Different ways of preserving fresh fruit
For the preparation of semi-finished fruit and berry puree during the season of fruit ripening, the latter are used directly fresh or prepared in advance by canning.
At the canning fruits aim is:
- slow down the enzymatic processes in the living tissue of the fruit, i.e. the processes of post-harvest ripening, respiration;
- eliminate the possibility of the development of microorganisms on the surface of the fruit or trapped in tissue, or paralyze their livelihoods.
Currently used methods of preserving fruit are very diverse and their selection depends on the destination of canned fruit on the terms of their storage and further processing
You can point to the following main methods of industrial conservation of fruit:
a) heat sterilization in hermetically sealed containers;
b) cold storage (psihroanabioz) and freezing (krioanabioz);
c) the chemical preservation (using various chemical agents or antibiotics);
g) drying the fruit (kseroanabioz);
e) cold preservation with the help of ionizing radiation or ultrasound.
In the confectionery industry, chemical preservation of fresh fruits and berries is most widespread, in particular, canning with sulfurous acid. The confectionery enterprises of Ukraine use significant amounts of sulphitized fruits, in particular apples, which are processed into applesauce for making marmalades, pastila, fruit and berry cases of sweets and toppings.
Action sulphurous acid and its salts in fruits
The action of sulphurous acid on fresh fruits basically boils down to this.
At certain concentrations, it inactivates the oxidative enzymes of plant tissue and suppresses the respiration of the latter, thus contributing to an increase in the “keeping quality” of fruits. At the same time, S02 stabilizes vitamin C of the fruit, inhibiting enzymes, catalysts for the oxidation of ascorbic acid.
Sulfuric acid acts as a strong antiseptic; it prevents the development of microbiological damage of fruits or suspends the process of such damage already begun. It has a particularly strong effect on mold microorganisms. S0 Concentration2necessary for canning fruits, ranges from 0,025 to 0,15%.
Processing of fruits and berries sulfurous acid prevents them from browning. Available data indicate that the sulfurous acid damage oksigeiazu fruit, but it does not affect the peroxidase and tannins. According to others S02 restores the hydrogen peroxide present in the fruit and contributing to their darkening.
Reacting with the yellow and green pigments of the fruit, sulfurous acid converts them to leuco compounds, which restore their color after removing S02.
Sulfuric acid chemically interacts with fruit sugars. Combined with aldehydes and ketones, sulfurous acid forms the oxysulfo group:
Accordingly, glucose-sulfurous acid is obtained by reaction with glucose:
Since fructose is obtained fruktozosernistaya acid:
In the sugar and sulfurous acid there is a state of unstable equilibrium
Sulfur sulphurous compounds are inactive in the sense of their preservative action, but they are easily split when heated, especially in the presence of acids (and alkalis).
Among other organic substances with which sulfurous acid is able to react, a number of authors call cellulose. It is possible that some other organic substances (tannic, protein) also bind sulfurous acid.
The free sulfurous acid remaining in the fruit (as well as a significant part of the bound sulfurous acid) is removed by heating. Desulfitization is based on this, that is, the release of fruits from sulfurous acid at the end of their storage period.
Changes in pectic substances under the influence of sulfurous acid and its effect on the pectin enzymes of fruits (especially apples) have been studied in detail recently by Samsonova . It has been established that the concentration of sulfurous acid required for canning apples (up to 0,1%) does not stop the enzymatic cleavage of pectic substances. During storage of sulfitated apples at the indicated concentrations of S02 there is a gradual destruction of the pectins and the deterioration of the ability studneobrazuyuschey apples.
The breakdown of pectin substances during storage of sulfitic apples, which is externally reflected in the softening of their consistency, is primarily a consequence of the vital activity of pectolytic enzymes. To terminate the enzymes that cause pectin demethylation, a concentration of at least 0,2% S0 is necessary.2, and inactivation of polygalacturonase (an enzyme catalyzing the depolymerization of the pectin molecule) requires a concentration of 0,4% S02.
Since these concentrations greatly exceed the concentrations S02, usually used for preserving fruits, sulfation of fresh fruits and berries should be considered an imperfect method of harvesting these raw materials for the confectionery industry. More perfect in this sense is the method of processing fruits in the form of mashed potatoes. However, due to the seasonal nature of the harvesting of fruits and the availability of the method of sulphitation of fresh fruits, it is widely used in the fruit processing industry, including at confectionery enterprises.
Technique sulfitation fruit
And depending on the method of sulfitating fruits, “dry” and “wet” sulfitation are distinguished.
In the first case, whole or sliced (halves, slices) fruits are treated with sulfur dioxide, obtained directly - by feeding sulfur on the air or from cylinders supplied with chemical plants with sulfur dioxide in purified and liquefied form. This is the so-called fumigation method.
In the second case, use an aqueous solution of sulfurous acid, which is poured fresh fruit (wet sulfitation).
Sulphitation of most fruits, in particular apples, can be done either way.
When harvesting apples for confectioneries often practiced their fumigation, which is a convenient means of preserving fruit aphids collected in the deep areas, i de often required urgent measures to save the fruit to lock them to the place of processing.
The technique of fumigating fruit is as follows. The graded fruits are placed in trellised boxes placed on tiers or in piles in a gas-tight room. In the last place the fireplaces with sulfur. Sulfur for this purpose should be applied purified, free of arsenic and other harmful impurities. Sulfur dioxide produced by burning sulfur in a closed room, diffuses through the skin into the fruit. S0 Accumulation2 in fruits occurs at different rates depending on the type, variety and state of maturity of the fruit, the concentration of S02 in the ambient air, the temperature of the latter. Hard fruits are saturated with gas more slowly than soft ones. When the temperature rises, the diffusion of sulfur dioxide into the fruit increases accordingly. In rationally arranged sulfation chambers, external furnaces placed outside the chamber, a special channel connected to it are used for burning sulfur, or special furnaces with artificial injection of the air necessary for burning sulfur are used. From these furnaces sulfur dioxide is sent to the chamber.
Simplification of work with fumigation is achieved by using portable sulfation chambers instead of stationary ones. They are canvas cloth, impregnated with a gas-tight composition. These panels close the piles of boxes with apples (and other fruits) to be fumigated. After the end of the fumigation, the cloth is removed and used to process the next batch of fruit.
Some companies use a method of fumigation gas bottled fruit, is poured into the capacious underground reservoirs. Recent serve as chambers for fumigation and as repositories for the same fruit in fumigated condition.
The method of wet sulfitation is used mainly in relation to fruits with delicate pulp. These include mainly stone fruits (plums, apricots, cornels) and summer berries: strawberries, raspberries. Significant quantities of apples are also harvested in this way. The latter consists in the fact that fresh fruits prepared in an appropriate way (sorting, washing, cleaning from stalks, branches, etc.) are placed in barrels with a capacity up to 150 kg and filled with an aqueous solution of sulfurous acid. The amount of this solution is taken in such a way that the concentration of sulfur dioxide is from 0,1 to 0,15% by weight of the fruit and that the preservative solution covers the fruit completely.
An aqueous solution with a concentration of up to 4 6% S02 can be obtained in finished form from chemical plants. Due to the fact that the transportation of such a weak solution is unprofitable, it is mostly prepared on site. To prepare the working solution saturate cold water S02 from cylinders containing liquid 100% 502, to obtain the required concentration. Saturation is carried out in the cold gradually, if possible without gas loss. If you want to get a working solution in a faster way, pour liquid B02 from a cylinder into water using a special device — a sulfitometer, which makes it possible to measure liquid S02 in exact volume quantities. The latter are converted by the specific weight of liquid B02 to the weight quantities (the specific weight of liquid S02 equal to 1,38 at 20 °).
Apples, apricots and peaches, they prepare by this method in the form of halves or slices. Apricots and peaches sulfitated with seeds and seedless.
Qualitative requirements for sulfitated fruits, S0 content standards2 for different types of sulfitized fruits and berries, the weight ratio between the fruits and the solution is regulated by the 3661-47 - 3671-47 GOST standards for sulfitized fruits and berries.
According to the regulations existing in Ukraine, it is allowed to use, in addition to sulphurous acid, sulphite and sodium bisulphite, for sulphitation of fruits and fruit and berry semi-finished products (Na2SO3NaNSO3) And calcium sulfite Ca (HSO3)2 provided the perfect purity of these chemicals. These salts must be taken to sulfitation fruit or of fruit semi-finished products in such a way that the total amount S02 and the amount of bound sulfurous acid in the product does not exceed the standards prescribed for a visit.
In the practice of some foreign countries, potassium or sodium pyrosulfite preparations are used for sulfation of fruit and berry blanks (K2S2O5 and Na2S2O5), which are commercially available in solid crystalline form. Their use should be carried out on the basis of an exact stoichiometric calculation, subject to the conditions specified above for bisulfites. The disadvantage is that their use is complicated by the need to simultaneously add hydrochloric acid to separate S0 from them.2 in free form.
Transportation and storage of fruits sulfited
When fumigating apples (and other hard fruits) in drawers, the latter are often used as containers for storing and transporting smoked fruits. A major disadvantage in this case is the presence of leaks with which volatilization is associated. S02 and the loss of the product itself from the flow of juice, released as a result of caking of the softened fruit. In view of this, it is necessary to avoid laying in the boxes of stoned fruits for long-term storage and transportation. For this purpose you should pack them in hermetically sealed barrels.
The fruit, canned solution S02They are usually laid in barrels with a capacity up to 200 l in which they can be transported, and also stored for a long time. To eliminate losses from leakage of the 802 solution through the gaps of the cells and from the absorption of fruit extractive substances with wood, the barrels are coated on the inside with a thin layer of paraffin or a special protective varnish.
If confectioneries processing sulphitized fruits are located in the areas of the latter’s billets, then they can be stored in stationary tanks of wood, iron, concrete and other materials equipped with hermetically sealed lids, hatches, etc. an appropriate acid-resistant coating of special tars, ebonite, bakelite, etc. should be applied. The pumping of fruits together with the solution for supplying them to production is carried out using anti-corrosion pumps or in x mechanical devices.
Of the other methods of canning fresh fruits and berries used in the confectionery industry, it should be noted mainly the method of harvesting watermelon and melon peels by salting. Crust of melon crops is used as a raw material for the production of candied fruits. For this purpose, the crust of special varieties of watermelon or melon is cleaned from the outer skin, freed from the pulp and cut into slices. The crust is placed in barrels and poured with a saline solution of such a concentration and in such quantity that the content of NaCl in the crust is about 10 — 12%.
Some fruits and berries (strawberries, cherries, plums) are harvested by pouring fresh fruit with alcohol. This method is used when harvesting fruit for the highest varieties of candy.
The recipe adopted at the Udarnitsa Moscow confectionery factory for semi-finished products of this type is composed as follows: 55 weight parts of berries, 25 weight parts of alcohol and 20 weight parts of 70% sugar syrup. The introduction of the sugar orphan is provided to mitigate the taste of this semi-finished product.
Freezing fresh fruits also ensures the preservation of their quality in terms of the requirements of confectionery production. However, this method is expensive for bulk procurement and inconvenient for factories, as it is associated with the prerequisite for quick defrosting of fruits and their immediate processing after receipt from the refrigerator.
The methods of preserving fresh fruits with ionizing radiation have not yet become widespread.