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I noticed that EMP produces 2 ATP and EDP produces 1 ATP. Does that mean that if more ATP is present that would give more energy for fermentation and lowering the pH of a system?
The Difference Between Fermentation and Anaerobic Respiration
- M.A., Technological Teaching and Learning, Ashford University
- B.A., Biochemistry and Molecular Biology, Cornell University
All living things must have constant sources of energy to continue performing even the most basic life functions. Whether that energy comes straight from the sun through photosynthesis or through eating plants or animals, the energy must be consumed and then changed into a usable form such as adenosine triphosphate (ATP).
Many mechanisms can convert the original energy source into ATP. The most efficient way is through aerobic respiration, which requires oxygen. This method gives the most ATP per energy input. However, if oxygen isn't available, the organism must still convert the energy using other means. Such processes that happen without oxygen are called anaerobic. Fermentation is a common way for living things to make ATP without oxygen. Does this make fermentation the same thing as anaerobic respiration?
The short answer is no. Even though they have similar parts and neither uses oxygen, there are differences between fermentation and anaerobic respiration. In fact, anaerobic respiration is much more like aerobic respiration than it is like fermentation.
pH affects the shape of proteins. In the case of fermentation a collection of enzymes is responsible for the metabolic processes that occur. - an enzyme is a protein which performs a metabolic process. For example sucrase is an enzyme which breaks sucrose down into fructose and glucose. They are kind of like organic catalysts.
Proteins are made of amino acids strung together in a long line, based off DNA. The amino acids bond up into a long polymer. Then cross linking occurs between the R groups on the amino acids. This makes the unique shape of the protein, because the cross-linking turns the protein into a 3-d shape.
Amino acids may be acidic amino acids, or basic amino acids, due to the R group on the amino acids. If the pH is increased, this affects the shape of proteins, by disrupting the bonds in the protein. In the case of fermentation, you say the rate increases when it get's more acidic - when the pH is lower. This is because the organisms - the yeast - producing the enzymes to ferment glucose, have adapted to acidic conditions. This means that through natural selection the enzymes today have been selected because they work best in acidic conditions, which bend the protein into the correct shape to allow fermentation to occur.
In this article it says that 10 enzymes turn glucose in pyruvic acid:http://en.wikipedia.org/wiki/File:Pyruvic-acid-2D-skeletal.png
And then two enzymes turn this into ethanol and CO2. The last two enzymes function best in acidic conditions, presumably because they have evolved to work best in the acidic conditions made by the pyruvic cid. However all fermentation stops after the pH drops below about 4.2. The optimum pH is about 4.8 - 5.0. After this we can assume that the pH bends the proteins out of shape too much, and the protein is said to have been denatured.
So to conclude. The rate increases because enzymes are all suited to specific conditions, dictated by natural selection - the conditions they have evolved around - and in the case of fermentation the last 2 enzymes - turning pyruvic acid to ethanol and CO2 - work best in acidic conditions, as they have evolved to those conditions. But increase the pH too much. and the protein denatures, and fermentation stops completely.
The word “ fermentation ” has undergone many changes in meaning during the past hundred years. According to the derivation of the term, it signifies merely a gentle bubbling or boiling condition. The term was first applied when the only known reaction of this kind was the production of wine, the bubbling, of course, being caused by the production of carbon dioxide.
It was not until Gay-Lussac studied the chemical aspects of the process that the meaning was changed to signify the breakdown of sugar into ethanol and carbon dioxide ( 316 ). It was Pasteur, however, who marked the birth of chemical microbiology with his association of microbes with fermentation in 1857. He used the terms “cell” and “ferment” interchangeably in referring to the microbe. The term “fermentation” thus became associated with the idea of cells, gas production, and the production of organic byproducts.
The evolution of gas and the presence of whole cells were invalidated as criteria for defining fermentation when it was discovered that in some fermentations, such as the production of lactic acid, no gas is liberated. Moreover, other fermentation processes could be obtained with cell-free extracts indicating that the whole cell may not be necessary.
The position was further complicated by the discovery that the ancient process of vinegar production, generally referred to as acetic acid fermentation, which yielded considerable quantities of organic byproducts, was a strictly aerobic process. Fermentation clearly needed to be redefined.
Although carbohydrates are often regarded as essential materials for fermentations, organic acids (including amino acids) and proteins, fats, and other organic compounds are fermentable substrates for selected microorganisms. It was soon realized that these substances play a dual role as a source of food and as a source of energy for the microorganisms ( 375 ). The energy produced by total combustion (oxidation) of the substance in a calorimeter is its potential energy. The nearest approach to complete oxidation biologically occurs with acidic oxidations, which, with glucose, yield carbon dioxide and water and result in the liberation of a considerable quantity of energy.
Under anaerobic conditions, only a fraction of the potential energy is liberated because oxidation is incomplete. In order to obtain an amount of energy equivalent to that obtained under aerobic conditions, several times as much glucose must be broken down under anaerobic conditions. There is, in consequence, a high yield of unoxidized organic byproduct.
Fermentation came to be regarded, then, as the anaerobic decomposition of organic compounds to organic products, which could not be further metabolized by the enzyme systems of the cells without the intervention of oxygen. The fermentation products differed with different microorganisms, being governed in the main by the enzyme complex of the cells and the environmental conditions. The economic value of these byproducts led to the development of industrial microbiology.
With the recognition of fermentation as an anaerobic process, parallels were drawn between the biochemistry of microorganisms and that of mammalian tissues. Because the intermediates of the metabolism of glucose were found to be the same, it was postulated that all fermentation processes must follow similar paths. Consequently, the microbial fermentation of carbohydrates was considered to be similar to mammalian glycolysis. This is why many authors use the terms “glycolysis” or “glycolytic pathway” to describe one method of anaerobic breakdown of carbohydrates by microorganisms and why “fermentation” became synonymous with “glycolysis.” The two processes differ, however, in two significant ways: (1) there is no storage of glycogen in bacteria, and (2) lactate is not always an end product or intermediate in the bacterial anaerobic breakdown of carbohydrates. In addition, during the 1950's it was discovered that various bacteria are able to use pathways other than the Embden-Meyerhof-Parnas pathway for anaerobic breakdown of carbohydrates. The application of “fermentation” to all of these processes required some other form of definition.
The intensive research into electron transport systems of microbial metabolism has partly clarified the position, although a number of aspects await attention. From research on the electron donor and acceptor systems, it is now clearly understood that all processes which have as a terminal electron acceptor an organic compound are called “fermentations.” With this definition, it is possible to state that acetic acid bacteria are not fermentative but respire aerobically. For other bacteria the definition is not restricted to the use of any particular pathway in the fermentative process.
It was also found that fermentative bacteria may dispense with the use of their cytochromes under anaerobic conditions, for their phosphorylation processes are substrate phosphorylations in which the electron donor is an organic substrate that transfers its electrons to an NAD + or NADP + system. The amount of NAD + in microorganisms, however, is limited and NAD + must therefore be regenerated if metabolism is to continue. Under anaerobic conditions, this regeneration can be accomplished by an oxidation–reduction mechanism involving pyruvate or other compounds derived from pyruvate. These reactions from pyruvate can vary considerably among microorganisms and therefore lead to the formation of characteristic end products that are used in bacterial classification. A short summary of the various end products formed from pyruvate is given in Table 9.1 and Fig. 9.1 . These end products and their formation are used in classification, and the various bacterial groups will be considered in more detail below.
The oxidative-fermentative test determines if certain gram-negative rods metabolize glucose by fermentation or aerobic respiration (oxidatively). During the anaerobic process of fermentation, pyruvate is converted to a variety of mixed acids depending on the type of fermentation. The high concentration of acid produced during fermentation will turn the bromthymol blue indicator in OF media from green to yellow in the presence or absence of oxygen .
Certain nonfermenting gram-negative bacteria metabolize glucose using aerobic respiration and therefore only produce a small amount of weak acids during glycolysis and Krebs cycle. The decrease amount of peptone and increase amount of glucose facilitates the detection of weak acids thus produced. Dipotassium phosphate buffer is added to further promote acid detection.
Fermentation Process of Cheese | Microbiology
Cheese can be defined as a consolidated curd of milk solids in which milk fat is entrapped by coagulated casein. Unlike fermented milks, the physical characteristics of cheese are far removed from those of milk.
This is because protein coagulation proceeds to a greater extent as a result of the use of proteolytic enzymes and much of the water content of the milk separates and is removed in the form of whey. Typically the yield of cheese from milk is of the order of 10%.
Cheese making can be broken down into a number of relatively simple unit operations. Slight variations of these and the use of different milks combine to generate the huge range of cheeses available today said to include 78 different types of blue cheese and 36 Camembert’s alone.
Classification of cheeses is made difficult by this diversity and the sometimes rather subtle distinctions between different types. Probably the most successful approach is one based on moisture content, with further subdivision depending on the milk type and the role of micro-organisms in cheese ripening (Table 9.7).
Cheese is a valuable means of conserving many of the nutrients in milk. In many people, it evokes a similar response to wine, playing an indispensible part in the gastronome’s diet and prompting Brillat-Savarin (1755-1826) to coin the rather discomforting aphorism that ‘Dessert without cheese is like a pretty woman with only one eye’.
Despite this, the attraction of a well-ripened cheese eludes many people and it is sometimes hard to understand how something that can smell distinctly pedal can yield such wonderful flavours. This paradox was encapsulated by a poet, Leon-Paul Fargue, who described Camembert as ‘the feet of God’.
Today cheese making is a major industry worldwide, producing something approaching 10 million tonnes per annum. Much is still practiced on a relatively small scale and accounts for the rich diversity of cheeses still available.
Large-scale industrialized production is increasingly important, however, and is dominated by one variety, Cheddar, which is now produced throughout the world, far removed from the small town in Somerset where it originated.
Cheddar cheese is particularly valued for its smooth texture and good keeping qualities, although products sharing the name can vary dramatically in flavour. In what follows we will describe the basic steps in cheese making with particular reference to the manufacture of Cheddar cheese.
Cow’s milk for cheese production must be free from antibiotics and sanitizing agents that might interfere with the fermentation. Although it is not compulsory, a heat treatment equivalent to pasteurization is usually applied at the start of processing. This helps to ensure a safe product and a reliable fermentation, although cheeses made from raw (unpasteurized) milk have been claimed to possess a better flavour.
The milk is then cooled to the fermentation temperature which, in the case of Cheddar and other English cheeses such as Stilton, Leicester and Wensleydale, is 29-31 °C. The starter organisms used in most cheese making are described as mesophilic starters, strains of Lactococcus lactis and its subspecies.
Thermophilic starters such as Lactobacillus helveticus, Lb. casei, Lb. lactis, Lb. delbrueckii subsp. bulgaricus and Strep, salivarius subsp. thermophilic are used in the production of cheeses like Emmental and Parmesan where a higher incubation temperature is employed.
The role of starter organisms in cheese making is both crucial and complex. Their central function is the fermentation of the milk sugar lactose to lactic acid. This and the resulting decrease in pH contribute to the shelf-life and safety of the cheese and gives a sharp, fresh flavour to the curd.
The stability of the colloidal suspension of casein is also weakened and calcium is released from the casein micelles improving the action of chymosin. After the protein has been coagulated, the acid aids in moisture expulsion and curd shrinkage, processes which govern the final cheese texture.
There are two different systems for uptake and metabolism of lactose in LAB. In most lactobacilli and Strep, salivarius subsp. thermophilus, lactose is taken up by a specific permease and is then hydrolysed intracellularly by β-galactosidase.
The glucose produced is fermented by the EMP pathway which the galactose also enters after conversion to glucose-6-phosphate by the Leloir pathway (Figure 9.7). Most lactococci and some lactobacilli such as Lb. casei take up lactose by a phosphoenol- pyruvate (PEP)-dependent phosphotransferase system (PTS) which phosphorylates lactose as it is transported into the cell.
The lactose phosphate is then hydrolysed by phospho-β-galactosidase to glucose, which enters the EMP pathway, and galactose- 6-phosphate which is eventually converted to pyruvate via the tagatose-6-phosphate pathway.
These pathways are of practical import in cheese making in the lactococci, lactose utilization is an unstable, plasmid encoded characteristic and loss of these genes can clearly have serious consequences for milk fermentation.
Using transduction techniques, molecular biologists have produced strains of Lactococcus lactis in which this property has been stabilized by integration of the lactose utilization genes in the chromosome.
The thermophilic lactobacilli, which employ a lactose permease and β- galactosidase, metabolize the glucose produced preferentially, turning to galactose only when lactose becomes limiting. This can be a problem in some products. The accumulation of galactose can give rise to a brown discolouration during the heat processing of Mozzarella cheese.
In Swiss cheeses such as Emmental, residual galactose can affect product flavour since propionic acid bacteria ferment it in preference to lactate. In doing so they produce a preponderance of acetic (ethanoic) acid which does not confer the usual nutty flavour associated with the equimolar concentrations of acetate and propionate produced by the Propionibacterium from lactate.
Lactic acid bacteria are nutritionally fastidious and require preformed nucleo­tides, vitamins, amino acids and peptides to support their growth. To grow to high cell densities and produce acid rapidly in milk, dairy starters must have proteolytic activity to overcome the limitation imposed by the low non-protein nitrogen pool in native milk.
These systems are comprised of proteinases, associated with the surface of the bacterial cell wall, which can hydrolyse casein proteins. Peptidases in the cell wall degrade the oligopeptides produced down to a size that can be transported into the cell (4-5 amino acid residues) where they are further degraded and utilized.
While this ability is essential to starter function, it also plays an important role in the development of cheese flavour during ripening or maturation. Citrate fermentation to diacetyl is required in some cheese varieties and starter cultures for these include species such as Lactococcus lactis subsp. diacetylactis or Leuconostoc cremoris.
Carbon dioxide is another product of this pathway and is important in producing the small eyes in Dutch cheese like Gouda or giving an open texture that will facilitate mould growth in blue-veined cheeses. In other cheese, such as Cheddar, this would be regarded as a textural defect.
To produce Cheddar cheese, starter culture is added at a level to give 10 6 -10 7 cfu ml -1 . In the past these cultures were grown-up in the dairy from stock cultures or from freeze-dried preparations bought in from commercial suppliers. Nowadays frozen, concentrated cultures that are added directly to the cheese vat are increasingly used because of their ease of handling and the greater security they offer the cheese maker.
This applies particularly to the risk of bacteriophage inhibition of the fermentation which has been a major preoccupation of the cheese maker since it was first identified in New Zealand in the 1930s. Problems of phage infection are not confined to cheese making but have also been encountered in the production of yoghurt and fermented meats.
A bacteriophage is a bacterial virus which in its virulent state infects the bacterial cell, multiplies within it, eventually causing the cell to burst (lysis). When this occurs during a cheese fermentation, acidification slows or even stops causing financial losses to the producer as well as an increased risk that pathogens might grow.
An important source of phage in cheese making is thought to be the starter culture organisms themselves which carry within them lysogenic phages that can be induced into a virulent state. Problems occur particularly when starters contain a single strain or only a few strains and the same culture is re-used over an extended period.
During this time, phages specific to that organism build up in the plant and can be isolated from the whey and from environmental sources such as drains and the atmosphere, increasing the chance of fermentation failure.
In the past, control of this problem has been based on the observation of rigorous hygiene in the dairy, the rotation of starter cultures with differing phage susceptibilities and propagation of starters in phage-inhibitory media which contain phosphate salts to chelate Ca 2+ and Mg 2+ required for successful phage adsorption to the bacterial cell.
LAB possess their own resistance mechanisms to phage infection which include restriction/ modification of non-host DNA, inhibition of phage adsorption by alteration or masking of specific receptors on the cell surface, and reduction of burst size (the number of phages released per infected cell).
Most of these mechanisms appear to be plasmid encoded and this has opened the way for new strategies for phage control so that trans-conjugants with enhanced phage resistance are now available.
A time course for the production of Cheddar cheese showing pH changes and the timing of different process stages is shown in Figure 9.8. A good starter should produce around 0.2% acidity within an hours incubation. It will multiply up to around 10 8 -10 9 cfu g -1 in the curd producing an acidity of 0.6-0.7% before its growth is stopped by salting.
After about 45 min rennet is added. The time of renneting and the amount added are other important variables in cheese making which differ with cheese type. Rennet is a preparation from the fourth stomach or abomasum of suckling calves, lambs or goats.
Its most important component is the proteolytic enzyme rennin or chymosin which cleaves k-casein, the protein responsible for the stability of the casein micelle, between phenylalanine 105 and methionine 106.
This releases a 64 amino acid macro-peptide into the whey leaving the hydrophobic para-k-casein attached to the micelle. Loss of the macro-peptide leads to the formation of cross-links between the micelles to form a network entrapping moisture and fat globules.
Authentic chymosin is produced as a slaughterhouse by-product but microbial rennets are available, produced from fungi such as Mucor miehei, Mucor pusillus and Endothia parasitica. These lack the specificity of animal rennet and have been associated with the production of bitter peptides in the cheese.
Now however the genes for chymosin have been cloned into a number of organisms and nature-identical chymosin is available commercially, produced using the bacterium E. coli and yeasts.
After 30-45 min, coagulation of the milk is complete and the process of whey expulsion is started by cutting the curds into approximately 1 cm cubes. Whey expulsion is further assisted by the process known as scalding when the curds, heated to 38-42 °C, shrink and become firmer.
The starter organisms are not inhibited by such temperatures and continue to produce acid which aids curd shrinkage. Cheeses produced using thermophilic starters can be scalded at higher temperatures without arresting acid development. When the acidity has reached the desired level (generally of the order of 0.25%), the whey is run off from the cheese vat.
It is at this stage that the process known as cheddaring occurs. The curd is formed into blocks which are piled up to compress and fuse the curds, expelling more whey. Nowadays the traditional manual process is mechanized in a cheddaring tower.
At the end of cheddaring, the curd has a characteristic fibrous appearance resembling cooked chicken breast. The blocks of curd are then milled into small chips. This facilitates the even distribution of salt which, in Cheddar, is added at a level of between 1.5 and 2% w/w. The salted curd is formed into blocks which are then pressed to expel trapped air and whey.
Finally the cheese is ripened or matured at 10°C to allow flavour development. During this stage, which can last up to five months to produce a mild Cheddar, the microflora is dominated by non-starter lactobacilli and a complex combination of bacterial and enzymic reactions give the cheese its characteristic flavour.
In particular, proteases and peptidases from the starter culture .continue to act, even though the organism can no longer grow. With other proteases from the rennet, they release free amino acids (principally glutamic acid and leucine in Cheddar) and peptides which contribute to the cheese flavour.
In some cases this can give rise to a flavour defect: casein proteins contain a high proportion of hydrophobic amino acid residues such as leucine, proline and phenylalanine and if they are degraded to produce peptides rich in hydrophobic residues, the cheese will have a bitter taste.
The lipolytic and proteolytic activities of moulds play an important role in the maturation of some cheeses. In blue cheeses such as Stilton, Penicillium roquefortii and P. glaucum grow throughout the cheese.
Both can grow at reduced oxygen tensions, but aeration is improved by not pressing the curds and by piercing the blocks of curd with needles. P. camembertii and P. caseicolum are associated with surface-ripened soft cheeses such as Camembert and Brie.
The keeping qualities of cheese vary with the type but are always much superior to those of milk. This is principally the result of the reduced pH (around 5.0 in Cheddar), the low water activity produced by whey removal and the dissolution of salt in the remaining moisture.
Under these conditions yeasts and moulds are the main organisms of concern. The latter are effectively controlled by traditional procedures to exclude air such as waxing or by modern refinements such as vacuum packing.
The Krebs cycle (also called the tricarboxylic acid cycle or citic acid cycle) functions oxidatively in respiration and is the metabolic process by which pyruvate or acetyl
SCoA is completely decarboxylated to CO2. In bacteria, this reaction occurs through acetyl
SCoA, which is the first product in the oxidative decarboxylation of pyruvate by pyruvate dehydrogenase. Bioenergetically, the following overall exergonic reaction occurs:
If 2 pyruvate molecules are obtained from the dissimilation of 1 glucose molecule, then 30 ATP molecules are generated in total. The decarboxylation of pyruvate, isocitrate, and α-ketoglutarate accounts for all CO2 molecules generated during the respiratory process. Figure 4-6 shows the enzymatic reactions in the Krebs cycle. The chemical energy conserved by the Krebs cycle is contained in the reduced compounds generated (NADH + H + , NADPH + H + , and succinate). The potential energy inherent in these reduced compounds is not available as ATP until the final step of respiration (electron transport and oxidative phosphorylation) occurs.
Krebs cycle (also tricarboxylic acid or citric acid cycle).
The Krebs cycle is therefore another preparatory stage in the respiratory process. If 1 molecule of pyruvate is oxidized completely to 3 molecules of CO2, generating 15 ATP molecules, the oxidation of 1 molecule of glucose will yield as many as 38 ATP molecules, provided glucose is dissimilated by glycolysis and the Krebs cycle (further assuming that the electron transport/oxidative phosphorylation reactions are bioenergetically identical to those of eukaryotic mitochondria).
Simple Kimchi recipe
Kimchi is one of the oldest fermented foods that might have been around for the past 2000 years. There are more than 150 different variations to the basic kimchi. The following recipe is rather simple and does not need any fish sauce, daikon radish or chili paste.
- 2 large heads of Napa cabbage sliced thinly
- Green onions – 2 large bunches – sliced
- 1 head of garlic minced
- 1-2 tbsp ginger grated
- 1-2 tbsp red pepper flakes
- 3-4 tbsp salt
- Combine all ingredients in a large bowl.
- Massage the salt into the veggies.
- Crush the veggies using a cabbage crusher to release juices.
- Keep pounding until enough liquid is formed. Ideally the liquid should cover the veggies.
- Place the mixture in clean, sterile glass jars and press the veggies down into the brine.
- Cover the jar with a tight lid.
- Culture at 65°F to 70°F (18°C to 21°C) until desired texture and flavor is achieved. You might have to burp the gas daily if you are using an airtight lock seal. This helps release pressure.
- Once the kimchi is done, store in tightly sealed jar in a cool place. The flavor will continue to develop as the kimchi ages.
Hi! I’m Gigi. A fermentation nerd passionate about healthy food and great diet. I believe that our wellbeing and beauty starts in our gut and that each of us has a responsibility to get informed, take action, and look after their body. I’m here to spread that message, bring back the benefits of ancient nutrition to modern life, and show you all the latest cool ways to ferment and preserve food at home.
Yeast Fermentation Lab Report
Fermentation is a metabolic pathway that produce ATP molecules under anaerobic conditions (only undergoes glycolysis), NAD+ is used directly in glycolysis to form ATP molecules, which is not as efficient as cellular respiration because only 2ATP molecules are formed during the glycolysis. One type of fermentation is alcohol fermentation, it produces pyruvate molecules made by glycolysis and the yeast will break it down to give off carbon dioxide, the reactant is glucose and the byproducts are ethanol and carbon dioxide. In this lab, the purpose is to measure whether the changes of substrate concentration will affect the rate of anaerobic respiration. Because the rate of reaction refers to how quickly the reactants are used up or how quickly the products are formed, one method is to measure the volume of gas given off, the more gas given off per time interval results faster reactions.
Will the changes in substrate concentration affect the rate of anaerobic reaction? Why or why not? What are the independent variable and dependent variable in this lab activity? What are some other controlled variables?
If substrate concentrations are changed, then as the concentration increase, the rate of anaerobic reaction will also increase, because the increase of the reactant concentration means there are more reactant particles, and there is a greater chance for these particles to collide and let reaction happen. The independent variable is the concentration of the substrate, and the dependent variable is the one will be measured, which is the volume of gas. The controlled variables are the temperature, the amount of yeast and water.
Three envelopes of active dry yeast
Three 500 mL bottles
Three Balloons (Medium-sized)
1) The room temperature water was prepared and measured by using thermometer. 2) The three bottles were labeled
1. 5 mL sugar
2. 10 mL sugar
3. 15 mL sugar
3) 150 mL of room temperature water was added to each 3 bottles 4) One package of active dry yeast was added to bottle labeled ‘5mL’ and solution was swirled. 5) 5 mL of sugar was added to the solution and a balloon was placed over the opening of the bottle to minimize the loss of any gas from the system. 6) The tape was used to measure gas accumulation in the balloon after 1minute. Measurement and qualitative observations were recorded. 7) The gas accumulation in the balloon was measured and recorded at one minute intervals for a total of 10 minutes (qualitative observations were included) 8) One package of active dry yeast was added to the bottle labeled ‘10 mL sugar’ and solution was swirled by rod gently. 9) 10 mL of sugar was added to the solution and the balloon was quickly placed over the opening of the bottle to minimize the loss of any gas from the system. 10) The tape was used to measure gas accumulation in the balloon after 1minute. Measurement and qualitative observations were recorded. 11) The gas accumulation in the balloon was measured and recorded at one minute intervals for a total of 10 minutes (qualitative observations were included) 12) The 8-11 steps for each of the remaining bottle was repeated, the sugar concentration was adjusted accordingly. Observation:
The bottle with higher concentration of sugar tends to produce more carbon dioxide. After 10 minutes, The 15mL/10% sugar bottle produced carbon dioxide, which occupied the balloon with 4.375inches, while 5ml/3% sugar bottle only released carbon dioxide that occupied 2.25inches. Results:
Carbon dioxide produced/1min
Carbon dioxide produced/5mins
Carbon dioxide produced/10mins
Most bacteria are neutrophiles, meaning they grow optimally at a pH within one or two pH units of the neutral pH of 7, between 5 and 8 (see Figure 9.35). Most familiar bacteria, like Escherichia coli , staphylococci, and Salmonella spp. are neutrophiles and do not fare well in the acidic pH of the stomach. However, there are pathogenic strains of E. coli, S. typhi, and other species of intestinal pathogens that are much more resistant to stomach acid. In comparison, fungi thrive at slightly acidic pH values of 5.0–6.0.
How to Maximize the Rate of Fermentation
Fermentation is the method that anaerobic organisms, such as yeast, produce energy from sugars. This process is best known when yeast is used to produce alcohol from mash or when it is used in dough to make bread rise. The output from fermentation is ethyl alcohol and carbon dioxide. There are times when it can be desirable to increase the fermentation rate to speed the production time for the output of alcohol or bread. While the fermentation rate has limits regarding how much it can be accelerated, increases in the 50 percent range can be attained with careful control of the fermentation environment.
Place the mixture being fermented in a warmer area. This is probably the easiest way to increase the fermentation rate. Yeast operates best in a range of 75 to 85 degrees Fahrenheit. For each degree that you increase the temperature within that range, you will increase the fermentation rate by three to five percent. A 10-degree rise in temperature within this range can achieve a 30 percent to 50 percent increase in the rate.
Lower the amount of salt and sugar in the mixture. Yeast likes sugar, but not too much. Amounts of sugar above five percent of the mixture will begin to inhibit the fermentation rate. Salt amounts that make the mixture more salty than the yeast will slow the fermentation rate because it will impede the rate of osmosis. Salt concentrations above one percent will inhibit the fermentation process.
Add more water to the mixture to increase the rate of fermentation. Bread dough that is less stiff will allow faster fermentation. Keeping any fermentation mixture more hydrated will speed up fermentation because the osmosis can occur more freely for the yeast cells.