History of Yeasts

 By Joseph W. Ward, Ph.D. and TJ Gaydos, DVM, MAM DACPV

 Years of study and research have shown live yeasts have a positive effect on animal health and welfare. The results have shown that live yeasts present a large number of benefits for animals. Their unique manufacturing process endows them with greater stability and guarantees a maximum number of active yeast cells reach the intestines or the rumen. Research has shown that feeding live yeasts offers several benefits. Yeast benefits includes the following:
• Stimulates the rumen’s metabolism;
• Improves the digestibility and absorption of feed;
• Reduces the risk of acidosis;
• Increases animal productivity (more milk, more persistent lactation, better growth, etc.)
With so much research being done and producer interest about what yeast is, let’s take a look at yeast and its history.

What are yeasts?
They are single-celled microorganisms that are classified, along with molds and mushrooms, as members of the Kingdom Fungi.  Over 600 species have now been identified. Yeast can be found throughout nature in a wide range of habitats. Yeasts are evolutionally diverse and are therefore classified into two separate phyla, Ascomycota or sac fungi and Basidiomycota or higher fungi. Saccharomyces cerevisiae is an example of a member of the phylum Ascomycota, and bread mold is an example of a member of Basidiomycota.   
Of the many strains of yeast, the most commonis S. cerevisiae, which is used in baking as a leavening agent, where it converts the food/fermentable sugars present in dough into carbon dioxide gas. This causes the dough to expand or rise as gas forms pockets or bubbles.
Yeasts are related to other types of fungi that people might be more familiar with such as edible mushrooms and molds that ripen blue cheese. Yeasts possess a cellular organization similar to that of higher organisms, including human beings.  Their genetic content is contained within a nucleus, which classifies them as eukaryotic organisms. This means they are a single cell with a complex structure. The typical yeast cell is a round or oval and about the same as a human red blood cell.
Aside from its traditional uses, like backing and brewing, scientists consider it a “model” organism for study and research because of its rapid growth. For instance, Its DNA can be easily manipulated, and it provides insight into basic human biological processes. Yeast has become an important agent in the study of human disease genes, based on the similarity between yeast genes and humans. At the same time, studies in yeast have the potential to help scientists identify drug targets or the drug that might be used to aid incombatting human disease. An interesting fact about yeast is that it can grow with or without air. Anaerobic growth, which is growth in the absence of oxygen, is quite slow and inefficient. For instance, in bread dough, the yeast will grow very little. Instead, the sugar that can sustain either fermentation or growth is used mainly to produce alcohol and carbon dioxide.
Some yeasts reproduce through binary fission, while others grow asexually through the process called budding. The parent cell forms a growth (bud) on its surface. It grows to a full size and forms a bud. As the bud grows, the parent cell’s nucleus divides into two (mitosis). Each yeast cell undergoes the budding process between 12-15 times before the cell is no longer capable of reproducing. Under ideal growth conditions, a yeast cell can reproduce every one and a half to two hours.

History of yeast
Research has documented that humans used yeast as far back as the ancient Egyptians, who used yeast and the fermentation process to produce alcoholic beverages and to leaven bread over 5,000 years ago. The process was replicated by taking a small portion of initial dough to start a new batch of dough. As a result, many consider yeast to be the oldest industrial microorganism. Yet, the biochemical process of fermentation was not understood centuries ago, and the process continued like this without much scientific advancement until the 1860s with the advent of the microscope.
It was then that Louis Pasteur identified yeast as a living organism and was the agent responsible for alcoholic fermentation and dough leavening. Shortly thereafter, scientists were able to isolate yeast in its pure culture form, and this knowledge by the early1900s, made it possible to commercially produce baker’s yeast. Even more exciting was the fact that since yeast was now considered a living organism, scientists now had the ability to isolate yeast strains in their pure culture form. This opened the door for researchers to isolate and produce pure strains of yeast that could meet the requirements of the baking industry.  
Øjvind Winge, a Danish biologist, is considered the real pioneer in yeast genetics. He and his Danish colleague Otto Laustsen devised techniques tomicromanipulate yeast so that they could be investigated genetically. This pioneering work earned him the title “The Father of Yeast Genetics.” Since that time, many other researchers have carried out groundbreaking research using budding yeast. Some of these researchers have been awarded the Nobel Prize for significant discoveries made during these studies. In recent years, researchers have found that through the selection of strains and development of propagation techniques, more specific applications of yeast are now being found in a wide range of industries, including brewing, malting, farming (animal feeds), pharmaceuticals and dietetics.

Modern day applications
Yeast is being used in the petrochemical industry where it has been adapted to produce biofuels such as ethanol and farnesene, a diesel and jet fuel precursor. At the same time, it has been used in the production of lubricants and detergents. Yeast is also used in the food industry for the production of food additives including colorants, antioxidants and flavor enhancers. Yeast has also been used in the production of pharmaceuticals including anti-parasitics, anti-cancer compounds, biopharmaceuticals such as insulin,vaccines and nutraceuticals. Yeast is also commonly used in the production of industrial enzymes and chemicals. In the field of bioremediation strains have ever been exploited for the removal of metal from mining waste.
The similarity between yeast genes and their humancounterparts, and conserved fundamental cellular biology has led researchers to use yeast as a popular model system for the study of human disease genes. Several approaches have been used to learn more about human genes once a connection between a human and yeast gene is made.

Agricultural research
This same type of research is now being used in animals. The use of feed additives containing live microorganisms and (or) their metabolites to alter rumen fermentation and improve animal performance has increased in response to demands for using more “natural” growth-promoting substances.
Research shows that including yeast in ruminant diets can lead to an increase of consumption of dry matter, utilization of fiber and other nutritive substances which, in turn, leads to an increase in gain. Yeast cells also help with digestibility and absorption of minerals such as phosphorous, magnesium, calcium copper, potassium,zinc and manganese. S. cerevisiae is generally recognized as safe (GRAS) by the Food and Drug Administration and thus is appropriate for use in animal feds.
In summary, yeast clearly affects many reactions occurring in the rumen. It stabilizes the rumen PH, stimulates certain cellulolytic bacteria, enhances fiber degradation, reduces methane production and nitrogen loss, increases milk production and thus increases gain and feed efficiency. By using yeasts, producers are able to address consumers’ concern about the safety and quality of animal products and environmental issues. The goal is to provide healthier cattle, higher quality milkproducts and safe meat products.  
There is little doubt that yeast has been a very helpful organism dating back to the Egyptians. Today, researchers have explored a wide range of yeasts that are used to better our lives in many different ways. Unlike the age-old argument of which came first, the chicken or the egg, with yeast, we know that the yeast came before the bread!  

Sources
Joseph W. Ward, Ph.D., Product Manager Phileo Lesaffre Animal Care, j.ward@phileo.lesaffre.com
TJ Gaydos, DMV, MAM, DACPV, Poultry Technical Service Manager, tjgaydos@phileo.lesaffre.com
http://en.engormix.com/MA-dairy-cattle/nutrition/articles/benefits-sacch...
http://wiki.yeastgenome.org/index.php/What_are_yeast%3F
http://www.dakotayeast.com/yeast_history.html