ES2328891A1 - Method for freezing hortofruticolas products (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

The procedure consists of subjecting the horticultural product to a relatively dry air stream, between 0 and 50% humidity and at a temperature between 10 and 30ºC to force the transpiration of the fruit to reduce its water content between 6 and 10%, after which it proceeds to quickly freeze these products in a tunnel or a cabinet with liquid nitrogen, carbon dioxide or mechanical cold depending on the size and shape of the product (whole, peeled and cut), at a lower temperature at -40ºc. The dry air can be supplied through a dehumidifier, or it can be dried by strong cooling of the air and subsequent heating. (Machine-translation by Google Translate, not legally binding)

Description

Method for freezing products fruit and vegetable

Object of the invention

The present invention relates to a process industrial specially designed for application in the sector of the processing of agricultural products, in which the whole or chopped, freshly harvested or fruit-bearing food taken from the tree or plant at the time of ripening optimal

The object of the invention is to provide a freezing procedure in which processes are reduced metabolic and the respiration of the fruits, allowing to prolong their storage time, all without destruction of its structure in said process, allowing to save frozen foods in the stages of greatest production to be supplied in the market in times of shortage, keeping all Its organoleptic qualities.

It is also the object of the invention to obtain a fast industrial freezing process, in order to allow treat high volumes of fruit and vegetable products in the smallest possible time.

Background of the invention

The freezing of food in the world Western was based on Clarence Birdseye's observations during his stay in Canada about the behavior of Eskimos, seeing how they froze the freshly caught fish, letting them freeze by simply depositing them on the ice.

He also found that when the cold was over intense freezing occurred more rapidly, so that ice crystals were much smaller, getting less damaged the cellular structure of the fish, its quality being much Better when eating them.

Based on these experiences he presented his first patents in the United States of America more than 80 years for freezing food, mainly meats, Fish and vegetables

What Birdseye couldn't get was freezing foods with a very high water content, as they are the largest part of fruit and vegetable products since freezing these food, the water contained, both inside and outside the cells, when transforming into ice it expands breaking the cellular structure, which by defrosting the food Broken cell membranes do not allow water to be retained in the themselves, and their organoleptic characteristics are very diminished, losing all its appeal to the consumer.

The growth of a fruit generally it comprises an initial period of cell multiplication, followed by a longer period of cell enlargement culminating in the maturation. A fruit is physiologically ripe when it has reached its last stage of growth and has developed the ability to mature normally after collection.

During ripening the fruits suffer a succession of important biochemical and physiological changes that lead to the achievement of optimal sensory characteristics for consumption

Behind the cell membranes are the juices Juices inside the fruit cells they are composed of substances dissolved in water, such as acids, pigments, sugars, minerals, vitamins, etc. Some of these substances or compounds of small volume, such as water or certain acids, can come out with some ease through the micro holes in the membrane or cell wall.

Fruit and vegetable products when they are mature have their cells completely filled with water, so that simple freezing by convection (gas or liquid) causes the water to freeze, forming ice crystals that they break the structure and crack the cell walls of the fruit.

After defrosting the fruit or Vegetable water leaves the cracked walls of cells, leaving with a deplorable texture.

The fruits of very small are an exception size, like the fruits of the forest, in which its freezing in the Freezing tunnels do not cause them great damage. The immediate consequence is that when these fruits are thawed they maintain their initial structure relatively well.

In meat and fish, having a lower percentage of water, freezing the damage are lower. The faster a product has frozen water crystals are smaller, tearing apart the walls of the cells, thereby releasing less liquid when thawing. TO domestic level, it is known that meat or fish should be left defrost on a plate, so that the liquid released does not dirty the kitchen marble. One cause of this is that freezing has Somewhat broken the cellular structure of these foods. How much less percentage of water has the lowest food is the effect described

When the cold chain breaks, on returning to freeze food, always much slower than in the tunnel freezing, freezes improperly, forming large ice crystals that break the structure of the food.

Multiple patents are known for the freezing of fruit and vegetable products with laboratory methods or industrial, but none of them has been effective, not get to place frozen fruit and vegetable products, such as apples or tomatoes, on supermarket shelves, of so that they do not lose their organoleptic characteristics after their defrosting

US Patent Document 2004/096559 describes a procedure to freeze vegetables or fruits in which products are partially dehydrated to significantly reduce The original water content of the product. According to this procedure, the products are dehydrated by hot air, at a temperature greater than 90 ° C preferably reducing the water content between 25% and 60%. They subsequently submit to an ultrafast freezing treatment, submerging the products in a liquid nitrogen or carbon dioxide bath liquid, at a temperature close to -200 ° C. When defrosting products keep their flavor well, but not look, which is very wrinkled, since they have removed a very important part of their Water.

In order to reduce the size of ice crystals produced inside fruits undergoing a freezing procedure, the document of EP 1525801 discloses a process in which the fruit is subjected to a temperature reduction regime in stages. The fruit is cooled slowly to 0ºC, then it is frozen slowly to a temperature between -8ºC and -12ºC at a rate cooling of 10ºC to more than 40ºC per hour, so that the temperature difference between the surface and the interior is of 1.5 ° C; and finally it is cooled further until it occurs Icing While this procedure manages to preserve the taste of the fruit better than other alternative procedures, in which the fruit is sprayed with sugary fluids or powders, it is oriented that the fruits are ingested in their frozen state. If the fruits are defrosted, they lose considerably its original texture.

Patent documents FR 2878412, EP 0572745 and US6004607 describe a procedure in which the products are immersed in an aqueous solution for pre-freezing superficial, before being cooled or frozen after using conventional methods According to these documents, at immersing the products in the aqueous solution produces the freezing of the envelope of the fruit, of its outermost layer, without the freezing of the nucleus of the fruit, which reduces the damage caused later in the product envelope when ice crystals form in their inside. These procedures suffer despite the important disadvantages: a) the change of flavor that the products added to the aqueous solution to decrease the point of Water freezing confer on submerged products. The Commonly used products are Sodium Chloride, Chloride Calcium, sugars or alcohols; and b) when frozen, the cell walls, which by defrosting also lose their texture.

In document P200701391 the dehydration is dehydrated. food lightly and slowly by convention with air, with a humidity preferably between 60% and 70%, a temperature between 5 ° C and 10 ° C to partially remove the water content of the food, especially its envelope or its outermost layer, between approximately 2% and approximately 10% by weight. Optionally, the fruit obtained is vacuum packed of the previous operations with a watertight, flexible and preferably transparent and retractable. The fruit is submitted packaged to a fast freezing treatment, by immersion in an aqueous solution of organic or inorganic salts under stirring, that keep the water in liquid state even though its temperature is below -50 ° C, for a period of time between 2 and 10 minutes depending on the type and size of the fruit.

The problem with this procedure is which is expensive, since it is excessively slow and accurate handling, so that when treating industrially large volumes of fruit and vegetable products, media and time that are needed to carry out such global treatment limits the amount of daily product obtained, with the consequent and negative economic repercussions that entails.

Description of the invention

The method for freezing products fruit and vegetable that the invention proposes solves in a way the problem described above is fully satisfactory, allowing to obtain a high quality frozen product, without rupture of the internal structure or of the cell walls of food, so that once defrosted, its appearance, taste, smell and texture are similar to those they had before their freezing, all with some execution times of noticeably reduced procedure.

To do this, the procedure that is recommended it consists in forcing the perspiration of the fruit in a way relatively fast, when subjected to an air current relatively dry, between 0 and 50% relative humidity and a temperature between 10 and 30 ° C, in order to reduce its content of water between 6 and 10%.

Then, after forced perspiration, proceeds to quickly freeze the fruits in a few minutes in a tunnel or closet with liquid nitrogen, carbon dioxide or mechanical cold, depending on the size and shape of the product fruit and vegetable, (whole or peeled and cut), in all cases to a temperature below -40 ° C.

As for the dry air flow, this one may come from an industrial dehumidifier, leaving the air with concentrations between 0 and 50% relative humidity, depending on whether the product to be dehydrated is a whole fruit, or Well cut and peeled.

Optionally, said dry air may consist in air cooled to a temperature of the order of 0 to 5 ° C for remove most of the water contained, and heat it later until about 15º to 30ºC, being with a humidity of the order of 20% at 50% RH, for which said heating can be obtained passing the product through the radiator of the refrigeration group that has been used to cool it; or by a heat source, if it has used another source to cool the air, such as nitrogen left over from the freezing tunnel.

Preferred Embodiment of the Invention

More specifically, the procedure consists of in making the food perspire for a certain time in some certain conditions to make you lose a slight percentage of its water content.

As mentioned above, the fruits mature have their cells completely filled with water, so if the fruit is forced to perspire, and lose the amount enough water, when it freezes, the ice, when growing, does not it will break the walls of the cells, which by defrosting the nothing will happen, since the water will relocate without problem in the cell. This prevents the structure from breaking molecular, but without changing its appearance.

Once forced perspiration is over it is passed either through a continuous freezing tunnel or through a Special closet to freeze by cycles.

Industrially, the processes should be fast and economical, so you should choose the most suitable for the desired purpose.

Perspiration is forced using air with low humidity between 0 and 50% RH, at a temperature between 10 and 30 ° C, so that the hotter and drier the air is faster It will be perspiration.

In whole fruits and with resistant skin, for example the tomato, it will be necessary to use a very dry air and relatively hot to force perspiration and in certain cases apply a permeabilization treatment, while for fruit peeled and cut into thin slices, for 8 mm example, the air should be less dry and cooler so as not to cause a too strong surface drying.

Industrially there are various methods to get it, such as:

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Happen drying air at the proper temperature by a dehumidifier industrial, such as silica gel, leaving the air between 0 and 50% relative humidity, depending on the product to be dehydrated (whole or cut and peeled).

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Cool the drying air to a temperature of the order of 0 to 5 ° C to eliminate most of the contained water, and then heat it to about 15º at 30ºC, remaining with a humidity of the order of 20% to 50% RH: either passing it through the radiator of the refrigeration unit that has been used to cool it or by a heat source, if it has been used another source to cool the air, such as excess nitrogen from freezing tunnel

It should be noted that fruit and vegetable food of the procedure are alive, so it is convenient that your industrial handling is carried out at a moderate temperature, since that if dehydration is carried out at temperatures of more than 35ºC, degrade quickly.

As for perspiration times, these they are very variable, since the peeled and chopped fruit can lose the necessary water with a light system in a few minutes, while that other products, such as whole tomatoes, have a very resistant skin, which requires the use of more intense systems during hours.

In this case, the amount of water to be removed from that we are talking about is much smaller than the one that can reach lose fruit, for example, when stored in cameras refrigerators for months waiting for commercialization, situation in which in the end they get to have wrinkled skin because of the amount of water lost

The freezing system depends essentially of the size of the product to be frozen, although it is always convenient that the freezing is very fast so that only very crystals form small that do not harm food at all.

In this freezing process it is not necessary pre-package food.

In the event that the freezing process is Freeze-oriented cut and peeled fruit, can use nitrogen, CO2 or mechanical cold tunnels, since, Being its very small size, freezing is done very quickly.

For the freezing of fruits and products Whole horticultural nitrogen tunnels are required or CO 2.

The aforementioned fruit and vegetable products, once they have left the tunnel, they are deposited in bulk in some deposits inside a frozen chamber at a temperature below -18 ° C, where they can be stored for months.

Subsequently, said frozen products are they can pack in the different commercial sizes that the customers, whether from a single product or a mixture of several. In In this sense, it is worth noting the fact that it is not convenient to pack said products under vacuum, since defrosting produces the "vacuum cooling" effect, output water inside the food, giving it an ugly wet appearance.

Thus, the great advantage of this system is that food texture, measured with a penetrometer before and after defrosting, it hardly varies, both in whole pieces and Peeled and cut.

Claims (4)

1. Method for freezing fruit and vegetable products, characterized in that it establishes the following operational phases:

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Submit the fruit and vegetable product to a relatively dry air flow, between 0 and 50% of humidity and at a temperature between 10 and 30 ° C to force fruit perspiration until reducing its water content between 6 and 10%.

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Quickly freeze products horticultural, after the aforementioned perspiration, in a tunnel or a cabinet with liquid nitrogen, carbon dioxide or mechanical cold according to the size and shape of the product (whole, peeled and cut), to a temperature below -40 ° C.

2. Method for freezing fruit and vegetable products, according to claim 1, characterized in that the process by which the perspiration of the fruit is forced is carried out by means of dry air from an industrial dehumidifier, with a relative humidity between 0 and 50% depending on the type of fruit and vegetable product in question, size and shape. 3. Method for freezing fruit and vegetable products, according to claim 1, characterized in that the process by which the perspiration of the fruit is forced is carried out by means of dry air previously cooled to a temperature of the order of 0 to 5 ° C, to eliminate the highest part of water contained in said air, to be subsequently subjected to a heating process until reaching a temperature between 15 and 30 ° C, obtaining a humidity for said air between 20 and 50% RH. 4. Method for freezing fruit and vegetable products according to claim 3, characterized in that the cooled air is heated by conduction through the radiator of the refrigeration group used for cooling, or a heat source, if another source has been used for cool the air, like the nitrogen left over from the freezing tunnel.