processes . The genetic
engineering strain of S. cerevisiae via metabolic activities under
different metabolism studied for production of various chemicals
of biotechnological industry. While talking about chemical product,
the ethanol should come first which is producing naturally from S.
cerevisiae. This fermentation process is illustrated the production
of ethanol from yeast fermentation where glucose is used as
substrate where one mole of glucose (180g) is converted to two
moles of ethanol (92g) plus two mole of carbon-dioxide (88g)
and it produces energy (26.4 Kcal) from this reaction . Ethanol
or related biofuel or bioenergy will discuss in the last part of this
Yeast can also be considered as an alternative source of fats. Some species are able to synthesize and accumulate more than 20% of the biomass in the form of neutral fats and for this reason it is called oleaginous yeast. Under conditions of optimal growth or as a result of genetic improvement, the level of fat accumulation can reach up to 70%. Oily yeast contains types such as, Saccharomycopsis, Pichia (Hansenula), Lipomyces, Pseudozyma, Rhodosporidium, Rhodotorula, Trichosporon, Trigonopsis and Yarrowia .
To obtain excretion products, yeasts are grown on a carbon source such as molasses, and molasses represents the lowest degree of purity on which sucrose is found, and molasses, besides sucrose, contain reduced sugars, mineral salts, organic materials and water, and it is considered a residue of the sugar industry, whether from cane or sugar beet or corn. Many industries depend on molasses, such as the manufacture of various alcohols, yeast and organic acids. The chemical composition and natural properties of molasses varies according to several things, including the type of sugar cane or beet used in industry, climatic factors during the planting season, agricultural factors in terms of soil type, fertilization, and so on. Among the most prominent substances or products excreted from yeast cells during the fermentation process, we mention the production of Ethanol Glycerol as follows .
It is worth noting that there are many factors that should be
controlled when producing ethyl alcohol. In the forefront comes
to make sure of the strain used and its purity. The fermentation
process is carried out by Saccharomyces cerivisae and must be
highly efficient in the production of alcohol and carbon dioxide, and
its ability to withstand high concentrations in the fermented sugar
and alcohol . The initiator is prepared from the preserved pure
select strain, and several successive activations are carried out from
this culture in a sterile fermentation solution at a temperature of
25-30 °C until cells are sufficient to inoculate 4 liters of the nutrient
medium, then the inoculation steps are transferred from the
laboratory to tanks [11,12].
The sugar concentration used in this industry ranges between 10-18% and the usual concentration is approximately 12%. It is known that Molasses contains most of the nutrients needed for fermentation. However, ammonium salts in the form of sulfate or ammonium phosphate are sometimes added to the fermentation solution as a source of nitrogen and phosphorous .
Glycerin is used in the manufacture of medicines and beverages
and in the manufacture of paints and cosmetics. The German
researcher Newporg published his research on the fermentation
that he observed when adding sodium sulfite to alcoholic
fermentation by the yeast. Note that the first observation of glycerin
production during the fermentation process was recorded by
Paster, where it was observed that yeast formed glycerin at a ratio
between 2.5-3.5% of the fermented sugar. The formation of glycerin
depends on the diversion of the alcoholic fermentation process
by withdrawing acetaldehyde when it is formed, so it becomes
unavailable for oxidation of NADH2, which in this case is used to
reduce P-3 - glyceraldehydes. The oxidation of NADH2, or by making
the fermentation medium alkaline, leads to directing NADH2 in the
reaction to reduction. P-3 - glyceraldehydes is commonly used in
the production of Saccharomyces cerevisiae glycerin .
With glycerine, ethyl alcohol and acetaldehyde are synthetically presented with only 20-25% glycerin, and the alcohol and acetaldehyde are separated by distillation. Note that glycerin production is increased by the use of acids and alkalis or their salts.
There are several known methods for producing glycerin by fermentation, and in all the methods they use a basic environment that contains fermentable sugar, to which the necessary salts and nutrients are added, and then pollinate the environment with a culture of yeast and keep it at a temperature of 30-37 °C to form additives of the year. The first method produced by the Germans, in which sodium sulfite is added to the fermenting liquid, usually the acetyldehyde is reduced to ethyl alcohol, but with the addition of sodium sulfite, it reacts with the acetaldehyde and turns it into a stable compound that is not amenable to receiving hydrogenhydroaldehyde. To reduce the acetaldehyde to ethanol it goes to the reduction of the glyceraldehyde-3-phosphate fraction to glycerin .
Glycerin is then obtained by distillation and then purified by
distillation under a certain pressure.
As for the second method for producing glycerin, it is known by the American method, in which an environment of sugars is fertilized with the selected strain of yeast and incubated at the appropriate temperature, and a substance that gives an alkaline effect, such as sodium carbogamate, is added gradually according to the speed of its disappearance. Ethyl This reaction is known as the Cannizzro reaction and the duration of fermentation ranges from five days to a week.
In nutritional biotechnology, the “phenotype” should be considered a fundamental characteristic when developing methods for selecting yeast. Functional traits are what matters most in a particular ecosystem when looking at the mechanisms of general microbiology. Previous studies have been extensively researched over the past decades through specialized research on the chemical determination of compounds derived from the metabolic activity of yeasts. From these studies it can be concluded that many Fermentation products, including ethyl and acetate esters, Higher alcohols, Fatty acids, Lactones and Sulfur compounds . Among the materials produced by special reactions, compounds made by special reactions, which are popular in yeast cell reactions, we mention Ephedrine, as well as hydrocarbon derivatives, in addition to what are known as radioactive biochemical .
One of dairy products is cheese, that is found usually in most
complex nature, fascinating, and diverse foods. Some strains of yeast
culture which are Kluyveromyces lactis and Debaryomyces hansenii
have been reported actively grown on soft-cheese model curds
[18,19] by taking a month periods for the ripening. Also, kefiris
reported as fermented milk product beverage, which is produced
by fermenting grains of the kefir through symbiotic interaction of
bacteria and yeasts exist in kefir grains. Some yeast strains have
been reported such as K. marxianus, Candida kefyr, D. hansenii
and K. lactis var. Kefir has shown the therapeutic characters as a
natural product beverage. These yeasts are actively involved in
development of favorable kefirsensory properties .
Other dairy product, koumiss is slightly alcoholic yeast fermented mare’s milk beverage. Koumiss is produced by applying a natural mixed starter of lactic acid bacteria and a strain of yeasts. It is processing for aroma, texture, as well as the nutrients beneficial to people health is done by using Saccharomyces cerevisiae and other yeast strains such as Candida pararugosa, Dekkera anomala, Geotrichum sp., Issatchenkia or-ientalis, Pichia deserti-cola, P. fermentans, P. manshurica, P. membranaefaciens, Kazachstania unispora, and Kluyveromyces marxianus . Acidophilus- yeast fermented milk has found to vary from Indian Dahlmainly in kind of microbes involved, flavor, body texture, consistency, antibacterial activity and chemical composition. In this beverage product the yeast strains such as Saccharomyces cerevisiae and Saccharomyces boulardii has been added to put the antioxidant characteristics of fermented milk and enhance the viability of bacterial strain. This beverage product has a lactic acid content (1·5 to 2.0%) that help in cure of human stomach disorder .
Saccharomyces cerevisiae yeast strains have shown cell factory
nature [22,23]. Many genetically modified or metabolic engineering
ome strains of Saccharomyces cerevisiae have been turned into
a producer of higher alcohols such as 1-butanol and iso-butanol,
farnesene, bisabolene, and biodiesel, Bioethanol is alcoholic
beverage and two carbon organic compounds, produced by genetic
engineered strain S cerevisiae ATCC 20602 in 7.5-l vessel, that
having glucose media, operated in fed-batch mode .
In an aerobic fermentation condition, ethanol concentration (20g l-1) was recorded while in an anaerobic system, ethanol concentration was reported 85g l-1 in 70 h with higher cell viability (88%). 1-Propanol is a primary alcohol with three carbon compounds. It has high numbers of octane and suitable for engine fuel use. While production of propanol has been reported too expensive to be a common engine fuel. So, suitable microorganism strain should be selected for biosynthesis of 1-propanol. The yeast strain influence has found to be very strong forn-propanol and less evident for the production of other alcohols. Increased production of n-Propanolin yeast strains has recorded due to having an impaired ability for formation of hydrogen sulfide .
Saccharomyces cerevisiae has been found to utilize not only glucose but also xylose as sugar component. Now a days researchers are trying to develop a modified engineered strain of the yeast Saccharomyces cerevisiae which can have 2-Keto acid decarboxylase and alcohol/aldehyde dehydrogenase in metabolic engineering and can develop 2-ketobutyrate compound to generat more quantity of 1-Propanol. Isopropanol or dimethyl carbinol is a flammable chemical with a strong odor and colorless. It has a wide industrial application and household usages, also involved in an ingredient of some chemicals such as detergents, antiseptics and disinfectants [25,26].
The yeast Saccharomyces cerevisiae is shown to be the best studied microorganism and one of the common widely used eukaryotes in a variety of industrial production processes, such as bread, ethanol, beverage and food biotechnology. Optimization of pathway and construction can be achieved by using metabolic engineering with revolutionized next generation sequencing and together improve the DNA synthesis technique . This review, describe the combination of both systems biology, biotechnology and attraction metabolic engineering. Also known as synthetic biology as a powerful framework to elaborate various industrial applications consisting mainly pharmaceuticals, chemical, dairy and biofuel.
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