BE1025404B1 - Method for improving the texture of a frozen and conditioned tuber vegetable after reheating - Google Patents

Abstract

The present invention relates to a method for improving the texture of a frozen and conditioned tuber vegetable after reheating, which belongs to the field of processing of agricultural products. In the present invention, by pre-treating the raw material, blanching in combination with low frequency ultrasound assisted osmotic dehydration, freezing, glass freeze storage and reheating, the entire process of improving the texture of a frozen and conditioned tuber vegetable after reheating is enabled. According to the invention, the glass transition temperature of tuber vegetables and fruits is increased by low-frequency ultrasound-assisted osmotic dehydration and the damage to the cell structure is reduced by the formation of ice crystals in the course of the freezing process, whereby the storage at glass-state temperatures largely results in the sensory quality and nutrients of the vegetables can be maintained. By later rewarming with several methods, rapid and stable rewarming of the raw material can be achieved, thereby improving the texture and nutritional value of the vegetable after reheating.

Description

Process to improve the texture of frozen and conditioned tuber vegetables after reheating

Field of the Invention

The present invention relates to a method for improving the texture of a frozen and conditioned tuber vegetable after reheating, in particular a method for processing deep-frozen tuber vegetables, which is used above all for frozen conditioned foods and belongs to the field of processing agricultural products.

Technical background

Frozen food is food that freezes quickly at a low temperature (below -30 ° C), so that the core temperature quickly within half an hour to a temperature range of -1 ° C to -11 ° C (i.e. the Temperature range for optimal formation of ice crystals, so that more than 80% of the water content is converted to ice crystals) is reduced, then packaged and refrigerated and traded at a temperature below -18 ° C. As a natural food without additives, frozen vegetables are becoming increasingly popular abroad thanks to their high nutritional value, simple consumption, good hygiene, excellent shelf life and simple production technology. Despite a later start in the production of frozen vegetables in China, it is developing rapidly and thanks to unique resource judgments, China has already become a major producer and exporter of frozen vegetables.

The deep-freezing of fruits and vegetables serves to maintain the original quality of the vegetables as well as possible and to freeze the vegetables in a partially glass state so that it is partly in the glass state, while maintaining the color, aroma, taste, shape and nutrients as far as possible can be. In the course of the freezing process, irreversible damage is caused to the cells by the formation of a large amount of ice crystals, which is why the selection of a suitable freezing process plays an important role in the later quality of the food. In addition, the final quality of frozen products depends on defrosting, with the various physical and chemical changes resulting from a defrosting process as well as an improper defrosting process having a major impact on the

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Osmotic dehydration as a pretreatment can not only reduce the water content in the vegetable system, but also allow some hypertonic substances to penetrate, whereby such substances of large molecules can change the state, the viscosity and the free volume of the water content in the fruit and vegetables, thus the glass transition temperature of fruits and vegetables. When the fruit and vegetables are frozen and stored at glass transition temperatures, the sensory quality and nutritional value of the food can be largely maintained. In addition, such hypertonic substances can serve as anti-freeze agents and contribute to improving the freezing quality of fruits and vegetables. Tang Mingxia (2012) used maltose and trehalose for the osmotic treatment of frozen edible soybeans under vacuum conditions and found that osmotic treatment can significantly increase the partial glass transition temperature of soybeans and suppress soybean texture softening. Research conducted by Marani (2007) found that pre-treatment osmotic dehydration can reduce the juice loss rate of frozen samples and improve the color and texture of some types of fruit. The difference with the present invention lies in the use of low-frequency, ultrasound-assisted, osmotic dehydration, which can significantly increase the dehydration efficiency.

In an ultrasonic defrosting process, energy is used that is generated by the thermal effect of ultrasonic waves and whose attenuation in frozen tissue is significantly higher than in defrosted tissue, so that the interface between the frozen and defrosted layer within the raw material is the main energy absorption point and through Setting the frequency and intensity of the ultrasonic wave, the thermal effect generated by the weakening of the ultrasonic wave can be stabilized in the vicinity of the freezing point, which is why the defrosting process takes place continuously with the shifting of the interface between frozen and defrosted part of the raw material, as a result of which local overheating within the food raw material occurs avoided and rapid and stable defrosting of the raw material is achieved. Kissam (1982) used a low-frequency ultrasonic wave with an intensity of 1500Hz and a power of 60W to defrost a cod

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BE2018 / 5082 a large head and found that a low-frequency ultrasonic wave reduces the defrost time by 71% and the defrost speed is increased significantly. Cheng et al. (2014) found through research that the defrost speed for frozen Edamame can be increased significantly with ultrasonic waves, whereby a maximum retention rate of the ascorbic acid and chlorophyll content and a minimal juice loss rate are achieved during a defrosting process with an ultrasonic power of 900W. The difference in the present invention is that the defrosting process is carried out by means of a micro wave, ultrasonic wave and water bath, which enables rapid defrosting of the raw material and the texture is largely retained.

Ling Dongdong et al. (Chinese Patent Specification No. 201410813812.8) invented a process for deep-freezing carrots, comprising the following steps: (1) taking the raw material, (2) storing the raw material, (3) selecting and washing, (4) peeling and cleaning, ( 5) cutting into pieces, (6) cutting into julienne strips, (7) bladder rinsing and dehairing with a dehairing machine, (8) bladder washing, (9) blanching, (10) cooling with pre-cooling ice water, (11) shaking and draining , (12) freezing, (13) shaking and sieving, (14) pre-storing in bags, (15) freezing. But freezing alone is unable to solve the problem of the breakdown of the cell structure due to the formation of ice crystals during a freezing process, so that problems such as juice loss and reduced hardness of defrosted fruits and vegetables occur. The difference in the present invention is that dehydration as a pretreatment before freezing and reheating with several methods maintains the quality and nutritional value of the vegetables well.

Jin Jieheng et al. (Chinese patent specification with the patent number from 201410657485.1) invented a process for processing frozen carrots, comprising the following steps: selection of the raw material, pre-cleaning, cutting with a cutting machine, ultrasound cleaning, selection with a machine, wrapping with film, blanching, cooling, draining, freezing, sorting out and packaging, etc. A loss of nutrients is prevented by a wrapping with fish holding film, whereby an incomplete blanching could lead to incomplete deactivation of the peroxidase, so that an enzymatic browning of the tissue is caused. The difference in the present invention is that blanching in combination with low frequency ultrasound assisted osmotic treatment

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BE2018 / 5082 takes place, which increases the glass transition temperature of the tuber vegetables and fruit and reduces the damage to the cell structure caused by the formation of ice crystals during a freezing process.

Chen Longhai et al. (Chinese patent specification with the patent number of

200610052645.5) invented a method for increasing the glass transition temperature of fruits and vegetables at individual deep freezing and freezing, whereby the individual fruits and vegetables are subjected to a treatment with saline solution, aqueous cyclodextrin solution and aqueous sodium alginate solution to 1 to 3 ° C cooled quickly, freezing at a temperature of -35 ° C to -55 ° C for 15 to 60 minutes. With such a method, various damages as a result of the formation of ice crystals are avoided, the loss of juice is reduced, the quality of frozen fruits and vegetables is improved, and the energy consumption is saved due to the state transition. The difference in the present invention is that for the fruits and vegetables, low-frequency ultrasound-assisted, osmotic dehydration takes place by means of an osmosis liquid composed of trehalose, calcium chloride and sodium chloride, which increases the glass transition temperature of fruits and vegetables.

Zhang Min et al. (Chinese patent specification with the patent number from 200510039034.2) invented a method for storage in the glass state with improved quality of rapidly frozen and conditioned fruits and vegetables, whereby an osmotic treatment by means of a solution of carbohydrate, sugar, table salt or spice under vacuum conditions and after deep freezing with liquid nitrogen or liquid carbon dioxide can be stored at a temperature of -30 ° C to -40 ° C, so that the original quality of the fruit and vegetables can be maintained. The difference in the present invention is that low-frequency ultrasound-assisted osmotic treatment is performed, which significantly increases the osmosis efficiency, increases the glass transition temperature of fruits and vegetables, and improves the quality of the fruits and vegetables when stored in the freezer.

Tan Ziyang et al. (Chinese patent specification with the patent number of

201010555551.6) invented a novel method to improve the quality of defrosted fruits and vegetables, the deep freezing of the fruits and vegetables is supported by ultrasound waves and the process comprises the following steps: selecting fruit and vegetable raw material, cleaning, cutting, blanching for enzyme deactivation, cooling and Ultrasound-assisted freezing, packaging, with which the

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BE2018 / 5082 defrost quality of frozen fruit and vegetable raw material is improved, such a method being characterized by a shortened freezing time, well-preserved original shape and low operating costs. Sun Jincai (Chinese Patent Specification No. 200710134436.X) invented a method of improving the defrost quality of frozen fruits and vegetables by means of low frequency ultrasound waves, whereby osmotic treatment and deep freezing of the fruits and vegetables are carried out in combination with ultrasound treatment, whereby the defrost quality is frozen Fruit and vegetable raw material is improved, wherein such a method is characterized by a shortened freezing time, well-preserved original shape and low operating costs. Sun Dawen (Chinese Patent No. 201310100261.6) invented a method of increasing the freezing speed and quality of lychee by means of variable frequency ultrasonic wave, which, according to the result, an appropriate ultrasonic wave can significantly shorten the freezing time of lychee and improve product quality, with no apparent color change the shell occurs after storage at a temperature of -18 ° C for one year. In such patents, the influence of different ultrasonic waves on the freezing speed and quality of the fruit and vegetables is examined, but without investigating the influence of ultrasonic defrosting on the quality of frozen tuber vegetables.

Wan Jing et al. (Chinese Patent Specification No. 201310588429.2) invented a method of uniformly defrosting frozen ingredients with maintained quality by defrosting the vegetables through three-stage dielectric heating, which improves the defrosting quality of frozen vegetables and maintains their texture well. The difference in the present invention is that treatment is carried out by means of microwaves, ultrasound waves and water baths, which enables rapid defrosting of the raw material and the quality and nutritional value of the vegetables are maintained.

Liang Dongwu et al. (Chinese Patent Specification No. 201510353383.5) invented a method for defrosting frozen food by placing frozen food in a microwave-safe container and entering water the weight of which is half to 100% of the weight of the frozen food, using microwave defrosting the microwave-safe container is placed in a microwave oven. Such a method enables a quick and uniform defrosting of various frozen foods, in addition to increased

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Defrosting efficiency at the same time largely maintains the original appearance, texture and proximity of frozen foods. The difference in the present invention is that the defrosting of the raw material is carried out by several methods, whereby local overheating within the raw material can be avoided and rapid and stable defrosting of the raw material can be achieved.

Disclosure of the invention

The present invention has for its object to provide a method for processing tuber vegetables, with which the texture of frozen tuber vegetables can be effectively improved and the quality of the vegetables can be maintained.

Process for improving the texture of a frozen and conditioned tuber vegetable after reheating, characterized in that it comprises the following steps:

(1) Pretreatment of the raw material: selection of fresh and undamaged tuber vegetables, washing, peeling and cutting in slices or cubes, (2) blanching in combination with a low-frequency ultrasound-supported, osmotic treatment:

a. Blanching: Blanch the chopped vegetables in hot water at a temperature of 85 ° C to 90 ° C for 1 to 2 minutes, enter calcium chloride with a concentration of 0.1% w / v and citric acid with a concentration of 0.4% w / v in the hot water to maintain crispness and for color protection, rinse and cool with tap water after completing blanching,

b. Osmotic treatment: Soaking the vegetables obtained in step a in an osmosis liquid with a temperature of 30 ° C to 35 ° C in a raw material-liquid ratio of 1: 4, ultrasonic treatment during the soaking with the parameters of 40KHz, 0, 33W / cm ² , 10s operation / l Os pause for a treatment time of 25 to 30 minutes, rinsing with distilled water for 30s to 40s after the end of the osmotic treatment, washing off superfluous osmosis liquid on the surface of the vegetables and draining, ( 3) Freezing: Freezing the vegetables obtained in step (2) at a freezing rate of 15 ° C to 20 ° C / min and ending the freezing process at a core temperature of -25 ° C to -30 ° C, (4) freezing storage in the glass state : Pack the frozen vegetables in step (3) and store them at a temperature below the glass transition temperature of

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BE2018 / 5082 -30 ° C to -35 ° C, (5) reheating: defrost with a 915MHz low frequency microwave for 30s to 40s, with a 40KHz low frequency ultrasonic wave for 40s to 45 s and with warm water that has a temperature of 40 ° C to 50 ° C, for 30s to 45s to quickly defrost the vegetables to 0 ° C, reheating in a 2450MHz microwave oven for 2 to 3 minutes to 80 ° C to 90 ° C, the Texture retention rate of conditioned tuber vegetables reached 75% to 90% after reheating.

Characterized in that the osmosis liquid in step (2) consists of trehalose with a concentration of 40% w / v, sodium chloride with a concentration of 1.5% w / v and calcium chloride with a concentration of 0.5% w / v v is composed.

The present invention is advantageously characterized in that low-frequency, ultrasound-assisted, osmotic dehydration not only reduces the water content in fruits and vegetables, but also increases the glass transition temperature of the vegetables and fruits. In addition, the sensory quality and nutrients of the food can be largely retained through freezing and storage at glass state temperatures. Subsequent reheating with several methods enables the raw material to be reheated quickly and stably, thereby improving the change in the texture and nutritional value of the vegetables after reheating.

Specific embodiments

First embodiment: Process for improving the texture of frozen and conditioned carrots after reheating

The partial glass transition temperature of osmotically dehydrated carrots is determined by means of DSC8500, the result being that the partial glass transition temperature of the treated sample compared to the untreated sample is increased by 4.03 ° C to -24.12 ° C.

(1) Pretreatment of the raw material: selection of fresh and undamaged carrots, washing, peeling and cutting in platelets, (2) blanching in combination with a low-frequency ultrasound-supported, osmotic treatment: blanching of the finely chopped carrots in hot water at a temperature of 85 ° C to 90 ° C for 1 to 2 minutes, enter calcium chloride with a concentration of 0.1% w / v and citric acid with a concentration of 0.4% w / v in the hot water to maintain the crispness and protect the color , Rinse and cool with tap water after blanching is complete. Soaking the

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BE2018 / 5082 Vegetables in an osmosis liquid, which is composed of trehalose with a concentration of 40% w / v, sodium chloride with a concentration of 1.5% w / v and calcium chloride with a concentration of 0.5% w / v , with a temperature of 35 ° C in a raw material-liquid ratio of 1: 4. Ultrasound treatment during the soaking with the parameters of 40KHz, 0.33W / cm ² , 10s operation / l Os pause for one

Treatment time from 25 to 30 minutes, rinsing with distilled water for 30s to 40s after the end of the osmotic treatment. Washing off superfluous osmosis liquid on the surface of the carrots and draining, (3) freezing: deep-freezing the carrots at a freezing rate of 15 ° C to 20 ° C / min and ending the freezing process at a core temperature of -25 ° C, (4) Freezer storage in the glass state: packaging the frozen carrots and storage at a temperature below the glass transition temperature of -30 ° C to -35 ° C, (5) reheating: defrosting with a 915MHz low-frequency microwave for 30s to 40s, with a 40KHz low-frequency ultrasonic wave for 40s to 45 s and with warm water at a temperature of 40 ° C to 50 ° C, for 30s to 45s to quickly defrost the carrots to 0 ° C. Reheat in a 2450MHz microwave oven for 2 to 3 minutes at 80 ° C to 90 ° C.

Compared to conventional freezing and reheating methods, the reheating efficiency of carrots treated in this way is increased by 270%, with the texture retention rate reaching 84%, the juice loss rate reduced by 14% and the mouthfeel, color and nutrients also being retained well.

Second embodiment: Process for improving the texture of frozen and conditioned bamboo shoots after reheating

The partial glass transition temperature of osmotically dehydrated bamboo shoots is determined by means of DSC8500, whereby according to the result the partial glass transition temperature of treated sample compared to untreated sample is increased by 5.12 ° C to -23.79 ° C.

(1) Pretreatment of the raw material: selection of fresh and undamaged bamboo shoots, washing, peeling and cutting into strips.

(2) Blanching in combination with a low-frequency, ultrasound-assisted, osmotic treatment: blanch the finely chopped bamboo shoots in hot water at a temperature of 85 ° C to 90 ° C for 1 to 2 minutes, enter calcium chloride with a concentration of 0, 1% w / v and citric acid with a concentration of 0.4% w / v in the hot water to maintain the crispness and for color protection, rinsing and cooling with tap water after completing the blanching.

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BE2018 / 5082 Soaking the bamboo shoots in an osmosis liquid consisting of trehalose with a concentration of 40% w / v, sodium chloride with a concentration of 1.5% w / v and calcium chloride with a concentration of 0.5% w / v v composed, with a temperature of 35 ° C in a raw material-liquid ratio of 1: 4. Ultrasound treatment during the soaking with the parameters of 40KHz, 0.33W / cm ² , 1 Os operation / 1 Os pause for a treatment time of 30 minutes, rinsing with distilled water for 30s after the end of the osmotic treatment. Washing off superfluous osmosis liquid on the surface of the bamboo shoots, (3) deep-freezing in the glass state: freezing the bamboo shoots at a freezing rate of 15 ° C to 20 ° C / min and ending the freezing process at a core temperature of -25 ° C, (4) Freezer storage in the glass state: packaging the frozen bamboo shoots and storage at a temperature which is below the glass transition temperature from -30 ° C to -35 ° C, (5) reheating: defrosting with a 915MHz low-frequency microwave for 30s to 40s, with one 40KHz low-frequency ultrasonic wave for 40s to 45 s and with warm water at a temperature of 40 ° C to 50 ° C for 30s to 45s to quickly defrost the bamboo shoots down to 0 ° C. Reheat in one

2450MHz microwave oven for 2 to 3 minutes at 80 ° C to 90 ° C.

Compared to conventional freezing and reheating methods, the

Reheating efficiency of bamboo shoots treated in this way is increased by 230%, with the texture retention rate reaching 82%, the juice loss rate reduced by 12% and the mouthfeel, color and nutrients are also well maintained.

Claims (2)

Expectations 1. A method for improving the texture of a frozen and conditioned tuber vegetable after reheating, characterized in that it comprises the following steps: (1) Pretreatment of the raw material: selection of fresh and undamaged tuber vegetables, washing, peeling and cutting in slices or cubes, (2) blanching in combination with a low-frequency ultrasound-supported, osmotic treatment: a. Blanching: Blanch the chopped vegetables in hot water at a temperature of 85 ° C to 90 ° C for 1 to 2 minutes, enter calcium chloride with a concentration of 0.1% w / v and citric acid with a concentration of 0.4% w / v in the hot water to maintain crispness and for color protection, rinse and cool with tap water after completing blanching, b. Osmotic treatment: Soaking the vegetables obtained in step a in an osmosis liquid with a temperature of 30 ° C to 35 ° C in a raw material-liquid ratio of 1: 4, ultrasonic treatment during the soaking with the parameters of 40KHz, 0, 33W / cm ² , 10s operation / l Os pause for a treatment time of 25 to 30 minutes, rinsing with distilled water for 30s to 40s after the end of the osmotic treatment, washing off superfluous osmosis liquid on the surface of the vegetables and draining, ( 3) Freezing: Freezing the vegetables obtained in step (2) at a freezing rate of 15 ° C to 20 ° C / min and ending the freezing process at a core temperature of -25 ° C to -30 ° C, (4) freezing storage in the glass state : Pack the frozen vegetables in step (3) and store them at a temperature below the glass transition temperature of -30 ° C to -35 ° C, (5) reheating: defrost with a 915MHz low frequency nz microwave for 30s to 40s, with a 40KHz low-frequency ultrasonic wave for 40s to 45s and with warm water that has a temperature of 40 ° C to 50 ° C, for 30s to 45s to quickly get the vegetables down to 0 ° C defrost, reheat in a 2450MHz microwave oven for 2 to 3 minutes at 80 ° C to 90 ° C, with the texture retention rate of the conditioned tuber vegetables reaching 75% to 90% after reheating. 2. Process to improve the texture of a frozen and conditioned 2018/5082 BE2018 / 5082 Tuber vegetables after reheating according to claim 1, characterized in that the osmosis liquid in step (2) consists of trehalose with a concentration of 40% w / v, sodium chloride with a concentration of 1.5% w / v and calcium chloride with a concentration composed of 0.5% w / v.