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.
Of fruit juices - apple and citrus. Concentrated fruit juices, which are also stored frozen, are beginning to acquire great importance.
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 prevail on fruits under storage at low temperatures (up to -10 ° C) due to the ability of these microorganisms to grow in acidic environments and high osmophilicity.
The fruit, which was stored at a temperature of -4 ° C for 4 weeks, propagated the yeast Torula sp., Mold Monilia. Slow propagation of fermenting yeast was observed at -8,89 °.
Analyzes of frozen berries, the temperature of which during storage increased to -4-g 5 °, showed an increase in the number of tremors
Gay. In strawberries, drenched in syrup, their number increased in 2 months from 283 thousand to 970 thousand per 1 g; in strawberries, sprinkled with sugar - from 236 thousand to 3010 thousand per 1 g; in 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 g. Yeast isolated from berries multiplied at -5 °, and some at -8 °. The reproduction of yeast was accompanied by a decrease in sucrose and the appearance of an alcohol smell. It should be noted that the decomposition of sugar in fruits and juices can also occur without the growth of yeast, i.e., below the temperature minimum of growth. In beer wort with the addition of 40% sugar and brewer's yeast in the amount of several million per 1 ml, the formation of alcohol to -8 ° was observed. These yeasts did not multiply in the substrate, since their temperature minimum of 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.
Change in the number of microorganisms during storage of frozen raspberries and strawberries at a temperature of –17,8 ° (per 1 g of product) at –12 –14 ° and during the first month of storage it is represented by the following data:
The results of analyzes of industrial batches of frozen fruits and berries showed that the content of microorganisms in 1-2 months of storage fell on average by 60-75%, in 6 months - by 75-90% and in 12 months - by 95-99%.
The rate of death of microorganisms during freezing and storage in frozen form also depends on temperature. Moreover, under long-term storage at a temperature of about 10 °, microorganisms die in a greater amount than at 18 °. This is due to the acid reaction of the medium and the high eutectic point of sugar and 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.
E. coli bacteria, introduced in an amount of 1500 thousand per 1 g of strawberry, which was kept for about a day at 0 ° C before freezing after filling with sugar, were not found after 2-3 months of storage.
E. coli bacteria, introduced in the amount of 7500 thousand per 1 g of currant, which, after pouring the syrup, was immediately placed in freezing at -18 ° C, after the same storage period were found in 0,0001 g. This is explained by the fact that at the time of strawberry freezing ended up in an acidic environment, since the juice was extracted from berries before freezing; in the currant, the bacteria were not exposed to the acidic environment, since after pouring it with syrup it was 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 a strawberry inoculated with some pathogenic bacteria with sugar, which was stored at -18 °, typhoid bacteria died after 6 months, paratyphoid bacteria died within a month and even during freezing. Moreover, after 5 months there was not even Staphylococcus aureus, which survives in other environments 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 did not break down in frozen cherries, strawberries and raspberries at –16 ° C for 12 months. This also indicates that freezing provides only partial sterilization of the fruit. The death of bacteria in frozen 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 establish the shelf life of defrosted fruits, a large batch of various berries and fruits was frozen. Some of the samples were frozen with naturally created microflora, some were additionally inoculated with Bact. coli-aerogenes and you. botulinus. 1500 thousand Bact was added to strawberries. coli, to cherry - 7500 thousand for 1 g. of you. botulinus was added in different amounts.
Frozen samples were stored at –18 °. After 2-3 months. they were thawed and stored at room temperature and at 2 °. Analyzes showed that yeast and mold propagated mainly in defrosted berries. So, in an experimental strawberry, where there was an increase in the content of yeast and mold, an increase in Bact. coli was not noted. Growth Bact. coli was also not noted in cherries; the amount of yeast increased.
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.
The change in the content of various groups of microorganisms in defrosted strawberries and raspberries at room temperature and at 5-10 ° for 1,5 days is given in 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 are not sterilized or treated with heat before consumption. Therefore, before freezing, they must be carefully processed. One of the main means of peeling fruit is washing. During washing, no more than 5-10% of the initial number of microbes should remain. With a thorough washing, the residual microflora decreases 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.):
In view of the fact that microorganisms causing damage to fruits and juices made from them are psychrophiles, crops on wort, as well as on meaopeptic agar should be kept at 22-24 °. Higher holding temperatures lead to underestimated results. This can be seen in the example of strawberry and cherry juices. When crops were aged on meeopeptic agar at 37 ° C, 74 thousand bacteria grew (in terms of 1 g of berries) And at 18–20 ° –299 thousand, 20 thousand and 495 thousand, respectively, on crops from cherry juice
Abroad, much attention is paid to the control of the production of concentrated fruit juices. When monitoring, the following indicators are recommended: in juices before concentration - the total number of microorganisms, the content of mold and bacteria of E. coli.
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.
In order to avoid an increase in the number of microorganisms, fruits are not recommended to be stored for a long time before freezing. Storage should be limited to: 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 microflora, such as yeast in the central part, can cause fermentation due to slow cooling.
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.