Author: Monica
One of the feared microbe is Clostridium botulinum. This strain is very common in under-processed meat products. The toxins produced by the bacterium causes botulism, a condition that can lead to paralysis of the patient. Botulism in humans is always caused by toxin types A, B or E and occasionally by toxin type F. C. botulinum type E (group II) is one of the food-borne pathogenic bacteria that can survive in temperature of 3oC (Blackistore, 1998).
Clostridium botulinum is an anaerobic, Gram-positive, spore forming rod-shaped bacterium that is found widely in the environment such as soil and animal guts. It was first being isolated from salted raw ham in 1897. Clostridium botulinum type E , one of the food-borne pathogenic produce heat resistant spore of up to 90 oC. In addition, most food are pH 5 or pH6 and above. Clostridium botulinum grows from pH 4.5 and above and at water activity level (a w) of 0.94. Inactivation of Clostridium botulinum’s spores is done when the pressure is increased to 600-1400 Megapascal (MPa) and an increase in temperature of 90 oC to 110 oC, the use of pressure-temperature to inhibit the spores during vacuum packaging (Doyle, 2001). Clostridium botulinum can grow in a salt environment of lower than 7% (Sprenger, 2004). Clostridium botulinum causes the food-borne illness botulism. Botulism is caused by neuron toxins produced during the growth of the bacterium in food before eating.
Symptoms of this disease may occur within 12 to 36 hours or after 8 days of consuming the contaminated food. The initial symptoms include vomiting and nausea (Labbe, 2001). The toxin first affects the neuromuscular junctions in the head and neck area, causing the person to have symptoms like double vision, not being able to focus, drooping eyelids, dry mouth, difficulty in speaking clearly and the inability to swallow. The muscles of the body will continue to fail, resulting in paralysis and in severe cases, death (Labbe, 2001).
The growing of spores in food causes the bacterium to produce botulinum toxins. The spores of the bacteria grow best in the presence of oxygen, a pH environment of 4.6 or higher, a low salt environment of 7% and below and a high moisture environment of 95%. This factors suits especially well during the scenario whereby the ham was taken out from its packaging and left in the air for a relatively long time before being served. This could be so if the ham is left on a tray while waiting to be put into a sandwich order. This allows the conversion of the dormant spores from the curing to be reactivated into spores that proliferate. To avoid the production of the toxin in food, it is important to destroy the spores of the bacteria such as cooking the ham (Eco Lab website).As mentioned earlier, one of the ways to destroy the spores of the bacterium is by adding food preservatives such as sufficient sodium nitrite in food to inhibit the growth of C. Botulinum. The food product should also not be stored in the temperature of above 3oC.
Wednesday 30 March 2011
source of salts and sugar in foods
Author: Monica
Nitrates and nitrites
Nitrates and nitrites
Nitrates helps in preventing oxidation (Doyle, 2007). Nitrate (NO3), in the form of either sodium nitrate or potassium nitrate, is used as a source for nitrite (NO2). Nitrate in meat products is converted into nitrite by the action of bacteria. The nitrite further breaks down in the meat into nitric oxide (NO), which then binds to the iron atom in the center of myoglobin's heme group, preventing oxidation (Sebranek, 1991). Nitrite acts as oxygen scavenger or anti-oxidative substance (Pegg, 2000). The interaction of nitrite in the meat acts as a chelating agent. Trace metals, as well as any liberated non-heme iron from denatured heme pigments are tied up and their effects inactivated (Sebranek, 1991). Nitrate act as decreasing the Oxidation reduction potential (Eh) of cured meat, therefore at low pH 5.5 and below, the meat is not prone to oxidation and in addition, the initial lag phase of bacteria is prolonged (Lawrie, 1998). Oxidation reduction potential is a measure of the tendency of a chemical to be reduced through acquiring electrons. It is measured in Eh (1 Eh = 1 mV).
According to the Sales of Food Act, the legal limit for nitrites in products is capped at 250ppm. This is the legal and sufficient inhibitory amount of nitrites. Furthermore, nitrites help to prevent the spoilage due to the growth of Clostridium botulium. In the study of the effect of nitrite on the pyruvate metabolism of anaerobes, it was found out that the addition of nitrites caused the rate of hydrogen and carbon dioxide to reduce (Hill, 1991). The amount of the Adenosine Triphosphate (ATP) in cell had reduced quickly. This means that the cell has lost much energy, since ATP is the energy source of cell. Thus it was concluded that the presence of nitrites inhibits the pyruvate metabolism of anaerobes (Hill, 1991).
The outgrowth and germination of bacterial spores happens chronologically in five stages; germination (becoming non-refractile, stainable, heat sensitive), swelling of germinated spore, forming new vegetative cells, elongation and cell division. The spore of Clostridium botulisum after germination are inhibited when insufficient concentrations of nitrites were used, while sufficient concentration at 250ppm of nitrites inhibited the germination process itself (Sebranek, 1991). This means although the germinated spores are inhibited with insufficient amount of nitrites, it is not able to prevent the dormant germinated spore’s activation when conditions are suitable. Therefore it is crucial that sufficient nitrites are used. Input concentrations of more than100 mg/kg (ppm) are used for protections against normal flora. At a concentration of 200 mg/kg at the pH of 6.0 is enough to inhibit the strains of Achromobacter, Aerobacter, Escherichia, Clostridium botulisum, Flavobacterium, Micrococcus, and Pseudomonas spp (Sebranek, 1991).
In addition to that, nitrites serves as an antioxidant giving the meat the stable colour and prevent the microbiological growth by retarding it. Apart from giving a pleasant flavor, it also help to prevent the development of oxidative rancidity in the beef. Nitrite also prevents lipid oxidation of cured meats by four mechanisms (Nation webmaster, 2005). The first mechanism is the formation of a stable complex between heem pigments and nitrites, thus preventing release of iron from porphyrin molecule. The second mechanism is the stabilization of unsaturated lipids within tissue membranes against oxidation. The third mechanism is the interaction of nitrite as a metal chelator so that it ties up trace metals in meat as well as any liberated non-heme iron from denatured heme pigments. And lastly, the fourth mechanism is the formation of nitroso and nitrosyl compounds in meat which possess antioxidative properties by acting as radical scavengers (Nation webmaster, 2005).
Salt (NaCl)
Salt is a multifunctional ingredient in cured meat. Sodium ions are responsible of contributing the flavor from salt. An important function of sodium in the perception of flavor is the increased intensity of other flavors that result in the presence of sodium (Ruusunen, 2005). Salt is also a flavor enhancer for the other flavor components in food.
Salt lowers the water activity of the food system by its osmotic property (Doyle, 2007). This also helps to make the conditions less suitable for micro-organisms to survive by inhibiting bacterial growth on the beef ham by dehydration and osmotic pressure (Hui, 2006). The salt penetrates through the beef ham and draw out moisture from it. Salt dehydrates the membranes of bacterial cells, thus inhibiting the growth of most pathogens in food (Ruusunen, 2005). Concluded from the study of Siegel (1981), a salt concentration of at least 13% is able to achieve inhibition of pathogenic microorganisms. However, a higher concentration, maximum 5g in one serving of the meat product, is needed to prevent loss of salt during process such as water drip. Five grams of salt is also the maximum recommended salt intake for adults (Health promotion board, 2010). Together with nitrates, both ingredients help inhibit C. botulinum spores from developing into toxins even at those higher smoking temperature (up to 82°C).
Sucrose
Widely known as table sugar, is used to lower the water activity (aw value) of the food system due to its hygroscopicity. Having the ability to retain water, it reduces water available in the food system and thus reduces the opportunities for the survival of micro-organisms. It gives the similar effect as the common salt (Forsythe, 1994). When sugar is rubbed onto the beef, it diffuses into the ham. Water present in the beef is extracted out through osmotic action, lowering the water activity (Doyle, 2007). Depending on the amount of water activity in the food, sugar is added accordingly to lower the water activity into the desired water activity.
Author: Monica
Enzymatic reaction in meat
Enzymatic reaction in meat
During early postmodern, enzymatic reactions take place due to the hydrolysis of fatty acid. The absence of blood allows lactic acid to be accumulated into muscle and produce pH drop to 5.6 within a few hours. In addition, during the rigor mortis, the pH levels decline (Toldrá, 2009). The amount of water retained in the myofibril structure also decreased, lead to contraction and meat size reduction. The reduction of the space within the structure is due to pH6, the isoelectric point of proteins. The higher the intramuscular content is present in the meat, the longer the time required for efficient salt diffusion (at pH6) and appropriate moisture loss levels will take longer to attain (Toldrá, 2007).
Meat composition
Red meat has many fibres large amount of myoglobin, lipid and high oxidative enzymatic activity. The dipeptides in the muscles are the anti-oxidant which to act as the neurotransmitter and modulators of in the enzyme reaction. As mentioned earlier, the higher the intramuscular content is present in the meat, the longer the time required for salt diffusion and moisture loss.
Apart from the addition of salt in cured meat, migration of water from depth of meat to surface of the meat also decrease the water activity in the meat (Toldrá, 2009). There are two types of water migration. One is from depth to product and second is water evaporation in the surface. Together with process such as curing and smoking, the decrease in water activity in cured meat products meant less favourable conditions are created for the microorganisms to thrive, since microorganism thrives lesser in levels 0.80aw. Diffusion coefficient depends on the salt and water, which is irreversible correlated to the fat content (Toldrá, 2007).
Fats in the meat also affect the dehydration process (Doyle, 2007). Although intramuscular fat gives marbling which is the main factor affecting the juicing, it also controls the reaction of desiccation and the development of flavour. Lipoxygenase catalyze the incorporation of molecular oxygen in polyunsaturated fatty acids, to give a conjugated hydroperoxide as final products (Toldrá, 2007).
Process
When the beef is slaughtered, the beef is drained off. After the drain off, the cow’s hide is carefully cut off. Care is also taken to prevent puncturing the intestine. This is to prevent microorganism from the hide and intestine from contaminating the meat. Water is then sprayed to wash off remaining blood and bone pieces. Then the cut meat is being rubbed with curing ingredients and is stored in the chiller at 0-4°C. It takes 12-15 hours to chill the meat to an internal temperature to 4°C (USDA, 2009). This is essential to prevent anaerobic bacteria at bone joints to cause bone souring spoilage before the salt penetrates the centre of the meat cut (Frederick K, 1981). Lower than 4 degree Celsius may slow down curing process or even halt it. This prevents the development of bacteria and may not be able to react with nitrites. Higher temperatures may increase the curing process but also encourage the growth of undesired micro-organisms.
Ordinary table salt (sodium chloride) is added because of its effect on flavor. Sugar is added to reduce the harshness of salt. Spices and other flavorings often are added to achieve a characteristic "brand" flavor. Nitrate is used as dry curing salt, having the mixture of nitrate, common salt and sucrose are rubbed into the meat. After which the cuts of meat are placed in the curing room. Curing process has other purpose such as removing water, activating some chemical reactions to develop taste and flavor. The refrigerator temperature is used as for optimum reaction between meat and nitrites. Also on the other hand, the low temperature discourages most microorganism growth
It takes about 24 hours to smoke and cook hams. Smoking is usually accomplished in three stages. During curing process first phase, or drying stage, the smokehouse is heated to 51°C. All dampers are opened to allow all excess moisture to escape and there is no smoking during this 8-hour period (Otwell, 2006). During the next eight-hour stage, the dampers are partially closed and the temperature on the house increased to 57°C. Smoke is generated at this phase. The smoke is continued throughout the third stage with all dampers closed, and the temperature on the house raised to 82°C (Otwell, 2006).. The humidity is kept at above 80% to increase heat transfer. The wood used to generate the smoke should be logs from hardwood species. Unlike pine or any other resinous wood or sawdust, smoke from hardwood does not give sooty smoke. Cured meat products are smoked after the curing process to impart a smoked meat flavor. The temperature of the smokehouse will maintain at 82°c, until the temperature inside the product reaches 61°C. During curing, water comes out from the ham, and as mentioned earlier, the decrease in water activity lesser chance for a variety of microorganisms to thrive.
Smoke
Smoking is usually combined with meat drying in meat preservation in many countries. Both smoking and curing reduce water activity reduction. In addition, smoking has bacteriostatic effect on pH (Doyle, 2007). Both techniques have uses the effect of enzymes and heat to help increase protein and lipid changes in the previously salted material. This helps in increasing nutritional quality and also increases the shelf life and safety quality of the product.
Smoke imparts flavor, color, and other sensory effects to foods. Smoking also creates a physical barrier for the meat. When the meat is being smoked, a layer of “skin” is being formed on the surface of the meat. Not only that, smoke also provides preservation to the food product. It functions as an antimicrobial and antifungal agent. In a study done by Wendorff (1981), the results of antibacterial and antifungal activities from a few smoke condensates show that the phenolic content of smoke contributes greatly to the antimicrobial and antifungal effects of smoke. But when it is faced with a few types of microorganisms, smoke is not an effective antimicrobial agent. Therefore, the usage of other hurdles such as salt or nitrates is used together with smoking.
In dry cured meat, the desired value of water value activity of 0.8, and moisture value of 24%. This is the value that can ensure good keeping shelf-quality. However, these moisture value and water activity are actually too dry for most preference. In order not to compromise the preservation quality while trying to retain enough moisture to suit most people’s taste, products which have undergone drying are accompanied with the use of smoking to increase the preservation of the product quality. In addition, drying and smoking are deployed with other technology in preservation, which are refrigeration, curing, salting, spicing, package and storage.
Packaging
Vacuum Packaging
Vacuum packaging is needed for the dry cured beef ham so as to prevent continued weight lost. Too much weight loss affects the sensory quality of the product. Vacuum packaging also prevents freezer burn by protecting the meat with vacuumed packed plastics. It also prevents unwanted colour change from freezer burn, thus preventing unsightly products (Stringer, 2000).
Vacuum packaging is widely used in the packaging industry. Before hermetic sealing, air is evacuated from a pack. The removal of atmospheric air inhibits the growth of aerobic and anaerobic spoilage micro-organism and thus, reduces the rate of oxidative deterioration. Therefore it is capable of extending the shelf life of perishable foods. It is an established technique for packaging chilled foods like primal red meats, cured meats and cheese. The presence of anaerobic Clostridium botulisum in the affected food product suggests that carbon dioxide from the atmospheric air has entered into the product due to faults from the packaging, since there should be no air in vacuum packaging (Doyle, 2007).
Refer to next post on the details of the packaging materials and the specific measurement regarding vacuum processing
Refer to next post on the details of the packaging materials and the specific measurement regarding vacuum processing
Material
Packing materials
Materials for vacuum products need to have high O2 barrier and high levels of seal integrity. The plastic bags normally used for vacuum packing are made of multi-ply formulations based on polyolefin resins, with either polyvinylidene chloride or ethylvinyl alcohol as the gas barrier component (Sprenger, 2004). The oxygen permeability of packaging films is measured in terms of the amount of oxygen which passes through a square metre of film in 24hours at atmospheric pressure. This measurement is called the oxygen transmission rate (OTR) and has units of ml/m2/24hr/atmosphere. O2 transmission rates of less than 15cm³m-²day-1atm-1 are required for vacuum packaging. Any greater OTR leads to oxygen and accumulation of oxygen in the pack (Otwell, 2006). The diffusion of atmospheric air will spoil the vacuum condition and make microorganisms viable. The material, in addition, must consist of coextruded or laminated films. This highly ductile plastic barrier laminate which will be draped gently over the food product (Stringer, 2000), this prevents formation of ice-crystals from gathering on the product surface during freezing. During the manufacturing process, the top and bottom web films are sealed from the edge of pack to edge of product, pack integrity is maximized and juice exudation is limited.
Therefore from the above discussed properties of an ideal vacuum packing material, PVDC (poly vinylinden chloride) is chosen. In addition of the properties mentioned above, it also has barrier properties which prevent the transmission of water vapor or oxygen (Sprenger, 2004). Apart from preventing the ice crystal formation, this plastic material also helps in eliminating freezer burn and dehydration, which helps in the preservation of the product’s sensory qualities.
There are 2 methods in which the process is carried out, Grace System and chamber system. The Grace system is carried out by subjecting the bag interiors to a vacuum i.e., reduced pressure after which the bags are sealed by any suitable means such as by the application of clips round the bag neck or by heat sealing the openings of the bag. The chamber system is carried out in a sealed vacuum chamber which is capable of being subjected to reduced pressure; in the chamber the bags previously filled with the meat, are sealed, and then the chamber is returned to atmospheric pressure by the admission of air so that the material of the bag is drawn into contact with the meat (Spooncer, 2010).
The reason for using curing and vacuum packaging
Vacuum packaging is needed for the dry cured beef ham so as to prevent continued weight lost. During curing, water comes out from the ham. During curing, salt is rubbed over the surface of the ham and it is pressed. This pressing helps draw out the moisture. Moisture is drawn out from the ham by the sodium chloride which preserves it. The salt penetrates through the beef ham and draw out moisture from it. Vacuum packaging also prevents freezer burn by protecting the meat with vacuumed packed plastics. It also prevents unwanted colour change from freezer burn, thus preventing unsightly products.
Storage
The spores of the bacteria grow best in the presence of oxygen, a pH environment of 4.6 or higher, a low salt environment of 7% and below and a high moisture environment of 95%. The food product should also not be stored in the temperature of above 3oC (Stringer, 2000). As light accelerates oxidation, the manufacturer can store the vacuum meat product in chiller storage with dim light. However, the light must be bright enough for workers to realize any damage in the products such as holes and discolouration (Doyle, 2007).
How safe are we?
PREREQUISITE PROGRAM (SSOP / GMP)
Good Manufacturing Practices (GMP) and Standard Operating Procedures (SOP) are two tools for a meat processing facility that help for the production of high quality and safe meat products. The programs established for GMP's and SOP's will provide the basis for other programs the help to assure the level of product quality such as standards for ISO 9000 and for product safety in the Hazard Analysis and Critical Control Point (HACCP) system. Many companies like to view these systems as a pyramid (Figure 1.) with the GMP's and SOP's supporting the more advanced program of HACCP and all three programs being important for the ISO 9000 system.
Figure 1. GMP's and SOP's form the foundation for the hazard analysis and critical control point system (HACCP) and ISO 9000.
GMP's and SOP's are not clearly separated as one may overlap the other. GMP's are ususally referred to as practices and procedures performed by a food processor which can affect the safety of the meat or food product. GMP's may refer to the people, equipment, process and the environment in the production process. SOP's may be thought of as one person's job or one task that is preformed in the production process.
GMP's are written into food regulations in the United States by the Food and Drug Administration (FDA) for most food products produced. Rules and regulations established by FDA are published in Title 21 of the Code of Federal Regulations (CFR) in Chapter 1, Part 110. In this regulation the term current good manufacturing practices is used and the criteria and definitions used apply to determining whether a food is adulterated; whether the food has been prepared, packed or held under insanitary conditions whereby it may have become contaminated with filth; or whereby it may have been rendered injurious to health. The regulations addresspersonnel, buildings and facilities, equipment and utensils, and production and process controls. These rules are not applied to meat processing facilities under the USDA FSIS in the United States, but provide an excellent framework for meat processing companies to establish GMP's in their production plants.
The Food Safety and Inspection Service (FSIS) within the United States Department of Agriculture (USDA) is the regulatory agency with enforcement over the meat processing industry. Rules and regulations to sanitation standard operation procedures established by FSIS are published in Title 9 of the Code of Federal Regulations (CFR) in Chapter 3, Part 416. Part 416 includes guidelines for grounds and facilities, equipment and utensils, employee hygiene and for Sanitation Standard Operating Procedures.
http://foodsafety.unl.edu/haccp/prerequisites/gmp.htm
Food safety
Food bourne illness is caused by many types of microorganisms which can be very harmful if food is not stored, packaged or even processed properly. Microorganisms are always introduced at any point of time when the corrective measurements are not carried out. Do you want to know more about the mircroorganisms??
E.COLI:
E.coli is a Gram negative, non-spore forming, facultative anaerobic rods of Family Enterobacteriaeceae. This microbe is mesophillic and grows from 7 - 10 ºC up to 50 ºC (optimum at 37 ºC). With a low minimum water activity for growth at 0.95, pH 4.4 – 8.5. Most E. coli strains are harmless inhabitants of the gut of humans and other warm-blooded animals. Infectious dose of E.coli is 102 CFU/g. In the case of being dried beef of water activity 0.9 and having it to be Barbequed, E.coli is not able to grow or survive at such temperature.
The identified presence of E.coli O157:H7 in related meat outbreaks are, having the cooking heat to be too slow or having short cooking time. When meat is only slightly undercooked this may result in infective dose of the pathogen to be present. E.coli will be present as well when meat is held at room temperature, sometimes even for short periods of time.
Symptoms of E.coli mainly causes diarrhea, abdominal cramps, vomiting and sometimes leading to dehydration.
Beatrice Trum Hunter.2009. Infectious Connections: How Short-term Foodborne Infections Can Lead to Long-term health problems.P55.United States of America: Basic Health Publications
Listeria monocytogenes:
It is a Gram positive, non-spore forming microbe, it is a facultatively anaerobic rod. It is Psychrotrophic and grows at a range of 3 - 4ºC, with an optimum at 30 - 35 ºC, pH 5.0 – 9.0, minimum pH 4.39, aw > 0.92. This microbe is able to grow in the presence of 10% salt content. Growth is enhanced at decreased oxygen levels even when there is presence of carbon dioxide. Listeria monocytogenes is not able to survive heating temperature and time at 60 ºC for 30 minutes. Produces Influenza like symptoms such as fever, headache and occasionally gastrointestinal symptoms. Listeria monocytogenes is mainly found in Water, soil, sewage, decaying vegetables, silage and faeces of numerous wild and domestic animals.
Samonella spp
It is a Gram negative, mesophillic, facultatively anaerobic, motile, non-spore forming rod, grows at 5 - 47 ºC, optimum at 37 ºC, pH > 4.0, minimum pH 4.2, optimum pH at 7.0 and aw >0.95, inhibited by high concentration of carbon dioxide of about 20 – 80% in MAP and salt concentrarion <3% (w/v).
Salmonella spp produces symptoms like Fever, headaches, nausea, vomiting, abdominal pain and diarrhoea . presence of this microbe in domestic animal is highly because of ingestion of the microorganism in food such as milk, meat, poultry and egg derived from infected animals. Food can be contaminated by infected food-handlers, pets and pests, or by cross-contamination as a result of poor hygiene. But with proper pre-requisite and good manufacturing practices in place, the possibility of occurance is very low in terms of contamination of food and water with faeces of infected animal or person. Initial contamination exacerbated by the prolonged storage at temperatures the microorganism is able to grow.
Staphylococcus aureus:
Amount of CFU that can result in health hazards is 105 to 107 cfu/ml with an acceptable number of <100 cfu/g .
S.aureus is a Gram positive, non-motile, non-spore forming, Spherical grape like shape in clusters, facultatively anaerobic coccus, grows at 7 - 48 ºC, optimum at 37 ºC, pH 4.0 – 9.3, optimum pH 7.0 – 7.5, the pH range over which enterotoxin is produced is narrower, with little toxin production below pH 6., 10 - 46 ºC, optimum at 35 - 45 ºC, optimum pH is 6 – 7, while bacterial growth will still occur at aw 0.83, toxin production does not occur below 0.86, this is the most resistant bacteria with regard to reduced water activity. The toxin that causes intoxication is formed in food, is relatively heat stable and can survive boiling for > 1 hour. It is therefore possible for well-cooked food to cause illness without containing viable microorganism.
Infection with this pathogen can cause severe nausea, cramps, vomiting and prostration, sometimes accompanied by diarrhea. If storage conditions are inadequate, the bacteria may multiply to produce toxin. Intoxication is often associated with cooked food via improper handling or contamination. But with proper pre-requisite and good manufacturing practices in place, the possibility of prevalence is very low
Agriculture Research Service, (2010), Pathogen Modeling Program Online, Eastern Regional Research Centre , United States Department of Agriculture, accessed on 30 march 2011 from
N. J. Rowan & J. G. Anderson, (1996), Applied and Environmental Microbiology, Department of Bioscience and Biotechnology, University of Strathclyde, Glasgow, Scotland, accessed 30 march 2011 from
Ibadan Biochemical Communication Group, (1989-2010), Bioline International Official Site (Site up-dated regularly), Environmental Information, CRIA, Brazil, accessed on 30 march 2011 from
Yersinia enterocolitica:
It is a Gram negative, facultatively anaerobic, non-spore forming rod of family Enterobacteriaeceae. Psychrotrophic, grows at 0 - 44 ºC, optimum at 29 ºC, pH 4.6 – 9.0, optimum pH 7 – 8, and in media containing 5% salt, no grow in media containing 7% salt
Causes symptoms like Abdominal pain, diarrhoea, mild fever, sometimes vomiting. It is mainly found in animals.
Clostridium botulinum:
Produces 2 types Exotoxin and enterotoxins . They are mainly found in soil and fecial contamination and passed to animals. Enterotoxins are produced when vegetative cells multiply in intestines
Richard Lawley, Laurie Curtis, Judy Davis , Page 32-35 The food safety hazard guidebooK,By RSC Publishing
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