Microbiology of food

Food microbiology
Chilled meat. Here the microflora of the surface is created during slaughter and preprocessing as a result of contact with inventory and equipment, clothes and hands of workers, air dust and water droplets deposited from the air, contamination of the intestines with cuts, etc.
The microflora of fresh, uncooled meat is very “speckled” by coloration of colony on crops in Petri dishes. It is represented by coccal forms of bacteria (streptococci and micrococci), non-spore bacteria (Achromobacter, Pseudomonas, Flavobacterium, bacteria of the E. coli group), various spore-forming bacteria, as well as molds and yeast. Psychrophils make up an insignificant part of the entire microflora (in the southern areas less than 1%) [39].
The microflora of carcasses may remain constant for some time, both qualitatively and quantitatively, and the time it takes to preserve it in this condition increases if a crust of drying develops on the carcasses or the meat immediately enters a room with a relatively low temperature.
When storing meat in chilled form, the composition of its microflora gradually changes. Mesophilic microorganisms stop multiplying and partially die. Psychrophils, on the contrary, continue to actively proliferate, and the microflora becomes more homogeneous in composition. So, in freshly minced meat, psychrophiles accounted for 40% of the entire microflora; in 98 hour. storage at a temperature of 0 ° the number of psychrophils reached 90%, and at 2,5 ° it approached 100%.
In 1 g of minced meat made from fresh raw materials, 18% bacteria was found that can cause spoilage during refrigerated storage. After 6 days of storage at a temperature of 1,4 °, their number increased to about 98% (fig. 17). In samples made from frozen meat products, bacteria that can cause spoilage were 78% of all microorganisms. By the third day of storage at a temperature of 4,4 °, these bacteria were already about 98% [40].
From psychrophilic bacteria increased the number of groups mainly Pseudomonas and Achromobacter.
Study 189 psychrophilic strains of bacteria isolated from the chilled meat and inventory showed that 182 strains were Gram-negative bacteria. Of these, 170 strains belonged to Pseudomonas. Only 7 strains were gram-positive, wherein only one of them treated cocci [41].17
Fig. 17. The growth of bacteria on the meat and its change with temperature 4,4 ° depending on the initial content psychrophiles: | - Frozen minced meat, II - fresh minced meat
Of the group of bacteria Pseudomonas, the most important microorganism is Ps. geniculata, it limits the shelf life of packaged packaged meat. The growth of these bacteria causes the formation of mucus, discoloration of meat and an unpleasant odor [42].
The dependence of the growth rate of psychrophilic bacteria on temperature is shown in Table. 17 and fig. 18.
As can be seen from the above data, a small temperature change in the range of about 0 ° strongly influences the duration of storage of chilled meat products.
When bacteria multiply on chilled meat, first separate colonies are formed (they can be seen primarily in more moist places), which then merge into a continuous smearing and slimy dull gray bloom (Fig. 19).
T a b l e »17. The duration of the generation time (in hours) at a slice psychrophilic bacteria (1,1 mm) raw meat at different temperatures [28]

bacteriaTemperature, ° C
-1241015202530
Achromobacter
sp. № 710,77,15,282,51,751,361,161,6
sp. № 48311,67,86,02,541,751,321,061,5
sp. № 516,2 7,353,051,831,411,200
Pseudomonas
sp. № 45]22,013,89,73,951,951,230,910,80

The minimum content of bacteria in meat to the onset of mucus, according to various data, ranges from 3 million to 32 — 5 (1 ml n. On 1 cm 2. On meat covered with a thick film of mucus, the number of bacteria reaches 109 — 1010 on 1 cm 2.
18Fig. 18. The duration of the generation of bacteria in meat products, depending on temperature (the left side depicts mixed cultures in minced meat and cutlets, the right - pure cultures in minced meat)
The microflora of mucus consists mainly of two groups of bacteria - Pseudomonas and Achromobacter. With a low level of sanitization of meat and storage in conditions above the temperature 5 °, other bacteria may be contained in the mucus. In addition, Achroniobacter and Pseudomonas (82%), protei (11%) and actinomycetes (7%) [43] were found in the mucus of such meat.
With long-term storage of meat and with a large content and mucus coloring the substrate Pseudomonas mucus becomes greenish and brown; the same color is attached to the product.
Changes in the color of meat during the reproduction of bacteria may be caused by other reasons. The red color of fresh meat is due to the presence of myoglobin pigment contained in muscle tissue. The color of the pigment logo depends on the amount of oxygen. With the active growth of aerobic bacteria such as Pseudomonas and Achromobacter, oxygen is used and it creates a deficiency on the surface. This causes darkening of the meat. The color change can also be caused by the oxidation of hemoglobin to methemoglobin [44, 45].
Such changes reduce the commercial quality of meat, but are not harmful to human health and do not affect the taste properties of the product.
Since mucus formation is closely related to the activity of bacteria causative agents of protein spoilage, it is recommended to stop the storage of meat when the first signs of mucus appear, especially since an alien, stagnant odor appears along with the mucus. Knowing the duration of the generation of psychrophilic bacteria for each given temperature (almost constant), the initial contamination of the meat with active psychrophilic bacteria and their content by the time the meat is smelled, it is possible (if we ignore the lag phase) to determine the period of permissible storage t according to the formula:2where b - the initial amount of bacteria; B - the final number of bacteria; g - generation duration.post 195Fig. 19. The growth of psychrophilic bacteria on meat
If the number of bacteria at the time of the appearance of mucus take equal 10,/гthenolav1
i.e., for a certain temperature, g can be considered a constant value (under the condition of standard pH and humidity) and, therefore, t will be inversely proportional to b.
This dependence is presented in Fig. 20. With the initial bacterial content on 1, cm2 in the number of 105 cells, the time until mucus appears on meat at 10 temperatures; 4,4 and 0 ° will be respectively less than 4 days, around 5 and about 7 days; when the content of 102 bacteria on 1 cm2 - about 6, about 10 and 15 days, etc.
Such a relationship between the initial bacterial content and the time until signs of deterioration appear is natural, when the content of active psychrophilic bacteria is taken into account (see Fig. 17),
The rate of bacterial growth on the meat surface also depends on moisture, and there is not only lower, but also the upper limit. (The latter is close to 100% cent and the water content is not important for meat.20Fig. 20. Dependence mucilaginized meat of the initial content of bacteria and temperature
The lower limits easily tolerated (Table. 18).
On the surface of the meat under refrigerated storage conditions, some surface drying occurs. Such shrinkage causes loss of quality and weight of meat, but it to some extent protects it from the rapid growth of microorganisms.
On a dry surface at temperatures from 7,2 to 10 °, bacteria multiply at about the same speed as on a wet surface at temperatures from 2,2 to 3,3 ° [47].
Surface moisture is a very important factor in determining the predominant group of microorganisms on the product.
Chilled meat is dominated mainly by bacteria. However, on less wet areas of the carcass surface, especially as the shelf life increases, the growth of mold and yeast becomes noticeable in accordance with lower moisture limits (see Table 18).
Table 18 lower limit of the water content for the growth of certain microorganisms [46]

organismsLower limit on value aẘCritical limits for water content per 100 g dry matter of product
Achromobacter (2 strain). . .96-96,285-90
Pseudomonas 2 strain)98-98,5140-180
Yeast: Candida 91-9250-54
Geotrichoides90-9147-50
Mycotorula 89-9045-47
t. e. relative partial vapor pressure of the solution

to the partial pressure of water,

Pénicillium is more frequent and more abundant, less commonly Mucor and Cladosporium, even less often Thamnidium, Trichoderma, Sporotrichum; then Rhizopus and Alternaria. Aspergillus, Botrytis, Verticillium, Monilia, etc. are not widely distributed in meat. Of the yeast, there are mainly non-spore pink rosy yeast (Rhodotorula).
During long-term storage or transportation of chilled and frozen meat (above —8, —9 °), especially with a low level of sanitary conditions of processing and pre-storage, molding occurs, resulting in black and other spots of color on the meat.
The appearance of mold on the wet surface of the meat may be imperceptible due to the fact that the process of mucus is more intense. Under less humid conditions and at a lower temperature, mold growth can be observed on meat simultaneously with depletion or even become predominant.
Pénicillium molds initially grow on meat in the form of white residue that does not rise above the substrate. With further development, when the formation of spores begins (conidia), the molds turn a bluish-greenish color and cover the meat with a fine powdery coating.
Pénicillium plaque is quite easily washed or washed off from the surface of the meat, and by this method the meat is sometimes “cleaned” from molding. However, the formation of a moldy odor is not eliminated. In addition, the cleaning of meat from molds in cold rooms leads to the spread of molds in the room and its pollution. From the room where such cleaning is carried out, the molds get into new batches of meat.
The growth of mukorovy mold appears on the meat in the form of a cobwebby, grayish-smoky color of fluffy plaque, a little, and sometimes quite noticeably rising above the substrate. From the Mukor group, Mucor, Rhizopus and Thamnidium are more common.
The difference between these molds is of practical importance, as it allows to determine the temperature at which the meat was stored. Thamnidium molds stop growing at lower temperatures than Mucor and Rhizopus. The development of Thamnidium causes the formation of an unpleasant odor. These molds actively break down meat proteins.
Cladosporium sometimes has dark green and almost black spots on meat. Unlike the above-described surface fouling of molds, these stains during long-term storage of the product (at temperatures below 0 °), when the formation of bacterial mucus is delayed, can be introduced into the muscle tissue to a rather great depth. Such stains cannot be removed, as this leads to a violation of the integrity of the upper layers of meat.
Thamnidium and Cladosporium mildews are considered to be the main causative agents of meat spoilage under cold storage conditions. temperatures —4-t 9 °, i.e. when the growth of other molds stops or is strongly delayed.
The cause of the unpleasant earthy smell can be Actinomyces growing on meat.
In addition to these defects (mucus, mold, odor), on the chilled meat, on the muscles, in the areas of adhesion to the bone, in the hip area of ​​the carcass can sometimes detect the bad smell of souring. This defect is formed as a result of the anaerobic proteolytic process caused by anaerobes, or the activity of aerobic bacteria under the anaerobic conditions that have been created in these places. This defect is rare and can occur only under abnormal conditions of refrigeration treatment, for example, with very slow cooling.
Even at 0 °, chilled meat is practically usually stored no longer than 2 — 3 weeks, and even with high initial contamination even less. This eliminates the possibility of transporting meat over long distances and shortens the storage time for chilled meat.
In this connection, more and more research is being carried out on means that could be used in addition to the cold to extend the shelf life of chilled meat.
Based on the positive results of experiments with antibiotics pa fish and poultry in recent years have been intensively carried out studies on the use of these drugs also for meat.
In the USSR (the Institute of the Meat Industry, the Institute of the Canning and Vegetable-Drying Industry, etc.), considerable success has already been achieved abroad, especially in the double processing of meat: by injecting antibiotics into the bloodstream of the animal and then spraying the carcass.
In addition, experiments on the treatment of meat with ionizing radiation are widely carried out. With appropriate doses, a significant delay in the multiplication of microorganisms is achieved. However, no data were obtained that could be recommended for practical use. The sensitivity of microorganisms to radiation is relatively low compared with various biological objects (Table 19).
Of all the microorganisms tested, bacteria Pseudomonas were the most sensitive to ionizing radiation (see Table 3). The dose in 100 of thousands of X-rays upon irradiation with gamma rays (Co60) caused the death of all Pseudomonas on meat without major changes in color, smell or taste. The effect was noticeable on meat stored at 2 ° [42].
On the thus-treated meat Psychrophilic Gram Gram-positive flora give way.
Conducted research poses a number of new challenges. It has been found, for example, that when a product is processed with large doses of radiation, a deep disintegration of some of its constituent parts occurs, as a result of which undesirable tastes appear [49]. If processing is carried out at low temperatures,
Table 19. Action radiation on biological systems [48]

Doses
in Roentgen (1renthen = 83,8 ERG / g)a W-h / kgexposure Result
0,3 (during the week)0.7ХІ0-6Man stands
8001.9Х10-3Man dies
120002,8Х10 2Delayed germination of potatoes and onions
50 000-500 0000,1-1,2Die off vegetative forms of bacteria
1 000 000-4 000 0002,3-9,2Bacterial spores die off
more 5 000 000> 12Inactivated viruses, toxins and enzymes

then the processes of decay are delayed; if the microorganisms subjected to the irradiation are then maintained at low temperatures, their recovery is observed.
With radiation, a change in the product is affected by vacuum. Thus, when irradiating chickens under vacuum, a strong odor was observed; there was no odor in the air, but the product became rancid. At a temperature of 1,1 °, unirradiated chickens in cryovac bags began to deteriorate after 17 days (mucus appeared); the treated bird acquired a strong odor after 40 days, although no increase in bacteria was observed [50].
The use of carbon dioxide (tab. 20) is of great importance for delaying the growth of microorganisms and lengthening the shelf life of products.
Table 20. Extension of the shelf life of meat with carbon dioxide [51]

SampleTehmperatura, ° CHumidity,

%

Content S02%Duration

store

Sirloin and tenderloin of beef butcher 1-070-85NoBakteryalnaya black spell on 9-day
Also 1-09614-19There was no damage through 14 days
Mutton average fatness94-98
0No14 days
Also 094-9810-1234 day
»»

Lamb is above average upi

094-9820-2246-50 days
Horodecki et al -2, -180-85020-21
Also -2, -180-851060-63
»»,,,,.-2, -180-852070-71

Studies on pure cultures have shown that microorganisms treat carbon dioxide differently. If psychrophilic bacteria are sensitive to carbon dioxide, then Proteus is resistant to its action. Thus, the use of carbon dioxide is effective only at temperatures that do not allow the growth of Proteus or other microorganisms that are important for meat and are resistant to carbon dioxide.
Frozen meat. Storage of frozen meat is recommended at a temperature of —18 °. At this temperature, the meat can be stored for over a year. In this mode, the effect of microorganisms causing food spoilage is eliminated, and the effect of other spoilage factors is significantly weakened. The content of mesophilic and psychrophilic microorganisms in the process of freezing meat often drops to 20 — 10% and even to fractions of a percent from the original.
The death of microorganisms under the action of freezing occurs both in the process of freezing of the medium and in the process of its storage in a frozen state. The rate of dying depends on the speed of freezing. With rapid freezing, especially at low temperatures (—18 ° and below), more bacteria die off than with slow freezing. Relative cold tolerance is provided on pages 31 and 32. Psychophilic bacteria, despite their ability to grow at low temperatures, are less resistant to freezing than staphylococci and bacterial spores (see Table 13, 14).
In frozen meat inoculated with pure cultures of psychrophilic bacteria, after 28 days of storage at —20 °, in one case there was 68% and in the other — 14% of bacteria from the initial [52].
If frozen meat is stored at a temperature higher than — 10 °, then the death of microorganisms stops and their number may increase with time (see Table 1).
The growth of psychrophilic molds at low temperatures on a frozen medium can be explained by their ability to grow with limited water content (about 6% of the initial content in the tissue), as well as with a high content of salts dissolved in the tissue fluid. Most bacteria are more sensitive to lack of moisture and to the concentration of the solution.
The composition of molds on frozen meat is in accordance with the mushroom flora of the chambers in which this meat is stored. The contents of the various groups of molds on the walls of the chambers are given in Table. Xnumx
Defrosted meat. Since frozen meat does not become sterile even during long-term storage, during the thawing process and after thawing, the microorganisms preserved during freezing can multiply and cause a change and spoilage of the product.
So far there is no consensus about whether defrosting facilitates the acceleration of the growth of microorganisms. Some believe
Table 21. The relative content of various types of molds in meat storage cells (% of total amount)

Mould
MucoralesTrichodermaMonilia nigraAcrostalagmus
PenicilliumMucorChaetosty-

lum

Thamni-

dium

RhizopuswoodpinkOidiumAspergillusNecklaces like tophilaBotrytisAlternaria
2-1002-931-311-48TO 15TO 4TO 9to 1TO 34TO 3to 6TO 1TO 10

that frozen and then defrosted meat is not more susceptible to spoilage than fresh [52,53]. Others believe that as a result of the extraction of juice during thawing, favorable conditions are created for the development of microorganisms [47]. On the other hand, this beneficial effect is delayed to some extent due to a decrease in the content of microorganisms as a result of freezing and lengthening the lag phase of bacterial growth.
The main factor determining the resistance of thawed meat (other than temperature), is its contamination. Therefore, the smaller the number of microorganisms on meat before freezing, the less is the following storage and can be stored longer thawed meat.
Thus, the duration of storage of meat in refrigerated form depends on a number of conditions: the initial content of microorganisms in meat and the activity of their reproduction.
Control during refrigerated storage is limited by only a few factors, mainly temperature and humidity, and sometimes the composition of the atmosphere.
The International Institute of Cold (1959) recommends the following mode of storing chilled meat (table 22) [54].
Table 22. Storage Mode chilled meat

ProductTemperature, ° СRelative humidity,%Expected storage time, weeks
Meat -1,5-0904-5
Meat 10% S02-1,590-95Until 7
Veal -1-0901-3
Mutton -1-085-901-2
Pork !

JV

1

о

85-901-2

Frozen meat at the currently recommended temperature regime (from —18 to —12 °) can be stored from a microbiological point of view, if other factors are not taken into account for almost an unlimited time.
The microflora of freshly caught sea fish is similar in composition to the microflora of sea water. Fresh fish caught in northern waters with temperatures from 4 to 8 ° contain mainly the psychrophilic bacteria Pseudomonas - Achromobacter and in a smaller amount of micrococci and bacteria of other groups (Table 23).
Table 23. Species belonging bacteria isolated from fresh fish (as% of total number)

FishPlace of catchPseudomonas and achromobacterFlavobac

Ministry

Coryneba-

ctere

MicrococcusvibrioAlcalige-

nes

Different

bacteria

11orvezhskaya winter herring [55]-64,517,7-16,7--1,1
Haddock [56]North

Nov

50,0-56,80-634,3-35,22,0-15,7
11loskie fish (2vida) [12] CodSame Sea66-745-91-21-39-126-82-2
76,4 *6,0 *8,7 *1,1 *5,9 * 1,9 *
[13]92,8 **1,5 **1,0 **0,7 **3,3 **-q 7**

* Crops conditioned at 20 ° ** At temperatures 0 °
On the fish caught in the waters of the southern seas with a temperature of up to 14 25 °, make up a significant portion of the bacteria micrococci.
At the same time, fish microflora in the same latitude varies somewhat depending on the fish species, the chemical composition of slime on the surface of the fishing place and time. microflora dependence on fishing time show the following data:

organisms
time fishingBacillusPseudo

Monas

Flavobac

Ministry

Micro

coccus

Achromo

bacter

дрожжиCorynebac-

Ministry

different
June

October

1,25

0,4

0

5,8

2,0

7,1

31,7

7,0

55,2

60,4

2,0

0,1

3,0

10,0

8,0

10,0

In fresh fish, bacteria are found on the skin, gills and intestines. Muscle tissue is usually sterile, but occasionally anaerobic bacteria can be found in it. Spore-forming anaerobes are also found in the intestines. Aerobic bacteria content on freshly caught fish varies widely: on a cod, for example, it was found from 102 to 107 on the 1 cm2 surface.
On delivery to the shore, an experimental batch of sprat on the surface contained from 11 thousand to 83 thousand bacteria per 1 g. In industrial fishing batches, the bacteria content rose to 132 thousand, and in individual batches to 3 million per 1 g.
The content of bacteria in the intestines also varies greatly. Thus, in the intestines of freshly caught haddock and cod Shuen contained from 8 X 106 to 420 X 10 bacteria on 1 ml, and according to Ashehugu and Westerkhuz from 3 X 103 to 20 g.
In the intestine of sprat, the number of bacteria growing on the meat-peptone agar ranged from 370 to 1000 cells, in some instances reaching 25 thousand.
In the intestine of sprat, there are undeniable bacteria, which are capable of causing gas formation in protein media, grow at 0 ° and lower with 6% PaC1. By properties, this bacterium is similar to Achg. gasoformans.
Of sanitary significance bacteria, only E. coli group bacteria were detected on the surface of freshly caught cod in seven washes from 50. E. coli bacteria of fecal origin were not found. Proteus bacteria have been found in fish mucus and intestines, but there is no evidence that these bacteria cause food poisoning. None of the micrococci isolated from fresh fish from clear waters gave a coagulase-positive reaction [57].
Pathogenic and toxigenic bacteria can still be found on fish caught in polluted coastal waters or treated under unsanitary conditions or stored on dirty ice.
Table 24. Changing the composition of the bacteria in fish during its refrigerated storage (in% to the total content)

Breed fishTime analysis of fishPseudomobas and AshromobacterFlavobacteriumMicrococcusDifferent
Norwegian wintersFresh64,517,716,71,1
NJ herring [55]After storage at 1 ^ 8 ° for 6 — 11 days92,27,00,8
Haddock in the NorthFresh50,0-56,80,634,3-35,22-15,7
Mr. Sea [56]After storage on ice for 12 days86-941,51,5-13,01-3
Cod in the NorthFresh60,0-30,010,0
Mr. Sea [56]After storage on ice for 12 days94,06,0

From the intestines and muscles stood out Vas.botulinus sturgeon. This Bacillus toxin can form at temperatures above 6 °.
After catching the fish microflora changes not only quantitatively (Table 24), but also qualitatively.
on a fishing boat fish contamination data are presented in Table. 25.
Table 25. Seeding of fish with bacteria of the group of Escherichia coli when it enters the port (in% of the number of fish examined) [58]

Quantitybacteriafecal
that was investigatedgroups of intestinesE.
GOVERNMENTAL fishtion sticksstick
10310092
1489678
1509968

The increase in and changes in the composition of the bacterial flora are caused by a number of reasons: the absence or imperfection of fish washing, low sanitary conditions of the room, equipment, etc. For example, staphylococcus most often falls on fish from pustules that hit the hands of workers.
Although fish caught in unpolluted waters do not contain coagulase-positive staphylococci, these bacteria were found in the fish fillets.
The number of micrococci isolated from fillets ranged from 42 to 96% of the number of other bacteria [57]. Some of these micrococci grew at 37 °. Of these, 10 — 16% did not differ from Staphylococcus aureus in a number of properties, and
they can be attributed to potentially pathogenic. and fecal streptococci were isolated from the fillets.
Damage to fish occurs when the content of active bacteria is approximately 10⁶ — 10⁷ per 1 cm2 / g. If known continuetions the generation g, then, using the formula2You can determine the approximate shelf life of fish.
The formula shows that the storage time is directly proportional to the duration of generation and inversely proportional to the logarithm of the initial bacterial content. The duration of generation depends on the temperature. Consequently, here the storage duration, besides other factors, is influenced by the initial seeding and temperature.
With the initial contamination of fish on ice 10₂ / cm2, damage occurs on the 14 day [59].
Ideally cooked fillets with initial contamination of 10 bacteria on 1 g fish were stored at 3,3 ° for 12-13 days. With an initial content equal to 10⁴ or 10⁶ of bacteria on 1 g, the shelf life of fillets at this temperature was reduced to 4 days.
The growth of psychrophilic bacteria on fish at different temperatures can be seen in Fig. 21, 22 and table. 26.
The shelf life of commercial fish at different temperatures, according Castella, are in the following relationship: when 10 ° the fish (cod) was stored for 1,5 days, for 5 ° - 3,5 days, for 2,8 ° - 5 days, and for 0 ° (on ice) - 8 days. The storage time at 0 °, as compared to other temperatures, increased accordingly in 5,3; 2,3 and 1,6 times. Laboratory experiments on cod, carried out by Rie, showed that her damage on subjective and objective21Excerpt day
Fig. 21. Sprat on bacterial growth (at 1 g) at different temperatures
indicators proceeded in 2,5 times faster at 6 °, than when 1 °. Cod spoiled in 2,5 times faster at 4,4 5,5 ° and fold faster with 10 °, than the temperature of melting ice [61].

26 Table. Bacterial growth on cod (in thousand. 1 on a fish) [60]

TemperaStorage, days
tour, ° C1235812
5,5

0

150

60

2100

80

45000

90

1600000

320

5500780000

Fish fillets stored at 25 ° from 22 30 to an hour. At ° 5 2 from 3 days before, when ° 2,8 5 from 6 days before, when ° 0,55 6 from 8 days before and -0,28 ° from the 11 12 days before.
Fillet, resulting in a production environment, the port at 5 3 -5 ° of days and 0 ° for 8-13 days.22Fig. 22. Changing fish (1g) and its content of bacteria during storage on ice: A - volatile bases, B - ammonia, C - bacteria, O - tertiary amines, E - trimethylamine oxide, P - secondary amines

From the relationship between the temperature, initial insemination and shelf life it implies that the fish should be cooled immediately after harvest. The effectiveness of rapid cooling from the following example. Fish, planted and ice immediately after the catch kept 18 days. Another party was kept before being placed in ice for 12-15 hours. at 7 °. The quality of it deteriorated after 14 days, t. E. On 4 days earlier than in the first case [60].
In practical terms, the ice can be very polluted, which reduces the cooling efficiency of the fish. In 1 g of ice on an industrial trawler, the bacteria content reached 5 X 10⁶. Sometimes ice, being pure, is polluted in bunkers by bacteria that actively grow at low temperatures. Natural ice from rivers and other bodies of water is particularly contaminated by bacteria.
So, in 1 g of such ice contained from 904 thousand to 1329 thousand bacteria. The microflora of polluted ice is very rich in fluorescent bacteria - the main causative agents of food spoilage during refrigerated storage. Contaminated ice may also contain E. coli bacteria and other pathogens. The content of bacteria in ice should not be higher than in seawater. Ice should not be stored in places of runoff and rising waters formed during the melting of snow in the spring.
The purification of water intended for the manufacture of ice can be carried out by adding to it before freezing various chemicals acting on bacteria (sodium hypochlorite, sodium nitrite, etc.).
Nowadays, tests are being widely conducted on using other means in addition to cold to delay the spoilage of fish by antibiotics, carbon dioxide, etc.
Of the many antibiotics used for these purposes, compounds from the tetracycline series, especially chlortetracycline (aureomycin, biomycin) and oxytetracycline (terramycin), proved to be the most suitable.
Antibiotics can be used in various ways: introduction directly into the fish by briefly immersing it in brine with an antibiotic (up to 20 parts per 1 million), storing in weak brine or sea water with an antibiotic (up to 10 parts per 1 million) or on ice, containing an antibiotic (up to 5 parts per 1 million).
At retail (storage temperature above 0 °) immersing the fillet on 10 min. in brine containing 10 parts of aureomycin per 1mln, the shelf life can be lengthened 2 — 3 times as compared to regular fillets, regardless of the initial fish quality before filleting [62].
Dubrova, Ravich-Scherbo and others [63] found that when treating fish with chlortetracycline, the best result is obtained when the fish are immersed in 5 minutes / solution for 5 minutes before putting it into ice with the 50 antibiotic in / ml. The preservation time of the fish, as compared with the control, was extended by 6 days. In industrial experiments conducted by Ravich-Scherbo, the shelf life of fresh fish treated with antibiotics doubled [64]. The use of antibiotic as a means of extending the shelf life of fish has great prospects. However, with the consumption of fish treated with antibiotics, antibiotic-resistant strains of bacteria can occur in the body.
The use of the most active antibiotics can be effective only if sanitary standards are observed during the processing and transportation of fish. Antibiotics have a very weak bactericidal action. They only delay the reproduction of bacteria, without causing them to die quickly. Carbon dioxide not only retards the growth of a number of microorganisms, but also slows down the oxidation of fat. It has been established that carbon dioxide is not suitable for all varieties of fish, for example, hamsa in this case deteriorates faster than with ordinary cooling at 0 °. This is explained by the action of cathepsin contained in the hamsa. Carbon dioxide in concentrations from 20 to 70% increases the shelf life of fish (perch, sprat, bream) with less active proteinases than cathepsin, 1,3 — 1,8 times, despite the activation of proteolysis. A higher concentration of carbon dioxide leads to increased proteolysis and a slight increase in shelf life. In carbon dioxide at elevated temperatures, anaerobes and putrefactive microorganisms can develop, in particular, those close to the type of Hisg. sanndus
If you store fish in an environment of carbon dioxide at lower temperatures, the shelf life increases significantly
The use of CO₂ for smoked fish (hamsa, herring, mackerel, horse mackerel, bream, etc.) turned out to be particularly suitable. The shelf life of this fish at 15 — 30 ° is extended 2 — 3 times Compared with storing air; at 2-8 ° storage times increase in 5-6 times; at 0-3 ° and 40-60% SO₂-in 3 times. The use of carbon dioxide for storage of smoked fish is still not widely used in practice [65].
In connection with the removal of fishing areas from the coast, as well as the development of refrigeration technology, freezing of fish directly on ships has recently been warming up.
Freezing and storage of fish is carried out at temperatures of about -25 °.
In the case of long-term storage at temperatures above -10 ° a frozen fish can be exposed to moldy.

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