Chilled and frozen foods

Frozen fruits and juices

Long-term storage of fruits and juices can only be refrigerated or frozen.

This section will be treated only questions of microbiology and frozen fruit juices.
From frozen fruits widespread industrial strawberries, currants, gooseberries, raspberries, cherries, plums and others in smaller numbers.
From fruit juices - apple and citrus. Of great importance are beginning to acquire fruit juice concentrates, which are also stored frozen.
The microflora of frozen fruit and juice is determined by their chemical composition, microflora of raw materials and processing conditions, freezing and storage temperatures.
Since fruits and fruit juices are rich in carbohydrates and acids, mainly yeast and mold develop on them. Some molds develop on fruits and berries still in natural conditions as causative agents of various diseases. Many molds affect fruits and berries only in storage conditions. A lot of yeasts and molds are found on overripe and mechanically damaged fruits and berries. Reproduction of yeasts and molds usually begins at the sites of damage. The microflora of fruits and juices is not limited to these groups of microorganisms. Fruits have contact with soil, which is abundantly populated with bacteria; Dust settles on them from the air. Therefore, even on high-quality fruits and berries that do not have mechanical damages, in addition to yeasts and molds, there are abundantly numerous different aerobic and anaerobic spore-forming bacteria.
Also safe for human health bacteria can live on fruits bacteria which do not grow in an acid medium, but, once in the human intestine, causing disease. Gak on fruits sometimes find salmonella bacteria, dysentery, E. coli and others.
According to our analysis, fresh strawberries, cherries, red currants contain mold: Monilia nigra and M. fusca (Dematium), Penicillium, Asp. flavus, Mucor racemosus, Clad, herbarum, Oidium (Oospora) lactis, Monilia sp., Alter, tenuis, Fusarium sp., Mucor sp., Sclerotinia sp. Sacch and yeast. apiculatus, Torula sp., Mycoderma sp., Pichia sp.
Bacteria were presented mostly spore forms, but met Aerob. aerogenes, Ps. fluorescens, Bact. carotovorum, Lactobacillus, Proteus, E. coli and others.
Yeast and mold dominate the fruit under storage conditions at low temperatures (down to - 10 °) due to the ability of these microorganisms to grow in acidic environments and high osmophilic.
In the fruits which have been stored at a temperature -4 ° within 4 weeks, breeding yeast Torula sp., Mildew Monilia. Slow reproduction fermenting yeast was observed at -8,89 °.
Analyses of frozen berries, which the temperature during storage increased to -4-g 5 °, showed an increase in the number of extr
Well. In the strawberry filled with syrup, their quantity increased for 2 month from 283 thousand to 970 thousand for 1 g; In a strawberry, covered with sugar, - from 236 thousand to 3010 thousand for 1 g; In a cherry, filled with syrup, for the same period - from 1399 thousand to 5100 thousand; In red currant in syrup-from 455 thousand to 3700 thousand in 1. The yeast isolated from berries multiplied at -5 °, and some at -8 °. Reproduction of yeast was accompanied by a decrease in sucrose and the appearance of an alcohol smell. It should be noted that the breakdown of sugar in fruits and juices can also occur without yeast growth, ie, below the temperature minimum of growth. In the beer wort with the addition of 40% sugar and brewer's yeast in the amount of several million for 1 ml, the formation of alcohol was observed up to -8 °. These yeasts did not multiply in the substrate, since their temperature minimum growth lies above 0 °.
The frozen fruits and juices during storage microorganisms gradually disappear, and at first less cold-resistant species of bacteria (E. coli and others.). However, even after long-term storage of frozen fruits do not become sterile. Microorganisms can be maintained albeit in small amounts, a long time. In most cases, with the highest rate of the microorganisms die during freezing. After the death of this process is slower (Table. 50).
The reduction of microorganisms (in thousands of. On 1 g) in frozen berries, syrup-soaked in the freezing process.
Changing the number of microorganisms during the storage of frozen raspberries and strawberries at -17,8 ° (on 1g product) when -12 -14 ° and during the first months of storage is represented by the following data:
Results of analyzes of commercial batches of frozen fruits and berries have shown that microbial content of 1-2 months of storage has dropped by an average of 60-75%, per month to at 6 75-90% and 12 months to at 95-99%.
Speed ​​microorganisms dying off upon freezing and storage in the frozen state is also dependent on temperature. In the long-term storage conditions at about 10 ° microorganisms die in more than 18 °. This is due to acidic medium, and high eutectic point and sugar acids.
Microbial resistance to freezing at different temperatures depends not only on the conditions in which they zamo razhivayutsya, but also on the conditions prior to freezing. Thus, when the yeast is incubated before freezing in 5,4% glucose solution at room temperature, yeast extinction occurred in accordance with decreasing temperature. The same phenomena were observed in the yeast during freezing 0,9% strength solution NaCl.
At the same temperatures microorganisms die faster with increasing acidity.
The bacteria Escherichia coli, made in the amount of thousand 1500. 1 g strawberries on which to freeze after filling sugar was kept overnight at 0 °, after 2-3 months of storage were not found.
The bacteria Escherichia coli, made in the amount of thousand 7500. 1 on g currants, which, after pouring the syrup immediately placed on freezing at -18 °, over the same period of storage were found in 0,0001, the reason for this is that at the time of freezing strawberries are in bacteria acidic medium, as the juice was removed before freezing of berries; in currants bacteria were effects it is acidic, because after pouring syrup it immediately frozen.
Thus, the addition of sugar syrup to or berries, on the one hand, increases the death of the microorganisms (where the addition of the syrup leads to the extraction of juice from berries acidic), but on the other hand, the destructive effect freezing is decreased by reducing the amount of ice formed.
In some pathogenic bacteria inoculated strawberries with sugar, which was stored at -18 °, typhoid bacteria were killed by 6 months parathyphoid - for a month, and even during freezing. Moreover, through 5 months was not even Staphylococcus aureus, which in other environments to survive for a long time.
Under all conditions and freezing fruit juices which have a maximum speed of die Nesporova sticks, eg coliform bacteria, and others. Micrococcus more resistant. Therefore, frozen fruits, these bacteria are contained in larger quantities.
You. botulinus not destroyed in the frozen cherries, strawberries and raspberries at -16 ° within 12 months. This also indicates that freezing provides only partial sterilization of fruit. Dieback frozen bacteria in substrates can be very slow.
Influence of freezing on the microflora juice is the same as in the case of fruit.
The citrus concentrates are important faecal streptococci.
Adding E. coli and faecal streptococci (Str. Faecalis and Str. Liquefaciens) in frozen orange juice showed greater survival of faecal streptococci in comparison with E. coli.
In order to determine the shelf life of defrosted frozen fruits was a large party of various berries and fruits. Part of the frozen samples with naturally created microflora, some further inoculated Bact. coli-aerogenes and you. botulinus. For strawberries 1500 thousand. Bact added. coli, a cherry - 7500 1 thousand on the city you are.. botulinus added in varying amounts.
Frozen samples were stored at-18 °. Through 2-3 months. they were thawed and stored at room temperature and at 2 °. Analyses showed that the defrosted berries bred primarily yeast and molds. Thus, strawberries in the test, where an increase in the content of yeast and molds was observed, increasing Bact. coli was noted. The growth of Bact. coli was not marked in cherry; increased amount of yeast.
Defrosted berries spoiled as a result of breeding yeast before coli bacterial growth was observed.
Also observed that, if the frozen berries to keep any bacteria such as Bact. coli, their extinction after thawing is very slow.
Changing the content of the various groups of microorganisms in the raspberry and strawberry defrosted at room temperature and at 5-10 ° 1,5 given during the day in the Table. 51.
Firmness of fruits and berries defrosted depends on the content of microorganisms, primarily yeast, before freezing.
Content of frozen fruits and berries microorganisms causing spoilage in a defrosted and microorganisms that serve as indices of their hygienic conditions, it is important to determine the quality of these products and the production of sanitary conditions.
Currently, there is still approved standards for permissible content of these groups of microorganisms, there are only re-recommendations on microbiological assessment of frozen fruits and berries.
Frozen fruits before eating is not sterilized or treated with heat. Therefore, they must be carefully handled prior to freezing. One of the main fruits of cleaning agents is a wash. The washing process should be not more than 5-10% of the initial amount of microbes. With careful cleaning residual microflora is reduced to 0,5-1%.
High efficiency is achieved under the following conditions: entering a car wash fruits should have a smooth surface, not be overripe, whole, with no mechanical damage and not moldy, if it is necessary to use the shower washing under pressure, with sufficient water supply.
One means of developing benign frozen fruit is to conduct microbiological control pro-production and finished products. Microbiological monitoring is not limited to microbiological analysis. Microbiologist should be familiar with the technological process, product treatment at each stage of production, as well as to outline ways
and means to influence the course of the process. The results of monitoring and microbiological analysis must be immediately reported to the technologist, the master and the workers for immediate rectification of violations and improve processing. Frozen fruits are flawless on sanitary and hygienic indicators provided: a thorough, effective cleaning of raw material, compliance with the sanitary conditions at all production stages, an immediate freeze on the production of fruit and avoid storage in thawed form.
To assess the quality of the frozen fruits and berries are recommended following microbial standards (Table 52.):
Because spoilage microorganisms and fruit juices made of them, are psychrophiles, crops to wort, and also on agar myaeopeptonnom be maintained at 22-24 °. Higher curing temperatures lead to low results. This can be seen in the case of strawberry and cherry juices. Upon exposure of crops on myaeopeptonnom agar at 37 74 ° grew thousands of bacteria (if based on 1 g berries) and 18-20 ° -299 thousand, respectively, on crops of cherry juice -.. 20 495 thousand and thousand..
Abroad a lot of attention is paid to control the production of fruit juice concentrates. When monitoring is recommended the following indicators: in juices before the concentration - the total number of microorganisms, mold content and coliform bacteria.
After concentrating the juice again investigated bacteriological and chemical and taste.
If the total number of microorganisms in the final sample of over 1 million. On 1 ml, the product is not available. The bacterial content of a few thousand on 1 ml, is taken as a measure of purity.
To prevent the growth of microorganisms fruit is recom-mended to store long before freezing. Storage should be limited to the terms: 24 hours at 4,5 °, 5 hours. at 10 ° and
2 hours at 26,6 °. These products should not be frozen in large packages, since microorganisms such as yeast, contained in the central part, because of the slow cooling can cause fermentation.
Currently, more research on the use of radiation before freezing in order to sterilize the product and ultra-high frequency currents in the process of thawing.

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