The organic nature of the food we eat every day means that they can be altered. Due to its Seasonal and their different backgrounds, it will normally have to be kept for some time before being consumed ...
1. Conservation
there foods that can be stored for an extended period of time. Within this group are called stable foods, do not freak out if treated with care (such as sugar, pulses, etc.), And unstable food, they need more careful handling (such as potatoes, fruits, etc.).
Other foods, however, enjoy a short shelf life and need specific treatments to prevent spoilage. Are foods semifrescos fresh or as meat, fish, eggs or milk.
2. Causes of altered
1. Conservation
there foods that can be stored for an extended period of time. Within this group are called stable foods, do not freak out if treated with care (such as sugar, pulses, etc.), And unstable food, they need more careful handling (such as potatoes, fruits, etc.).
Other foods, however, enjoy a short shelf life and need specific treatments to prevent spoilage. Are foods semifrescos fresh or as meat, fish, eggs or milk.
2. Causes of altered
Physical causes
The presence of excessively high or too low, the gain or loss of moisture and radiation can cause disruption of food.
The presence of excessively high or too low, the gain or loss of moisture and radiation can cause disruption of food.
also causes chemical changes occur due to chemical. Fats in foods are oxidized flavor and odor characteristic to food, even when they are in low proportion.
Causes
biological causes Previous almost always are associated with the biological causes such as microorganisms, parasites, insects or rodents.
biological causes Previous almost always are associated with the biological causes such as microorganisms, parasites, insects or rodents.
Of all the causes that will further discuss the biological cause. In general, microorganisms are associated with particular food groups. They can survive the heat treatment required for canning or contaminate the food after treatment due to sutures or container leaks.
When pollution is before treatment, it is possible to predict the organism responsible if they are aware of the nature of the food and the conditions under which the food has undergone. However, microorganisms that are introduced by leaks can be varied as the composition of the cooling means.
When pollution is before treatment, it is possible to predict the organism responsible if they are aware of the nature of the food and the conditions under which the food has undergone. However, microorganisms that are introduced by leaks can be varied as the composition of the cooling means.
Table. Classification of foods according to their acidity ( Cameron and Esty, 1940 ) groups of spoilage organisms in canned foods.
| groups according to degree of acidity | pH range | food groups | Microorganisms |
| Group 1: Low-acid | > = \u200b\u200b5 | meat products, marine products, milk, vegetables | Aerobic sporulated sporulated anaerobes, yeasts, molds and bacteria spore |
| Group 2: semi-acid | 4.5> = pH <> | Mixed meat and vegetables, soups, sauces | |
| Group 3: acid 3.7 | <= pH <> | Tomatoes, Pears, Figs, Pineapple Other fruits | spore bacteria, non spore bacteria, Yeasts, molds |
| Group 4: very acidic PH | <> | Pickles Grapefruit, Citrus Juices |
According
heat requirements microorganisms can be From less to more demanding: psychrophiles, mesophiles, thermophiles and thermoduric, the latter two the most interesting from the standpoint of heat treatment. Thermophiles are able to develop at high temperatures (55 º C and above), while thermoduric are able to withstand the effect of high temperatures. However, mesophilic organisms can be thermoduric because its spores, as spores may be thermophilic bacteria ( Desrosier, 1987 ). In turn, Cameron and Esty ( 1926 ) classify thermophilic organisms into two groups: thermophilic required (growing at 55 ° C but not at 37 º C) and thermophilic facultative (grown at 55 ° C and 37 ° C). According
oxygen requirements of microorganisms include: aerobic (requiring the presence of oxygen), anerobios (only develop in the absence of oxygen or low oxygen tension) and facultative anaerobes.
2. MICROORGANISMS IN FOODS OF LOW ACID AND MEDIA
2.1. Aerobic spore
The most widespread are those of the genus Bacillus , which has its roots in the soil and water, which almost always present in the raw materials used in preserves.
Its optimum growth temperature ranges between 28 and 40 º C for most, although some thermophiles, which can grow at 55 ° C and even 70 º C.
Among these we find both obligate aerobes, and facultative anaerobes, the latter can grow in vacuum.
The types of alterations that may take place are the simple fermentation, producing gas and acid and gas.
Bacillus cereus
simple fermentation is the most common and is due to attack of the carbohydrates with production of acid and no gas production. B. and B. stearothermophilus coagulans are the main cause of fermentation thermophilic simple. The first, low acid products (peas, vegetables ..., does not grow with a pH less than 5), subject to relatively intense heat treatment, although no alteration occurs when cooling is fast and if done in cold storage. B. is aciduric coagulans (up to pH 4.2) and has less heat-resistant spores, so that changes occur in canned meats, and that the heat treatment for them is lower than in vegetables. It also appears associated with acidic (tomato juice), because its low pH and heat treatment is light.
gas production by aerobic spore is due to the denitrification of nitrate in cured meats, canned corn, peas, etc.. B. and B. cereus mesentericus displayed in salmon, crab and shrimp.
B. and B. macerans Polymix form acid and gas.
2.2. Anaerobic spore
sporulated anaerobes come mainly from the soil, which are widely found in milk, vegetables and other foodstuffs. It is also possible to find them in the flesh, as some species also grow in the intestines of humans and animals.
The most important genus is Clostridium , may find thermophiles and mesophiles. Among the former, are the most important saccharolytic, producing large quantities of gas from carbohydrates, mainly carbon dioxide and hydrogen, leading the bulging of the cans. These changes are accompanied by a butyric odor. Not produce hydrogen sulfide. The optimum growth temperature is around 55 degrees C, appearing mostly in hot countries, where storage temperatures can exceed 35 º C. Thermophiles can also cause a change in sulfur, in this case hydrogen sulfide production.
mesophilic organisms are second in importance after the cause of simple fermentation. Among these is Clostridium botulinum . It is a Gram-positive bacteria, anaerobic and sporogenous, whose growth is inhibited at pH lower than 4.5. However, aerobic organisms of a food can grow and use oxygen in a container, creating anaerobic conditions conducive to their development and an acidic product can grow C. botulinum, if present, when the acid has been used by other agencies, increasing the pH. It is the toughest of food poisoning microorganisms, as canning industry generally supports all non-acid treated products must meet the basic requirements necessary to destroy C. botulinum (sterilization for 2.8 minutes at 121.1 ° C). In no processed foods properly allowed the development of this bacterium, although there are foods with solid portions in which there may be heterogeneity of pH for some time, so it should be kept below 4.5 pH as a safety margin. This organism deserves special mention because of its significance to human health. Occurs in both vegetative and spore form, the latter being as important from the standpoint of food canning. The vegetative form is easily destroyed at temperatures below 100 º C, while spores, which come from dust and soil, can survive 300 minutes of boiling at 100 ° C. They vary their resistance to heat, making it difficult to obtain a spore suspension of uniform resistance heat for study. Has proteolytic and saccharolytic powers. Botulinum toxin is soluble in water and extremely lethal to humans (types A and B). The spores must germinate to produce a vegetative cell that produces the toxin, so this is unlikely to find the body with toxins, so that food can be ingested by the absence of evidence of contamination (taste and smell). This toxin is destroyed by ten minutes exposure to wet heat at 100 º C. Determining the type of toxin was carried out by antigenic reactions.
The optimum temperature for growth of mesophilic organisms between 20 and 50 º C (some less and others, but generally is 37 º C). According to their ability to attack carbohydrates can be of two types: proteolytic and saccharolytic or putrefactive. The former are soft to spoilage of food degradation and production of odor compounds. These are more important in foods of low acidity and a half, except for canned ham, which is disturbed due saccharolytic type C. perfringens. Highlights C. hystolyticum , C. and C. sporogenes bifermentans. Among the most common type are saccharolytic C. butyricum , C. pasteurianum, C. perfringens and others.
2.3. Yeasts, molds and bacteria spore
The only important in low-acid foods and half are those with relatively low thermal resistance, which changes occur due to leaks in the can and those that cause changes in the condensed milk and meat canned cured (ham, bacon, etc.)..
Among the highlights yeast fermenting sucrose developed in condensed milk, since this food is not subjected to any heat treatment, but the basis of conservation lies in its high sugar content. Torula globosa , round cells, causes the relaxation of the lids. Torula lactiscondensis , oval cell, produces a more vigorous muco fermentation, so that the cans may explode in a few days.
Aspergillus repens is a mold that leads to the formation of buttons on the surface of condensed milk. Within
spore bacteria include:
- Pseudomonas fluorescens, which poduce rancidity.
- Streptococcus liquefaciens, which causes liquefaction of the gelatin of canned ham.
- S. faecicum and S. faecalis are faecal streptococci produce odors and tastes in canned hams. The first is of interest because of its higher heat resistance.
- The Enterobacteriaceae (coliforms, Aerobacter, Proteus sp., Etc.) Are responsible for the ballooning of the canned ham.
3. MICROORGANISMS IN ACID PRODUCTS
In most cases easily handled with a relatively short heat treatment at a temperature below 100 ° C.
3.1. Spore bacteria can be found
and other saccharolytic anaerobic bacteria responsible for fermentation simple. Within the first stand Clostridium pasteurianum, which produces gaseous alteration of fruits and canned tomatoes and do not develop a pH below 3.7, and C. butyricum, which also affects canned fruits. Bacillus coagulans
is responsible for simple fermentation in canned tomato juice, besides causing abnormal flavors. It is thermophilic and grows even pH of 4.2.
B. macerans produces alterations in canned fruits and soft drinks along with B. Polymix, canned vegetables and fruits.
3.2.
spore bacteria are Gram positive
lactic acid (cocci and bacilli) and some are producing gas. Can be developed with low oxygen tension and are responsible for fermentation of vegetables. Destroyed by heat treatment below 100 º C.
Lactobacillus brevis causes a vigorous fermentation in ketchup and similar products and is forming gas. Leuconostoc
pleofructi of altered fruit juices, leading to the formation of a layer of slime in sugar solutions (altered tomato products).
Leuconostoc mesenteroides results in the alteration of canned pineapple soda.
3.3. Yeast
presents little resistance
heat, so are not common in heat-treated canned and yes when treatment is subtérmico or leakage.
are responsible for the fermentation of acidic sauces, jellies and similar products whose retention depends on the acid, sugar and salt.
3.4.
mold Byssochlamys fulva is the species of mold of greater importance in acid canned foods. Affects canned and bottled fruit. Is responsible for the disintegration of the fruit by decomposition of scallop. Cans sometimes bulge due to the release of carbon dioxide. Its optimum growth temperature is 30-37 º C and is highly resistant to heat.
Byssochlamys nivea is similar to the previous and is much more frequent alteration inthe canned strawberries. Penicillium
affects canned gooseberries and is highly heat resistant.
Aspergillus is also heat resistant and comes in canned strawberries. Rhizopus nigricans
is responsible for the degradation of canned fruit, especially apricot.
Rhizopus stolonifer causes softening of canned apricots.
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