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Microbial growth of spoilage and pathogenic bacteria
Bacillus cereus is a gram- positive, rod shaped bacterium which was cultured from the blood and pleural fluid. It is mesophilic which grows optimally in temperature between 20 degree Celsius and 40 degree Celsius. The organism is capable of adapting to a wide range of environmental conditions. It also derives nutrient from its host and is found in the rhizosphere of some plants (Guyon, Meynier and de Lamballerie, 2016).
Bacillus cereus is a type of bacteria that produces toxins which can cause two type of illness such (wherein one is characterised by diarrhea and other one called as emetic toxin which leads to nausea and vomiting (Dantas, Sampaio and Saldanha, 2015). These bacteria are present in foods and can multiply at room temperature. Cereus develops on a sheep blood and it builds up in a rod shaped. Gram stains are required to be performed on each microbe for the purpose of determining the stain colour and shape of the cells. Biochemical test for Bacillus cereus concludes that Escherichia coli was the gram negative of unknown 112 bacterium that grows and isolated in a nutrient agar plate.
Bacillus cereus is a great contributor to the microflora of insects which drives nutrients from its host and is also found in the rhizosphere of some plants (Cheng, Sun and Liu, 2015).
It develops in food products which are rich in proteins and vitamins such as dairy products and seafood items (How Moist Heat Kills Spores of Bacillus subtilis. 2007). Thus, it can be said that Bacillus cereus has high moisture content which leads to spoilage of food products.
There is a combination of mild acidification in Bacillus cereus which has pH 5.0 level and that is also inhibited for 60 days in vegetables. However, if it is preserved in appropriate manner, then it can expose to temperature of mild abuse (Influence of pH and temperature on growth of Bacillus cereus in vegetable substrates. 2003).
Bacillus cereus seems to be a supporting aspect for food items by using gradient gel plates. Sorbate was completely effective against E. coli in all temperature combination. In 25 degree Celsius, sorbate was more effective preservative as compared to benzoate which has higher concentration of NaCI. However, on the other hand, at 35 degrees C benzoate was the most effective preservative against St. aureus especially when used at pH
The heat resistance of the spores is highly dependent on the food matrix. Sometimes, it also corresponds with mesophilic spore forming bacteria that grows optimally at mean temperature; but at the same time strain variability is very much high. Temperature below 100 degree Celsius allow to survive the individual spores. This is sufficient and requires rapid cooling after heat treatment which prevents the germination of the spores.
Oxygen seems to be essential factor for production of the emetic toxin by Bacillus cereus. It is also analysed that when beans, rice and soy broth were inoculated with cereulide, it produces strains B203, B116 or strain F-4810/70. However, at the same time packaging with modified atmosphere low in oxygen could also be used for the purpose of reducing the risk of cereulide formation during storage of food (Shu, Liu-gu and Yan-jun, 2015). Anoxic storage is useful in preventing cereulide production at the time of supplying the amino acids.
The disease syndrome it causes
It is a type of bacteria that produces toxins and mainly it develops two types of diseases such as diarrhea and vomiting. Bacillus anthracis also causes anthrax and Bacillus thuringiensis. Moreover, it also results in two types of food positioning such as emetic and diarrheal syndrome. The symptoms include abdominal cramps, watery diarrhea, nausea and vomiting (Tomohiro, Nakabayashi and Morimoto, 2016). Diarrheal illness remains in human body with an incubation time of approximately 10 to 16 hours and at the same time, vomiting illness remains with an incubation time of one to six hours. Further, nonhemolytic enterotoxin is also associated with diarrheal syndromes. It also causes gastrointestinal illness which comprises of food poisoning.
What food it is associated with:
- Meat pies
- Cooked rice and fried rice
- Starchy foods such as pasta and potato
- Food mixtures like soups, sauces and casseroles
- Puddings and deserts (Amid and et.al., 2015)
This type of bacterium is responsible for food positioning during the element of moisture included in it. Thought, it has a positive effect in the form of probiotic food additive for animals. It develops in food items because of improperly prepared and stored food. This is the reason that allows the bacteria to multiply and along with that, it also results in enterotoxins which directly causes to health illness.
How widespread it is
It is detected in cooked foods such as rice noodles, wet wheat noodles, spices, grains and legume products. Bacillus cereus has major prevalence in fried rice due to variety of ingredients such as chicken, seafood, egg and beef (Nakae and et.al., 2013). It has also been observed that due to involvement of colony forming, the infectious particles of Bacillus cereus increases in the food items. However, on the other side, the type of rice and the quantity boiled per day were not independent risk factor for high B as cereus counts majority of B in food poisoning.
Are toxins produced (details about toxins)
Patients that have symptoms of diarrhea are thought to stem from three basic toxins such as hemolysin BL (Hbl), nonhemolytic enterotoxin (Nhe) and Cytotoxin K (CytK). Both the Hbl and Nhe toxins are pore-forming toxins that are closely associated to ClyA of E. Further, emetic syndrome is caused by cereulide which is found in emetic strains. Such toxins are heat resistant and causes two types of food poisoning (Zeng and et.al., 2014). Bacillus cereus are facultative anaerobes which is like other members of the genus bacillus that can produce endospores. Its virulence factors typically include cereolysin and phospholipase C. The timing of the toxin production was previously responsible for two different courses of diseases. It is also known to cause difficult to eradicate chronic skin infection; instead of developing less aggressive necrotizing fasciitis. Further, among the toxins, it can also cause keratitis (Setyowati, Suminta and Gunawan, 2015).
How it spreads
Bacillus cereus grows mainly in dirty and contaminated areas. Toxins produced by the bacteria spreads mostly in starchy foods and contaminated water. Rice and potato being the highest source of starch, are best media for transportation of strains of Bacillus cereus. Starchy toxins cause vomiting, nausea, malaise and ocular infections (Lu and Li, 2014). Raw food materials is targeted medium for secretion of toxins by Bacillus cereus. Diarrhoea causing toxins are also secreted through this bacteria. It spreads with help of contaminated water, meat, vegetables and milk products. Spore formation and continuous exposure to contaminated environment causes spread of these strains.
Example of outbreak
From 2007 to 2012, Belgium witnessed a critical outbreak of diseases in small children and infants of age 10-18 months. The cause of their disease was Bacillus cereus pathogen. The major cause behind this outbreak was incorrect use of raw agricultural produce (Alkasrawi, Jrai and Ala’a, 2013). About 188 cases were reported which indicated similar symptoms that is diarrhoea and vomiting with nausea. General causes of diseases caused by Bacillus cereus were unhygienic food practises and inappropriate storage conditions. On the other hand, reports described that a disease struck staff member of kindergarten was responsible for interfacing bacteria to food for toddlers. Several measures were taken by doctors to spread awareness regarding precautions from this bacterial consequences (Kobayashi, Shimojo and Watanabe, 2016)
Significance in production
The organism commonly develops in food items due to their resistant endospores. This leads the organism to survive in the food items during production processes such as dying and heat treatment. It is also considered as a well-known food borne pathogen that causes two types of illness (Occurrence and signiﬁcance of Bacillus cereus and Bacillus thuringiensis in ready-to-eat food. 2005). In addition to this, cereulide is produced in the food of enterotoxins and it is also belives to be produced in the intestine after ingestion of Bacillus cereus organisms. The two most well characterised enterotoxins changes the level of food products. These toxins act in a combination with Cry proteins to cause cytolysis.
Strategies that food industry may use to reduce spoilage
Bacillus cereus are heat resistant; hence food should be cooked at proper temperature so that it could destroy most of the foodborne pathogens that includes the vegetative cells of Bacillus cereus. It will assist in destroying the spores (Grose, Belnap and Breakwell, 2014). There are several guidelines provided by National Institutes of Health and the National Food Processors Association which can be adopted by the food industry to reduce the amount of spoilage.
- Steaming under pressure, roasting and grilling food can destroy the vegetable cells and spores.
- Food infested with the diarrheal toxin can also be inactivated by heating for minutes at 133 degree Fahrenheit.
- Food that could be infested with the emetic toxin need to be heated to 259 degree Fahrenheit for more than 90 minutes so that the amount of spoilage could be reduced.
- Further, reheating of food should be done on continuous basis (Delbrassinne, Botteldoorn and Denayer, 2015).
- Hot foods should be kept on above 60 degree Celsius and cold foods should be kept below 4 degree Celsius to prevent the formation of spores.
What fermentation can occur in this food, what cause it and how to test it
Fermented fish is a traditional preparation of fish and it is highly important method that preserves the food items. It is observed that fish rapidly spoils, goes rotten unless some method is applied to stop the bacteria (Influence of pH and temperature on growth of Bacillus cereus in vegetable substrates. 2003). Food poisoning from raw fish occurs when people consume raw fish that has become too warm before serving or been contaminated with an infectious organism. Scromboid poisoning usually occurs when the fish becomes too warm when they caught. Hence, as a result, a chemical substance called histamine builds up in the fish and when consumed, this substance causes a food poisoning reaction that is similar to allergic reaction. Since, the fish is cooked, these organism are not killed; thus they invade the body. Fish needs to be fermented so as to protect it from microorganisms and if enzymes present in the flesh, then it leads to more contamination (Diomandé, Nguyen-the and Brillard, 2015).
It occurs in raw fish due to the risk of contamination with pathogenic bacteria namely clostridium botulinum. These aspects highly prevails in fermented fish and in other categories of foods. Universal salt iodization promotes the use of iodates salt for producing industrial food products, however at the same time it may affect quality of product along with its iodine stability. After fermentation, raw fish can be tested for sensory acceptability by Laotian and Thai panellist afterwards they are cooked and served in the traditional way (Banerjee and Ghoshal, 2016). It is also essential to ferment the fish with iodized salt so that to maintain suitable level of iodine. Further, test can also be conducted through modern approach such as bio preservation which adds lactic acid bacteria to the fish to be fermented. This produces active antimicrobials like as lactic and acetic acid, hydrogen peroxide and peptide bacteriocins (Medina-Meza, Barnaba and Barbosa-Cánovas, 2014).
The test needs to be conducted because it aids in producing antimicrobial nisin which is the most effective preservative. This highly aids in safeguarding the fish from fermentation. In raw fish, biogenic amines present which is affected by many factors; thus the process of fermentation is essential because it ensures to have tight control over food products (Shu, Liu-gu and Yan-jun, 2015). With the help of proper fermentation, life cycle of the food products could be enhanced. Any fish which is subjected to a salting process is likely to be subjected to a degree of fermentation. It depends on the factors such as gutted element, fat element and etc. Proper temperature is essential because that keeps the fish fresh and useful.
What enzyme reactions can occur in this food and what can cause it and how to test it
It is an apparent fact that processing and cooking destroy enzymes in food. In raw fish, enzymes are used for the production and processing of fish and seafood. Due to the catalyst nature, enzymes are utilized in food production and processing (Tomohiro, Nakabayashi and Morimoto, 2016). Since, raw fish is less stable due to high content of moisture; hence appropriate methods are required to be adopted to maintain the perishability of the food products. Spoilage is caused by the action of enzymes, bacteria and chemicals that present in the fish. High moisture, high fat content, high protein, ambient temperature and weak muscle tissue are some of the factors that contribute to the spoilage of fish (Amid and et.al., 2015). The enzyme that present in the muscle convert glycogen into lactic acid wherein the pH of the fish muscle falls.
In this respect, autolysis can be described as an internal breakdown of the structure of protein and fats because of the reactions of enzymes.
In cooked fish products, lipid oxidation is non-enzymatic element that is present and have been denatured at the cook temperature (Nakae and et.al., 2013). Thus, this is the reason the warned- over flavour that can be associated with cooked and reheated meat and fish. This further results in non-enzymatic reactions. For instance- in raw fish there is the potential for lipid oxidation which needs to be catalysed by several enzymes. At the same time, in the second type of oxidation, the enzymes are involved in reducing iron complexes such as haem proteins (that react with hydrogen peroxide). These radicals turn into oxidise lipid which includes the microsomal lipid enzymes. The eating quality of fish become less pleasant due to the attributes of spoilage and deteriorative changes (Zeng and et.al., 2014). For instance – oily fish like herring, mackerel can become rotten due to the reaction of oil within oxygen which further also creates unpleasant odours and flavours.
Therefore, chemical tests can be conducted to measure the extent of such oxidation. It occurs slowly in iced fish. At the same time, sensory method of assessment can also be applied so as to identify the freshness of the fish (Setyowati, Suminta and Gunawan, 2015). Further, taste panel can also be conducted wherein trained and expert advice can be taken for the purpose of assessing the quality of the fish. At the same time, non- sensory assessment can also be conducted which is not based on subjective responses. Nonetheless, these methods are highly reliable and objective as compared to other methods. On the other level, it is also ascertained that non- sensory tests measure only one aspect of spoilage which assess a few changes only that is concerned with spoilage (Lu and Li, 2014). From general test, chemical methods and physical methods could be conducted which need laboratory facilities and trained staff members.
What oxidation reactions can occur in this food and what can cause it and how to test it
Oxidation is regarded as a reaction that takes place in any particular product when oxygen has access to products which contains fat and pigments. If elements of fat oxidize in any product, then they produce off odours and flavours (What is oxidation, and how does it alter food products. 2009). At the same time, most often when fat oxidise, vitamins in the product also oxidize and as a result, it loses their activity. However, on the other hand, it pigments oxidize, they can change the colour of the product totally. For instance – raw fish turns gray in colour when the myoglobin pigment oxidizes. However, after this, raw fish is not unsafe; hence generally wrapping is done to prevent the freshness of food products (Alkasrawi, Jrai and Ala’a, 2013). Lipid oxidation occurs in fresh and frozen seafood and that can be analysed by metal ions which aids in identifying the texture of the organism.
From a few sources, it has been ascertained that lipid oxidation is an important cause that affects the quality element of seafood particularly in those products which contain high concentrations of lipid (Kobayashi, Shimojo and Watanabe, 2016). It presents basically in raw fish because of the high content of polyunsaturated fatty acids (which is found in organisms from the marine environment). It occurs in raw fish because of the increased reactivity of unsaturated fatty acids with their chain lengths. After getting started once, this keeps on increasing due to the cascade of reactions which occurs with each new molecule (Grose, Belnap and Breakwell, 2014). This also changes the reaction speed and variability. It also leads to the formation of lipid radicals which further reacts to lipid peroxides and hydroperoxides. It is also ascertained that auto oxidation in meat and fish can be initiated by light, heart and presence of metal ions and radicals. Low concentration radicals are required to be started so that it can increase the level of reaction.
In order to test the oxidation reaction, peroxide value can be determined which states the amount of hydroperoxides. The test states that the peroxides are not stable and that react further with an on-going oxidation of the peroxides (Delbrassinne, Botteldoorn and Denayer, 2015). Another method that is used is TBARS (Thiobarbituric Reactive Substances) which reacts with malondialdehyd that is a secondary oxidation product. However, the method shows other substance in coloured complexes also which might result in wrong estimation of the oxidation status (Diomandé, Nguyen-the and Brillard, 2015). Besides this, another traditional method is followed to test the oxidation reaction is to measure the iodine value so as to find out the amount of lipid double bonds.
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