CA1058007A - Process for the preservation of root-crop plants - Google Patents

Abstract

PROCESS FOR THE PRESERVATION OF ROOT-CROP PLANTS
Abstract of the Disclosure A process for treatment of root-crop plants, such as potatoes, carrots and turnips to enable such plants to be kept longer without spoiling comprises heating peeled product to hydrolize a starch content until to the reaction to the enzyme peroxidase is negative on the surface of the root and for about 5-7 mm towards the core; and then cooling such plant. Treatment with a preservative such as "sorbic" said and a compound which liberates sulphur dioxide may be used to enhance the treated products.

Description

~58~7 It has become more and more customary to in-troduce peeled or scraped root-crop plants, such as potatoes, carrots, ~- Swedish turnips and similar products suitable for human con-~ sumption to the market, packed in such a way that the consumer - can prepare the products for consumption in a simple manner.
For that purpose the root-crop has been treated with ~- sulphur dioxide or with a compound producing sulphur dioxi~de, ~....
`; like sodium metabisulphite and thereupon packed.

It appears, however, that the products thus obtained ;~
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` ~ 10 cannot - not even under refrigeration - be kept for a long period, i.e. only for one day. The keeping qualities could -be improved by means of a higher sulphur dioxide-content of the ;
root-crop~ e.g. a content of more than 50 ppm SO2, but this is `
not desirable for several reasons. -From the Netherlands Patent Application No. 6913969 a heat treatment for vegetables and fruits is known, in which these are treated with a hot solution and thereupon cooled to a temperature below 5C. It is, among others, the purpose of this method to inactivate the enzymes present in the vegetables ; 20 and fruits. To this effect a period of 12 - 20 minutes is `; suggested as duration of the heat treatment. Especially with potatoes this method lead~ to a more or less cooked product, - which differs markedly from the fresh potato~
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~ From the American Patent Specification No.2,506,793 a process is known for the preservation of potatoes in which `~
these are peeled, subjected to a heat treatment and thereupon ~ treated with sulphite. The heat treatment is such that the :
~; potatoes are being hydrolised only partly, whereas in the core ;,,,~,!, practically the entire en%yme-activity is preserved. According to this Patent Specification also the treatment with sulphite is essential.

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; in which products are obtained which, under refrigeration, ;~ can be kept many days, e.g. 13 days, and, at room temperature, at least 3 days, while the products thus treated remain very , tasteful unlike those products preserved according to known methods.
According to the present invention there is provided a process for the preservation of peeled or scraped root-crop products in which said product is subjected firstly to heating -;,:
10 with steam at temperatures of from 70C to 100C for a period of 5-7 minutes, until substantially all starch present in said ~` product is just hydrolyzed and until reaction to peroxidase is negative both at the outer surface of said product and at a . .. .. .
~~ depth of about 7 mm. from said outer surface, and thereafter i cooling said products to at least 5C.
or heat treatment a minimum temperature of approxi-mately 70C is required, because only at such temperature hydrolising will occur. The maximum treatment temperature is `~ not critical, because the effect to be achieved is a function of time and temperature. It is of importance that, as a , . . .
result of the treatment, the enzyme "peroxidase" in the interior part of the root-crop remains active, while the starch present has become hydrolised to the proper extent. It ~ -will be clear that, with a higher treatment temperature, a shorter duration of treatment can be applied and conversely.
Heat treatment is to be performed in such a manner, that the . ~, ;.
formation of loose starchy parts and loose cell parts on the ` surface of the root-crop is avoided, because such parts will cause pollution of the packing material. In general, a treatment between 70 and 100C is chosen.
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; Cooling is generally performed with a gas that has ,~ no deleterious effect on the root-crop treated. Preferably air is used for this purpose, which is previously filtered in ; order to remove microorganisms and particles of dust. Direct ; cooling with water should be avoided, because the treated ;~ root-crop, when cooled in this manner, absorb much water which they give up again in the packing material.
Treatment with a preservative agent may, for , instance, take place in a solution of same and, preferably, ;~

(I~sorbic~ acid is used as a preservative agent. -It will have a favourable effect, if the root-crop - are treated after heat treatment, with sulphur dioxide or with - a compound which liberate sulphur dioxide. This treatment ,. . .
i may take place before, during, or after treatment with the :., `~ preservative agent. To this end, a solution of sodium bisulphite may be used, but also, for example, a solution con-taining the preservative agent as well as sodium bisulphite.
The keeping qualities of the products treated in ,-~ .:
~r'' accordance with the invention, as we~l as of the comparable ;~; 20 products were valued organoleptically, microbiologically as well as for appearance.
ProductS that had not been treated according to the invention were, after their maximum period for keeping, ~' sour, they had a hard skin, were discoloured and were con-;,,,~ ;~: .
sidered not attractive by the consumer.
Th~ products according to the invention could, at the moment of appraisal, not be distinguished from fresh ~`
products. ~
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f'l The invention is explained more fully by means of -the following examples.
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~5~ 7 ~^ Example I
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A quantity of 500 kgs. of peeled potatoes was treated with steam. Heat treatment was checked by taking ; ~ samples and was continued until the reaction to peroxidase .... : .
with the potatoes was negative down to a depth of 5-7 mms "" from the outer surface and the starch present in the potatoes had just hydrolized. This was achieved at a tem-,. . .
perature o~ 95C and after a period of 5 minutes.
After heat treatment the potatoes were cooled with pre-cooled, purified air during 90 minutes. Cooling was continued until the temperature in the interior of the potatoes had fallen to 3-5C.
The potatoes thus treated were packed and stored ~ -.:; . . .
at a temperature of 1-5C and it was proved that they main-.. . .
; tained their keeping qualities for at least 8 days.

xample II
~ .f ~: ' `~ Example I was repeated, but now the potatoes were, .,~ . .~ .
~'1 after they had been cooled, dippecl into a solution contain-;;~ ing 0,5 per cent by weight of sodium metabisulphite and 0,2 per cent by weight of "sorbic" acid.
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; The potatoes thus treated were packed and stored ,.:.................................................................... .
at a temperature of 1-5C. The potatoes kepttheir quality " ` during storage at that temperature for at least 13 days and during storage at room temperature ~20C) the potatoes ;~' appeared to keep their quality for at least three days. ' f~
Potatoes whlch had not been treated according to the inven- -~
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',f',~ tion could, at a temperature of 1-5C, only be kept for a maximum of 3 days, whereas, at room temperature, they were already unsuitable for consumption after 1 day.
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!~," Example III
A quantity of 400 kgs. of scraped carrots was -treated in a way as described in Example I.
The temperature for treatment was 98C and the :~ .:: , duration of treatment was 6 minutes.

After cooling with purified air, as described in Example I, the carrots were dipped in a solution containing -~; 0.2~ by weight of "sorbic" acid for 1 minute.
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~ The packed carrots were stored at 2-5C and :, `; 10 appeared to have kept their quality for 12 days. With storage at 20C they kept their quality for at least 2 days.
Example IV
,, -~ Example III was repeated, but now dipping was done `~- in a solution, which, apart from "sorbici' acid, also contained ,i;. :~
0.5~ by weight of sodium sulphite The results during StOI-age were mainly the same as indicated in Example III, however, the keeping quality of . . .
)l the carrots at room temperature had slightly increased.
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Claims (7)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for the preservation of peeled or scraped root-crop products in which said product is subjected firstly to heating with steam at temperatures of from 70°C to 100°C
for a period of 5-7 minutes, until substantially all starch present in said product is just hydrolyzed and until reaction to peroxidase is negative both at the outer surface of said product and at a depth of about 7 mm. from said outer surface, and thereafter cooling said products to at least 5°c.

2. The process of claim 1, in which said product is treated after cooling with a compound diffusing sulfur dioxide.

3. The process of claim 2, in which said product is cooled by air.

4. The process of claims 1, 2 or 3, in which after cooling said product is treated with "sorbic" acid as a preservative.

5. The process of claims 2 or 3, wherein said compound is sulphur dioxide.

6. The process of claims 1, 2 or 3, in which said product is stored after treatment at a temperature from about 1°C to about 10°C.

7. Edible root-crop treated by the process of claims 1, 2 or 3.