CA2000546C - Vegetable products with improved stability at freezer temperatures and process for producing same - Google Patents
Vegetable products with improved stability at freezer temperatures and process for producing same Download PDFInfo
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- CA2000546C CA2000546C CA 2000546 CA2000546A CA2000546C CA 2000546 C CA2000546 C CA 2000546C CA 2000546 CA2000546 CA 2000546 CA 2000546 A CA2000546 A CA 2000546A CA 2000546 C CA2000546 C CA 2000546C
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- water activity
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- A—HUMAN NECESSITIES
- A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
- A23B—PRESERVING, e.g. BY CANNING, MEAT, FISH, EGGS, FRUIT, VEGETABLES, EDIBLE SEEDS; CHEMICAL RIPENING OF FRUIT OR VEGETABLES; THE PRESERVED, RIPENED, OR CANNED PRODUCTS
- A23B7/00—Preservation or chemical ripening of fruit or vegetables
- A23B7/04—Freezing; Subsequent thawing; Cooling
- A23B7/05—Freezing; Subsequent thawing; Cooling with addition of chemicals or treatment with chemicals other than cryogenics, before or during cooling, e.g. in the form of an ice coating or frozen block
-
- A—HUMAN NECESSITIES
- A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
- A23B—PRESERVING, e.g. BY CANNING, MEAT, FISH, EGGS, FRUIT, VEGETABLES, EDIBLE SEEDS; CHEMICAL RIPENING OF FRUIT OR VEGETABLES; THE PRESERVED, RIPENED, OR CANNED PRODUCTS
- A23B7/00—Preservation or chemical ripening of fruit or vegetables
- A23B7/02—Dehydrating; Subsequent reconstitution
- A23B7/022—Dehydrating; Subsequent reconstitution with addition of chemicals before or during drying, e.g. semi-moist products
-
- A—HUMAN NECESSITIES
- A23—FOODS OR FOODSTUFFS; TREATMENT THEREOF, NOT COVERED BY OTHER CLASSES
- A23B—PRESERVING, e.g. BY CANNING, MEAT, FISH, EGGS, FRUIT, VEGETABLES, EDIBLE SEEDS; CHEMICAL RIPENING OF FRUIT OR VEGETABLES; THE PRESERVED, RIPENED, OR CANNED PRODUCTS
- A23B7/00—Preservation or chemical ripening of fruit or vegetables
- A23B7/04—Freezing; Subsequent thawing; Cooling
- A23B7/0441—Treatment other than blanching preparatory to freezing
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- General Chemical & Material Sciences (AREA)
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- Food Science & Technology (AREA)
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Abstract
A method for preserving a vegetable product at sub-zero Celcius temperatures is described, which involves partially dehydrating and adding one or mare water activity controlling substances to the vegetable product before reducing its, temperature. The vegetable product remains flexible and unfrozen at typical frozen food storage temperatures. The water activity of the product is below 1, and is preferably below 0.9, measured at 20°C. Suitable water'activity controlling substances are, for example, salts, sugars, and polyhydric alcohols. A vegetable product is also described having improved stability at typical freezer temperatures. The product is partially dehydrated and one or more water activity controlling substances have been added to it so that its water activity is less than 1, and it remains flexible and unfrozen at typical freezer temperatures.
Description
VEGETABLE PRODUCTS WITH IMPROVED STABILITY AT
FREEZER TEMPERATURES AND PROCESS FOR PRODUCING SAME
The present invention relates to a new type of low temperature stable vegetable product and a process for the production thereof.
Many processes are known far the preserving and storage of foods for short-term and long-term periods of time.
Freezing is one such process.
Frozen food products, in particular vegetables and vegetable products, are important products of commerce having uses in industrial, consumer, and food service markets. While the quality and acceptability of frozen vegetables is generally regarded as satisfactory, several inherent disadvantages are encountered with this type of food storage.
After having been frozen, foods products, including vegetables, must be kept at sub-zero (Celsius) temperatures.
Frozen food products which have been allawed to thaw partially or fully and are then refrozen suffer severe loss of quality.
Frozen food products that have been allowed to thaw either accidentally of if thawed for a period awaiting use can present a spoilage and public health hazard:
While some products such as peas, beans and carrot dice can be individually qo~zick frozen, other vegetables will freeze into a solid block which needs to be thawed so that measured quantities can be usedo Even individually quick frozen vegetables tend to agglomerate into lumps on storage as a result of water freezing between the vegetables pieces.
The energy required to freeze the water in vegetables is -z-0138e/AC
considerable and as well as this cost, freezer storage is expensive, as is freezer transport. Freezer transport is always precarious so far as maintaining the product in a frozen condition is concerned.
Some of the costs involved in storage and transport can be reduced considerably by the known process of "dehydrofreezing". In this process, vegetables are dehydrated to as much as 30% of their original weight, and are then frozen. Dehydrofreezing can reduce freezing, packing, storage and transport costs by up to 60%. However, the products still freeze hard, with consequent loss of texture and, having higher solids contents than normal, the products thaw more readily.
This can lead to problems of spoilage of the thawed product in much the same way as for thawed conventionally frozen products.
Various methods of vegetable dehydration are known and several are used industrially. In most of these methods the vegetables are dried to low moisture contents, usually below 2%, and in the case of freeze-dried vegetables the vegetables axe dried often as low as 2% to 3%. At these moisture contents the vegetables are hard and very brittle. There is a great deal of breakage and excessive production of fines (small vegetables pieces and Eibres). This is particularly so with leafy vegetables. Normal air-dried vegetables which are exposed to relatively high storage temperatures at low moisture contents for long periods of time suffer substawtial-flavour, colour and aroma deterioration.
Stable dehydrated vegetables having higher than normal moisture contents can be produced by the addition of salt to 0138e/AC
lower the water activity of partially dried vegetables, as described by Lewis and Lewis (Australian Patent No. 532414, US
Patents 4,447,460 and 4.683,141). With these the upper moisture level is 25%, but in general longer shelf stability is attained at moisture levels at 'the lower end of the moisture scale.
Onions for instance, tend to discolour slowly when stored at moisture levels above 10%. At moisture contents of 10% or lower the onion slices are brittle enough to allow breakage of the slices. Many dEhydrated white vegetables or the pale tissues of other vegetables, for example the inner petioles of celery, the white tissue of zucchini, the inner pale yellow leaves of cabbage or Chinese cabbage and white cucumber tissue will darken relatively quickly in storage. Furthermore, many green and pale-green vegetables, whether in solute-added or conventionally dried form, suffer deterioratian of the green chlorophyll pigment when stored at ambient temperatures at water activa.ties above 0.50 for more than a few months. Still other vegetables, particularly the leafy ones, become brittle and fragile when dehydrated in any form and, as a result, are only available as flakes or powders: ~~amples of such products includes spinach, parsley, sweet basil, cabbage, leeks, and similar types of vegetables and herbs.
The shelf-life of dehydrated vegetable products can be increased by storage at low temperatures: At lower storage temperatures the rates of the chemical reactions leading to deterioration are reduced. However, at freezer storage temperatures, generally between 0°C and -25°C, the normal - 4 _ 0138e/AC
dehydrated and solute added products become even more brittle and subject to breakage.
A number of food products that can be stored at freezer temperatures without freezing have been described. These include batters (Kahn et al U.S. Patent 4,154,863) emulsion cream type products (Kahn et al U.S. 4,313,967) egg yolk (Kahn et al U.S. Patent 4,244,976), fruit juices (Kahn et al U.S.
Patent 4,418,082) fruits (Kahn et al U.S. Patent 4,350,711) oil in water emulsions (U. S. Patent 4,387,109) and °'whippable"
foods (Kahn et al U.S. Patent 4,146,652). These all depend for their non-freeze performance on very high levels of sugars.
These levels of sugars would not be compatible with fresh vegetable products.
The addition of solutes to control water activity in intermediate moisture foods is well documented (Lewis et al U.S. Patent 4,447,460, U.S. Patent 4,683,141 and U.S. Patent 4,384,009). Solutes have also been added to foodstuffs to produce frozen foods with particular claimed advantages, Lamb U.S. Patent 3,219,461, Aries et al U.S. 4,478,868, but not with the aim of producing non-freezable food products.
We have now surprisingly found that very stable, high duality vegetable products, intended for storage at below 0°C, can be produced in a "non-breakable", and flexible form.
The present invention concerns a method for preserving a vegetable product at sub-zero temperatures which comprises firstly treating the product by partially dehydrating and adding to the product at least one water activity controlling substance whereby the water activify is less than 1 (measured -0138e/AC
at 20°C), the moisture content is less than that of the untreated vegetable product, and both the water activity and moisture content is within a range whereby the product remains flexible arid unfrozen at typical sub-zero frozen food storage temperatures, and secondly reducing the temperature of the .. - product to a typical sub-zero frozen food storage temperture.
The inventian also concerns a vegetable product preserved at a typical sub-zero frozen food storage temperature which has previously been partially dehydrated and to which at least one water activity controlling substance has previously been added, characterized in that, the product has a water activity less than ~. (measured at 20°), a moisture content less than that of the unpreserved vegetable product, and both the water activity and moisture content is within a range whereby the product remains flexible and unfrozen at typical sub-zero frozen food storage termperatures.
The term °°freeze" as used herein is meant to convey a state where ice crystals and/or solute crystals are formed in the product and thus make it hard and/or brittle. The aim of the present invention is to produce products that do not "freeze°' in this manner at typical geezer temperatures.
In one preferred form the water activity of the invention is below about 0.90, and mare preferably below about 0.85. The water acta:vity may a~,so be above about 05 and more preferably above'about 0.7. The water activity is measured at 20°C: The actual values for the limits of the water activity will depend on the type of vegetable chosen; as well as factors such as the type and amount of water actzvity controlling substance added, 0138e/AC
24~~~'~~'~
and the moisture content of the chosen vegetable.
The moisture content is chosen such that the product remains flexible at typical frozen storage temperatures.
The moisture content will preferably be between about 20 and 50%. More preferably the moisture content is between about 25 and 45%.
The final form of the vegetable product produced in accordance with the invention includes sliced vegetables, uncut or coarsley cut leaf vegetables, and other forms of prepared vegetables. These vegetable praducts are stable at low temperatures, can lbe stored for short periods of time at temperatures above those typically used for the storage of conventional frozen vegetables, do not readily spoil any; do not freeze solid. Also, they will not freeze or become brittle at normal freezer temperatures. Tn general, suitable typical frozen faad storage temperatures will be about -20°C.
The water activity and moisture content is affected by adjusting the composition of vegetables by a combination of dehydration, and the addition of one or more water activity controlling substances, including but not limited to sodium chloride and other salts, sugars such as sucrose, dextrose and invert sugars and polyhydric alcohols such as glyceiol.
Prior to the introduction of solutes the vegetables to be treated can be peeled, and blanched or otherwise prepared in accor~lanes with any customary manner. and then may be dried in air or vacuum, for example. Solutes may be added by any method including but not limited to presteeping before or after drying, tumbling with known quantities of solute before drying, 01~8e/AC
or with solutions or solid solutes initially or at intermediate stages.
Solutes may also be added to vegetables by the process described in Australian Patent 532414, for example, by (a) partially dehydrating the vegetables(s) in air or vacuum, (b) introducing, at a suitable stage, one or more water activity controlling solutes into the vegetable(s), and (c) dehydrating the treated vegetables) to the desired moisture content.
Alternatively, the water activity controlling substances can be added before, or at the same time as the vegetable pieces are dehydrated. For example, salt may be added and briefly mixed with the vegetable pieces to coat the pieces, which are then partially dehydrated in air or vacuum.
Suitable water activity controlling solutes include sodium chloride, sodium citrate, potassium chloride and other such salts, sugars such as sucrose dextrose and invert sugars, and polyhydric alcohols such as glycerol, sorbitol or propylene glycol, but are not limited to these. Tf a sugar or sugars are selected as the water activity controlling substance then the total added sugar level is preferably below 15% by weight in the finished product, so that the vegetable product has an acceptable taste.
The concentration of the solutes is dependent on such variables as flavour considerations, the nature of the solutes, and the types of vegetable being treated.
The,term '°vegetable" as used herein denotes plants and plant parts normally considered as vegetables,' and includes leaves, petioles roots; bulbs; corms; tubers, etc. as well as 0138e/AC
~~.?~~;~4~
fruits such as tomatoes, squash, pumpkin and seeds such as sweetcorn or peas etc. The definition of vegetables also includes mixtures of different vegetables.
Water activity depends on the amount of moisture present as well as the amounts of the other substances present in the food. The expression "aw" is used to describe water activity, and is calculated by the formula:
aw = p/po where p is the vapour pressure of the food, and po is the vapour pressure of water, at the same termperature.
The final composition of the vegetable product is adjusted by selecting the type and concentration of solutes) added into the vegetable and adjusting the moisture content of the vegetable product such that when the vegetable product is subjected to sub-zero temperatures as low as -20°C or thereabouts the product will not freeze: The moisture content of the treated vegetable which ensures that it does not freeze will vary with the concentration of solutes added and the nature of these solutes, and may be in the order of 20 to 50%.
In general, the higher the concentration of solutes the lower will be the moisture content at which the vegetable pxoduct Freezes. If the moisture level is too low, relative to the solutes added, the vegetable, product will become hard, brittle and fragile at freezing temperatures due to the crystallization of the solutes: If the moisture content is too high, relative to the solutes, the vegetable pieces will freeze :hard due to the formation of ice crystals, the cell structure of the vegetable will be damaged, and the pieces can become 0138e/AC
fragile and may matt into a block.
Vegetable products produced in accordance with the present invention are flexible at the time the dehydration process is completed and stay flexible when held at conventional freezer temperatures at which they are to be stored. Furthermore, by judicious selection of the solutes) and final moisture content, the water activity of these ~aroducts at *20°C may preferably be adjusted below the level of 0.90 and preferably below 0.85 and may also be above 0.5, preferably 0.7. At such water activity levels, if the vegetable product increases in temperature above zero the vegetable product is not subject to bacterial deterioration, nor is it subject to mycological deterioration at other than a very slow rate. Storage at low temperatures greatly retards changes in colour and flavour and significantly prolongs shelf-life.
Non-freezable dehydrated vegetable products in accordance with the invention have a substantially higher moisture content than conventional dehydrated vegetables and a generally higher moisture content than the solute-added vegetables described in Australian Patent No. 582914. They are therefore subject to shortex processing times, suffer less heat damage and require less energy to dehydrate.
While these non-freezable vegetable products may contain relatively high levels of added water activity contro113ng substances, they are prepared ~or use by rehydra~ion end cooking with substantial'voj.umes of water, usually in the ratio of about 10:1. This gives salt and sugar levels in the 0138e/AC
products as consumed within the normal seasoning levels.
Furthermore, these products rehydrate more rapidly because they are at a higher moisture content than conventional dehydrated vegetables and because the presence of solutes induces the more rapid absorption of water into the vegetable tissue.
The invention is illustrated below by means of the following non-limiting examples.
Leaves of spinach with a total solids content of 7% were washed to remove grit and dirt and were coarsely cut into strips about 5cm wide. They were dehydrated to approximately 40% moisture. Aliquots of the spinach were then mixed with a solution of salt and sugar in a tumbler for three minutes, the quantity of solutes being calculated to give final contents 5%
salt and 10% sugar at moisture contents of 60%, 55%, 45%. 30%, 20% and 15%.
The finished products had the following composition:
Sample Water Activity Moisture °~ Freeze or Not at -20°C
1 .91 60 Yes 2 .89 55 Yes 3 .86 43 No .4 .75 28 No .58 17 No 6 .40 14 Yes Samples 3, 4 and 5 had a soft texture and rehydrated instantly when covered with boiling water to give spinach of excellent flavour, colour and texture: The pieces of leaf were in the same whole large piece'as they were before dehydration.
0138e/AC
Parsley leaves of the "curley" variety were removed from the coarse stems, and washed in water. The total solids was 8%. They were tumbled with fine grained salt and sugar in aliquots, the salt and sugar added being such that at moisture contents of 55%, 45%, 35%, 30% and 20%, the final, product would contain 10% of added salt and 10% of added sugar.
The parsley was dehydrated to approximately the predetermined moisture content. The finished product has the following composition:
am 1 Water Activity Moisture % Freeze or Not at -20°C
1 0.90 54 No 2 0.87 46 No 3 0,79 35 No 4 0.75 32 No 0.62 19 Yes - frozen Samples 1 to 4 were flexible, in whole leaf form, had excellent colour and rehydrated to a product with fresh parsley aroma instantly when immersed in hot water.
EXAMPLE ~
Fresh Savoy cabbage was shredded, blanched in boiling water for 3 minutes and drained. The total soli.c~s content of the drained cabbage was 6%, Four aliquots of 500g each of the drained blanched cabbage were tumbled for three minutes raith fine grained salt 'and sugar so that an intimate mixture was obtained. The quantitg of salt amd sugar added to each aliquot was such that at final moisture contents of 60%, 4~ %. 35%: '25 % and 15%. the 0138e/AC
added salt content would be 5% and added sugar 5%.
The cabbage shreds were dehydrated to weights calculated to give the required moisture contents. The finished products had the following compositions:
Sample Water Activity ri~loisture % Freeze or Not 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 minutes when covered with boiling water to give a product with excellent natural colour, flavour and texture.
Fresh carrots were hand peeled and shredded into shreds 3mm x 3mm. The shreds were steam blanched for 3 minutes, at which stage they had a total solids content of 8%. Sufficient glycerol was mixed thoroughly with the blanched shreds such that at a moisture content of 30% finished product would contact 10% of glycerol. The shreds were then dried at 70°C to the predetermined moisture content 30%: The dried shreds containing 10% of gllrcerol remained quite flexible at -20°C.
The water activity was 0.T1: On boiling in 20 parts by weight of water, they were tender and well rehydrated in three minutes, and had good valour and texture.
Some additional vegetables were preserved in accordance with the 'invention, and the results are,shown as Figures 1 to 9'in the drawings, and in the tables provided below.
0138e/AC
The vegetables were treated with salt (NaCl) solution so that they contained 5% added NaCl at the moisture levels specified. The vegetables were at a temperature of -20°C.
In the drawings, the symbol "o" indicates the treatment freezing was successful and the vegetables remained flexible and unfrozen at -20° in accordance with the invention, while the symbol "x" indicates an unsuccessful result, whereby the vegetables froze solid.
Figure 1 shows the results of preserving sliced potatoes in accordance with the invention as specified in the following table:
am 1 Water Activity (Aw) Mois ure % Frozen Solid?
1 0:92 43 Yes 2 0.87 36 No 3 0.80 25 No 4 0.78 22 No 0.73 18 No 6 0.68 Z5 Yes 7 0.64 14 Yes Figure 2 shows the results of preserving spinach as specified in the following table:
am 1 Aw Moisture % Frozen Solid?
1 0.90 55 Yes 2 0.89 52 Yes 3 0x83 90: No 4 0:82 3z No 5 0.80 30 No 6 0:72 28 No 7 0.58 18 Yes 14 ~.
0138e/AC
Figure 3 shows the results of preserving carrot shreds as specified in the following table:
Sample Aw Moisture % Frozen Solid?
1 0.86 46 Yes 2 0.82 40 No 3 0.81 37 No 4 0.77 33 No 0.71 27 No 6 0.63 20 No ? 0.53 16 Yes Figure 4 shows the results of preserving sliced zucchini as specified in the Following table:
Sample Aw Moisture ~ Frozen Solid?
Z 0.87 49 Yes 2 0.83 42 No 3 0.82 41 No 4 0.76 34 No ' 5 0:73 30 No 6 p.64 27 No 7 ' 0.51 19 Yes 14a Figure 5 shows the greenpeas as results of preserving specified in the tablebelow:
m 1 Aw Moisture ~ Fro zen Solid?
1 0.91 53 Yes 2 0.88 36 No 3 0.79 27 No 4 0.78 24 No 0.72 21 No 6 0.67 17 Yes 0.62 14 Yes Figure 6 shows the dicedtomatoes as results of preserving specified in the tablebelow:
am t Aw Moisture ~ Frozen Solid?
l 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 greenonion tops as results of preserving specified in the tablebelow:
~"'~m. lp~ ~w ~ re Frozen Solid?
1 0.88 59 Yes 2 0.8~ 51 No 3 0,83 46 No 4 0:66 28 No 5 0,49 14 Yes 0138e/AC
Figure 8 shows the results of preserving green bell peppers as specified in the table below:
Sample Aw Moisture % Frozen Solid?
1 0.87 60 Yes 2 0.82 49 No 3 0.70 34 i~o 4 0.56 20 Xes 0.40 13 Yes Figure 9 shows the results of preserving sliced onions as specified in the table below:
m 1 Aw Moisture % Frozen Solid?
0.94 67 Yes 2 0.91 53 Yes 3 0.88 43 1~0 4 0.83 25 ~o 5 0.61 l5 Yes The above description is only illustrative of the invention, and obvious alterations and modifications may be made without departing fxorn the spirit of the invention.
FREEZER TEMPERATURES AND PROCESS FOR PRODUCING SAME
The present invention relates to a new type of low temperature stable vegetable product and a process for the production thereof.
Many processes are known far the preserving and storage of foods for short-term and long-term periods of time.
Freezing is one such process.
Frozen food products, in particular vegetables and vegetable products, are important products of commerce having uses in industrial, consumer, and food service markets. While the quality and acceptability of frozen vegetables is generally regarded as satisfactory, several inherent disadvantages are encountered with this type of food storage.
After having been frozen, foods products, including vegetables, must be kept at sub-zero (Celsius) temperatures.
Frozen food products which have been allawed to thaw partially or fully and are then refrozen suffer severe loss of quality.
Frozen food products that have been allowed to thaw either accidentally of if thawed for a period awaiting use can present a spoilage and public health hazard:
While some products such as peas, beans and carrot dice can be individually qo~zick frozen, other vegetables will freeze into a solid block which needs to be thawed so that measured quantities can be usedo Even individually quick frozen vegetables tend to agglomerate into lumps on storage as a result of water freezing between the vegetables pieces.
The energy required to freeze the water in vegetables is -z-0138e/AC
considerable and as well as this cost, freezer storage is expensive, as is freezer transport. Freezer transport is always precarious so far as maintaining the product in a frozen condition is concerned.
Some of the costs involved in storage and transport can be reduced considerably by the known process of "dehydrofreezing". In this process, vegetables are dehydrated to as much as 30% of their original weight, and are then frozen. Dehydrofreezing can reduce freezing, packing, storage and transport costs by up to 60%. However, the products still freeze hard, with consequent loss of texture and, having higher solids contents than normal, the products thaw more readily.
This can lead to problems of spoilage of the thawed product in much the same way as for thawed conventionally frozen products.
Various methods of vegetable dehydration are known and several are used industrially. In most of these methods the vegetables are dried to low moisture contents, usually below 2%, and in the case of freeze-dried vegetables the vegetables axe dried often as low as 2% to 3%. At these moisture contents the vegetables are hard and very brittle. There is a great deal of breakage and excessive production of fines (small vegetables pieces and Eibres). This is particularly so with leafy vegetables. Normal air-dried vegetables which are exposed to relatively high storage temperatures at low moisture contents for long periods of time suffer substawtial-flavour, colour and aroma deterioration.
Stable dehydrated vegetables having higher than normal moisture contents can be produced by the addition of salt to 0138e/AC
lower the water activity of partially dried vegetables, as described by Lewis and Lewis (Australian Patent No. 532414, US
Patents 4,447,460 and 4.683,141). With these the upper moisture level is 25%, but in general longer shelf stability is attained at moisture levels at 'the lower end of the moisture scale.
Onions for instance, tend to discolour slowly when stored at moisture levels above 10%. At moisture contents of 10% or lower the onion slices are brittle enough to allow breakage of the slices. Many dEhydrated white vegetables or the pale tissues of other vegetables, for example the inner petioles of celery, the white tissue of zucchini, the inner pale yellow leaves of cabbage or Chinese cabbage and white cucumber tissue will darken relatively quickly in storage. Furthermore, many green and pale-green vegetables, whether in solute-added or conventionally dried form, suffer deterioratian of the green chlorophyll pigment when stored at ambient temperatures at water activa.ties above 0.50 for more than a few months. Still other vegetables, particularly the leafy ones, become brittle and fragile when dehydrated in any form and, as a result, are only available as flakes or powders: ~~amples of such products includes spinach, parsley, sweet basil, cabbage, leeks, and similar types of vegetables and herbs.
The shelf-life of dehydrated vegetable products can be increased by storage at low temperatures: At lower storage temperatures the rates of the chemical reactions leading to deterioration are reduced. However, at freezer storage temperatures, generally between 0°C and -25°C, the normal - 4 _ 0138e/AC
dehydrated and solute added products become even more brittle and subject to breakage.
A number of food products that can be stored at freezer temperatures without freezing have been described. These include batters (Kahn et al U.S. Patent 4,154,863) emulsion cream type products (Kahn et al U.S. 4,313,967) egg yolk (Kahn et al U.S. Patent 4,244,976), fruit juices (Kahn et al U.S.
Patent 4,418,082) fruits (Kahn et al U.S. Patent 4,350,711) oil in water emulsions (U. S. Patent 4,387,109) and °'whippable"
foods (Kahn et al U.S. Patent 4,146,652). These all depend for their non-freeze performance on very high levels of sugars.
These levels of sugars would not be compatible with fresh vegetable products.
The addition of solutes to control water activity in intermediate moisture foods is well documented (Lewis et al U.S. Patent 4,447,460, U.S. Patent 4,683,141 and U.S. Patent 4,384,009). Solutes have also been added to foodstuffs to produce frozen foods with particular claimed advantages, Lamb U.S. Patent 3,219,461, Aries et al U.S. 4,478,868, but not with the aim of producing non-freezable food products.
We have now surprisingly found that very stable, high duality vegetable products, intended for storage at below 0°C, can be produced in a "non-breakable", and flexible form.
The present invention concerns a method for preserving a vegetable product at sub-zero temperatures which comprises firstly treating the product by partially dehydrating and adding to the product at least one water activity controlling substance whereby the water activify is less than 1 (measured -0138e/AC
at 20°C), the moisture content is less than that of the untreated vegetable product, and both the water activity and moisture content is within a range whereby the product remains flexible arid unfrozen at typical sub-zero frozen food storage temperatures, and secondly reducing the temperature of the .. - product to a typical sub-zero frozen food storage temperture.
The inventian also concerns a vegetable product preserved at a typical sub-zero frozen food storage temperature which has previously been partially dehydrated and to which at least one water activity controlling substance has previously been added, characterized in that, the product has a water activity less than ~. (measured at 20°), a moisture content less than that of the unpreserved vegetable product, and both the water activity and moisture content is within a range whereby the product remains flexible and unfrozen at typical sub-zero frozen food storage termperatures.
The term °°freeze" as used herein is meant to convey a state where ice crystals and/or solute crystals are formed in the product and thus make it hard and/or brittle. The aim of the present invention is to produce products that do not "freeze°' in this manner at typical geezer temperatures.
In one preferred form the water activity of the invention is below about 0.90, and mare preferably below about 0.85. The water acta:vity may a~,so be above about 05 and more preferably above'about 0.7. The water activity is measured at 20°C: The actual values for the limits of the water activity will depend on the type of vegetable chosen; as well as factors such as the type and amount of water actzvity controlling substance added, 0138e/AC
24~~~'~~'~
and the moisture content of the chosen vegetable.
The moisture content is chosen such that the product remains flexible at typical frozen storage temperatures.
The moisture content will preferably be between about 20 and 50%. More preferably the moisture content is between about 25 and 45%.
The final form of the vegetable product produced in accordance with the invention includes sliced vegetables, uncut or coarsley cut leaf vegetables, and other forms of prepared vegetables. These vegetable praducts are stable at low temperatures, can lbe stored for short periods of time at temperatures above those typically used for the storage of conventional frozen vegetables, do not readily spoil any; do not freeze solid. Also, they will not freeze or become brittle at normal freezer temperatures. Tn general, suitable typical frozen faad storage temperatures will be about -20°C.
The water activity and moisture content is affected by adjusting the composition of vegetables by a combination of dehydration, and the addition of one or more water activity controlling substances, including but not limited to sodium chloride and other salts, sugars such as sucrose, dextrose and invert sugars and polyhydric alcohols such as glyceiol.
Prior to the introduction of solutes the vegetables to be treated can be peeled, and blanched or otherwise prepared in accor~lanes with any customary manner. and then may be dried in air or vacuum, for example. Solutes may be added by any method including but not limited to presteeping before or after drying, tumbling with known quantities of solute before drying, 01~8e/AC
or with solutions or solid solutes initially or at intermediate stages.
Solutes may also be added to vegetables by the process described in Australian Patent 532414, for example, by (a) partially dehydrating the vegetables(s) in air or vacuum, (b) introducing, at a suitable stage, one or more water activity controlling solutes into the vegetable(s), and (c) dehydrating the treated vegetables) to the desired moisture content.
Alternatively, the water activity controlling substances can be added before, or at the same time as the vegetable pieces are dehydrated. For example, salt may be added and briefly mixed with the vegetable pieces to coat the pieces, which are then partially dehydrated in air or vacuum.
Suitable water activity controlling solutes include sodium chloride, sodium citrate, potassium chloride and other such salts, sugars such as sucrose dextrose and invert sugars, and polyhydric alcohols such as glycerol, sorbitol or propylene glycol, but are not limited to these. Tf a sugar or sugars are selected as the water activity controlling substance then the total added sugar level is preferably below 15% by weight in the finished product, so that the vegetable product has an acceptable taste.
The concentration of the solutes is dependent on such variables as flavour considerations, the nature of the solutes, and the types of vegetable being treated.
The,term '°vegetable" as used herein denotes plants and plant parts normally considered as vegetables,' and includes leaves, petioles roots; bulbs; corms; tubers, etc. as well as 0138e/AC
~~.?~~;~4~
fruits such as tomatoes, squash, pumpkin and seeds such as sweetcorn or peas etc. The definition of vegetables also includes mixtures of different vegetables.
Water activity depends on the amount of moisture present as well as the amounts of the other substances present in the food. The expression "aw" is used to describe water activity, and is calculated by the formula:
aw = p/po where p is the vapour pressure of the food, and po is the vapour pressure of water, at the same termperature.
The final composition of the vegetable product is adjusted by selecting the type and concentration of solutes) added into the vegetable and adjusting the moisture content of the vegetable product such that when the vegetable product is subjected to sub-zero temperatures as low as -20°C or thereabouts the product will not freeze: The moisture content of the treated vegetable which ensures that it does not freeze will vary with the concentration of solutes added and the nature of these solutes, and may be in the order of 20 to 50%.
In general, the higher the concentration of solutes the lower will be the moisture content at which the vegetable pxoduct Freezes. If the moisture level is too low, relative to the solutes added, the vegetable, product will become hard, brittle and fragile at freezing temperatures due to the crystallization of the solutes: If the moisture content is too high, relative to the solutes, the vegetable pieces will freeze :hard due to the formation of ice crystals, the cell structure of the vegetable will be damaged, and the pieces can become 0138e/AC
fragile and may matt into a block.
Vegetable products produced in accordance with the present invention are flexible at the time the dehydration process is completed and stay flexible when held at conventional freezer temperatures at which they are to be stored. Furthermore, by judicious selection of the solutes) and final moisture content, the water activity of these ~aroducts at *20°C may preferably be adjusted below the level of 0.90 and preferably below 0.85 and may also be above 0.5, preferably 0.7. At such water activity levels, if the vegetable product increases in temperature above zero the vegetable product is not subject to bacterial deterioration, nor is it subject to mycological deterioration at other than a very slow rate. Storage at low temperatures greatly retards changes in colour and flavour and significantly prolongs shelf-life.
Non-freezable dehydrated vegetable products in accordance with the invention have a substantially higher moisture content than conventional dehydrated vegetables and a generally higher moisture content than the solute-added vegetables described in Australian Patent No. 582914. They are therefore subject to shortex processing times, suffer less heat damage and require less energy to dehydrate.
While these non-freezable vegetable products may contain relatively high levels of added water activity contro113ng substances, they are prepared ~or use by rehydra~ion end cooking with substantial'voj.umes of water, usually in the ratio of about 10:1. This gives salt and sugar levels in the 0138e/AC
products as consumed within the normal seasoning levels.
Furthermore, these products rehydrate more rapidly because they are at a higher moisture content than conventional dehydrated vegetables and because the presence of solutes induces the more rapid absorption of water into the vegetable tissue.
The invention is illustrated below by means of the following non-limiting examples.
Leaves of spinach with a total solids content of 7% were washed to remove grit and dirt and were coarsely cut into strips about 5cm wide. They were dehydrated to approximately 40% moisture. Aliquots of the spinach were then mixed with a solution of salt and sugar in a tumbler for three minutes, the quantity of solutes being calculated to give final contents 5%
salt and 10% sugar at moisture contents of 60%, 55%, 45%. 30%, 20% and 15%.
The finished products had the following composition:
Sample Water Activity Moisture °~ Freeze or Not at -20°C
1 .91 60 Yes 2 .89 55 Yes 3 .86 43 No .4 .75 28 No .58 17 No 6 .40 14 Yes Samples 3, 4 and 5 had a soft texture and rehydrated instantly when covered with boiling water to give spinach of excellent flavour, colour and texture: The pieces of leaf were in the same whole large piece'as they were before dehydration.
0138e/AC
Parsley leaves of the "curley" variety were removed from the coarse stems, and washed in water. The total solids was 8%. They were tumbled with fine grained salt and sugar in aliquots, the salt and sugar added being such that at moisture contents of 55%, 45%, 35%, 30% and 20%, the final, product would contain 10% of added salt and 10% of added sugar.
The parsley was dehydrated to approximately the predetermined moisture content. The finished product has the following composition:
am 1 Water Activity Moisture % Freeze or Not at -20°C
1 0.90 54 No 2 0.87 46 No 3 0,79 35 No 4 0.75 32 No 0.62 19 Yes - frozen Samples 1 to 4 were flexible, in whole leaf form, had excellent colour and rehydrated to a product with fresh parsley aroma instantly when immersed in hot water.
EXAMPLE ~
Fresh Savoy cabbage was shredded, blanched in boiling water for 3 minutes and drained. The total soli.c~s content of the drained cabbage was 6%, Four aliquots of 500g each of the drained blanched cabbage were tumbled for three minutes raith fine grained salt 'and sugar so that an intimate mixture was obtained. The quantitg of salt amd sugar added to each aliquot was such that at final moisture contents of 60%, 4~ %. 35%: '25 % and 15%. the 0138e/AC
added salt content would be 5% and added sugar 5%.
The cabbage shreds were dehydrated to weights calculated to give the required moisture contents. The finished products had the following compositions:
Sample Water Activity ri~loisture % Freeze or Not 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 minutes when covered with boiling water to give a product with excellent natural colour, flavour and texture.
Fresh carrots were hand peeled and shredded into shreds 3mm x 3mm. The shreds were steam blanched for 3 minutes, at which stage they had a total solids content of 8%. Sufficient glycerol was mixed thoroughly with the blanched shreds such that at a moisture content of 30% finished product would contact 10% of glycerol. The shreds were then dried at 70°C to the predetermined moisture content 30%: The dried shreds containing 10% of gllrcerol remained quite flexible at -20°C.
The water activity was 0.T1: On boiling in 20 parts by weight of water, they were tender and well rehydrated in three minutes, and had good valour and texture.
Some additional vegetables were preserved in accordance with the 'invention, and the results are,shown as Figures 1 to 9'in the drawings, and in the tables provided below.
0138e/AC
The vegetables were treated with salt (NaCl) solution so that they contained 5% added NaCl at the moisture levels specified. The vegetables were at a temperature of -20°C.
In the drawings, the symbol "o" indicates the treatment freezing was successful and the vegetables remained flexible and unfrozen at -20° in accordance with the invention, while the symbol "x" indicates an unsuccessful result, whereby the vegetables froze solid.
Figure 1 shows the results of preserving sliced potatoes in accordance with the invention as specified in the following table:
am 1 Water Activity (Aw) Mois ure % Frozen Solid?
1 0:92 43 Yes 2 0.87 36 No 3 0.80 25 No 4 0.78 22 No 0.73 18 No 6 0.68 Z5 Yes 7 0.64 14 Yes Figure 2 shows the results of preserving spinach as specified in the following table:
am 1 Aw Moisture % Frozen Solid?
1 0.90 55 Yes 2 0.89 52 Yes 3 0x83 90: No 4 0:82 3z No 5 0.80 30 No 6 0:72 28 No 7 0.58 18 Yes 14 ~.
0138e/AC
Figure 3 shows the results of preserving carrot shreds as specified in the following table:
Sample Aw Moisture % Frozen Solid?
1 0.86 46 Yes 2 0.82 40 No 3 0.81 37 No 4 0.77 33 No 0.71 27 No 6 0.63 20 No ? 0.53 16 Yes Figure 4 shows the results of preserving sliced zucchini as specified in the Following table:
Sample Aw Moisture ~ Frozen Solid?
Z 0.87 49 Yes 2 0.83 42 No 3 0.82 41 No 4 0.76 34 No ' 5 0:73 30 No 6 p.64 27 No 7 ' 0.51 19 Yes 14a Figure 5 shows the greenpeas as results of preserving specified in the tablebelow:
m 1 Aw Moisture ~ Fro zen Solid?
1 0.91 53 Yes 2 0.88 36 No 3 0.79 27 No 4 0.78 24 No 0.72 21 No 6 0.67 17 Yes 0.62 14 Yes Figure 6 shows the dicedtomatoes as results of preserving specified in the tablebelow:
am t Aw Moisture ~ Frozen Solid?
l 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 greenonion tops as results of preserving specified in the tablebelow:
~"'~m. lp~ ~w ~ re Frozen Solid?
1 0.88 59 Yes 2 0.8~ 51 No 3 0,83 46 No 4 0:66 28 No 5 0,49 14 Yes 0138e/AC
Figure 8 shows the results of preserving green bell peppers as specified in the table below:
Sample Aw Moisture % Frozen Solid?
1 0.87 60 Yes 2 0.82 49 No 3 0.70 34 i~o 4 0.56 20 Xes 0.40 13 Yes Figure 9 shows the results of preserving sliced onions as specified in the table below:
m 1 Aw Moisture % Frozen Solid?
0.94 67 Yes 2 0.91 53 Yes 3 0.88 43 1~0 4 0.83 25 ~o 5 0.61 l5 Yes The above description is only illustrative of the invention, and obvious alterations and modifications may be made without departing fxorn the spirit of the invention.
Claims (12)
1. A method for preserving a vegetable product at sub-zero temperatures which comprises firstly treating said product by partially dehydrating and adding to said product at least one water activity controlling substance whereby the water activity is less than 1 (measured at 20°C), the moisture content is less than that of the untreated vegetable product, and both said water activity and moisture content is within a range whereby said product remains flexible and unfrozen at typical sub-zero frozen food storage temperatures, and secondly reducing the temperature of said product to a typical sub-zero frozen food storage temperture.
2. The method of claim 1, whereby said water activity controlling substance is added at the same time as, or before, partially dehydrating said product.
3. The method of claim 1, whereby said product is partially dehydrated before adding said water activity controlling substance.
4. The method of claim 1 wherein said water activity is within a range of from about 0.5 to about 0.9 (measured at 20°C) and said moisture content is within a range of from about 20 to about 50%.
5. The method of claim 1 wherein said water activity is within a range of from about 0.7 to about 0.85 (measured at 20°C) and said moisture content is within a range of from about 25 to about 45%.
6. The method of claim 1 wherein said water activity controlling substance is selected from one or more of sodium chloride, sodium citrate, potassium chloride, sucrose, dextrose, invert sugars, glycerol, sorbitol and propylene glycol.
7. The method of claim 1 wherein the typical frozen food storage temperature is about -20°C.
8. Vegetable product preserved at a typical sub-zero frozen food storage temperature which has been partially dehydrated and to which at least one water activity controlling substance has previously been added, characterized in that said product has a water activity less than 1 (measured at 20°), a moisture content less than that of the unpreserved vegetable product, and both said water activity and moisture content is within a range whereby said product remains flexible and unfrozen at typical sub-zero frozen food storage termperatures.
9. The vegetable product of claim 8 wherein said water activity is within a range of from about 0.5 to about 0.9 (measured at 20°) and said moisture content is within a range of from about 20 to about 50%.
10. The vegetable product of claim 8 wherein said water activity is within a range of from about 0.7 to about 0.85 (measured at 20°) and said moisture content is within a range of from about 25 to about 45%.
11. The vegetable product of claim 8 wherein said water activity controlling substance is selected from one or more of sodium chloride, sodium citrate, potassium chloride, sucrose, dextrose, invert sugars, glycerol, sorbitol and propylene glycol.
12. The vegetable product of claim 8 wherein the typical frozen food storage temperature is about -20°C.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| AUPJ099888 | 1988-10-17 | ||
| AUPJ0998 | 1988-10-17 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2000546A1 CA2000546A1 (en) | 1990-04-17 |
| CA2000546C true CA2000546C (en) | 2000-01-25 |
Family
ID=3773448
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2000546 Expired - Lifetime CA2000546C (en) | 1988-10-17 | 1989-10-12 | Vegetable products with improved stability at freezer temperatures and process for producing same |
Country Status (6)
| Country | Link |
|---|---|
| JP (1) | JP2866117B2 (en) |
| AU (1) | AU622225B2 (en) |
| CA (1) | CA2000546C (en) |
| FR (1) | FR2638062B1 (en) |
| GB (1) | GB2225521B (en) |
| NZ (1) | NZ230946A (en) |
Families Citing this family (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2649297B1 (en) * | 1989-07-04 | 1993-04-16 | Daregal Sa | PROCESS FOR DEHYDRATION OF EDIBLE PLANTS |
| GB8927434D0 (en) * | 1989-12-05 | 1990-02-07 | Unilever Plc | Treating fruit material |
| AU653886B2 (en) * | 1992-02-26 | 1994-10-13 | Byron Agricultural Company Pty Ltd | Quick-cooking dehydrated vegetables |
| US5338558A (en) * | 1992-12-09 | 1994-08-16 | Mccormick & Company, Inc. | Process for preparing stabilized, partially-dehydrated aromatic plant products |
| US5397584A (en) * | 1992-12-09 | 1995-03-14 | Mccormick & Company, Inc. | Process for preparing stabilized, partially-dehydrated aromatic plant products |
| FR2725111B1 (en) | 1994-09-29 | 1996-11-29 | Sodiape | PLANTS STORABLE AT LOW POSITIVE AND NEGATIVE TEMPERATURE AND METHOD FOR TREATMENT OF FRESH PLANTS WITH A VIEW TO OBTAINING THEM |
| AUPN020294A0 (en) * | 1994-12-21 | 1995-01-27 | Byron Agricultural Company Pty Ltd | Compressed frozen vegetable |
| AUPP475398A0 (en) * | 1998-07-20 | 1998-08-13 | Byron Australia Pty Ltd | Quick-cook dehdrates vegetables |
| US8007852B2 (en) * | 2002-11-18 | 2011-08-30 | Olam West Coast, Inc. | Method for production of frozen vegetables or fruits |
| US7943189B2 (en) | 2007-10-26 | 2011-05-17 | Lee Ferrell | Food preservation packaging system |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3219461A (en) * | 1964-07-17 | 1965-11-23 | Lamb Weston Inc | Process for partially dehydrating, impregnating and freezing food products |
| US3952112A (en) * | 1973-07-11 | 1976-04-20 | Kellogg Company | Methods for treating dried fruits to improve softness retention characteristics |
| US4350711A (en) * | 1977-01-28 | 1982-09-21 | Rich Products Corporation | Methods of infusing fruits |
| BE875783A (en) * | 1978-04-24 | 1979-10-23 | Mars Ltd | FOOD PRODUCTS AND THEIR PREPARATION METHODS |
| US4313967A (en) * | 1979-03-26 | 1982-02-02 | Rich Products Corporation | Intermediate-moisture frozen foods |
| AU532414B2 (en) * | 1979-07-11 | 1983-09-29 | Byron Agricultural Company Pty Ltd | Dehydration of vegetables |
| US4364968A (en) * | 1981-03-31 | 1982-12-21 | General Foods Corporation | Process for preparing a dried grape product |
| US4713252A (en) * | 1985-09-12 | 1987-12-15 | Maine Wild Blueberry Co. | Process for producing a semi-moist fruit product and the products therefrom |
-
1989
- 1989-10-09 NZ NZ23094689A patent/NZ230946A/en unknown
- 1989-10-11 AU AU42800/89A patent/AU622225B2/en not_active Expired
- 1989-10-12 CA CA 2000546 patent/CA2000546C/en not_active Expired - Lifetime
- 1989-10-13 GB GB8923061A patent/GB2225521B/en not_active Expired - Lifetime
- 1989-10-17 FR FR8913574A patent/FR2638062B1/en not_active Expired - Lifetime
- 1989-10-17 JP JP27016789A patent/JP2866117B2/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| GB8923061D0 (en) | 1989-11-29 |
| FR2638062B1 (en) | 1993-10-22 |
| AU4280089A (en) | 1990-04-26 |
| CA2000546A1 (en) | 1990-04-17 |
| JPH02257827A (en) | 1990-10-18 |
| AU622225B2 (en) | 1992-04-02 |
| GB2225521B (en) | 1992-08-05 |
| FR2638062A1 (en) | 1990-04-27 |
| GB2225521A (en) | 1990-06-06 |
| NZ230946A (en) | 1992-05-26 |
| JP2866117B2 (en) | 1999-03-08 |
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