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As a hobby, I've been trying to “grow” crystals of from supersaturated solutions of aluminium potassium sulphate.
I noticed that my solutions are also rather successful at growing a type of fungus.
The fungus grows bigger and bigger in the saturated solution and leaves behind yellow spores as the salt solution evaporated (see photos).
I've always thought that salt is antifungal and anti bacterial, and I'm surprised to see that there is a fungus actually growing bigger in a supersaturated salt solution.
I have tried boiling and filtering (with tea mesh filter so the spores probably got through) the salt solution, but the fungus keeps coming back, so the spores survive boiling too, unless there are spores floating around my room.
Is there a way to identify what sort of fungus it is? What sort of fungus is it likely to be? Have I bred a type of super fungus? Is my life in danger by allowing this to grow?
I live in Sydney, Australia if that helps with identifying the fungus.
A piece of bread kept under moisture and high temperature develops mold on its surface.
- Slice of bread
- Plastic zipper bag
- Masking tape
- Camera (optional)
- Sprinkle water on the slice of bread.
- Put the bread in the plastic bag and zip it.
- Use the tape to secure it further.
- Write today’s date on the tape with the marker.
- Leave the bag undisturbed for 7 days in a warm place outside the house.
- Track the growth of the mold by checking the sample every day. Collect data in the notebook on the size and color of the colony. You can also take a photograph of the bread each day.
- In the end, throw away the bag with the moldy bread without consumption or inhalation near it.
Intermediate-Level Science Projects: What Materials Make the Best Crystals?
Growing crystals isn't difficult, and it makes a great science fair project. You can grow crystals on a sheet of black construction paper on a sunny day. You also can make them on a paper clip that's tied to a piece of yarn and suspended in a supersaturated liquid solution.
If you're going to use the construction paper method, you'll need to cut a piece of black paper so it fits into the bottom of a glass or metal pie plate. For the paper clip method, you can tie a paper clip to a piece of yarn, and then pull the paper clip and part of the thread through a piece of cardboard in which a small hole has been cut.
We talk about ?growing? crystals in this section, but you're not growing them in the strict sense of the word. You're causing them to form by supersaturating a solution of water and either salt or sugar.
The key to either method of growing crystals is to make a supersaturated solution of water and salt or sugar. In this experiment, water is called the solvent, and the salt or sugar is called the solute. You can use regular old sugar, and either rock salt or Epsom salt. You probably have at least one of those materials available in your home. If not, you can buy any of them in the grocery store. Designate one solute as your control and the other two as variables.
Don't forget to state your problem, formulate a hypothesis, and follow the other steps of the scientific method.
To make a supersaturated solution, you simply need to add salt or sugar to hot water until the water is incapable of dissolving any more of the solute. That happens when the molecules of the solvent get so crowded together that there's no more room between them for solute molecules.
Start with a large glass jar or metal pot filled with two liters of very hot water. Working with one tablespoon (15 ml) at a time, add either the sugar or the salt to the water, stirring the solution well after each addition. Eventually, you'll see undissolved solute starting to collect at the bottom of the container. When this happens, your solution is supersaturated.
If you're using the construction paper method, pour enough of the supersaturated solution into the pie pan so that the paper is just covered. Set the pan in the sun and allow the water to evaporate. When it does, you should be able to see crystals formed in the bottom of the pan.
If you're using the paper clip method, fill a clean jar with the supersaturated solution. Then, place the cardboard over the mouth of the jar and secure the yarn to the cardboard so that the paper clip hangs in the middle of the jar. The bottom of the paper clip should be about five centimeters from the bottom of the jar.
As the hot solution cools and the water evaporates, the solute molecules will begin to cling to the yarn and crystallize.
You'll need to repeat the experiment three times, using all three solutes in order to see which one makes the best crystals. Photographing your results would be a good idea. And be sure to record your observations.
Excerpted from The Complete Idiot's Guide to Science Fair Projects 2003 by Nancy K. O'Leary and Susan Shelly. All rights reserved including the right of reproduction in whole or in part in any form. Used by arrangement with Alpha Books, a member of Penguin Group (USA) Inc.
Human illnesses caused by foodborne microorganisms are popularly referred to as food poisoning. The common use of a single classification is due primarily to similarities of symptoms of various food-related diseases (see Table 5). Apart from illness due to food allergy or food sensitivity, foodborne illness may be divided into two major classes, food infection and food intoxication. Food infection results when foods contaminated with pathogenic, invasive, food poisoning bacteria are eaten. These bacteria then proliferate in the human body and eventually cause illness. Food intoxication follows the ingestion of preformed toxic substances which accumulate during the growth of certain bacterial types in foods.
The period of time between the consumption of contaminated foods and the appearance of illness is called the incubation period. The incubation period can range anywhere from less than one hour to more than three days, depending on the causative organisms or the toxic product.
|Disease||Etiologic Agent||Incubation Period||Symptons|
|Botulism||Clostridium botulinum A.B.E.F toxin||Usually 1 to 2 days range 12 hours to more than 1 week||Difficulty in swalling, double vision, difficulty in speech. Occasionally nausea, vomiting, and diarrhea in early stages. Constipation and subnormal temperature. Respiration becomes difficult, often followed by death from paralysis of muscles of respiration.|
|Staphylococcal food poisoning||Staphyloccal enterotoxin||1 to 6 hours average 3 hours||Nausea, vomiting, abdominal cramps, diarrhea, and acute prostration. Temperature subnormal during acute attack, may be elevated later. Rapid recovery-usually within 1 day.|
|Salmonellosis||Specific infection by Salmonella spp.||Average about 18 hours range 7 to 72 hours||Abdominal pains, diarrhea, chills, fever, frequent vomiting, prostration. Duration of illness: 1 day to 1 week.|
|Shigellosis (bacillary dysentery)||Shigella sonnei, s. flexneri, s. dysenteriae, s. boydii||Usually 24 to 48 hours range 7 to 48 hours||Abdominal cramps, fever, chills, diarrhea, watery stool (frequently containing blood, mucus, or pus), spasm, headache, nausea, dehydration, prostration. Duration: a few days.|
|Enteropathogenic Escherichia coli infection||Escherichia coli serotypes associated with infant and adult infections||Usually 10 to 12 hours range 5 to 48 hours||Headache, malaise, fever, chills, diarrhea, vomiting, abdominal pain. Duration: a few days.|
|Clostridium perfringens food poisoning||Clostridium perfringens||Usually 10 to 12 hours range 8 to 22 hours||Abdominal cramps and diarrhea, nausea, and malaise, vomiting very rare. Meat and poultry products usually involved. Rapid Recovery.|
|Bacillus cereus food poisoning||Bacillus cereus||Usually about 12 hours range about 8 to 16 hours||Similar to Clostridium perfringens poisoning|
|Vibrio Parahaemolyticus food poisoning||Vibrio Parahaemolyticus||Usually 12 to 14 hours range 2 to 48 hours||Abdominal pain, server watery diarrhea, usually nausea and vomiting, mild fever, chills and headache. Duration: 2 to 5 days.|
* Repeated from Prevention of Microbial and Parasitic Hazards Associated with Processed Foods, pages 6-7, with the permission of the National Academy of Sciences, Washington, DC.
Foodborne Disease Organisms
A few of the E. Coli strains found in human feces are in themselves pathogenic, causing infection and disease. These are called Enteropathogenic E. Coli or EEC. In one extensive study of the feces of food handlers (Hal and Hause, 1966), 6.4% of the workers harbored the EEC organisms as carriers.
S. aureus, commonly referred to as “staph,” is normally present on the skin, the mucous membranes, and in pimples and boils of human beings and other animals. It is nearly always present in small numbers in raw meats and in foods handled extensively by human hands. The food poisoning strains generally come from human sources. Pasteurizing or cooking destroys the organism, but not its toxin. Foods contaminated by staph organisms can cause food poisoning after the organisms have been destroyed by heat.
The presence of staph in a cooked food has two levels of significance.
- Low numbers (not over a few hundred per gram) indicate the degree of contact with human skin or nasal mucous, cross-contamination from raw meat, or survivors of a larger population.
- High numbers (100,000 or more per gram) indicate that the bacteria were allowed to grow in the food, thereby creating the potential serious hazard of the presence of toxin.
Keeping foods completely free from staph contamination is often difficult or impossible. Therefore, the processor should store the food at temperatures that preclude the growth of staph (see Table 1). It is only during growth that staph forms the toxin. An epidemiological investigation to determine the source of the organism is tedious, but visual inspection of workers’ hands can be useful. The well-informed sanitarian will also seek time-temperature abuses of foods contaminated with staph.
The National Academy of Science’s National Research Council has listed the following steps to limit the incidence and level of staph in foods (NAS-NRC, 1975):
- Reduce direct and indirect exposure of foods, particularly cooked foods, to human contact as much as possible. If handling is necessary, use sanitary rubber or plastic gloves, or sanitize hands. Persons with infected cuts, abrasions, boils, or pimples should never handle cooked foods.
- Test raw materials and eliminate production lots that contain high levels of S. aureus.
- Process to destroy the microorganisms.
- Eliminate cross-contamination from raw to cooked food.
- Keep cooked foods no longer than 2 to 3 hours between 40°F and 140°F.
Control of staph growth in fermented foods, such as cheese or sausages, requires controlling a number of processing factors (see NAS-NRC, 1975). Low pH, relatively high levels of lactic bacteria, salt, and nitrite help to inhibit toxin formation.
Salmonella infection, or salmonellosis, is almost always caused by eating contaminated food or drink. Contamination originates from the intestinal tract of human beings or animals who harbor Salmonella organisms. Most adults can resist infection from a few cells, but become ill when ingesting millions. Infants, the aged, and the infirm are much more sensitive and can be affected by a few Salmonella cells. After recovery, the victim may remain a carrier for a period varying from a week to permanency.
Domestic animals, such as dogs, poultry, swine, horses, sheep, and cattle are carriers of these pathogens. Carriers show no outward symptoms of the disease at the time of slaughter. As long as abattoirs continue to receive Salmonella carriers for slaughter, Salmonella contamination of the finished raw meat is inevitable. Even with apparently satisfactory sanitation, slaughtering and dressing procedures may spread traces of feces from a carrier animal to subsequently slaughtered animals by way of equipment, water, and hand contact (NAS-NRC, 1969).
Salmonella is often discussed as if it were a single organism. There are actually more than 1,300 serotypes identified within the genus Salmonella. All are quite sensitive to heat, so freshly pasteurized or cooked foods are free of the organism (USDA, 1966). The principal routes of its entry into cooked foods are cross-contamination from raw foods or animals (via hands, equipment, air, water), recontamination from human carriers, or gross undercooking. Regulatory agencies are quick to institute seizures, recalls, and other legal action against products and firms shipping Salmonella-contaminated processed foods.
Dry and semi-dry fermented sausages rarely cause food borne diseases. However, recent investigations by USDA have shown that Salmonella can survive the fermentation and drying process (Smith et. al., 1975). Salmonella in natural animal casings likewise survives short periods of salting, but dies more rapidly in acidified or alkalized casings (Gabis and Silliker, 1974).
Salmonella can also grow outside the animal body when conditions are favorable. For this reason, it has appeared in a wide variety of foods and feeds, in addition to meat and poultry products. Some of these are brewers yeast, coconut meat, cochineal dye, dried or frozen eggs, noodles, custards, dried animal feeds, cottonseed flour, candy, chocolate, dried milk, fish and shellfish, cream-filled pastries, sausage casings, and watermelon. The NAS-NRC (1969-1975) has made extensive recommendations for evaluation, control, and eradication of the Salmonella problem.
C. botulinum produces a rare but often fatal disease called botulism. It is caused by a neurotoxin produced during growth in the absence of air. Except in the case of infantile botulism the intact spores are harmless. Infants ingesting spores, usually from honey, have developed symptoms of botulism. Botulism usually occurs after a food containing the preformed toxin has been eaten, but sometimes the organism infects wounds, forming the toxin in the muscle of the victim. There are seven types of C. botulinum (A to G), of which four (A, and B associated with meats and vegetables, E, marine environment and F) cause human disease. Only once has type C been reported to cause human illness. Type G is a new incompletely studied discovery (Schmidt, 1964, USPHS, 1974).
Fortunately, the toxins, regardless of type, have very little resistance to heat and are inactivated by boiling for 10 minutes. Thus, all freshly, but adequately, cooked foods are safe (Riemann, 1973). All C. botulinum strains can form spores which exhibit varying resistance to heat. The spores of types A and B are highly resistant. Spores of type E die in a fraction of a minute at 212°F (Perkins, 1964). The canning industry, under the technical leadership of the National Food Processors Association (formerly the National Canners Association), has established times and temperatures of retorting necessary to insure the commercial sterility of low-acid canned foods (NCA, 1968, 1971b, 1976b). The NFPA also submitted to the FDA the initial petition which eventually developed in the GMP regulations for low-acid canned foods.
Botulinum spores are widely distributed in soils. Type A predominates in the western states and in New England type B, in the eastern and southern states. Type E is usually associated with marine or fresh water environments throughout the world and is psychrotropic (Riemann, 1973). Type F has been isolated too rarely to establish its distribution pattern (Eklund et.al., 1967).
C. botulinum will not grow below pH 4.8. Therefore, botulism is a concern only in low acid foods, which are defined as foods with a finished equilibrium pH greater than 4.6. The majority of outbreaks occur from home canned vegetables, meats, fish, and over-ripe fruits (USPHS, 1974).
Canned cured meats contain salt and nitrite. The preservatives protect against the outgrowth of botulinum spores that may have survived the minimal processing, which is frequently at or below boiling (Halvorson, 1955 Ingram and Hobbs, 1954 Pivnick et. al, 1969).
There have been 34 outbreaks of type E botulism among fish products prepared in the U.S. and Canada (Lechowich, 1972). Most have been smoked or lightly salted products. The FDA isolated botulinum types B, E, and F from pasteurized meat of the blue crab (Kautter et. al., 1974). The NAS-NRC (1975) has reviewed steps to minimize the possibility of out-breaks from smoked fish and FDA has published regulations designed to control the problem (FDA, 1970).
C. perfringens is a spore-forming organism which, like botulinum, grows only in the absence of air. It grows best in meat or poultry dishes, stews, or gravies kept warm. Such foods meet its exacting nutritional requirements and the warm holding temperature, up to 122°F, encourages its growth. The spores themselves are harmless, but the vegetative cells, which can grow to enormous numbers in these foods, form spores in the intestinal tract of the victim. During the sporulation process, the remainder of the vegetative cell dissolves, releasing the poison that causes illness.
The vegetative cells which cause the disease are very delicate. They can be destroyed or reduced to low, safe levels by cooking or freezing. The spores are widely distributed in nature and are present in small numbers in various foods (Hall and Angelotti, 1965 Strong et. al., 1963). They occur in feces, soils, dust, water, marine sediments, raw foods, and even cooked foods.
C. perfringens poisoning is a problem specific to the food service industry. Only proper temperature control prevents the problem. A good rule of thumb is to keep ready-to-eat moist foods below 40°F or above 140°F. Time-temperature abuse is a severe health hazard. Since the spores are everywhere, epidemiologic investigation of strains to determine the source of spores is a relatively futile exercise. However, if serological tests show that the same types are present in the victim’s food and feces, a particular dish can be incriminated. Unfortunately, the biological materials (antisera) for this purpose are not yet commercially available. Therefore, the determination that large numbers of C. perfringens cells are present remains the most suitable investigative test.
B. cereus is a spore-forming organism that grows in the presence of oxygen and is widely distributed in most raw foods. Since the spores survive boiling for several minutes, they remain viable in cooked foods in small numbers. The organism does not compete well with other bacteria in raw foods, but in moist, cooked dishes held warm (up to 122°F), it grows to millions per gram in a few hours. Under these conditions the food becomes poisonous. B. cereus grows well in a wide variety of cooked foods, such as meats, poultry, sauces, puddings, soups, rice, potatoes, and vegetables. The disease is similar to that of perfringens (see Table 5), although the mechanism of the disease is unknown. Adults have rather mild symptoms, but small children may become seriously ill. In most instances, the victims recover quickly and do not seek medical attention. Therefore, only large outbreaks are reported and become part of the statistical record.
Similar to C. perfringens, B. cereus is primarily a concern of the food service industries. The appropriate control is to keep hot foods hot (over 140°F) and cold foods cold (under 40°F). Epidemiologic investigation of strains to determine the source of the spores proves equally futile.
V. parahaemolyticus is a non-spore forming, slightly curved rod, closely related to the organism that causes cholera. It is widely distributed and grows in brackfish waters, estuarine sediments, raw fish, and shellfish throughout the world. It competes well with spoilage organisms at temperatures of 41°F or above. It occurs in greatest numbers in the summer when higher temperatures engender rapid growth.
V. parahaemolyticus is the principal cause of food poisoning in Japan where raw fish is regularly consumed. Elsewhere, the disease occurs less frequently because the organism dies readily during pasteurization or cooking. Nevertheless, cooked seafoods can be recontaminated from water or raw seafood. The first confirmed outbreaks in the United States occurred in 1971 and 1972 from crabmeat, shrimp, and lobster. In one Japanese outbreak, 22 people died and 250 others became ill.
The human pathogenicity of the organism is determined by culturing it on a special medium, a salt agar containing human blood. If the organism can grow and destroy blood cells on this medium, the so-called Kanagawa test, it is labeled “Kanagawa positive” and assumed capable of causing human disease. The Japanese have found that about 1% of the strains of V. parahaemolyticus from waters near their shores are Kanagawa positive (Sakazaki et. al., 1968). On the other hand, Twedt et. al. (1970) reported that up to 90% of the strains from U.S. estuarial waters are Kanagawa positive. However, the significance of the Kanagawa test is not fully understood.
To reduce the incidence of these outbreaks, the seafood industry should:
- Hold raw seafoods at or below 40°F
- Keep cooked seafoods carefully apart from raw seafood, sea water, insanitary equipment, and unclean containers and
- Hold cooked seafood below 40°F or above 140°F
Before the 1980’s most problems associated with diseases caused by Listeria were related to cattle or sheep. This changed with food related outbreaks in Nova Scotia, Massachusetts, California and Texas. As a result of its widespread distribution in the environment, its ability to survive long periods of time under adverse conditions, and its ability to grow at refrigeration temperatures, Listeria is now recognized as an important food borne pathogen.
Immunocompromised humans such as pregnant women or the elderly are highly susceptible to virulent Listeria. Listeria monocytogenes is the most consistently pathogenic species causing listeriosis. In humans, ingestion of the bacteria may be marked by a flu-like illness or symptoms may be so mild that they go unnoticed. A carrier state can develop.
Following invasion of macrophages virulent strains of Listeria may then multiply, resulting in disruption of these cells and septicimia. At this time the organism has access to all parts of the body. Death is rare in healthy adults however, the mortality rate may approximate 30% in the immunocompromised, newborn or very young.
As mentioned earlier Listeria monocytogenes is a special problem since it can survive adverse conditions. It can grow in a pH range of 5.0-9.5, in good growth medium. The organism has survived the pH 5 environment of cottage cheese and ripening Cheddar. It is salt tolerant surviving concentrations as high as 30.5% for 100 days at 39.2°F. But only 5 days if held at 98.6°F.
The key point is that refrigeration temperatures do not stop growth of Listeria. It is capable of doubling in numbers every 1.5 days at 39.2°F. Since high heat, greater than 175°F, will inactivate the Listeria organisms, post-process contamination from environmental sources then becomes a critical control point for many foods.
Even though Yersinia enterocolitica is not a frequent cause of human infection in the U.S., it is often involved in illness with very severe symptoms. Yersiniosis, infection caused by this microorganism, occurs most commonly in the form of gastroenteritis. Children are most severely affected. Symptoms of pseudo-appendicitis have resulted, in many unnecessary appendectomies. Death is rare and recovery is generally complete in 1 – 2 days. Arthritis has been identified as an infrequent but significant sequela of this infection.
Y. enterocolitica is commonly present in foods but with the exception of pork, most isolates do not cause disease. Like Listeria this organism is also one that can grow at refrigeration temperatures. It is sensitive to heat (122 F., sodium chloride (5%) and acidity (pH 4.6), and will normally be inactivated by environmental conditions that will kill salmonellae.
C. jejuni was first isolated from human diarrheal stools in 1971. Since, then it has continually gained recognition as a disease causing organism in humans.
C. jejuni enteritis is primarily transferred from animal origin foods to humans in developed countries. However, fecal contamination of food and water and contact with sick people or animals predominates in developing countries.
Although milk has been most frequently identified throughout the world to be a vehicle for Campylobacter, one anticipates that future investigations will identify poultry and its products and meats (beef, pork and lamb) as major reservoirs and vehicles.
C. jejuni dies off rapidly at ambient temperature and atmosphere, and grows poorly in food.
The principles of animal science will play a significant role in the control of this ubiquitous organism. Hygienic slaughter and processing procedures will preclude cross-contamination while adequate cooling and aeration will cause a decrease in the microbial load. In addition, thorough cooking of meat and poultry products followed by proper storage should assist in maintaining food integrity and less contamination.
Mycotoxins are harmful byproducts from molds that grow on foods and feeds. They have caused severe illness and death in animals for centuries. They first came to the attention of modern scientists in 1960 when 100,000 turkey poults died in England after eating moldy peanut meal from Africa and South America. The mycotoxins involved were later shown to be aflatoxins, a group of closely related organic compounds that can cause acute disease and death. Stimulated by these first discoveries and by research in antibiotics, investigators have discovered dozens of mold strains which produce a wide variety of mycotoxins that affect animals. There are now about 60 identified toxins. Of these, only a few have been designated human food contaminants. These numbers will likely increase as mycotoxin investigations continue and identification methods are improved.
Historically, mycotoxins have been associated with human poisoning and even death. Ergot is among the first mycotoxins recognized as affecting human beings. It is produced by a mold growing on cereal grains. Ergot poisoning occurred in the Rhine Valley in the year 857 and has been reported several times since. The most recent outbreak was in 1951 in southern France. Many Russians died during World War II from eating moldy grains. The Japanese have reported human toxicity from eating moldy rice the disease caused severe liver damage, hemorrhaging, and some fatalities (Mirocha, 1969).
Although such incidents are rare occurrences, there is evidence that low dietary levels of aflatoxins contribute to cancer of the liver in human beings. Extensive laboratory studies have also shown that even at very low dietary levels, aflatoxin can produce liver cancer in rats, mice, monkey, ducks, ferrets, and rainbow trout. Epidemiological studies in Southeast Asia and Africa have related a high incidence of human liver cancer to aflatoxin levels up to 300 parts per billion (ppb) in 20% of the food staples, and 3 to 4 ppb in 7% of the foods as eaten. In one geographical area, 95% of the corn and 80% of the peanuts contained aflatoxin at an average level of 100 ppb.
Although there is no direct evidence that aflatoxins cause human liver cancer in the United States, FDA is concerned about the effect of long-term, low-level consumption of a known, highly carcinogenic substance in our food supply. FDA established an informal defect action level tolerance of 30 ppb on peanuts and peanut products in 1965. With improved harvesting, storage, and sorting practices developed by USDA and industry, the level of aflatoxins contamination gradually declined and FDA lowered the informal action level to 20 ppb in 1969. FDA proposed in the Federal Register of December 6, 1974, a regulation establishing a tolerance of 15 ppb for total aflatoxins in shelled peanuts and peanut products used as human food. Today the limits are 0.5 ppb for milk, 20 ppb for food, and 100 ppb for feed.
Molds which form mycotoxins can be present on any food not heated in a closed container. One must assume, therefore, that they are present and capable of producing, toxin if conditions permit. But finding a toxigenic mold in a food does not imply that the food contains a mycotoxin. Conversely, the absence of visible growth of an aflatoxin producing mold does not mean toxin is absent since aflatoxins may be produced when there is little visible mold growth.
There are several ways to determine whether molds growing in an abused food will produce mycotoxins. The food can be held with its naturally contaminating molds, or inoculated with a toxigenic strain, and kept until the molds develop. The food can then be tested for the presence or absence of toxin. Such experiments have demonstrated that molds produce mycotoxins on a large variety of cereal grains and seeds, dry beans and fruits, spices, nuts, and cured meats. As do bacteria, molds have moisture, temperature, and nutritional requirements for optimal growth and toxin production. In most cases the initial mold invasion occurs in the fields before or during harvest. Mold growth continues during storage if the moisture content and storage temperatures remain high.
Aflatoxin has been found throughout the world on corn, barley, copra, cassava, spices, dry milk, tree nuts, cottonseed, peanuts, rice, wheat, and grain sorghum. In the U.S. it has been found in corn, figs, grain sorghum, cottonseed, peanuts, and certain tree nuts.
The industry has relied on electronic and visual sorting methods, as well as blowing and vacuuming, to control aflatoxin levels in walnuts arid pecans. Corn mill operators use a high intensity ultraviolet (“black”) light to detect possible aflatoxin contamination. Roasting reduces the level of aflatoxin up to 50% in some cases (Escher et. al., 1973).
The universal solution to the problem is eliminating conditions that permit mold growth, whenever it is feasible to do so, and thereby preventing the formation of mycotoxins. In some cases (corn, peanuts) mold growth and toxin production occur before harvest. Insect and bird damaged corn kernels are very susceptible therefore, controlling these pests will help alleviate mold problems. For most susceptible foods, the critical period is immediately following harvest, during storage and initial drying when the moisture content is high enough to allow mold growth.
Which Cheese Grows Mold The Fastest?
Wear safety goggles, rubber gloves and an apron or old shirt as a lab coat when handling mold. Use a dilute bleach solution for clean up.
Most of basic materials and equipment can be found in any kitchen. The cheeses can be purchased in the local super market or grocery store. The mold, rhizopus, available in a Petri dish can be purchased from Ward`s Natural Science. Note: The Petri dish arrangement makes it easy to transport the fungus to the different cheeses.
Approximate Time Required to Complete the Project
3 to 4 weeks. This includes the experimentation and the collection, recording and analysis of data, summary of results and completion of bibliography.
To determine which cheese grows mold fastest: Vermont Cheddar, American, Brie, or Camembert?
Materials and Equipment Required
- samples of Vermont Cheddar, American, American, Brie and Camembert
- cutting board
- 8 Petri dishes
- centimeter ruler
- Petri dish of the rhizopus mold
- sterile swabs
- paper toweling or blotting paper
- rubber gloves, apron or shirt as lab coatsanitizer such as dilute liquid bleach.
On the information level, this experiment serves to introduce students to the conditions under which molds grow, how they can be useful to us and how their growth can be controlled. In addition, the students learn how to conduct the experiment in a safe manner to prevent the effects of contamination. On the level of experimentation, this experience serves to acquaint students with the essential components of sciencing such as the importance of clearly defining the problem to be investigated, stating their hypothesis and their rationale for the hypothesis, the use of a control, of identifying dependent and independent variables, of data collection, of pictorial and or graphic presentation of data and of being able to make better judgments as to the validity and reliability of their findings. They take on the role of scientists and in the process they learn to act as one.
- natural cheese
- processed cheese
- aging of cheese
- What are molds?
- Where are molds found?
- Under what kinds of conditions do molds grow?
- How are molds useful to us?
- What is cheese and how is it made?
- What is the relationship between molds and the flavor of cheeses?
- What is penicillin?
- How are molds harmful to us?
- What are fungi?
- Are all fungi molds?
Terms, Concepts and Questions to Start Background Research
- What is a hypothesis? A hypothesis is a prediction as to what the results or outcomes of the research will be.
- What is a control? A control is the variable that is not changed in the experiment.
- What purpose does a control serve? It is used to make comparisons as to what changed or possibly caused the change.
- What are variables? Variables are factors that can be changed in an experiment.
- What is an independent variable? The independent variable is the one that is changed in the experiment.
- What is a dependent variable? The dependent variable is the one that changes as a result of the change in the independent variable.
Charting and Graphing Data
In each section of the experiment, use charts to display the obtained data such the following sample:
- State the problem you are going to investigate in this science fair project.
- Create the data sheets you will use to record your observations.
- Gather all your materials.
- Put on your safety glasses, apron and rubber gloves.
- Clean the surface you will be working on with a dilute solution of bleach and water.
- Set up the 8 Petri dishes into 4 sets of two labeling them with specimen numbers such as# 1 and #2 will contain Vermont Cheddar, #3 and #4 will contain Swiss ,# 5 and #6 will be Camembert etc.
- Set up 4 Petri dishes, each of which will contain a sample of each cheese to serve as a control and label them.
- Cut the paper toweling to fit the Petri dishes, line the Petri dishes with the paper and soak each of the papers with a medicine dropper of water.
- Slice all the cheeses into equal segments and place them in the labeled Petri dishes and in the controls.
- Using sterile swabs open the Petri dish of rhizopus and transfer an equal amount of the mold to each of the cheeses. Do not inoculate the controls!
- Store the dishes in a warm place (75-80 degrees F) and in a dark place, a drawer or in a closed box.
- Observe, measure and record the growth of the mold using your centimeter ruler on a daily basis for two weeks.
- You may wish to make sketches of your observations and /or take photos of the mold growth to substantiate your observations.
- Graph your data. A graph presents an instant picture of the findings.
- Prepare your report and include all of the following: a clear statement of the problem, your hypothesis, the rationale for your hypothesis, and a list the materials used. Include the safety precautions taken. Describe the procedures used. Include all the data that were gathered. Include all charts and graphs. Formulate your conclusions. For dramatic value, you may include photos of the materials used or of you in the process of conducting this investigation. Include a bibliography of sources you used. You may wish to assess what you did and describe what you would do differently if you were to do this project again. In addition, you may include what you view as the practical applications of your project as well as what further research you may wish to conduct on this subject.
- Ammirati, Joe F. &ldquoMold,&rdquo World Book Encyclopedia, 2002.
- Edelman, E. and Grodnick, S. The Ideal Cheese Book, 1986. December 8, 2004.
Disclaimer and Safety Precautions
Warning is hereby given that not all Project Ideas are appropriate for all individuals or in all circumstances. Implementation of any Science Project Idea should be undertaken only in appropriate settings and with appropriate parental or other supervision. Reading and following the safety precautions of all materials used in a project is the sole responsibility of each individual. For further information, consult your state's handbook of Science Safety.
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A Guide to the Salmonella Outbreak
Protection of foods from microbial spoilage using salt (usually sodium chloride) or sugar (usually sucrose) has ancient roots and is often referred to as salting, salt curing, corning or sugar curing. (Pieces of rock salt used for curing are sometimes called corns, hence the name "corned beef.") Curing may utilize solid forms of salt and sugar or solutions in which salt or sugar is mixed with water. For instance, brine is the term for salt solutions used in curing or pickling preservation processes. Examples of foods preserved with salt or sugar include the aforementioned corned beef as well as bacon, salt pork, sugar-cured ham, fruit preserves, jams and jellies, among others.
There are numerous descriptions and permutations of curing which may include additional preservation techniques such as smoking or ingredients such as spices. However, all curing processes fundamentally depend on the use of salt and/or sugar as the primary preservation agent(s). Incidentally, these processes not only prevent spoilage of foods, but more importantly serve to inhibit or prevent growth of food-borne pathogens such as Salmonella or Clostridium botulinum when properly applied.
There are several ways in which salt and sugar inhibit microbial growth. The most notable is simple osmosis, or dehydration. Salt or sugar, whether in solid or aqueous form, attempts to reach equilibrium with the salt or sugar content of the food product with which it is in contact. This has the effect of drawing available water from within the food to the outside and inserting salt or sugar molecules into the food interior. The result is a reduction of the so-called product water activity (aw), a measure of unbound, free water molecules in the food that is necessary for microbial survival and growth. The aw of most fresh foods is 0.99 whereas the aw necessary to inhibit growth of most bacteria is roughly 0.91. Yeasts and molds, on the other hand, usually require even lower aw to prevent growth.
Salt and sugar's other antimicrobial mechanisms include interference with a microbe's enzyme activity and weakening the molecular structure of its DNA. Sugar may also provide an indirect form of preservation by serving to accelerate accumulation of antimicrobial compounds from the growth of certain other organisms. Examples include the conversion of sugar to ethanol in wine by fermentative yeasts or the conversion of sugar to organic acids in sauerkraut by lactic acid bacteria.
Microorganisms differ widely in their ability to resist salt- or sugar-induced reductions of aw. Most disease-causing bacteria do not grow below 0.94 aw (roughly 10 percent sodium chloride concentration), whereas most molds that spoil foods grow at an aw as low as 0.80, corresponding to highly concentrated salt or sugar solutions. Yet other microorganisms grow quite well under even more highly osmotic, low aw conditions. For example, halophiles are an entire class of "salt-loving" bacteria that actually require a significant level of salt to grow and are capable of spoiling salt-cured foods. These include members of the genera Halobacillus and Halococcus. Food products that are concentrated sugar solutions, such as concentrated fruit juices, can be spoiled by sugar-loving yeasts such as species of Zygosaccharomyces. Nevertheless, use of salt and sugar curing to prevent microbial growth is an ancient technique that remains important today for the preservation of foods.
Salt Sculpture Stalactites
Did you know you can grow your own crystals at home? You can&mdashand it's easy! Crystals have a definite geometric pattern and if all goes well, the crystals you grow will be sharply defined, with crisp right angles and smooth faces that vary in size.
Table salt is made of many tiny crystals. When you mix these salt crystals with water, they dissolve, losing their crystalline form. When the water evaporates, the salt crystals form once again. The science of crystals, or crystallography, calls crystals shaped like these &ldquocubic.&rdquo This shape is determined by the way the individual atoms in salt pack together, much as the shape of a pile of oranges would be determined by the way they stack together. Your finished salt crystals should be strikingly beautiful. The key to growing these stunning crystals is quick evaporation&mdashand some string.
- One-quarter cup of table salt
- One cup of water
- About three feet of cotton string
- A saucepan (Enlist an adult's help when working with hot objects and using the stove.)
- Spoon to stir a hot solution
- Cup or small jar (It should have sides at least five inches high and able to hold boiling water.)
- Food coloring (optional)
- A tray or plate to hold the cup
- Newspapers or towel to put under the object (optional)
- Cut the string into six or seven pieces, each about five inches long, and tie them together at one end so they look like a string bouquet.
- Place the cup or jar on a safe surface where it can remain undisturbed for a few days. Use newspapers or a towel underneath the container to protect the surface if necessary.
- To prepare the salt solution bring the water to a rolling boil in the saucepan.
- Add about a quarter of the salt (optional: a couple of drops of food coloring). Mix with a spoon to help dissolve. What happens to the boiling water&rsquos appearance?
- Continue adding and mixing in salt until no more will dissolve into the water. How much salt were you able to add before it stopped dissolving? You should now have a &ldquosupersaturated&rdquo solution. What does the solution look like now? You might notice a film of salt crystals forming in a layer on the surface of your solution.
- Turn off the heat and carefully pour the solution into your cup.
- Carefully submerge the knotted end of your strings into the solution and arrange strings evenly so that the ends dangle over and around the rim of your cup. What purpose do you think the strings will serve? Did you notice the strings begin to soak up the saltwater solution?
- Leave the container someplace where it won&rsquot be disturbed.
- Wait and occasionally check in on your crystals. What do you see happening after one hour? One day? Two days?
- Extra: Once the salt solution evaporates enough that it is no longer covering the knot of the strings, you can repeat the above steps and make a new batch of salt solution to add. What happens over the course of the next day or two?
- Extra: Repeat the activity, but this time use different lengths of string, hanging over different objects&mdashat different angles. How does this change the way your salt strings grow?
- Extra: Try to make your crystals different colors by adding food coloring. Make a first batch of salt solution with one color. Wait until the crystals have grown and the solution has evaporated. Now make a second batch with a different color. Add this to the same container without removing the strings. What happens as this second color evaporates and forms crystals?
Observations and results
When you add salt to water, the crystals dissolve and the salt goes into solution. But you can't dissolve an infinite amount of salt into a fixed volume of water. When as much salt has been dissolved into a solution as possible, the solution is &ldquosaturated.&rdquo
This saturation point is different at different temperatures the higher the temperature, the more salt that can be held in the solution. When you boil a batch of saltwater, you cook the salt and water to an extremely high temperature, so the excess salt remains in the solution. But when the saltwater begins to cool, there is more salt in solution than is normally possible. The solution is therefore &ldquosupersaturated&rdquo with salt.
Supersaturation is an unstable state, and the salt molecules will begin to crystallize back into a solid. This begins at a "crystallization nucleation" site&mdashsuch as the fuzzy end of the string. Stirring or jostling of any kind can also cause the supersaturated salt to begin crystallizing.
In a couple of days you should be able to see that your strings grew fatter from the crystallizing salt. If you continued adding salt solution when it's evaporated below the knot, you should be able to grow long salt crystal stalactites.
More to explore
What Are Crystals? From Science Kids at Home
Crystal Creations, from Exploratorium
How to Make Rock Candy, from WikiHow
Quick Crystal Cup, from Home Science Tools
Mold contamination in sea salts could potentially spoil food
Credit: CC0 Public Domain
Like fine wines, sea salts are artisanal products that inspire talk of terroir, texture and provenance. Now there's evidence that they can also be sources of spoilage molds.
Research from Cornell University mycologist Kathie Hodge and doctoral candidate Megan Biango-Daniels reveals varying levels of mold contamination in commercial sea salts. Among those molds were important food spoilage molds like Aspergillus and Penicillium, and even some notorious producers of mycotoxins.
"This new finding contradicts the conventional wisdom that salts are sterile ingredients," said Biango-Daniels. The research stressed the importance of understanding the risk of using sea salt during food production.
Starting with seven different commercial salts, the researchers extracted living fungi and grew them in the lab for identification. The fungi discovered in the salt have the potential to spoil food when used as an ingredient and can introduce mycotoxins or allergens when consumed.
At the levels discovered in the study, about 1.7 spores per gram, you're not risking your health by sprinkling sea salt on food you are about to eat. But big problems may result when sea salts are used at home or industrially to make cured meats, fermented pickles or brined cheeses that mature over time - when molds introduced with sea salt can begin to grow and spoil food, maybe even rendering it toxic.
"Fungi can survive in surprisingly hostile places. They can't increase or grow in a container of sea salt - nothing can - but spores of some fungi survive quite happily there. Later they can wake up and make trouble in our food," said Hodge, associate professor in the Plant Pathology and Plant-Microbe Biology Section in Cornell's College of Agriculture and Life Sciences.
Fungi likely make their way into sea salts during their production from seawater or during storage and packaging. Sea salt production starts with seawater trapped in outdoor ponds called salterns. As the seawater evaporates, salt crystals form and are scraped up from the ponds and dried. Fungi may remain from microbes that live in the salterns, or their spores may fall in from the air over weeks of evaporation. Once fungi are in the salt, they have the potential to grow again once they encounter a moister environment. The researchers said microbial safety standards for this currently unregulated ingredient are needed to prevent food spoilage.
How Can Moldy Bread Be Prevented?
The environment in which bread is stored will have the largest impact on the growth of mold on the bread. Bread should be stored in a dry and cool place. It can be kept in the refrigerator, but that will cause the bread to dry out rapidly and become stale. Instead, store your bread in an airtight container away from heat and moisture. You can also freeze your bread to help keep it fresh. To make this a convenient alternative, slice your bread and freeze it with pieces of wax paper or parchment paper between slices. Place your bread in a freezer bag and ensure that minimal air is trapped in the bag before placing it in the freezer. The bread should last for approximately 6 months in the freezer. Scientists have also been working on storage methods for reducing mold growth on food based on packaging.
“The baker’s skill in managing fermentation, not the type of oven used, is what makes good bread.” — Chad Robertson
Home-made tends to have few or no preservative agents added, which allows mold to colonize and grow on the bread more rapidly. You can add some preservatives to your own bread that you bake at home. Some flavoring agents that act as natural preservatives that you could use include garlic, honey, cinnamon, or ginger. You could also add ascorbic acid or lecithin. You can also use sourdough starter as your yeast culture, as the sourdough culture is a mixture of yeast and lactobacilli, and the lactic acid produced by the lactobacilli lowers the pH of the bread, resulting in a reduced ability of molds to colonize the bread.