Sunday, May 6, 2007

Molds

Molds exhibit some of the characteristics of the higher plants. They are multiple cell organisms forming tubular filaments. Molds demonstrate branching and reproduce by means of fruiting bodies, called spores, which are borne in or on aerial structures. Their mycelia, or intertwined filaments, may resemble roots. They are many times larger than bacteria and somewhat longer than yeasts.

Molds are widely distributed in nature, both in the soil and in the dust carried by air. Under suitable conditions of moisture, air and temperature, molds will grow on almost any food. The black or green discoloration that appears on moldy bread is familiar evidence of such growth. Molds are also able to survive on a wide variety of substances not normally thought suitable for the support of life. These include concentrated solutions of some acids and water containing minute quantities of certain salts, as well as on building structures.

Mold growth can even occur in refrigerators, because molds are much more tolerant to cold than to heat. Molds can grow at reduced water activities (Aw) and can be a problem in improperly processed dry and semi-dry fermented products.

Mold growth in thermally processed commercially sterile and shelf-stable foods has to date not been shown to present a public health problem. In fact, mold is used in the ripening process of some sausages.

Yeasts

Another microorganism of importance to food preservation/spoilage is yeast. Yeasts are single cell, microscopic living bodies, usually egg-shaped. They are smaller than molds, but larger than bacteria. Their greatest thickness is about 1/2,000 of an inch. Yeasts reproduce mainly by budding. A small bud forms on the parent yeast cell and gradually enlarges and breaks off into another yeast cell. A few varieties reproduce by forming spores within a special cell; later these spores may form new yeast cells.

Yeasts are widely found in nature and are particularly associated with liquid foods containing sugars and acids. They are quite adaptive to adverse conditions such as acidity and dehydration. Like molds, yeasts are more tolerant to cold than to heat. Compared to bacterial spores, yeasts and their spores possess little resistance to heat.

Most yeast forms are destroyed on heating to 77ºC. Spoilage may result from the presence of yeast in canned food, but if this happens, gross under-processing or leakage must be suspected. Usually the growth of yeasts results in the production of alcohol and large amounts of carbon dioxide gas, which swells the container. Yeast growth in processed foods does not present a public health problem.


Parasites

The parasites of concern in the production of meat and poultry products include worms and protozoa. Some of them are large enough to be seen with the naked eye, whereas others are microscopic. Parasites cannot multiply in food, only in a host cell, and they are not heat resistant.

Parasitic worms of public health importance are the beef and pork tapeworms (Taenia saginata and Taenia solium, respectively) and the roundworm that causes Trichinosis (Trichinella spiralis, also referred to as trichinae) found in pork.

These small cysticerci (refered to as Cysticercus cellulosae) are approximately 6- 18mm wide by 4 - 6mm in length when found in the muscles or subcutaneous tissues (the normal sites for the larvae of this parasite). The cysticerci may however be found in other tissues, such as those of the central nervous system, where they may grow much larger up to several cm in diameter.

Muscle and organs of animals with severe tapeworm infection are usually visually detected by government inspection personnel or by plant employees through evidence of the immature stages (larval stage in a cyst known as a cysticercus) of tapeworms, which are 6- 18 mm wide by 4 – 6 mm in length when found in the muscles. Such product cannot be further processed for human consumption.

When the cysts are less severe or evident, infected meat may enter the human food chain, however illness will not occur if meat is properly cooked.
Humans consuming undercooked meat infected with these tapeworms become ill with Taeniasis generally after the mature stages of the tapeworms, which develop from the cysticercus, invade the intestinal tract. Most cases of infection with adult worms are without symptoms. Some persons may experience abdominal pain, weight loss, digestive disturbances, and possible intestinal obstruction. Taeniasis may last many years without medical treatment.

People can get a more serious illness called Cysticercosis by consuming food or water contaminated with the eggs of T. solium (pork tapeworm). Worm eggs hatch and the larvae then migrate to various parts of the body and form cysts (cysticerci). This can be a serious or fatal disease if it involves organs such as the central nervous system, heart, or eyes. Symptoms may vary depending on the organ or organ system involved. Death is common.

Trichinella spiralis is an intestinal worm that produces larvae that migrate to and encyst in muscles of a number of animals, particularly swine. Humans consuming infected pork that is undercooked get ill from the cysts, which then live in the muscles of the human hosts. The first symptoms are nausea, diarrhea, vomiting, fever, and abdominal pain, followed by headaches, eye swelling, aching joints and muscles, weakness, and itchy skin. In severe infections, persons may experience difficulty with coordination and have heart and breathing problems. Death may occur in severe cases.

Parasitic protozoa of concern in meat processing include Cryptosporidium parvum and Toxoplasma gondii.

Cryptosporidium is typically transmitted to humans from fecal material of animals, primarily cattle, via contaminated water or occasionally, food. The organism is destroyed by boiling water.

Toxoplasma gondii is carried by cats but can infect many warm-blooded animals. A form known as the oocyst is shed and can sporulate and survive in soil and other environments for extended times; the sporulated oocyst is infectious to all warm-blooded hosts. When ingested, the sporulated oocysts go through several forms, eventually forming cysts in tissue such as muscle. These cysts are infective if ingested. Toxoplasma can cross the placenta and affect the fetus, resulting in blindness and more serious effects in the brain.

Parasites are readily destroyed at cooking temperature and are not a major concern in thermally processed commercially sterile meat and poultry products since they are subjected to temperatures well in excess of what is needed to destroy parasites. Parasites are a concern with respect to shelf-stable products that are not cooked. For example, trichinae are a concern with respect to shelf-stable products, such as dried sausages, containing pork.


Bacterial hazards of concern in meat and poultry

Of the microbiological hazards of concern in meat and poultry, the most important are bacteria. Illness from meat and poultry is primarily caused by bacterial pathogens.

The pathogens that are most likely to be found in livestock (cattle, sheep, and swine) and poultry (chicken and turkey) include Salmonella, Campylobacter, and Listeria monocytogenes. Listeria monocytogenes also is widespread in the environment.

Escherichia coli is also found in livestock and poultry, but most strains are not pathogenic; the pathogenic E. coli of primary concern is known as E. coli O157:H7 and is found in beef.

Yersinia enterocolitica is a pathogen most commonly associated with pork; only certain serotypes (strains) are pathogenic.

Clostridium perfringens can also be found in meat and poultry; the spores may survive cooking and grow to high numbers in foods due to temperature abuse.

Clostridium botulinum is rare in meats. When present, it is there in very low numbers (estimates are 0.1 spore to 7 spores per kg meat).

Bacillus cereus is another sporeformer of concern in meat and poultry products, especially those containing spices, which is a common source of the spores.

All of these pathogens have been implicated in food borne disease outbreaks associated with the consumption of meat and poultry products in which these hazards were not properly controlled. Proper cooking or thermal processing, fermentation, cooling, and storage of food can destroy and/or prevent growth of these bacteria.


Sources of Microorganisms

Raw materials and ingredients are the primary sources of microorganisms that must be addressed in the production of thermally processed commercially sterile and shelf-stable products.

Although muscle tissue is generally considered to be sterile, raw meat and poultry become contaminated during slaughter and further processing. The ultimate source for pathogens in raw meat and poultry is apparently-healthy animals that may shed these bacteria in their feces. While dressing the carcasses during the slaughter process, these bacteria may be transferred from the hide, skin, feathers, gastrointestinal tract and other offal to the carcass, causing contamination. This is also a major source of spoilage microorganisms.

Contamination can also come from the processing environment. Utensils such as knives used in slaughter and fabrication, workers hands and gloves, equipment, and occasionally aerosols with dust and other particles carrying microorganisms can all contribute to the microbial load of products.

Contaminants may be present on containers and other packaging materials, although this is generally not a likely source of pathogens. Proper sanitation of the environment and protecting containers from environmental contamination can prevent these from being major sources of contamination such that they will negatively impact thermally processed commercially sterile and shelf-stable products.


P.S.
guys, both yiting and me are doing on pepperoni. As for the information, all have to refer to us both as we are not repeating the information. THANKS. ((:


References:
http://www.fsis.usda.gov/PDF/FSRE_SS_2Microbiology.pdf