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''Products using fermentation with fungi.''


[edit] Wine Fermentation

[edit] Introduction

The process by which wine is produced is called wine fermentation. Grapes are combined with sugar and yeast to yield alcohol and carbon dioxide. The process occurs in two major steps:

  1. Primary Fermentation
  2. Secondary Fermentation

The general formula for wine fermentation includes:

  • reactants - sugar and yeast
  • products - alcohol and carbon dioxide

The following list summarizes the process of wine fermentation in a few steps:

  • yeast is added to grapes
  • yeast converts natural sugars (glucose and fructose) into ethanol (alcohol) and carbon dioxide
  • carbon dioxide is released into air while alcohol remains in solution
  • fermentation is complete when alcohol content is tested to be 15% and yeast has been completely used up


[edit] Species Involved

The most common yeast used in wine fermentation is Saccharomyces cerevisiae. It is part of a fungal group called Ascomycota, a group which is characterized by the formation of asci (sac-like structure for spore formation)[2]. Saccharomyces cerevisiae, also known as 'baker's yeast', is a fungal organism with many uses in the food and beverage world. It is commonly used for these types of fermentation because of its use of glucose for energy, and its strong ability to adapt to differing environmental conditions. Some of these adaptations include:

  • Use of both aerobic and anaerobic fermentation to break down foods
  • Can survive in oxygen deficient environments
  • Can reproduce both sexually and asexually


Sexual and Asexual Reproduction in S. cerevisiae yeast
Sexual and Asexual Reproduction in S. cerevisiae yeast [4]
S. cerevisiae - Scanning Electron Micrograph (SEM) image
S. cerevisiae - Scanning Electron Micrograph (SEM) image [5]

Some examples of other yeasts involved in wine making from the Saccharomyces species are:

  • S. bayanus
  • S. beticus
  • S. chevalieri
  • S. fructum
  • S. diastaticus


Saccharomyces sp. are characterized by:

  • being a eukaryote - organisms which possess a membrane bound nucleus
  • have vegetative growth as haploid (1N) and diploid (2N)
  • can undergo conjugation (haploid to diploid)
  • can undergo sporulation (diploid to haploid)
  • reproduce by budding


[edit] History

Wine has been with us since the dawn of civilization and has followed humans and agriculture along diverse migration paths. Serendipity presumably played a part in its genesis more than 7,000 years ago: damaged grapes spontaneously fermented in harvesting vessels; curious farmers tasted the resultant alcoholic beverage; the curious farmers liked what they tasted and enjoyed its effects; said farmers preferred fermented grape juice to the unfermented fruit. The fate of the grape was sealed.

Wine Microbiology History
Wine Microbiology History [8]

One might argue that the seeds of science and technology, particularly biotechnology, were also sown at this time. Empirical observations of natural events and processes were harnessed in repeat experiments—which is to say, vintages—and improvements were made by trialling modifications to practices, retaining those that were beneficial and discarding failures, with the results communicated down through the generations.

Of course, early inventions and innovations in grape and wine production were based on little or no knowledge of the biology of grapevines or the microbes that drive fermentation. In fact, it would be several thousand years before it was even known that microscopic organisms exist: using a primitive microscope, Antonie van Leeuwenhoek observed cells for the first time in 1680.

Scientific knowledge grows at an exponential rate, and nowhere is this more evident than in the historical milestones of chemistry and biology that have shaped our understanding of the biology of the microorganisms that drive fermentation. Throughout the early decades of the twentienth century the place for S. cerevisiae in fundamental research was affirmed.

Genetics Research in Wine Science
Genetics Research in Wine Science [9]

The 1970s set the stage for another explosion of knowledge, sparked by the advent of gene technology and driven by a convergence of genetics, biochemistry, cell biology, microbiology, physical and analytical chemistry, as well as computing brought together under the banner of molecular biology. The research community now had a eukaryotic host that was amenable to genetic engineering, benefiting both fundamental research and offering the potential of precise engineering of novel strains for industrial applications. Ever since, S. cerevisiae has been one of the most important model organisms in molecular biology and emerging fields; breakthroughs and technological advances in molecular, systems, and now synthetic biology rarely happen without S. cerevisiae figuring somewhere prominently in the story.


[edit] Primary Fermentation

The first step in the fermentation of wine is called primary fermentation. It is also known as aerobic fermentation, because the reaction is open to the air. It is extremely important for oxygen to be present in the reaction for the Saccharomyces cerevisiae yeast to multiply rapidly. This process generally lasts for about 3-5 days, and is responsible for approximately 70% of the overall fermentation. Secondary metabolism is responsible for the other 30%, which is significantly less due to its anaerobic conditions.

[edit] Temperature Regulation

The temperature of the fermentation process must stay constant for primary fermentation to be effective. This optimal temperature is 72 degrees fahrenheit, but often ranges from 70-75 degrees. This range can still produce wine sufficiently and with a great flavour. If the temperature raises too high, primary fermentation may still proceed but the flavour of the wine will suffer. Other organisms that thrive in these temperatures may be the cause of this undesired flavour. If the temperature falls too low, the yeast may not ferment at all. The juice stays as it is, and no alcohol is produced. [11]

[edit] Processes Involved

Aerobic fermentation in S. cerevisiae is responsible for the production of alcohol through the breakdown of glucose. It occurs in the presence of oxygen. It is the ideal method of yeast to ferment because it produces the highest yield of ATP (energy providing molecule). This process is ultimately known as cellular respiration. In cellular respiration of fungal organisms, the major processes are:

  1. glycolysis
    1. Embden-Meyerhof-Parnass (EMP) pathway
    2. Pentose Phosphate Pathway (PPP) [12]
  2. citric acid cycle

The glycolysis pathway, which is in the presence of oxygen, yields 36 ATP per one molecule of glucose.

Glycolysis and Krebs/Citric Acid Cycle
Glycolysis and Krebs/Citric Acid Cycle

An important part of primary fermentation is the process of mixing. This process is important to allow continual oxygen into the wine barrel for continued aerobic fermentation. Carbon dioxide is realeased from the barrel when it is mixed, and is seen as a bubbling-like action of the liquid. This process is demonstrated and explained in further detail in this video:

[edit] Factors Affecting Alcohol Production

  • type of yeast strain
  • quantity of yeast population
  • temperature
  • wine cellar conditions (moisture, etc.)


[edit] Secondary Fermentation

Secondary fermentation of wine is also referred to as anaerobic or Malolactic Fermentation (MLF). During this process, L-malic acid is converted to L-lactic acid and CO2.

Conversion of malic acid to lactic acid by malolactic fermentation [15]

One consequence of MLF is a reduction in wine acidity with an increase in pH of about 0.2 units [16]. Malolactic fermentation can be carried out by a number of lactic acid bacteria but commercial strains of O. oeni such as ML-34, PSU-1, MCW, EQ-54, Viniflora, to name a few, have been used. [17].

[edit] Preparation of Starter Cultures

Before the availability of commercial cultures, wineries relied on native microflora to induce MLF. Under these conditions, promotion of MLF is accomplished by maintaining a temperature of 21ºC/70ºF, avoid adding sulfites, and maintaining a pH greater than 3.2. [18] Given that MLF can occur immediately after or several months after completion of alcoholic fermentation [19], there is a risk of spoilage because the wine is unprotected. Moreover, spontaneous MLF by unidentified lactic acid bacteria can produce unpredictable and/or undesirable flavor characteristics in wines. [20] Because of this, monitor the wine microscopically, check for off-aromas, and perform routine analysis such as quantifying malic and acetic acids is essencial. Although some wineries continue the tradition of using native microflora, winemakers increasingly inoculate grape must or wine with lactic acid bacteria starter cultures to improve the success of MLF. [21] Many strains of O. oeni are available in lyophilized, cultures frozen concentrates, and liquid forms.

Lyophilized starter cultures usually contain high populations of viable bacteria (>108 CFU/g) and are easy to ship and store. Media for preparing malolactic starter cultures frequently contain grape or apple juice supplemented with other nutrients like yeast extract, peptone, and Tween 80. [22]

[edit] Strain Selection

Many strains of O. oeni are now commercially available to winemakers for inducing MLF in wine. [23]


[edit] Timing of Inoculation

When MLF starter cultures are used in the winery, the winemaker will be faced with the decision as to the timing of bacterial inoculation. Some researchers suggest that early inoculation of malolactic bacteria is best for inducing MLF because rapid fermentation would allow winemakers to complete finishing operations sooner. [25] This notion suggests that yeast may not yet have depleted nutrients also essential for malolactic bacteria. Furthermore, ethanol and SO2, compounds known to be inhibitory to O. oeni [26], would be present in lower concentrations. Early inoculation of malolactic bacteria has resulted in successful completion of both the alcoholic and malolactic fermentations. [27]

[edit] Use of Schizosaccharomyces

Since Schizosaccharomyces utilizes L-malic acid, this yeast has been proposed as an alternative to using bacteria for deacidification of high-acid musts. [28]


[edit] Beer Fermentation

Beer is a trademark item in many situations in every day life. It is consumed at parties, at home with friends, with meals, beer tasting events or general stress relief, beer has become an accepted part of many lives. In Canada, the legal drinking age in most provinces is 19 years. At this age and beyond, people consume beer in various amounts and often times, do not even know how their beverage is actually made! Beer comes in two main types: Ale and Lager. These are in essence the same in the sense that they contain a certain percentage of ethanol yet how the reaction to make the beer is quiet different visually. Ales are "top-fermenting", in other words, the yeast ferments and is release at the top of the vessel. Whereas, lagers are "bottom-fermenting" and the release is from the bottom of the vessel. [30]

Beer favourites are based on the overall taste of the beer: initial, on-going, and after taste. If you are a person whom enjoys tasting varieties of beers you will come across those which are bitter, sweet, have an awful initial taste and some with no after taste. These are all reliant on the type of grain used and how the fermentation occurs in the vessel.

[edit] History

In Ancient Times, beer was used in many different ways by different colonies of people. It was a crucial part of the culture for many groups. According to Professor Linda Raley of Texas Tech University, Babylonian clay tablets held the recipe for the beloved beverage as early as 4300 B.C. Beer was used in burial and medicinal rituals as well as certain rites and ceremonies. Unlike modern day society, beer was often reserved for royalty because it symbolized the riches they had. At this point in time, the variety was nothing compared to what it is today. Merely 20 varieties of beer existed in the Babylonian colony, which is present day Iraq. Each group of people in these times used grains that were native to their lands, thus giving rise to the different varieties. These varieties include:

  • Millet (Africa)
  • Maize (Africa)
  • Cassava (Africa)
  • Persimmon (North America)
  • Sweet potato (Brazil)
  • Rice (Japan)
  • Wheat (China)
  • Guass (Russia)
  • Barley (Egyptians)
  • And unrecorded, potentially dozens more!

(L. Raley) [31]

At this point in time, beer was brewed in small barrels and bottles. At such a small scale, beer was not easy to come by like it is today. As time has passed, developments of various methods, in which to produce mass amounts of beer at one time, have been created. Large silos filled with beer that is fermenting can now be found at the many beer factories! Mass production has taken a lift, beer is made and sold at high rates thanks to the use of large fermenting vessels such as the one below. Although beer making has revolutionized, the yeast species (Saccharomyces spp.)that acts as a catalysis has remained the same for all of these years!


[edit] Requirements for Fermentation

Beer is not magically created! In order for the fermentation of beer, microorganisms, water and grain are required.

  • Saccharomyces sp. is the most common organism used in the fermentation of beer. Ales (top-fermenting beer) require Saccharomyces cerevisiae in order for the correct processes to occur. Lagers (bottom-fermenting beer) require Saccharomyces uvarum which produces run-off from the bottom of the vessel. The yeast created during fermentation is generally a thick, white-yellow puff.
  • Water that is purified and free of toxins is needed
  • Refined grains are also required. These grains contain glucose molecules which are the starting point of the fermentation pathway.

All of these materials together in specific portions are based on the type of ale or lager being produced.

[edit] Chemical Process

Glucose found in the grains is the starting material for the process known as Glycolysis. Glycolysis is the anaerobic catabolism of glucose. This process is a series of electron transfers which lead to the production of two pyruvic acid molecules. These molecules can become ethanol and carbon dioxide. Glycolysis produces NADH; which is an electron transport molecule. The surplus of this molecule must be used up, this is why oxidation occurs. This oxidation finalizes the reaction moving the reaction from pyruvate to ethanol.

Summary of Process

1. Carbon dioxide is released from pyruvate

2. Carbon dioxide is converted into acetaldehyde

3. Acetaldehyde is reduced by NADH to ethyl alcohol thus regenerating the requirement of production of NAD+ which is produced in Glycolysis. [33]


[edit] Fun Facts About Beer

Brought to you by The Beer Store

  • A person whom enjoys consuming beer can be called a CEREVISAPHILE!
  • The recipe for beer is one of the oldest known to man!
  • "Beer Beer Beer, Babala, Beer Beer Beer". This rhyme stems from the Babylonians whom are the creators of the world known BEER!

[edit] Bread Fermentation

[edit] Introduction


There are many different types of dough’s and pastries that require the process of fermentation. These can vary from normal breads to cinnamon buns, pizza dough, croissants, and many more. Without the process of fermentation breads would be very hard and flat. The process of fermentation allows the bread to have different textures depending on how it was fermented. The fermentation process in bread can also depend on the breakdown of different starches in the flour that are aiding in the formation of carbon dioxide bubbles [35]. The carbon dioxide bubbles produced allows the bread to expand and have bubbly structures within the dough. There are hundreds of different bread recipes that can be used for bread fermentation as well as many different species that can be used in order for the fermentation process to occur. Bread fermentation is a very old process that is widely known and used across the entire world.

[edit] History

The first evidence of bread fermentation was in the ancient Egyptian hieroglyphs over 5000 years ago [35]. Bread was first made with flour from raw grain, malt, and yeast [35]. In 1859, Louis Pasteur discovered that wine yeast cells must be living organisms in order for the process of fermentation to occur[35]. From this discovery, the use of beer barm was then used to aid the process of bread fermentation [35]. Beer barm is the yeast which is formed on malt liquors while they are fermenting [35]. Many years later it was then discovered that specialized yeasts could be used in the process of bread fermentation. These specialized yeasts are now commercially produced across the world for many other fermentation processes [35]. The main process of bread fermentation remains very similar to the process used many years ago. Now days, bread is commercially made in large portions therefore, large equipment is required for production. There is also much more complexity now as to what type of bread can be made compared to 5000 years ago when only one recipe was used.

[edit] Processes Involved


The process of bread fermentation is relatively simple, with very few ingredients involved. Bread recipes generally call for yeast, sugar, milk, water, flour, butter and salt [35]. The first step of making bread is to combine the yeast, sugar, water and milk in a warm area until fermentation begins to occur[35]. Once fermentation begins to occur, the flour, butter and salt are then added to the mixture and mixed until the dough is smooth[35]. The final mixture is then left in a warm place to double in size. Once the dough has doubled in size it is then kneaded and placed in a baking sheet where it is left for one more our to rise before baking[35]. The loaf is then baked in the oven at various temperatures and times depending on what the recipe calls for. Typical temperatures are usually between 75 and 85 degrees Fahrenheit.

Throughout the process of making bread there are two different stages of fermentation that occur. The first stage of fermentation occurs while the bread is left to double in size for the first time[35]. During this time the yeast produces carbon dioxide bubbles, which will determine the breads final texture once it is left to bake[35]. The second stage of fermentation is called proofing or proving. During the proofing stage carbon dioxide is also formed which allows the dough to double in size one last time before baking[35].

The chemical equation for the process of bread fermentation is: C6H12O6 → C2H5OH + 2 CO2[35]

[edit] Species Involved


There are many different types of species that can be used in bread fermentation but the most common is Saccharomyces cerevisiae. Saccharomyces cerevisiae is also widely known as bakers yeast in the baking industry. Saccharomyces cerevisiae is also commonly used in many other types of fermentation processes such as beer and wine fermentation.

Saccharomyces cerevisiae is not the only type of yeast that can be used in bread fermentation. Many other species from the Saccharomyces sp. can also be used such as:

  • Saccharomyces paradoxus
  • Saccharomyces cariocanus
  • Saccharomyces mikatae
  • Saccharomyces kudriavzevii
  • Saccharomyces arboricolus[38]

[edit] Gasoline Fermentation

[edit] Introduction

E85 pump
E85 pump

E85 is a gasoline blend composed of high levels of ethanol mixed with petrol. It can be used in Flexible Fuel Vehicles (FFVs) which are automobiles that can run on fuel containing a combination of unleaded gasoline and up to 85% ethanol [40]. Possible sources of plant material for conversion to ethanol include sugarcane, wheat straw, rice, stover (remaining leaves and stalks of maize crop post-harvest), cereal grains, and bagasse (the fibrous leftover sugarcane material after sugarcane juice has been extracted). [41]

[edit] Processes and Organisms Involved

Ethanol production from corn can go through either a dry milling process or a wet milling process. In dry milling, corn is ground up to a powder and then water and enzymes such as amylase are added to produce sugars. Yeasts are subsequently added to the mixture to convert the sugars into ethanol.[42] Wet milling involves separation of the fiber, gluten and starches of the corn by addition of water and acid. [42] The starch and water undergo fermentation to produce ethanol and carbon dioxide. [42]

Dry milling process
Dry milling process
Wet milling process
Wet milling process

Trichoderma viride, Chrysosoporium lucknowense, and Penicilium verruculosum are some of the fungal species utilized by humans for their biodegradative properties on plant biomass material. [41] Often times plant biomass material contain lignin and hemicellulose which must be degraded before glucose fermentation to ethanol can occur. In such cases, a biological pretreatment process involving fungal species such as Phanerochaete chrysosporium which can secrete lignin degrading enzymes can help pre-digest the plant material.[45] Gloeophyllum trabeum, a saprophytic species important for mantaining soil fertility, can also be used to break down cellulose. [45]

Trichoderma viride, a soft-rot mould, [45]was originally isolated by Mandels and Elwyn T. Reese from rotting military uniforms in the Solomon Islands during World War II. [41] Discovery of this species inspired further research investigating the fungal mechanisms and enzymes used to convert polymeric cellulosic material into ethanol or glucose. Subsequent experiments using high-energy electrons and UV irradiation on Trichoderma viride found that this species secretes a protein containing a mixture of enzymes. These enzymes include cellobiohydrolase (~70%) capable of cleaving cellobiose (beta, 1-4 diglucoside) in cellulose, endoglucanases (~30%) which split internal linkages by hydrolysis at random, and beta-glucosidases (~1%) which produce glucose via hydrolysis of cellobiose and cellodextrins.[41]

This process can be summarized in this equation: The proposed process of cellulose degradation and subsequent conversion to ethanol [41]

Here is an animation explaining the simplified process of producing E85 gasoline fuel from various crops:


[edit] History

Rising petrol prices and the fact that fossil based fuels are non-renewable resources have driven research towards finding alternate renewable fuel sources. In addition, signing of the Kyoto Accord was motivation for countries to search for energy sources which produce less pollution than gasoline. Brazil is one of the first countries to use ethanol based gasoline, using fermentation of sugarcane as the source of glucose for ethanol production, and producing most of their cars to run on 95% ethanol by the 1980s. [45] There has been concern that converting corn into fuel (such as its use in E85 gasoline) will drive up the prices of corn and other staple foods such as rice, wheat and maize. [41]

[edit] Trivia

T. reesi is a strain of Trichoderma viride that produces high yields of cellulase, and is named after Elwyn T. Reese, the scientist whose work helped to illuminate the process by which this fungus converts plant biomass into ethanol. [41]

[edit] Bioremediation

Yeasts have recently begun to be used to clean up oil spills and other polluted environments through bioremediation, which is the process whereby living organisms, such as bacteria or plants, are used to remove or neutralize contaminants in the environment, such as polluted soil or water [46]. In particular, oil spills typically occur due to:

  • Routine shipping operations
  • Oil refineries
  • Industrial and municipal waste disposal
  • Tankers accidents
  • And more [47]

Bioremediation can be subdivided into 2 categories:

  • Bioaugmentation
  • Biostimulation

Bioaugmentation is the addition of microorganisms that degrade hydrocarbons to an environment in order to lower the amount of contaminants in that environment [48]. This method is not typically used mainly because there are already microorganisms present in the environment that can degrade the crude products the majority of the time. Also, adding in non-native microorganisms may result in competition between the introduced species and the native species, which may cause problems for the ecosystem [48].

Biostimulation is the addition of nutrients to the contaminated environment so that microorganisms that degrade hydrocarbons which are already present in the environment can break down the pollutants more efficiently [48]. This method is used more frequently in industry because it removes the factor of competition between organisms. Typically, the limiting factors in the degradation process are nitrogen and phosphorus, and carbon is present in excess due to the pollutant [48]. There are many factors that need to be examined before nutrients can be added into the environment in order to ensure the nutrients will be taken up effectively and remain in the system. These include:

  • Density of water
  • Tides
  • Current

The speed of the bioremedial process is also affected by various physical and chemical factors [48]:

  • Temperature
  • Surface area of the pollutant
  • Oxygen
  • Nutrients
  • pH
  • composition of the pollutant

Temperature plays a major role. Warmer temperatures will allow for higher rates of degradation because the pollutant will not be as thick, meaning the organisms will have a greater surface area to access for their enzymes to attack. A lighter, thinner pollutant will also help the microorganisms to access oxygen for fermentation.

[edit] Historical Methods of Bioremediation

In the past, there have been various methods for cleaning up oil spills, [49]:

  • Physical methods:
    • Booms
    • Washing
    • Soil movement and tilling
    • Mechanical removal
  • Chemical methods:
    • Demulsifiers
    • Solidifiers

These methods can be time consuming and expensive depending on the required equipment. Some of the methods, such as mechanical removal, can only be used under certain conditions, such as when there is only a small amount of oil in the water. Others, such as the chemical methods, are very effective but are not healthy for the environment [49]. The natural methods used, such as soil movement and tilling, are preferred for the environment, but they take the most amount of time [49].


There are a few disadvantages to using bioremediation:

  • Competition between native and introduced organisms
  • Difficult to perform field studies for data

[edit] Organisms and Breakdown Processes

There are many different types of yeast that are used in bioremediation. The following table gives some examples of these species:


The most common yeast used in bioremediation is Yarrowia lipolytica [50]. Y. lipolytica is part of the Ascomycota and can be isolated from dairy products and other chilled foods including cheese, yogurt, and sausages. This yeast is also naturally found in oil fields, indicating that it uses oil as a carbon source naturally. This yeast is non-pathogenic and is an obligate aerobe, meaning it cannot live without oxygen. [51] In order for Y. lipolytica to be able to survive the anaerobic (oxygen-lacking) conditions, it uses its hyphae to obtain oxygen from the surface. These hyphae, which are long filamentous structures that are the main mode of vegetative growth of a fungus, also secrete hydrolytic enzymes that are able to degrade oil and other crude heavy metals [52][53].


Another type of yeast, Pichia guilliermondii, is used to help remove harmful metals and metalloids from contaminated environments [55]. This yeast traps the metals in small vesicles and takes them up into the cell to get rid of them through various reduction-oxidation reactions (reactions in the cell that use the transferring of electrons to help drive other reactive processes).


Yeasts secrete hydrolytic enzymes from their hyphae into the extracellular space (outside of the cell). These enzymes cleave the hydrocarbon chains in oil and other pollutants into carbon dioxide and water. Yeasts perform this reaction without the production of insoluble polycyclic aromatic hydrocarbons (PAHs) that are known as ‘tailings’ and are highly toxic to the atmosphere [57]. This is possible because the yeasts use up the hydrocarbons in their own metabolic processes (i.e. during fermentation). During this process, toxins and other pathogens are also removed from the contaminated environment, leaving clean water or soil.


In order for these processes to occur efficiently, oxygen (either from the atmosphere or from water) and a balance between carbon, nitrogen, and phosphorus are required[59]. The following video further explains the breakdown of hydrocarbons in contaminants by yeasts and demonstrates just how effective this process is:

[edit] Cheese Fermentation

Yeast, depending on its properties, can have a negative or positive effect in the producing a certain type of cheese. It can reduce acidity, lower pH, develop a distinct aroma or it can give unpleasant taste and texture. Processing milk to ferment allow longer storage and easily transport without spoilage. Cheese making was made from milk produce animals such as goat, buffalo, cattle, reindeer.

[edit] History

A story of a traveller from a nomadic tribe in Asia was heading towards Europe when the traveller discovered the milk stored in the stomach pouch of a sheep was turned into curds. Exposure of the stomach pouch to the sun, activated the enzyme renin which cause the milk to curdle but scholar have agreed that anyone with milk producing animals may have stumble on the cheese incident. Archeologist have discovered fragments of sieved-like pottery, along with cattle bones, in north central Poland that was theorized and proven to be used to separate the curds from the whey in milk fermenting. The pottery was dated to between 7,200 to 6,8000 B.C.E.[60] The Romans is known to have master the cheese ripening after conquering Gaul and bringing the artisan of cheese making. The word cheese have been made reference by Homer(c.1184 B.C.E.) which first mention of feta, Aristotle(384-322 B.C.E.) milk used by horse and mule, Varro (c.127 B.C.E.) the production of cheese went from home to commercial production,and Columella (c.50 B.C.E.) gave detail accounts of processing cheese.[61] After the fall of the Roman Empire, some cheese recipes were stored in some monasteries or forgotten, and few innovative cheese were created in the Middle Ages and still existed today. The European monks developed new ripening and aging techniques of cheese and examples of these cheeses are: Gorgonzola 879 C.E., Roquefort 1070 C.E., English Cheddar 1500 C.E., Parmesan 1579 C.E., Gouda 1697 C.E., and Camembert 1791 C.E.[61] Cheese travelled to the New World by pilgrims in 1620. The first cheese factory was built in the United States by Jesse Williams in Oneida County, New York in 1851.[62] The first Canadian cheese factory was opened in Norwich, Ontario, in 1864, known as 'The Pioneer'.[63] In 1880, the United States had 3,923 dairy factories which were reported to have made 216 million pounds of cheese that same year.[62] In 1968, France aired the first television ad for cheese le Boursin.

[edit] Process

The process of curdling milk and goes to cheddar or introduce secondary microflora.
The process of curdling milk and goes to cheddar or introduce secondary microflora.[64]

Extracting the cheese, also known as curds is the result of introducing bacteria to separate the two proteins in the milk. The two proteins present are the casien, 80%, and the whey 20%.[65] To produce a sour curd a culture of bacteria is introduced and to give the curd a sweeter taste, the enzyme renin to curdle the milk. The curd can immediately be processed for soft cheese, unripened stage, or go through further stages for ripening. Moisture is further extracted from the curds to its desired quantity for specific cheese to ripen. Too much moisture will prevent the cheese to ripen to desire taste and cut down its shelf life. The curds are molded and shaped and given secondary microflora to give its desirable texture and aroma.[64] Yeast role in dairy fermentation may interact differently with other microorganisms in three situations where it can inhibit or eliminate undesired microorganims, or inhibit starter culture, or be a positive contribution for starter cultures in fermenting and maturing of cheese ripening.[66] Most mould cheese examined have yeast culture that are lipolytic activity and consume lactose, glucose, galactose, and citrate.[66]

Homemade curds with whey being strained.
Homemade curds with whey being strained.[67]

[edit] Yeast Organism Involved

Two types of yeast involved in the ripening are classified either by their lipolytic or proteolytic activity. Lipolytic activity consist of lipases enzymes breaking down the lipids. Proteolytic activity is carried out by small peptide and amino acids to breakdown bitter peptides.

The one yeast species to be predorminant found in semi-soft cheese is Debaryomyces hansenii with its anamorph form C. famata, G. geotrichum with teleomorph form Galactomyces candidus are present in soft cheese, followed by other yeast species Yarrowia lipolytica, Saccharomyces cerevisiae, Kluyvermyces lactis and K. marxianus.[66]

D. hansenii is NaCL tolerant species and is used as a model organism for study of NaCl tolerance mechanisms in eukaryotic cells. Some strains of D. hansenii can uptake lactic and citric acids as well as galactose in the presence of high concentrations of salt.[66] It plays an important role on the surface under high humidity, low, temperature, low pH, and high concentration of salt and as a starter culture for blue and white mould cheeses.

Yarrowia lipolytica is found in some blue cheese, preferably the interior, and can grow 4.0-6.0 pH at 10o C but are inhibited by high concentration of NaCl. It has been scored highest for texture, flavour, and body and is a proteolytic specie that can compete with D. hansenii and S. cerevisiae making a great starter for ripening.[66] Chritine Dodd, a professor from University of Nottigham revealed that Y. lipolytica the only secondary microflora to give a distinct aroma to blue cheese.[68]

Geotrichum candidum assist on developing soft cheeses, such as Camembert, and semihard cheeses, such as St. Nectaire and Reblochon. G. candidum strains with filament fungi and high proteolytic activity are selected for aiding in texture and thickness of the rind, and plays a role in gas exchange on the surface with low density.[69] G. candidum consumes lactate raising the pH and contributes to the development of Penicillium and Brevibacterium linens.[70] Some strains of G. candidum are able to produce thioesters and sulphides which contributes to a typical taste giving soft cheese its flavour.[70] Also, it produces alkaline metabolites, nutrients for Penicillium increasing pH whereby mould can be formed on the surface of the cheese to give cream texture to Camemembert type.[71]

Wyder and Puhan examined selected yeast involvement in some cheese process and found Clavispora lusitaniae, Pichia jadinii, and Williopsis californica fermented the cheese using lactose, giving a high pH yielding an alcoholic, acidic, fermented or fruity aroma.[72]

In blue cheese D. hansenii, Yarrowia lipolytica, Kluyveromyces marxianus, Kluyveromyces lactis and Candida spp. have been found in its ripening stage as proteolytic and lipolytic activity assisting Penicillium roqueforti development. In a study by Viljoen et al. examining the content of yeast present in blue cheese either in Danish-style or Gorgonzola-style found D. hansenii to be the dominant species representing greater than 50% isolated on surface and interior on Danish-style.[73] Torulaspora delbrueckii was the next in abundance that can found but was not detected in the raw milk and a possibility it cannot be killed through pasturization. For Gorgonzola-styled, D. hansenii, C. versatilis, Trichosporon beigelii and T. delbrueckii were isolated mainly on the exterior surface and the interior consisted of D. hansenii with more than 30% of the population followed by C. versatilis second most abundant species.[73]

S. cerevisiae has been found less abundant in cheese though it can be a used as a culture starter making smaller curds by assimilating casein thereby giving a softer texture and aid in the growth of Penicillium roqueforti increasing the aroma.[66] It is found in Water Buffalo mozarella breaking down the galatose which the bacteria cannot metabolize.[66]

[edit] Fun Facts

Remains of cheese has been found in 4,000 year old Egyptian tomb.[74] It takes 10 litres of milk to make 1 kilogram of hard cheese.[74] Pizza Hut uses about 140 million kilograms of cheese per year.[74] Carrot juice and marigold petals have been used to colour cheese.[75] A giant wheel of cheddar weighing 1,000 lbs was given to Queen Victoria as a wedding gift.[75]

[edit] References

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