FR2638062A1 - PLANT PRODUCTS WITH IMPROVED STABILITY AT FREEZING TEMPERATURES AND PROCESS FOR OBTAINING THEM - Google Patents

Abstract

The present invention relates to plant products with improved stability at freezing temperatures and their process for obtaining them. These plant products, stored at a temperature below 0 degree (s) C, which have been partially dehydrated beforehand and to which at least one substance regulating the activity of water has been added beforehand, are characterized in that they have a water activity of less than 1, a moisture content lower than that of non-preserved plant products, and in that the water activity and the moisture content are within a range such that said products remain flexible and not frozen at temperatures below 0 degree (s) C typical of frozen food storage. The invention applies in particular to the preservation of vegetables such as spinach, parsley, onions, cabbages and carrots.

Description

The present invention relates to a new type of plant products

  stable at low temperatures and a process

for their obtaining.

  Many processes are known for the preservation and storage of food products for short periods of time and for

  long periods. Freezing is one of these processes.

  Frozen food products, especially vegetables and plant products, are commercially important products that find uses in industrial markets, consumption and food supply. While it is generally considered that the quantity of frozen vegetables is satisfactory, there are a number of disadvantages inherent in this type of vegetable.

food storage.

  After being frozen, food products, including vegetables, must be kept at temperatures below 0 C. Frozen food products, which have been allowed to thaw partially or completely and are then refrozen, suffer severe losses. quality. Frozen food products, which have been allowed to thaw accidentally or for a period of time while waiting to be used, may be damaged and pose a danger to public health. While some products such as peas, beans and diced carrots can be frozen quickly individually, other vegetables freeze in a solid block that must be thawed so that the amount can be want to use. Even rapidly frozen individual vegetables tend to agglomerate in blocks during storage, as a result of freezing water between

pieces of vegetables.

  The energy required to freeze the water contained in the vegetables is considerable and expensive, as is storage and transport in the frozen state. Frozen transport is always risky when it comes to keeping the product frozen. Some of the costs involved in storage and transportation can be reduced considerably by the known method of freezing with dehydration. In this process, the vegetables are dehydrated up to 30% of their original weight and then frozen. Freezing with dehydration can reduce

  % the costs of freezing, packing, storing and transporting

  Harbor. However, the products always harden during freezing, which results in a loss of texture and, since they have a higher solids content, these products thaw more easily. This can cause problems of rotting of the defrosted product of the same type

  only in products that are frozen in the traditional way and thawed.

  Various methods of dehydrating vegetables are known and some of them are used on an industrial scale. In most of these processes, the vegetables are dried to a low moisture content, usually less than 7%, and in the case of frozen and dried vegetables, these are often dried to 2 or 3%. For these levels of humility, vegetables are hard and very brittle. There are many breaks and excessive production of fines (fragments and small fibers). This is particularly the case for leafy vegetables. Normally air-dried vegetables, which are exposed to relatively high storage temperatures at low moisture levels for long periods of time, are subject to

  significant losses of taste, color and aroma.

  Stable dehydrated vegetables can be obtained

  both above average levels of moisture by adding salt to lower the water activity of the partially dried vegetables, as described by Lewis and Lewis (Australian Patent No. 532,414, US Patent Nos. 4,447,460 and 683,141). In these vegetables, the upper level of humidity is 25%, but in general one reaches a storage stability longer for levels

  humidity at the lower end of the moisture scale.

  Onions, for example, tend to fade slowly when stored at moisture levels above 10%. For a moisture content of 10% or less, onion slices are fragile enough to break. Many dehydrated white vegetables or pale tissues of other vegetables, for example the internal petioles of celery, the white tissue of zucchini, the pale yellow leaves internal to

  cabbage or Chinese cabbage and the white tissue of the cucumber becomes

  break relatively quickly to storage. In addition, many green and pale green vegetables, whether in the form of dissolved or conventionally dried forms, undergo deterioration of the green chlorophyll pigment when stored at room temperature for more than 0.50 for periods longer than a few months. Still other vegetables, especially leafy vegetables, become brittle and brittle when dehydrated in any form, and as a result they are available only in the form of flakes or powders. Examples of such products include spinach, parsley, basil, cabbage,

  leeks and similar types of vegetables and herbs.

  The shelf life of plant products

  dehydrated can be increased by storage at low temperatures.

  erasures. At low storage temperatures, the speed of

  Chemical reactions leading to deterioration is reduced.

  However, at congeLated storage temperatures, generally between 0.degree. C. and -25.degree. C., the normally dehydrated products and the products containing dissolved substances become

  even more brittle and likely to break.

  A number of food products that can be stored at freezing temperatures without being frozen have been described. These include plain pastes (Kahn et al., U.S. Patent No. 4,154,863), creamy emulsion products (Kahn et al., U.S. Patent No. 4,313,967), Egg Yolk (Kahn et al. No. 4,244,976), fruit juices (Kahn et al., US Pat. No. 4,418,082), fruit (Kahn et al., US Pat. No. 4,350,711), oil emulsions in the US Pat. water (US Patent No. 4,387,109) and foods that can be beaten (Kahn et al., U.S. Patent No. 4,146,652). The unfrozen behavior of all these products depends on very high levels of sugar. These

  sugar levels are not compatible with vegetable products.

fresh rate.

  The addition of solutes to regulate water activity in intermediate moisture foods is well documented (Lewis et al., U.S. Patent No. 4,447,460, US Patent No. 4,683,141, and US Pat. U.S. 4,384,009). Dissolved bodies have also been added to food products to obtain frozen foods with particular advantages (Lamb, U.S. Patent No. 3,219,461, Ariss et al., U.S. Patent No. 4,478,868), but not

  for the purpose of obtaining unfrozen food products.

  We have surprisingly found that it is possible to obtain very stable plant products and

  high quality, intended to be stored at lower temperatures than

  O0 C, in a flexible form and not subject to breakage.

  The present invention relates to a method for conserving

  a vegetable product at temperatures below 0 C,

  in that it comprises firstly the treatment of the product by partial dehydration and adding to said product at least one substance regulating the activity of the water, so that the activity of the water (measured at 200 ° C.) is less than 1, that the moisture content is lower than that of the untreated vegetable product, and that said water activity and the moisture content are both in a range such that said product remains soft and not frozen at temperatures below 0 C typical of the storage of frozen food, and secondly the reduction of the temperature of said product to a temperature below

  0 C typical of frozen food storage.

  The present invention also relates to a plant product stored at a temperature below 0 ° C. typical of

  storage of frozen food, which has been partially

  dehydrated and to which has been added beforehand at least one substance regulating the activity of water, characterized in that said product has a water activity (measured at 20 C) of less than 1, a moisture content of less than that of the non-preserved plant product, and in that the water activity and the moisture content are both in a range such that said product remains soft and not frozen at temperatures below 0 ° C

  typical of storing frozen food.

  The term "freezing" as used herein means conferring a state in which ice crystals and / or crystals of dissolved bones form in the product and render it hard and / or brittle. The object of the present invention is to obtain products which do not freeze in this way at

typical freezing.

  In a preferred embodiment, the water activity is less than about 0.90, and more preferably about C, 85. The activity of the water may also be greater than about C, and more preferably greater than about 0.7. The water activity is measured at 20 ° C. The actual values for the mites of water activity depend on the type of vegetable chosen, as well as on factors such as the type and amount of the substance. regulating the activity of the added water and the

moisture of the chosen vegetable.

  The moisture content is chosen such that the product remains flexible at typical frozen storage temperatures. Preferably, the moisture content is from about 20 to about 50%. More preferably, the content of

  humidity is from about 25 to about 45%.

  The final form of the plant product obtained according to the present invention includes sliced vegetables, uncut or coarsely cut leaf vegetables, and other forms of prepared vegetables. These plant products are stable at low temperatures, can be stored for short periods of time at temperatures higher than those normally used for storing conventional frozen vegetables, do not spoil easily and do not congeal when becoming solid. Also, they do not freeze and do not

  become not fragile at normal freezing temperatures.

  In general, the appropriate temperatures typical of the storage of

  Frozen foods are around -20cC.

  Water activity and moisture content are modi-

  by the setting of vegetable composition, by combining dehydration and the addition of one or more substances regulating the activity of water, which include but are not limited to sodium chloride and other salts, sugars such as sucrose, dextrose and invert sugars and alcohols

pzlyvalents such as glycerol.

  Before introducing dissolved bodies, it is possible to peel and blanch the vegetables to be treated or to prepare them otherwise, in any usual way, then they can be dried in air or under vacuum for example. Dissolved bodies can be added at. starting at intermediate stages, by any means including, but not limited to, pre-soaking before or after drying, stirring with known amounts of dissolved solids before

  drying, or by means of solutions of dissolved bodies.

  Dissolved bodies can also be added to the vegetables by the process described in Australian Patent No. 532,414, by

  example, in (a) partially desiccant or vegetable (s) to-

  air or vacuum, (b) introducing into the vegetable (s), at an appropriate stage, one or more dissolved bodies regulating the activity of the water, and (c) desiccating the treated vegetable (s) 'to the

desired moisture content.

  Alternatively, the substances regulating the activity of the water can be added before or during the dehydration of the vegetable crumbs. For example, you can add salt and mix it briefly with the vegetable pieces, so that it covers the pieces that are then partially dehydrated.

air or vacuum.

  Suitable water-controlling dissolved substances include sodium chloride, sodium citrate, potassium chloride and other such salts, sugars such as sucrose, dextrose and invert sugars, and polyvalent alcohols such as glycerol, sorbitol or propylene glycol, but are not limited thereto. If one or more sugars are selected as substances controlling the activity of the water, the total added sugar level is preferably less than 15% by weight in the finished product so that it has a

acceptable taste.

  The concentration of dissolved substances depends on variables such as taste considerations, the nature of dissolved substances

and types of processed vegetables.

  The term "vegetable" as used herein refers to plants and plant parts which are normally considered to be vegetables, and includes leaves, petioles, plants, bulbs, solid bulbs, plants, and plants. tubers, etc., as well as fruits such as tomatoes, pumpkins, pumpkins and grains such as sweet corn or peas, etc. The definition of vegetables also includes mixtures of

different vegetables.

  The activity of the water depends on the amount of moisture present as well as the quantities of other substances present in the atmosphere. The term "a" - is used to describe the activity of water, and is calculated by the following formula: a = P / P eo where p is the vapor pressure of the food, and po0 is here

  vapor pressure this Water at the same temperature.

  The final composition of the plant product is regulated by choosing the tyoe and the concentration of the dissolved substance (s) added to the vegetable and by regulating the moisture content of the vegetable product, as tele, when the vegetable product is subjected to temperatures. below 0 C as low as -20 C, the product does not freeze. The moisture content of the treated Vegetable,

  thanks to which this one does not freeze, varies with the concentration

  addition of the dissolved substances and the nature of these

  dissolved, and may be in the range of 20 to 50%.

  In general, the higher the concentration of the solutes, the lower the moisture content at which the plant product is frozen. If the moisture content is too low, relative to the added dissolved bodies, the plant product becomes hard, break and frail at freezing temperatures due to the crystallization of the dissolved bodies. If the moisture content is very high, in comparison with the dissolved bodies, the vegetable pieces freeze, becoming hard due to the formation of gel crystals, the cell structure of the vegetable is deteriorated and the cells can become brittle and can agglomerate in one block. The plant products obtained according to the present invention are flexible when the dehydration process is complete and remain flexible when maintained at conventional freezing temperatures at which they must be stored. In

  in addition, by a judicious choice of the dissolved body (s) and

  As a final moisture content, the water activity of these products at + 20 ° C. can be adjusted to preferably be less than 0.90 and preferably less than 0.85 and may also be above

  0.5, preferably above 0.7. At such levels of activity

  water temperature, if the temperature of the plant product rises above

  0 C, the vegetable product does not undergo any bacterial deterioration

  and undergoes only a very slow mycological deterioration. A

  storage at low temperatures significantly delays

  of color and taste and significantly prolongs the

shelf life.

  The non-freeze dehydrated vegetable products according to the present invention have a substantially higher moisture content than conventional dehydrated vegetables and a moisture content generally higher than that of the added vegetable solids disclosed in Australian Patent No. 532,414. in fact, they undergo shorter treatment times, less thermal damage and require less

of energy for dehydration.

  While these non-congenable plant products may contain relatively high levels of substances regulating water activity, they are made ready for use by

  rehydration and cooking with sensitive volumes of water, usually

  In the ratio of about 10: 1, this leads to salt and sugar levels in the products consumed in the normal range of seasoning levels. In addition, these products rehydrate faster because they have a higher moisture content than conventional dehydrated vegetables, because the presence of dissolved

  faster water absorption in plant tissues.

  Other advantages and characteristics of the invention

  will appear better in the following nonlimiting examples.

Example I

  Spinach leaves with a total solids content of 7% were washed to remove sand and soil and

  were cut roughly into wide strips of about 5 cm.

  These were dehydrated to about 40% moisture. Spinach fractions were then mixed with a solution of salt and sugar in a stirring device for 3 min, the amount of added bodies being calculated to give final contents of -5% of set and 10%. % sugar for levels of

  humidity of 60%, 55%, 45%, 30%, 20% and 15%.

  The finished products had the following composition: Sample Water activity Moisture freeze or not (a) (%) at -200 C 1 r, 91 60 yes 2 0.89 55 yes 3 0.86 43 no 4 0.75 28 no 0.58 17 no 6 0.40 14 yes Samples 3, 4 and 5 had a soft texture and rehydrated instantly when they were covered with boiling water to give spinach with a taste, an excellent color and texture. Leaf fragments have

  preserved the large size they had before dehydration

tation.

Example 2

  Parsley leaves of the curly variety were removed from the stems and washed with water. The total solids content was 8%. They were stirred with fine salt and sugar in fractions, salt and sugar being added in such a way that for moisture contents of 55%, 45%, 35%, 30% and 20%, the

  final product contains 10% added salt and 10% added sugar.

  The parsley was dehydrated to approximately the predetermined moisture content. The finished product had the following composition: Sample Water activity Moisture freeze or not (a) (%) a -20 C e 1 0.90 54 no 2 0.87 46 no 3 0.79 35 no 4 0 , 75 32 no 0.62 19 yes Samples 1 to 4 were soft, in the form of whole leaves, had excellent color and, when immersed in hot water, rehydrated

  instantly into a fresh parsley aroma product.

  Exempt 3 Kale from Milan was grated, blanched in boiling water for 3 min and drained. The total solids content of the

Dried cabbage was 6%.

  Four fractions of 50 g each of the drained milled cabbage were stirred for 3 minutes with the slurry and sugar to obtain an intimate mixture. The amount of salt and sugar added to each fraction was such that, for final moisture contents of 60%, 45%, 35%, 25% and 15%, the added salt content

  was 5% and the added sugar content was 5%.

  The grated cabbage was dehydrated to calculated weights to give the required moisture content. The finished products had the following compositions: Sample Activity Water Moisture freeze or not (a) (%) at -20 C 1 0.92 63 yes 2 0.84 42 no 3 0.80 33.5 no 4 0.73 25 partially 0.43 12 yes Samples 2 and 3 had a soft texture at -20 C, and rehydrated in 5 min when covered with boiling water to give a product having a color,

  excellent natural taste and texture.

Example 4

  Fresh carrots were peeled by hand and grated into 3 mm x 3 mm pieces. The grated carrots were steam blanched for 3 minutes at which point they had a total solids content of 8%. A sufficient amount of glycerol was thoroughly mixed with the blanched shredded carrots such that, for a moisture content of 30%, the finished product is in contact with 10% glycerol. The grated carrots have

  then dried at 70 ° C until the moisture content predefined

  completed by 30%. Dried grated carrots containing 10% of

  glycerol remained quite flexible at -20 C.

  The water activity was 0.71. When they were boiled in 20 parts by weight of water, they were soft and well rehydrated in 3 minutes, and showed a good

  satisfactory color and texture.

Example 5

  Some additional vegetables have been preserved according to the present invention, and the results are presented in the

  Figures I to 9 of the drawings, and in the tables below.

  The vegetables were treated with a salt solution (NaCl) in such a way that they contained 5% of salt (NaCl) added

  at specified humidity levels. The vegetables were at a tempera-

ture of -20 C.

  In the figures, the symbol "o" indicates that the freezing treatment was successful and that the vegetables remained soft and not frozen at -20 C according to the present invention, while the symbol "x" indicates failure, the vegetables

freezing by becoming solid.

  FIG. 1 shows the results of the storage of sliced potatoes according to the present invention, these

  The results are presented in the following table.

  Sample Activity Water Moisture Freezing in (a)% solid e 1 0, 92 43 yes 2 0.87 36 no 3 0.80 25 no 4 0.78 22 no 5 0.73 18 no 6 0> 68 15 yes 7 0.64 14 yes Figure 2 shows the results of the spinach storage under the conditions specified in the following table: Sample Moisture Frozen% Solid 1 0.90 55 yes 2 0.89 52 yes 3 0.83 40 no 4 0.82 32 no 0.80 30 no 6 0.72 28 no 7 0.58 18 yes Figure 3 shows the results of the preservation of grated carrots under the conditions specified in the following table: Sample moisture Moisture *% solids I 0.86 46 yes 2 0, E2 40 no 3 0.81 37 no 4 0.77 33. no 0.71 27 no 6 0.63 20 no 7 0.53 16 yes Figure 4 shows the results of the preservation of zucchini cut into slices under the conditions specified in the following table: E-ar.t L; Or a Hum dite Frozen in e% a solid 1 0.87 49 yes 2 C, 83 42 no 3 5, E2 41 no 4 0.76 34 no 2 5 C, 73 30 no 6 G, S6L 27 no 7 ,. 19 yes Figure 5 shows the results of the conservation of green beans under the conditions specified in the following table: EcnantiLlorn Moisture Frozen in% a solid 1 0.91 53 yes 2 0.88 36 no 3 0.79 27 no 4 0.78 24 no 0.7- 21 no 6 0.67 17 yes 7 0.62 14 yes

At - 26358062

  Figure 6 shows the results of the storage of diced tomatoes under the conditions specified in the following table: Sample at Frozen Moisture in e% Solid 1 0.71 31 No 2 0.65 28 No 3 0.56 26 No 4 0.52 23 no 5 0.49 20 yes Figure 7 shows the results of the conservation of green onion leaves under the conditions specified in the following table: Sampling at Frozen Moisture in e% solid 1 0.88 59 yes 2 0.84 51 no 3 0.83 46 no 4 0.66 28 no 0.49 14 yes Figure 8 shows the results of green pepper conservation under the conditions specified in the following table: Sample with Frozen Moisture in e % solid 1 0.87 60 yes 2 0.82 49 no 3 0.70 34 no 4 0.56 20 yes 0.40 13 yes Figure 9 shows the results of keeping sliced onions under the conditions specified in the following table: Ec-anilLon a Moisture CongeLed in% a solids I 0.94 67 yes 2 0j91 53 yes 3 0.88 43 no 4 0.83 25 no 0.61 15 Yes

  Of course The description is not. not limiting and the man

  art can make changes without going out for this

of the field of the invention.

Claims (12)

  1. A method for preserving a plant product at temperatures below 0 C, characterized in that it comprises firstly the treatment of said product by partial dehydration and addition to said product of at least one substance regulating the activity of the water, so that the water activity (measured at 20 C) is less than 1, that the moisture content is lower than that of the untreated vegetable product, and that said water activity and moisture content are both in a range such that said product remains flexible and not frozen at temperatures below 0 C typical of storage   frozen food, and secondly the reduction of the temperature   ture of said product to a temperature below 0 C typical storage of frozen foods.   2. Method according to claim 1, characterized in that said substance regulating the activity of water is added to   moment of, or before Partial dehydration of said product.   3. Method according to claim 1, characterized in that said procjit is partially dehydrated before the addition of   said substance regulating the activity of water.   The process according to claim 1, characterized in that said water activity (measured at 20 ° C) is in a range of about 0.5 to about 0.9 and that said   moisture is in a range of about 20 to about 50%.   The method of claim 1, characterized in that said water activity (measured at 20 ° C) is in a range of about 0.7 to about 0.85 and that said   Moisture is in a range of about 25 to about 45%.   6. Method according to claim 1, characterized in that said substance regulating the activity of water is chosen from one or more of the following substances: sodium chloride, sodium citrate, potassium chloride, sucrose, dextrose,   invert sugars, glycerol, sorbitol and propylene glycol.   7. Process according to claim 1, characterized in that the typical storage temperature of the frozen food is about -20 C.   8. Vegetable product stored at a temperature below 0 C typical frozen food storage, which was previously partially dehydrated and to which was added beforehand at least one substance regulating the activity of water, characterized in that said product has a water activity (measured at 20 ° C) of less than 1, a moisture content of less than that of the non-preserved plant product, and in that the water activity and the moisture content are all both in a range such that said product remains flexible and not frozen at temperatures below 0 C typical of frozen food storage. Plant product according to claim 8, characterized in that said water activity (measured at 20 ° C) is in a range of about 0.5 to about 0.9 and that said moisture content is in a range of about 20 to about 50%.   10. Vegetable product according to claim 8, characterized in that said water activity (measured at 20 0C) is in a range of about 0.7 to about 0.85 and in that said moisture content is included in a range of about 25 to about 45%.   11. Vegetable product according to claim 8, characterized in that said substance regulating the activity of water is chosen from one or more of the following substances: sodium chloride, sodium citrate, potassium chloride, sucrose,   dextrose, invert sugars, glycerol, sorbitol and propylene glycol.   12. Vegetable product according to claim 8, characterized in that the typical temperature of frozen food storage is about -20 C.