Cold dipping processing method of preserved fruits

Abstract

The invention belongs to the technical field of preserved fruit preparation, and particularly relates to a cold dipping processing method of preserved fruits. According to the method, firstly, the cleaned and cut fruits and vegetables are moderately dehydrated to remove part of water in the fruits and vegetables so as to improve the compactness and flexibility of the pulp, so that the pulp is prevented from being soft and rotten in the sugar permeation process, and the sugar consumption and the loss of nutritional flavor substances of the fruits and vegetables in the sugar permeation process are reduced; low-temperature sugar infusion treatment is carried out after dehydration, a composite color fixative and a hardening agent are added into a sugar solution at the same time, the hardening and color protection effects are completed while the sugar infusion treatment is carried out on the pulp, the operation steps are reduced, the production efficiency is improved, and the loss of nutrient substances of fruits and vegetables caused by repeated rinsing in the conventional hardening and color protection process is avoided; most importantly, heating is not needed in the whole process of soaking the fruits and vegetables in the sugar solution, sugar permeation is completed at 0 DEG C or below, damage to nutritional ingredients and deterioration of flavor quality caused by heating in conventional preserved fruit processing are avoided, the original flavor quality of the preserved fruits is kept, and energy conservation and consumption reduction are achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of preserved fruit preparation, and particularly relates to a cold-immersion processing method for preserved fruits. Background Art

[0002] Preserved fruit is a product made from fruits and vegetables as the main raw materials, with (or without) food additives and other auxiliary materials, and pickled (or without) sugar, honey or salt. Common preserved fruits include apricots, peaches and apples. Preserved fruit is a food with ethnic characteristics and has evolved into a traditional food. It is not only sweet and sour, but also a good form of processing and storage of fresh fruits.

[0003] There are many processing techniques for preserved fruits, which can be classified into different types of preserved fruits based on different preparation processes, such as Beijing preserved fruits, Hangzhou preserved fruits, and Suzhou preserved fruits. However, the typical processing method of existing preserved fruits is boiling (i.e., sugar boiling), the most representative of which are one-time boiling method and multiple boiling method. The one-time boiling method continuously boils the fruit and vegetable raw materials in the sugar solution for nearly 1 hour; the multiple boiling method is that each batch of raw materials needs to be intermittently heated and boiled three times, and long-term heating or multiple heating causes the nutritional efficacy components of fruits and vegetables to be destroyed, the flesh to be soft and rotten, and the flavor quality to deteriorate, especially some heat-sensitive fruits and vegetables, which is not conducive to the maintenance of the original ecological characteristic flavor. Furthermore, repeated heating steps are cumbersome, which not only increases energy consumption, but also has low production efficiency and high cost. The light and simple processing of preserved fruits that can maintain the nutrition and original ecological flavor quality of preserved fruits, save energy and reduce consumption, and improve efficiency has become an important direction for technological breakthroughs and innovations in this field. Summary of the invention

[0004] The object of the present invention is to provide a cold soaking processing method for preserved fruits, which can reduce the loss of nutritional and flavor substances in fruits and vegetables, ensure the improvement of the quality of preserved fruits, and realize light and simple processing and green and low-carbon processing.

[0005] The present invention provides a cold soaking processing method for preserved fruits, comprising the following steps:

[0006] 1) washing and cutting the fruits and vegetables to obtain processed fruits and vegetables;

[0007] 2) partially dehydrating the treated fruits and vegetables to obtain partially dehydrated fruits and vegetables, wherein the mass of the partially dehydrated fruits and vegetables is 50% to 80% of the mass of the fruits and vegetables before the dehydration treatment;

[0008] 3) immersing the partially dehydrated fruits and vegetables in a color-protecting and hardening complex sugar solution for vacuum treatment to obtain vacuumized fruits and vegetables;

[0009] The color-protecting and hardening composite sugar liquid comprises composite sugar liquid, color-protecting agent and hardener, wherein the composite sugar liquid is a composite sugar liquid with a sugar content of 30% to 35% prepared by mixing composite sugar and water in a ratio of 1:1.5 to 2; the composite sugar of the composite sugar liquid comprises maltose and granulated sugar, and the mass ratio of maltose to granulated sugar is 1:9 to 3:7; the mass of the color-protecting agent is 0.3% to 0.5% of the mass of the composite sugar liquid, and the mass of the hardener is 0.01% to 0.03% of the mass of the composite sugar liquid;

[0010] 4) placing the vacuumed fruits and vegetables and the color-protecting and hardened complex sugar in a sugar infiltration device for a first low-temperature sugar infiltration treatment to obtain a complex of the first low-temperature infiltration candied fruit and complex sugar solution; the temperature of the first low-temperature sugar infiltration treatment is -2 to 0°C;

[0011] 5) Adding complex sugar to the complex of the first low-temperature infiltration sugar candy and the complex sugar solution until the mass concentration of the sugar solution in the sugar infiltration device reaches 40% to 45%, and then filling the sugar infiltration device with carbon dioxide and sealing it for a second low-temperature infiltration sugar treatment to obtain a complex of the second low-temperature infiltration sugar candy and the complex sugar solution; the temperature of the second low-temperature infiltration sugar treatment is -5 to -2°C;

[0012] 6) Adding complex sugar to the complex of the second low-temperature infiltration sugar candy and the complex sugar solution until the sugar solution concentration in the sugar infiltration device reaches 55% to 60%, and then filling the sugar infiltration device with carbon dioxide and sealing it for a third low-temperature infiltration sugar treatment to obtain a complex of the third low-temperature infiltration sugar candy and the complex sugar solution; the temperature of the third low-temperature infiltration sugar treatment is -8 to -5°C;

[0013] 7) The preserved fruits are taken out from the complex of the preserved fruits and the compound sugar solution after the third low-temperature infiltration, and the sugar solution is drained and then dried to obtain the cold-soaked preserved fruits.

[0014] Preferably, the dehydration method includes room temperature airflow dehydration and hot air dehydration, the temperature of the room temperature airflow dehydration is 15-35°C, and the temperature of the hot air dehydration is 30-50°C.

[0015] Preferably, the color protecting agent comprises phytic acid, ascorbic acid and citric acid, and the mass ratio of the phytic acid, ascorbic acid and citric acid is 3:3:4; the hardening agent comprises organic acid calcium or inorganic calcium salt.

[0016] Preferably, in step 3), the mass ratio of the partially dehydrated fruits and vegetables to the color-protecting and hardened composite sugar solution is 1:1 to 1:2.

[0017] Preferably, the pressure of the vacuum treatment in step 3) is ≤15 kPa, and the time is 20 to 30 minutes.

[0018] Preferably, the duration of the first low-temperature sugar infiltration treatment in step 4) is 3 to 15 days.

[0019] Preferably, the duration of the second low-temperature sugar infiltration treatment in step 5) is 5 to 30 days.

[0020] Preferably, the duration of the third low-temperature sugar infiltration treatment in step 6) is 10 to 300 days.

[0021] Preferably, the drying method in step 7) is air flow drying, and the air flow drying temperature is 15 to 50° C. and the time is 12 to 36 hours.

[0022] Preferably, the fruits and vegetables include fruits and vegetables; the fruits include one or more of apricots, dates, apples, crabapples and melons.

[0023] Beneficial effects:

[0024] The present invention provides a cold soaking processing method for preserved fruits, wherein the processing method sequentially performs moderate dehydration treatment on the processed fruits and vegetables, vacuuming, three-time low-temperature sugar infiltration treatment and drying to obtain cold soaked preserved fruits. The present invention first performs moderate dehydration treatment on the washed and cut fruits and vegetables to improve the firmness and flexibility of the fruits and vegetables, avoid the softness and rottenness of the flesh during the sugar infiltration process, reduce the amount of sugar used during the sugar infiltration process, and reduce the loss of nutrient and flavor substances of fruits and vegetables; in the process of low-temperature sugar infiltration treatment after dehydration, a color preservative and a hardener are added to the composite sugar solution, so that hardening and color protection are completed while sugar infiltration is performed, the operation links are reduced, the production efficiency is improved, and the loss of nutrient substances of fruits and vegetables caused by repeated soaking and rinsing during conventional hardening and color protection is avoided; most importantly, the present invention does not heat during the whole process of preserved fruit infiltration, and the sugar infiltration temperature is completed at or below 0°C, avoiding the destruction of nutrients and deterioration of flavor quality caused by heating in conventional preserved fruit processing, which not only improves the quality of preserved fruits, but also achieves energy saving and consumption reduction. At the same time, the three-step sugar infiltration treatment method of gradually cooling the temperature and gradually increasing the sugar solution concentration can avoid the destruction of the texture caused by freezing of the pulp due to too low a cold soaking temperature, while effectively inhibiting microorganisms and achieving the effect of long-term storage of raw materials or semi-finished products, thereby extending the production period of the enterprise and improving the utilization rate of processing facilities. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required to be used in the embodiments are briefly introduced below.

[0026] Figure 1 It is the color protection effect diagram of different color protection agents in Experimental Example 1;

[0027] Figure 2 The light transmittance test results of apricot juice after color protection with different color protectants in Experimental Example 1;

[0028] Figure 3 This is a diagram showing the combined effect of the hardener and the color preservative on cold-soaked apricots in Experimental Example 2;

[0029] Figure 4 This is the result diagram of the effect of partial dehydration on the quality of apricots in Experimental Example 3;

[0030] Figure 5 The results of flavonoids and total phenol content in apricot preserves prepared by three treatment methods in Experimental Example 4;

[0031] Figure 6 The gas chromatography-mass spectra of the preserved apricots and fresh apricots prepared by the three treatment methods in Experimental Example 5 are shown in FIG.

[0032] Figure 7 The types and relative contents of volatile components in preserved apricots and fresh apricots prepared by the three treatment methods in Experimental Example 5;

[0033] Figure 8 The number and types of volatile compounds in the preserved apricots and fresh apricots prepared by the three treatment methods in Experimental Example 5;

[0034] Fig. 9 This is the OPLS-DA analysis result of preserved apricots and fresh apricots prepared by three processing methods in Experimental Example 5. DETAILED DESCRIPTION

[0035] The present invention provides a cold soaking processing method for preserved fruits, comprising the following steps:

[0036] 1) washing and cutting the fruits and vegetables to obtain processed fruits and vegetables;

[0037] 2) partially dehydrating the treated fruits and vegetables to obtain partially dehydrated fruits and vegetables, wherein the mass of the partially dehydrated fruits and vegetables is 50% to 80% of the mass of the fruits and vegetables before the dehydration treatment;

[0038] 3) immersing the dehydrated fruits and vegetables in a color-protecting and hardening composite sugar solution and performing vacuum treatment to obtain vacuumized fruits and vegetables;

[0039] The color-protecting and hardening composite sugar solution comprises a composite sugar solution, a color-protecting agent and a hardening agent. The composite sugar solution is a composite sugar solution with a sugar content of 30% to 35% prepared by mixing composite sugar and water in a ratio of 1:1.5 to 2. The composite sugar of the composite sugar solution comprises maltose and granulated sugar, and the mass ratio of maltose to granulated sugar is 1:9 to 3:7. The mass of the color-protecting agent is 0.3% to 0.5% of the mass of the composite sugar solution, and the mass of the hardening agent is 0.01% to 0.03% of the mass of the composite sugar solution. The mass ratio of the partially dehydrated fruits and vegetables to the color-protecting and hardening composite sugar solution is 1:1 to 1:2.

[0040] 4) placing the vacuumed fruits and vegetables and the color-protecting and hardened complex sugar in a sugar infiltration device for a first low-temperature sugar infiltration treatment to obtain a complex of the first low-temperature infiltration candied fruit and complex sugar solution; the temperature of the first low-temperature sugar infiltration treatment is -2 to 0°C;

[0041] 5) adding complex sugar to the complex of the first low-temperature infiltration sugared preserved fruit and the complex sugar solution until the mass concentration of the sugar solution in the sugar infiltration device reaches 40% to 45%, and filling the sugar infiltration device with carbon dioxide and sealing it to perform a second low-temperature infiltration sugar treatment to obtain a complex of the second low-temperature infiltration sugared preserved fruit and the complex sugar solution; the temperature of the second low-temperature infiltration sugar treatment is -5 to -2°C;

[0042] 6) adding complex sugar to the complex of the second low-temperature infiltration sugared preserved fruit and the complex sugar solution until the concentration of the sugar solution in the sugar infiltration device reaches 55% to 60%, and filling the sugar infiltration device with carbon dioxide and sealing it to perform a third low-temperature infiltration sugar treatment to obtain a complex of the third low-temperature infiltration sugared preserved fruit and the complex sugar solution; the temperature of the third low-temperature infiltration sugar treatment is -8 to -5°C;

[0043] 7) The preserved fruits are taken out from the complex of the preserved fruits and the composite sugar solution after the third low-temperature infiltration, and the sugar solution is drained and then dried to obtain the cold-infused preserved fruits.

[0044] As an embodiment, the present invention selects fruits and vegetables. As an embodiment, the fruits and vegetables described in the present invention may be fruits and vegetables; as another embodiment, the fruits may be one or more of, but not limited to, apricots, dates, apples, crabapples, and melons. As an embodiment, for different fruits and vegetables, the selection method is different. For example, in a specific embodiment, when selecting apricots, it is necessary to select fresh, firm, pit-free, good color and flavor, and a maturity of 7 to 8.5, and at the same time, remove rotten and worm-infested apricots. When selecting dates, fresh dates, dried dates, peeled dates, or broken dates may be selected, and rotten and worm-infested dates may be removed; at the same time, the dried dates are rehydrated to ensure that the water content of the dates used to prepare preserved fruits is between 20% and 22%. When selecting melons, fresh, firm, flavorful, red, orange-red or yellow melon flesh color, and a maturity of 7.5 to 8.5 may be selected.

[0045] After the selection, the present invention washes and cuts the selected fruits and vegetables to obtain processed fruits and vegetables. The present invention does not specifically limit the washing process, and the conventional washing process in the art can be used. As an embodiment, before the cutting, it also includes the process of peeling and removing the core of the fruits and vegetables containing cores. The specific process is not specifically limited, and the conventional peeling and removing the core steps in the art can be used.

[0046] After obtaining the processed fruits and vegetables, the present invention partially dehydrates the processed fruits and vegetables to obtain partially dehydrated fruits and vegetables. The mass of the partially dehydrated fruits and vegetables of the present invention is 50% to 80% of the mass of the fruits and vegetables before the dehydration treatment. As an embodiment, the mass of the partially dehydrated fruits and vegetables is 70% to 80% of the mass of the fruits and vegetables before the dehydration treatment. As an embodiment, the dehydration method includes room temperature airflow dehydration or hot air dehydration, and the temperature of the room temperature airflow dehydration is 15 to 35°C; the temperature of the hot air dehydration is 30 to 50°C. As another embodiment, the temperature of the room temperature airflow dehydration is 20 to 30°C; the temperature of the hot air dehydration can be 35 to 45°C.

[0047] The technical advantages of the present invention of first dehydrating and then carrying out the subsequent preparation steps are as follows: 1) After the fruit and vegetable raw materials lose part of their water, their texture becomes relatively firm and has good flexibility. They are not easy to become soft and rotten during the sugar infiltration process, and they maintain a good appearance. They can better withstand mechanical treatments such as stirring and turning during processing, and are particularly suitable for fruits and vegetables with soft and rotten flesh, such as apricots, peaches, melons, etc.; it is confirmed through gradient tests that when the water is dehydrated to 50% to 80% of the original fruit and vegetable mass, especially 70% to 80%, the color, fullness and texture characteristics of the prepared preserved fruit are more excellent. 2) Fruits and vegetables that have lost part of their water content can significantly reduce the amount of sugar used by about 30% compared to fruits and vegetables that have not lost water. For example, taking 100 kg of fresh fruit with a sugar content of 20% and losing 30% of water before processing the preserved fruit as an example, the water seepage in the fresh fruit during the sugar infiltration process is not considered. To reach 50% sugar content, fresh fruit without dehydration needs to absorb 80kg of sugar; if 30kg of water is removed from fresh fruit before sugar infiltration, to reach 50% sugar content, fruit only needs to absorb 50kg of sugar, reducing 30kg of sugar per 100kg of raw materials, which is 37.5% less than without dehydration. 3) After fruits and vegetables are immersed in sugar solution, the osmotic pressure of the sugar solution causes water in the pulp to separate out, diluting the sugar solution and reducing the concentration of the sugar solution, while also causing the loss of nutritional flavor substances with the seepage of water; after removing part of the water, fruits and vegetables can effectively reduce water infiltration after entering the sugar solution, avoiding a significant reduction in the concentration of the sugar solution.

[0048] After obtaining the partially dehydrated fruits and vegetables, the present invention immerses the partially dehydrated fruits and vegetables in a color-protecting and hardening composite sugar solution for vacuum treatment to obtain vacuumized fruits and vegetables.

[0049] The color-protecting and hardening composite sugar liquid of the present invention comprises a composite sugar liquid, a color-protecting agent and a hardener. As an embodiment, the composite sugar liquid of the present invention comprises a composite sugar and water, and the mass ratio of the composite sugar to water is 1:1.5-2; as another embodiment, the mass ratio of the composite sugar to water is 1:1.7. The composite sugar of the present invention is maltose and granulated sugar; the mass ratio of the maltose to granulated sugar is 1:9-3:7; the composite sugar liquid prepared with maltose and granulated sugar has the advantages of reducing sugar content and sweetness, and avoiding the crystallization of sugar in the product. As an embodiment, the color-protecting agent of the present invention comprises phytic acid, ascorbic acid and citric acid, and the mass ratio of the phytic acid, ascorbic acid and citric acid is 3:3:4. The mass of the color-protecting agent of the present invention is 0.3%-0.5% of the mass of the composite sugar liquid; as an embodiment, the mass of the color-protecting agent is 0.3%-0.4% of the mass of the composite sugar liquid. As an embodiment, the hardener of the present invention includes organic acid calcium or inorganic calcium salt; as another embodiment, the hardener can be organic acid calcium; as another embodiment, the organic acid calcium can be calcium citrate, calcium gluconate, calcium lactate or calcium acetate; as another embodiment, the organic acid calcium can be calcium citrate. The mass of the hardener of the present invention is 0.01% to 0.03% of the mass of the complex sugar solution; as an embodiment, the mass of the hardener is 0.015% to 0.025% of the mass of the complex sugar solution. The hardener of the present invention uses organic acid calcium or inorganic calcium salt, which, in addition to playing a hardening role, also has a certain calcium supplementation effect, especially calcium citrate is a high-quality calcium supplementation source. The present invention innovatively compounds the color preservative and the hardener with the composite sugar solution, controls the added amount to the minimum dose to achieve the color protection and hardening effect, and gives full play to the time effect of the long immersion time, completes the hardening and color protection while the fruit and vegetable raw materials are infiltrated with sugar, and eliminates the traditional cumbersome operation of first hardening, color protection, and then rinsing to remove the hardening and color preservative, improves production efficiency while reducing production costs, and avoids the loss of fruit and vegetable nutrients caused by repeated rinsing. At the same time, the color preservative used in the present invention is a sulfur-free color preservative, which is not only highly safe, but also has certain nutritional value.

[0050] As an embodiment, the mass ratio of the partially dehydrated fruits and vegetables to the color-protecting and hardening composite sugar solution of the present invention is 1:1 to 1:2; and the dehydrated fruits and vegetables are immersed in the color-protecting and hardening composite sugar solution. As an embodiment, the pressure of the vacuum treatment of the present invention is ≤15kPa, and the time is 20 to 30min; as another embodiment, the pressure of the vacuum treatment is ≤10kPa; as another embodiment, the pressure of the vacuum treatment is ≤5kPa.

[0051] The present invention places the vacuumed fruits and vegetables and the color-protecting and hardened composite sugar solution in a sugar infiltration device for a first low-temperature sugar infiltration treatment to obtain a complex of fruits and vegetables and the composite sugar solution for the first low-temperature sugar infiltration. As an embodiment, the sugar infiltration device can be a sugar infiltration barrel or a sugar infiltration tank. The temperature of the first low-temperature sugar infiltration treatment of the present invention is -2 to 0°C; the -2 to 0°C condition can be achieved by placing devices such as sugar infiltration barrels and sugar infiltration tanks in a cold storage, or by using a sugar infiltration device with refrigeration, heat preservation and temperature control functions, such as a sugar infiltration tank with refrigeration, heat preservation and temperature control functions. As an embodiment, the time of the first low-temperature sugar infiltration treatment is 3 to 15 days; as another embodiment, the time of the first low-temperature sugar infiltration is 7 to 10 days.

[0052] After obtaining the complex of the fruits and vegetables subjected to the first low-temperature sugar infiltration and the composite sugar solution, the present invention adds composite sugar to the complex of the fruits and vegetables subjected to the first low-temperature sugar infiltration and the composite sugar solution until the mass concentration of the sugar solution in the sugar infiltration device reaches 40% to 45%, and then fills the sugar infiltration device with carbon dioxide and seals it for a second low-temperature sugar infiltration treatment to obtain the complex of the fruits and vegetables subjected to the second low-temperature sugar infiltration and the composite sugar solution.

[0053] As an embodiment, the step of adding complex sugar to the complex of the fruits and vegetables and the complex sugar solution of the first low-temperature sugar infiltration to the sugar solution mass concentration in the sugar infiltration device reaches 40% to 45% can be as follows: taking out part of the sugar solution from the complex of the fruits and vegetables and the complex sugar solution of the first low-temperature sugar infiltration, mixing the part of the sugar solution with the complex sugar until the mass concentration of the newly mixed sugar solution reaches 60% to 65%, and obtaining the first supplementary sugar solution; supplementing the first supplementary sugar solution to the sugar infiltration device so that the mass concentration of the sugar solution in the sugar infiltration device reaches 40% to 45%. As another embodiment, the part of the sugar solution is 1 / 2 to 1 / 3 of the mass of the sugar solution in the complex of the fruits and vegetables and the complex sugar solution of the first low-temperature sugar infiltration. As another embodiment, the mass ratio of the part of the sugar solution to the complex sugar is 2:1. The temperature of the second low-temperature sugar infiltration treatment of the present invention is -5 to -2°C; as an embodiment, the temperature of the second low-temperature sugar infiltration treatment is -4 to -3°C. As an embodiment, the second low-temperature sugar infiltration treatment lasts for 5 to 30 days; as another embodiment, the second low-temperature sugar infiltration treatment lasts for 10 to 25 days; as another embodiment, the second low-temperature sugar infiltration treatment lasts for 15 to 20 days. The role of filling the sugar infiltration device with carbon dioxide during the second low-temperature sugar infiltration treatment of the present invention is to inhibit possible fungal activity below 0°C.

[0054] After obtaining the complex of the fruits and vegetables subjected to the second low-temperature sugar infiltration and the composite sugar solution, the present invention adds composite sugar to the complex of the fruits and vegetables subjected to the second low-temperature sugar infiltration and the composite sugar solution until the concentration of the sugar solution in the sugar infiltration device reaches 55% to 60%, and then fills the sugar infiltration device with carbon dioxide and seals it for a third low-temperature sugar infiltration treatment to obtain the complex of the fruits and vegetables subjected to the third low-temperature sugar infiltration and the composite sugar solution.

[0055] As an embodiment, the step of adding complex sugar to the complex of the fruits and vegetables and the complex sugar solution of the second low-temperature sugar infiltration according to the present invention until the sugar solution concentration in the sugar infiltration device reaches 55% to 60% can be: taking out part of the sugar solution from the complex of the fruits and vegetables and the complex sugar solution of the second low-temperature sugar infiltration, mixing the part of the sugar solution with the complex sugar until the mass concentration of the newly mixed sugar solution reaches 60% to 65%, and obtaining the second supplemented sugar solution; supplementing the second supplemented sugar solution to the sugar infiltration device so that the mass concentration of the sugar solution in the sugar infiltration device reaches 55% to 60%. As an embodiment, the part of the sugar solution is 1 / 2 to 2 / 3 of the mass of the sugar solution in the complex of the fruits and vegetables and the complex sugar solution of the second low-temperature sugar infiltration. As another embodiment, the mass ratio of the part of the sugar solution to the complex sugar is 4:3. The temperature of the third low-temperature sugar infiltration treatment according to the present invention is -8 to -5°C; as an embodiment, the temperature of the third low-temperature sugar infiltration treatment is -7 to -6°C. As one embodiment, the time for the third low-temperature sugar infiltration treatment is 10 to 300 days; as another embodiment, the time for the third low-temperature sugar infiltration treatment is 20 to 200 days; as another embodiment, the time for the third low-temperature sugar infiltration treatment is 25 to 90 days; as another embodiment, the time for the third low-temperature sugar infiltration treatment is 30 to 60 days.

[0056] The present invention adopts three low-temperature sugar infiltration methods to carry out the sugar infiltration process in the processing of preserved fruits, which has the following advantages: 1) In terms of product quality, the temperature of the whole process of the preserved fruit infiltration processing of the present invention is carried out at 0°C or below, which avoids the destruction of nutritional ingredients by heating and the deterioration of flavor quality caused by heating, especially some heat-sensitive fruits and vegetables (such as melons, which will produce an unpleasant cooked smell when heated), which is beneficial to the preservation of the original ecological flavor of fruits and vegetables, and can also avoid the fruits and vegetables from becoming soft and rotten after repeated heating, thereby improving the quality of preserved fruits; at the same time, the low-temperature sugar infiltration method of the present invention can inhibit the activity of microorganisms, and the sugar infiltration temperature used is not lower than the freezing point of the complex sugar solution and the pulp, so as to avoid freezing of the sugar solution and fruits and vegetables, especially to avoid the destruction of the texture of the pulp tissue and the soft and rotten texture after the pulp is frozen; in addition, in order to effectively inhibit the activity of microorganisms and increase the storage time of the semi-finished preserved fruits, the present invention gradually reduces the sugar infiltration temperature and increases the sugar content. Carbon dioxide is filled into the sugar infiltration device and then sealed, so as to achieve effective inhibition of mold that can still grow slowly at ≤0°C, and effectively prolong the storage of the semi-finished preserved fruits. 2) In terms of energy saving and consumption reduction, compared with the conventional method of preparing preserved fruits by heating and boiling, the whole process of the preserved fruits infiltration sugar of the present invention does not require heating, and there is no need to quickly cool the heated materials. The required energy consumption is greatly reduced, which is only 1 / 3 to 1 / 5 of the energy consumption of heating and preparing preserved fruits. The more favorable advantage is that the north is a natural cold storage after November, and there is no need to invest too much refrigeration energy consumption, and this low temperature can last for 4 to 5 months, which also realizes the effective utilization of climate low temperature resources. 3) In terms of simplicity of operation, in the traditional method of heating and boiling preserved fruits, the pulp and sugar solution need to be added to the heating equipment every time the preserved fruits are boiled, and the materials need to be taken out after the boiling is completed to avoid occupying the heating equipment. In the present invention, when the concentration of the sugar solution is increased each time, only part of the sugar solution is removed from the complex of the fruit and vegetable-composite sugar solution, and the sugar solution is added back to the sugar infiltration device after the concentration is increased, without moving the pulp, which can not only reduce the amount of operation in the processing process, but also avoid the damage caused by repeated movement of the pulp. 4) From the perspective of extending the production season: the low-temperature sugar infiltration operation of the present invention also plays a role in preserving semi-finished fruits and melons, which can effectively extend the processing period of the enterprise and increase production capacity. For example, for apricots, the harvest time is about one month, but the traditional processing of a batch of preserved fruits requires at least 3 to 5 days. In the case of limited factory production capacity, there will be no raw materials after a few batches are produced; although the preservation time of raw materials can be extended by salting combined with sun-drying to make salt embryos or cold storage, the preparation process of salt embryos is cumbersome, and the nutrients in the fruits and melons are also lost, and the salt solution discharged during the preparation process also has a large pollution; the cold storage method, but the refrigeration time of fresh fruits is generally about 30 days, and the fruits and melons can be frozen for more than 1 year, but after the pulp is frozen, the cells and tissue structure are greatly damaged, and the pulp is very easy to become soft and rotten during the processing of preserved fruits.On the one hand, the present invention utilizes the appropriate dehydration of raw materials to increase the soluble solid concentration of the fruit and vegetable raw materials themselves. On the other hand, by immersing them in a certain concentration of sugar solution, the sugar can penetrate into the cell tissue of the fruit and vegetables and lower the freezing point of the pulp, thus preventing the pulp from freezing below 0°C and causing damage to the pulp cell tissue. As the concentration of the sugar solution and the sugar content in the pulp gradually increase, the freezing points of both gradually decrease, and the sugar infiltration temperature can be gradually reduced. At the same time, the gradually decreasing sugar infiltration temperature and the gradually increasing sugar concentration are effectively utilized to produce a strong inhibitory effect on microorganisms, otherwise the fermentation of microorganisms will still occur below 0°C. By utilizing the low-temperature sugar infiltration and storage method of the present invention, during the fruit and vegetable harvest season, we can concentrate on collecting and storing a large amount of fruit and vegetable raw materials, cold soaking and sugar infiltration and preservation of the raw materials, and gradually complete the subsequent processing after the harvest season, thereby improving the utilization rate of enterprise facilities and the production cycle.

[0057] After obtaining the complex of the third low-temperature infiltration of sugar and vegetables and the composite sugar solution, the present invention separates the complex of the third low-temperature infiltration of sugar and vegetables and the composite sugar solution, removes the preserved fruit in the sugar solution, drains the sugar solution and dries it to obtain the cold-soaked preserved fruit. As an embodiment, the present invention places the removed preserved fruit on a porous sieve plate, drains the excess sugar solution and dries it. As an embodiment, the drying method is airflow drying, the airflow drying temperature is 15 to 50°C, and the time is 12 to 36 hours. As another embodiment, the airflow drying is a room temperature airflow drying method, the room temperature airflow drying temperature is 15 to 35°C, and the time is 18 to 24 hours. The room temperature airflow drying method of the present invention makes full use of the fact that the harvest season of fruits and vegetables in the north, especially Xinjiang, is hot summer and autumn. The most advantageous thing is that the air is extremely dry, with a relative humidity of 20% to 50%. This dry hot air is a good drying medium. Drying preserved fruit with this dry hot air does not require energy input, and has the advantages of energy saving and consumption reduction. The preserved fruit dried at this low temperature can better maintain the characteristic flavor quality of the original fruit.

[0058] In order to further illustrate the present invention, the technical solution provided by the present invention is described in detail below in combination with embodiments and drawings, but they should not be understood as limiting the protection scope of the present invention.

[0059] Experimental Example 1

[0060] 1. Materials and Methods

[0061] In order to study the color protection effect of different color protection agents, apricot juice was selected as the experimental material to facilitate the observation of the color protection effect of various color protection agents.

[0062] Select ripe apricots and squeeze to obtain clarified apricot juice. Add sodium bisulfite, sodium sulfite, tea polyphenols, citric acid, cysteine, phytic acid, ascorbic acid and sodium chloride with a final concentration of 0.2 g / 100 mL to the apricot juice respectively. Take the juice without adding color preservative as control. Let it stand for 12 hours to observe its color protection effect and measure the transmittance.

[0063] 2. Experimental results

[0064] The color protection effect of different color protectants is shown in Figure 1 In the figure, the color protection effects are from worst to best, from left to right: control, color protection effects of adding tea polyphenols, citric acid, sodium chloride, sodium bisulfite, sodium sulfite, ascorbic acid, cysteine ​​and phytic acid.

[0065] The light transmittance of apricot juice after color protection by color protectant was tested. The results are shown in Figure 2 It can be seen that among various color preservatives, phytic acid, cysteine ​​and ascorbic acid have the best color preservative effect. Apricot juice still maintains a light yellow color without obvious browning. There is no significant difference among the three treatments; followed by sodium bisulfite and sodium sulfite. The browning degree of apricot juice is very low, and there is no significant difference between the two; sodium chloride also has a certain color preservative effect, and the browning degree of apricot juice is relatively high, which is different from the other treatments; citric acid has a very poor color preservative effect, which is different from the other treatments, but in actual applications citric acid is not used to directly protect color, but has a good synergistic effect on other color preservatives; tea polyphenols have basically no color preservative effect, and the browning degree is not much different from that of the control, and there is no significant difference in light transmittance with the control.

[0066] Therefore, after comprehensive consideration, a combination of phytic acid, ascorbic acid and citric acid was subsequently selected as a color preservative for the cold soaking process of preserved fruits.

[0067] Experimental Example 2

[0068] In order to investigate the combined effects of hardeners and color preservatives on cold-soaked apricots, the following experiments were conducted:

[0069] 1. Experimental methods

[0070] Select fresh, firm, pit-free, good color and flavor apricot varieties, mature at 7-8.5, cut into two pieces along the apricot seam, remove the apricot pit. Use the following treatments:

[0071] 1) Hardener + cold soaking treatment: Add compound sugar solution to apricot flesh. The compound sugar is composed of maltose and granulated sugar. The mass ratio of maltose and granulated sugar is 3:7. The ratio of compound sugar to water is 1:1.6. A compound sugar solution with a sugar content of 35% is prepared. The ratio of apricot flesh to compound sugar solution is 1:1. Add hardener calcium citrate to the compound sugar solution. The addition amount is 0.03% of the mass of the compound sugar solution.

[0072] 2) Color preservative + cold soaking treatment: Add compound sugar solution to apricot meat, the compound sugar is composed of maltose and granulated sugar, the mass ratio of maltose and granulated sugar is 3:7, the ratio of compound sugar to water is 1:1.6, and a compound sugar solution with a sugar content of 35% is prepared. The ratio of apricot meat to the compound sugar solution is 1:1, and a color preservative is added to the compound sugar solution, the color preservative is composed of phytic acid, ascorbic acid and citric acid, the mass ratio of phytic acid, ascorbic acid and citric acid is 3:3:4, and the amount of color preservative added is 0.5% of the mass of the compound sugar solution.

[0073] 3) Hardener + color preservative + cold soaking treatment: Add compound sugar solution to apricot flesh. The compound sugar is composed of maltose and granulated sugar. The mass ratio of maltose and granulated sugar is 3:7. The ratio of compound sugar to water is 1:1.6. A compound sugar solution with a sugar content of 35% is prepared. The ratio of apricot flesh to the compound sugar solution is 1:1. Add hardener calcium citrate to the compound sugar solution. The added amount is 0.03% of the mass of the compound sugar solution. Add a color preservative to the compound sugar solution. The color preservative is composed of phytic acid, ascorbic acid and citric acid. The mass ratio of phytic acid, ascorbic acid and citric acid is 3:3:4. The added amount of the color preservative is 0.5% of the mass of the compound sugar solution.

[0074] The apricot flesh of the three treatments were all vacuumed under 10 kPa for 30 min. The vacuumed apricot flesh and the color-protecting and hardened composite sugar solution were put into a sugar infiltration tank together. The temperature was controlled at -2 to 0°C and the low-temperature sugar infiltration time was 10 days.

[0075] 2 Experimental results

[0076] Apricot meat is a fruit raw material that is easy to brown and rot during the processing of preserved fruits, and is difficult to process. Figure 3 It can be seen that after the hardener + cold soaking treatment, the apricot flesh browned more seriously because no color preservative was used; but the flesh appearance was intact and the texture was well maintained, the apricot flesh had a certain degree of firmness, and no obvious softness or rot occurred. The apricot flesh treated with color preservative + cold soaking had a lesser degree of browning and better maintained the color of the apricot fruit, but the flesh appearance was not intact, and the apricot flesh had a certain degree of softness or rot. The color protection effect of apricot flesh treated with hardener + color preservative + cold soaking was better than that of the treatment with color preservative alone, and the flesh appearance was intact and the texture was well maintained, the apricot flesh was firm, and no softness or rot occurred.

[0077] Experimental Example 3

[0078] In order to investigate the effect of partial dehydration on the quality of apricots, the following experiment was designed. The steps are as follows:

[0079] 1. Experimental methods

[0080] Select fresh, firm, pit-free, good color and flavor apricot varieties, mature at 7-8.5, cut into two pieces along the apricot seam, remove the apricot pit. Place the halved apricots with the bowl facing up on a drying tray, and dehydrate at room temperature of 25-35℃ in airflow until the apricot meat mass before dehydration is 50% of the raw material mass.

[0081] The compound sugar is composed of maltose and granulated sugar, the mass ratio of maltose and granulated sugar is 3:7, the ratio of compound sugar to water is 1:1.6, and a compound sugar liquid with a sugar content of 35% is prepared, and the ratio of apricot flesh to the compound sugar liquid is 1:1. Add calcium citrate, a hardener, to the compound sugar liquid, and the addition amount is 0.03% of the mass of the compound sugar liquid; add a color-protecting agent to the compound sugar liquid, the color-protecting agent is composed of phytic acid, ascorbic acid and citric acid, the mass ratio of phytic acid, ascorbic acid and citric acid is 3:3:4, and the addition amount of the color-protecting agent is 0.5% of the mass of the compound sugar liquid, and a color-protecting hardened compound sugar liquid is obtained. Partially dehydrated apricot flesh is immersed in the color-protecting hardened compound sugar liquid for vacuum treatment, and the vacuum treatment is carried out for 30 minutes under the condition of 10kPa. The vacuumized apricot flesh and the color-protecting hardened compound sugar liquid are put into a sugar infiltration tank together, and the temperature is controlled at 0-2°C, and the low-temperature sugar infiltration time is 10 days.

[0082] 2. Experimental results

[0083] Apricot flesh is very easy to become soft and rotten during the processing of preserved fruits. Experiments have found that if the apricot flesh is properly dehydrated before infiltration with sugar, its structural stability can be enhanced, and the phenomenon of softness and rottenness in the subsequent preparation of preserved fruits can be reduced, thereby improving the quality and shelf life of the preserved fruits. Figure 4 ,exist Figure 4 The middle left picture shows the state of partially dehydrated apricot flesh, the middle picture shows the state of partially dehydrated apricot flesh after hardening, color protection and vacuum treatment, and the right picture shows cold-soaked apricot flesh. It can be seen that after the apricot meat lost 50% of its weight, the apricot meat had shrunk. Since there was no color protection treatment before dehydration, the browning of the apricot meat was also serious. After the apricot meat was soaked in the color protection and hardening composite sugar solution, vacuumed and cold soaked, the quality of the apricot meat changed greatly: 1) After the flesh absorbed sugar and water, it became very full, and the shape of the flesh was close to that of fresh apricots; 2) The degree of browning was greatly improved, and the color was close to that of fresh apricots; 3) Since the apricot meat lost some water before candied, the flesh became firmer and had better flexibility. It was not easy to soften and rot during the sugar infiltration process, maintained a good appearance, and could better tolerate mechanical treatments such as stirring and turning during processing; 4) In the experiment, the apricot dehydration used a water loss of 50% of the fresh weight, which is the limit water loss in the technical solution of this patent. The focus was on investigating the effect of apricot meat in this dehydrated state on the quality of apricot preserves. From the experimental results, this degree of water loss can still achieve good process effects under the conditions of cold soaking and sugar infiltration.

[0084] Experimental Example 4

[0085] This experiment compared the technical effects of traditional preserved fruit sugar infiltration and cold soaking sugar infiltration. The steps are as follows:

[0086] 1. Experimental methods

[0087] (1) Traditional three-cooking method apricot dried meat (HAD): Cut the apricot meat in half and remove the pits. Use 0.1% sulfite solution to protect the color for 10 min. Add complex sugar solution (35%, the preparation method of the complex sugar solution is the same as that of Experimental Example 3), boil the mixture once, candied at room temperature for 24 hours, add complex sugar to increase the concentration of the sugar solution to 45%, boil the mixture twice, candied at room temperature for 24 hours, add complex sugar to increase the concentration of the sugar solution to 60%, boil the mixture three times, candied at room temperature for 24 hours, remove the apricot dried meat, drain the sugar, and dry it in air flow at room temperature at 25-30°C.

[0088] (2) Traditional one-time boiling method (BSW): Cut the apricot pulp in half and remove the pits. Use 0.1% sulfite solution to protect the color for 10 min. Add complex sugar solution (35%, the preparation method of complex sugar solution is the same as that of Experimental Example 3) and boil. Turn to low heat and continue boiling for 45 min. The concentration of sugar solution is gradually increased to 60% by evaporation of water. Take out the apricots, drain the sugar, and dry them at room temperature in airflow at 25°C.

[0089] (3) Hardening and color-protecting compound sugar solution + cold soaking apricots (WMD): Compound sugar solution is added to the halved pitted apricot meat, the sugar content of the compound sugar is 35% (the preparation method of the compound sugar solution is the same as that of Experimental Example 3), and the hardening agent calcium citrate is added to the compound sugar solution, the addition amount is 0.03% of the mass of the compound sugar solution; the color-protecting agent is added to the compound sugar solution, and the addition amount of the color-protecting agent is 0.5% of the mass of the compound sugar solution. Vacuum treatment is carried out under 10kPa for 30 minutes, and the vacuumed apricot meat and the color-protecting and hardened compound sugar solution are put into a sugar infiltration tank together, the temperature is controlled at 0℃, the low-temperature sugar infiltration time is 5 days, the sugar concentration is increased to 45%, the sugar infiltration time is -2℃ for 7 days, the sugar concentration is increased to 60%, and the sugar infiltration time is -5℃ for 10 days. After the sugar infiltration is completed, the apricot bowl is removed to drain the sugar solution, and the apricot petals are evenly placed face up on a drying tray and dried at room temperature airflow at 25℃.

[0090] The physical and chemical indices were measured after the three different sugar infiltration treatments.

[0091] 2. Experimental results

[0092] The content of flavonoids and total phenols, the unique bioactive components in apricots, can significantly indicate the effect of processing technology on the nutritional value of preserved fruits. The content of flavonoids and total phenols in preserved apricots obtained by three experimental methods was determined. The results are as follows: Figure 5As shown in the figure, the flavonoids and total phenolic contents are ranked from high to low in WMD, HAD and BSW, and there are significant differences among the treatments (P < 0.05). Since flavonoids and total phenolic are easily oxidized and lost during processing, the WMD process is low-temperature sugar infiltration below 0°C, and the low-temperature environment reduces the oxidative damage of flavonoids and total phenolic. In contrast, the BSW process causes a more serious loss of flavonoids and total phenolic due to long-term high-temperature cooking. Comprehensive analysis of these results shows that the WMD treatment method can effectively reduce the loss of nutrients and active ingredients during sugar infiltration, and this processing technology helps to improve the overall processing quality of preserved fruits.

[0093] Experimental Example 5

[0094] The apricots prepared in Experimental Example 4 were used as experimental materials, and the volatile components of the apricots prepared by various methods were detected and analyzed, with fresh apricots as a control.

[0095] The volatile components of the obtained apricots and the fresh apricots in the control were analyzed by HS-SPME / GC-MS technology. Figure 6 ), and then determine the types and relative contents of volatile substances, see Table 1. Figure 6 The results show that the chromatographic peak areas of samples treated with WMD, BSW, and HAD exceed those of samples treated with FA (fresh apricots), indicating that the processing can enhance the characteristic aroma components of apricots. At the same time, under the same analytical conditions, samples obtained by different processing methods have obvious differences in aroma types and relative contents.

[0096] In fruits and their processed products, alcohol compounds play an important role with their fresh herbal and fruity flavors. A total of 19 alcohol compounds were found in apricots treated with different methods, and their content distribution is as follows: the alcohol content in apricots treated with WMD was the highest (14.25%), followed by FA treatment (7.68%), BSW treatment (5.84%), and the alcohol content in apricots treated with HAD was the lowest (2.97%).

[0097] Ketone compounds play a vital role in the flavor composition of preserved fruits. They can neutralize and alleviate the taste brought by alcohols and esters, and are one of the common aroma components in fruit foods. In this four-group test of 24 samples (6 biological replicates in each group), a total of 13 ketone compounds were found. Specifically for each treatment method, the total content of ketone compounds in HAD, BSW, WMD, and FA was 0.45%, 1.10%, 2.97%, and 1.47%, respectively. Three representative aroma components, L-menthone, piperitone, and piperonene, were detected in the WMD sample, with contents of 0.81%, 1.41%, and 0.16%, respectively, which together create a fresh mint and herbal aroma. These ketone compounds help balance the strong smell of ethanol and 1-amino-2-propanol, giving the preserved fruits a more refreshing and pleasant flavor experience.

[0098] Figure 5 The data showed that different treatment methods had a significant impact on the types and relative contents of volatile components in apricot preserves. Figure 7 It can be seen that the volatile components of apricots treated with HAD and BSW are mainly aldehydes and acids; in apricots treated with WMD, acids and other types of volatile components are more prominent; while in fresh fruits, alcohols and other types are the main components. The total relative content of volatile components is ranked from high to low: FA, WMD, HAD, BSW. Figure 8 The number of volatile components unique to each treatment method was further revealed: WMD treatment had the most characteristic volatile components in apricots, reaching 26; HAD had 12 unique components; FA had 7; BSW and FA had 7 volatile substances in common; the four treatments had 7 volatile components in common; and BSW, FA, and HAD had 5 volatile components in common. These data not only show the effects of different treatments on the volatile components of apricots, but also reflect the uniqueness of these components under different processing conditions.

[0099] As shown in Table 1, 13 substances were screened out from the samples treated with WMD, of which 11 had ROAV values ​​exceeding 0.1. Further analysis identified nonanoic acid, 3-octanol, and benzoic acid as characteristic aroma substances, which have the aromas of coconut, wax, wood, spicy, mint, and cranberry, respectively. Fig. 9 This example identified the key different aroma components in the four types of samples. The key aroma components in the HAD treatment include furan, biphenyl and 3-furfural; the key aroma components in the BSW treatment are linalool, hexanal and cis-geraniol; the key aroma components in the WMD treatment are hexanal, linalool and 3-octanol. Linalool and (E,E)-2,4-hexadienal are the characteristic aroma components of the FA treatment.

[0100] Table 1 ROAV values ​​of volatile components in preserved apricots and fresh apricots under different treatment conditions

[0101]

[0102]

[0103] From the above results, it can be seen that the WMD-treated apricot samples (i.e., apricots prepared according to the preparation method of the present invention) significantly reduced the loss of nutrients and active ingredients during the sugar infiltration process, thereby significantly improving the overall processing quality of the preserved fruits. In the apricots treated with WMD, the most types of characteristic volatile components were detected, totaling 26, among which the content of alcohol compounds was the highest, reaching 14.25%. In addition, these preserved fruits are also rich in representative aroma components such as L-menthone, piperitone and piperonene, which work together to give the preserved fruits a refreshing herbal aroma and fruity aroma, bringing a more refreshing and pleasant taste enjoyment. It is particularly worth mentioning that the key aroma components in the apricots treated with WMD include hexanal, linalool and 3-octanol, which have obvious differentiation compared with the apricots in other treatment groups and show more superior aroma characteristics. These findings not only confirm the advantages of WMD treatment in maintaining the flavor of apricots, but also highlight its potential in improving the processing quality of preserved fruits.

[0104] Based on the above conclusions, it can be seen that the cold soaking processing method of the preserved fruit described in the present invention can reduce the loss of nutrients in the preserved fruit and improve the aroma components and quality of the preserved fruit compared to the conventional preparation method. Therefore, the method described in the present invention can also be used to prepare various types of preserved fruit, as shown in Examples 1 to 3.

[0105] Example 1

[0106] A cold soaking processing method for preserved apricots, comprising the following steps:

[0107] (1) Pretreatment of fresh apricots

[0108] Choose apricot varieties that are fresh, firm, pit-free, and have good color and flavor, with a maturity of 7-8.5. Remove raw materials that are rotten, worm-infested, and do not meet processing requirements. Cut them into two pieces along the apricot seam and remove the apricot pit.

[0109] (2) Dehydration

[0110] Place the bowl with the cut apricots facing up on a baking tray or drying tray and dehydrate them in air flow at room temperature of 30°C until the mass of the apricot flesh before dehydration is 70% of the mass of the raw material.

[0111] (3) Compound sugar solution and color-protecting and hardening compound sugar solution formula

[0112] Compound sugar solution: Compound sugar is composed of maltose and granulated sugar, and the mass ratio of maltose to granulated sugar is 3:7. The ratio of compound sugar to water is 1:1.6, and a compound sugar solution with a sugar content of 33% (calculated by mass fraction) is prepared.

[0113] Color-protecting and hardening compound sugar solution: Add color-protecting agent and hardening agent to the above compound sugar solution. The color-protecting agent is composed of phytic acid, ascorbic acid and citric acid. The mass ratio of phytic acid, ascorbic acid and citric acid is 3:3:4. The amount of color-protecting agent added is 0.5% of the mass of the compound sugar solution. The hardening agent is calcium citrate, and the amount of addition is 0.03% of the mass of the compound sugar solution.

[0114] (4) Vacuum treatment

[0115] Put the pre-treated apricot pulp into a vacuum tank, add the color-protecting and hardening composite sugar solution in step (3), the mass ratio of apricot pulp to color-protecting and hardening composite sugar solution is 1:2, press the apricot pulp into the color-protecting and hardening composite sugar solution, and vacuum treat for 20 minutes at ≤5kPa.

[0116] (5) First low temperature infiltration

[0117] The vacuumized apricot pulp and the color-protecting and hardened composite sugar solution are put into a sugar infiltration tank, which is then placed in a cold storage; the temperature of the materials in the sugar infiltration tank is controlled at -1°C, and the first low-temperature sugar infiltration time is 10 days.

[0118] (6) Second low temperature infiltration

[0119] Take out part of the sugar solution from the infiltration sugar tank (the amount taken out accounts for 1 / 2 of the total mass of the sugar solution in the infiltration sugar tank), add the newly prepared complex sugar (maltose: sugar = 3:7), no color preservative and hardener are needed in this complex sugar, the mass ratio of part of the sugar solution to the complex sugar is 2:1, stir and dissolve, the mass concentration of the newly mixed sugar solution reaches 60%, then add it back to the infiltration sugar tank, stir gently to make the sugar solution concentration evenly distributed, so that the mass concentration of the sugar solution in the infiltration sugar tank reaches 43%. Reduce the temperature of the material in the infiltration sugar tank to -3, fill the infiltration sugar tank with carbon dioxide, seal it, and conduct the second low-temperature infiltration sugar for 20 days.

[0120] (7) The third low temperature infiltration

[0121] Take out part of the sugar solution from the sugar infiltration tank (the amount taken out accounts for 2 / 3 of the total mass of the sugar solution in the sugar infiltration tank), add the newly prepared complex sugar (maltose: granulated sugar = 3:7, this complex sugar solution does not need to add color preservatives and hardeners, the mass ratio of part of the sugar solution to the complex sugar is 4:3, stir and dissolve, so that the concentration of the sugar solution reaches 65%, add the prepared complex sugar solution back to the sugar infiltration tank, stir gently to make the concentration of the sugar solution evenly distributed, so that the mass concentration of the sugar solution in the sugar infiltration tank reaches 60%. Reduce the temperature of the material in the sugar infiltration tank to -5~-8℃, fill the sugar infiltration tank with carbon dioxide, seal it, and the third low-temperature sugar infiltration time is 60 days.

[0122] (8) Drying

[0123] Take out the dried apricots from the sugar solution and place them on a porous sieve plate, drain off excess sugar solution, place the apricots bowl upward on a baking tray, and dry them in air flow at 25°C for 24 hours until the moisture content is 17-18%, thereby obtaining cold-soaked dried apricots.

[0124] Example 2

[0125] A cold soaking processing method for preserved red dates, comprising the following steps:

[0126] (1) Raw materials and pretreatment

[0127] We select red dates purchased in the current year and remove the rotten, worm-infested and other raw materials that do not meet the processing requirements. After the red dates are washed, dehydrated and dried, the moisture content is adjusted to about 20-22%, and the date pits are removed using a red date pitting machine.

[0128] (2) Compound sugar solution formula

[0129] The compound sugar is a compound sugar of maltose and granulated sugar, and the mass ratio of maltose to granulated sugar is 1:9. The ratio of the compound sugar to water is 1:1.8, and a compound sugar liquid with a sugar content of 36% by mass concentration is prepared.

[0130] (3) Vacuum treatment

[0131] Put the pre-treated jujube meat into a vacuum tank, add the compound sugar solution, the ratio of jujube meat to compound sugar solution is 1:1 (mass ratio), press the jujube meat into the sugar solution, and vacuum treat it for 25 minutes under the condition of ≤15kPa.

[0132] (4) First low temperature sugar infiltration

[0133] The vacuumed red dates pulp and compound sugar solution are put into the sugar infiltration barrel and then placed in the cold storage. The temperature of the materials in the sugar infiltration barrel is controlled at -2℃, and the first low-temperature sugar infiltration time is 5 days.

[0134] (5) Second low temperature infiltration

[0135] Take out part of the sugar solution from the sugar infiltration barrel (the amount taken out accounts for 1 / 3 of the total mass of the sugar solution in the sugar infiltration barrel), add the newly prepared complex sugar (maltose: granulated sugar = 1:9), the mass ratio of part of the sugar solution to the complex sugar is 2:1, stir and dissolve, make the concentration of the complex sugar solution reach 55%, then add it back to the sugar infiltration barrel, stir gently to make the concentration of the sugar solution evenly distributed, make the mass concentration of the sugar solution in the sugar infiltration barrel reach 45%. Reduce the temperature of the material in the sugar infiltration barrel to -5℃, fill the sugar infiltration barrel with carbon dioxide, seal it, and conduct the second low-temperature sugar infiltration for 10 days.

[0136] (6) The third low temperature infiltration

[0137] Take out part of the sugar solution from the sugar infiltration barrel (the amount taken out accounts for 1 / 2 of the total mass of the sugar solution in the sugar infiltration barrel), add the newly prepared complex sugar (maltose: granulated sugar = 1:9, the mass ratio of part of the sugar solution to the complex sugar is 2:1, stir and dissolve, so that the concentration of the sugar solution reaches 65%, and then add the prepared complex sugar solution back to the sugar infiltration barrel, stir gently to make the concentration of the sugar solution evenly distributed, so that the mass concentration of the sugar solution in the sugar infiltration barrel reaches 58%. Reduce the temperature of the material in the sugar infiltration barrel to -8℃, fill the sugar infiltration barrel with carbon dioxide, seal it, and the third low-temperature sugar infiltration time is 20 days.

[0138] (7) Drying

[0139] The preserved red dates were fished out from the sugar solution and placed on a porous sieve plate, excess sugar solution was drained off, and the preserved red dates were placed on a drying plate and dried at 50° C. for 15 hours with air flow until the water content was 17%, thereby obtaining cold-soaked preserved red dates.

[0140] Example 3

[0141] A cold soaking processing method for preserved melon, comprising the following steps:

[0142] (1) Melon pretreatment

[0143] Select melon varieties that are fresh, firm, good in flavor, and with red, orange-red or yellow flesh, and mature at 7.5 to 8.5 degrees. Remove the raw materials that do not meet the processing requirements, peel and deseed, cut the melon into four evenly along the longitudinal direction, and then cut each melon into slices about 1 cm thick along the transverse direction.

[0144] (2) Dehydration

[0145] Place the sliced ​​melons on a baking tray or drying tray and dehydrate them in air flow at room temperature of 25°C until the weight of the melon flesh is reduced to 85% of the weight of the raw material.

[0146] (3) Compound sugar solution and color-protecting and hardening compound sugar solution formula

[0147] Compound sugar solution: Compound sugar is composed of maltose and granulated sugar, and the mass ratio of maltose to granulated sugar is 2:8. The ratio of compound sugar to water is 1:1.7, and a compound sugar solution with a sugar content of 34% (calculated by mass fraction) is prepared.

[0148] Color-protecting and hardening compound sugar solution: Add color-protecting agent and hardening agent to the above compound sugar solution. The color-protecting agent is composed of phytic acid, ascorbic acid and citric acid. The mass ratio of phytic acid, ascorbic acid and citric acid is 3:3:4. The amount of color-protecting agent added is 0.3% of the mass of the compound sugar solution. The hardening agent is calcium gluconate, and the amount of added is 0.02% of the mass of the compound sugar solution.

[0149] (4) Vacuum treatment

[0150] Put the pre-treated melon flesh into a vacuum tank, add color-protecting and hardening composite sugar solution, the ratio of melon flesh to color-protecting and hardening composite sugar solution is 1:1.7 (mass ratio), press the melon flesh into the sugar solution, and vacuum treat it for 30 minutes under ≤10kPa conditions.

[0151] (5) First low temperature infiltration

[0152] The vacuumed melon flesh and the color-protecting and hardened composite sugar solution are put into a sugar infiltration tank (stainless steel tank, tank capacity of 0.2-5 tons) that can refrigerate, insulate and control temperature. The temperature of the materials in the sugar infiltration tank is controlled at 0 to -1°C, and the first low-temperature sugar infiltration time is 15 days.

[0153] (6) Second low temperature infiltration

[0154] Take out part of the sugar solution from the sugar infiltration barrel (the amount taken out accounts for 2 / 3 of the total mass of the sugar solution in the sugar infiltration tank), add the newly prepared complex sugar (maltose: granulated sugar = 2:8), no color preservative and hardener are needed in this complex sugar), the mass ratio of part of the sugar solution to the complex sugar is 2:1, stir and dissolve, make the mass concentration of the complex sugar solution reach 57%, then add it back to the sugar infiltration tank, stir gently to make the concentration of the sugar solution evenly distributed, make the mass concentration of the sugar solution in the sugar infiltration tank reach 44%. Reduce the temperature of the material in the sugar infiltration tank to -3℃, fill the sugar infiltration tank with carbon dioxide, seal it, and carry out the second low-temperature sugar infiltration for 15 days.

[0155] (7) The third low temperature infiltration

[0156] Take out part of the sugar solution from the sugar infiltration tank (the amount taken out accounts for 2 / 3 of the total mass of the sugar solution in the sugar infiltration tank), add the newly prepared complex sugar (maltose: granulated sugar = 2:8, this complex sugar solution does not need to add color preservatives and hardeners, the mass ratio of part of the sugar solution to the complex sugar is 4:3, stir and dissolve, so that the concentration of the sugar solution reaches 63%, and add the prepared complex sugar solution back to the sugar infiltration tank, stir gently to make the concentration of the sugar solution evenly distributed, so that the mass concentration of the sugar solution in the sugar infiltration tank reaches 56%. Reduce the temperature of the material in the sugar infiltration tank to -5℃, fill the sugar infiltration tank with carbon dioxide, seal it, and the third low-temperature sugar infiltration time is 50 days.

[0157] (8) Drying

[0158] The preserved melons are taken out from the sugar solution and placed on a porous sieve plate to drain off excess sugar solution. The melons are placed on a baking tray and air dried at 30° C. for 28 hours until the water content is 13-15%, thereby obtaining preserved melons.

[0159] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. People can also obtain other embodiments based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for cold soaking of preserved fruits, characterized in that: The steps include: 1) washing and cutting the fruits and vegetables to obtain processed fruits and vegetables; 2) partially dehydrating the treated fruits and vegetables to obtain partially dehydrated fruits and vegetables, wherein the mass of the partially dehydrated fruits and vegetables is 50% to 80% of the mass of the fruits and vegetables before dehydration; 3) immersing the partially dehydrated fruits and vegetables in a color-protecting and hardening complex sugar solution for vacuum treatment to obtain vacuumized fruits and vegetables; The color-protecting and hardening composite sugar liquid comprises composite sugar liquid, color-protecting agent and hardener, wherein the composite sugar liquid is a composite sugar liquid with a sugar content of 30% to 35% prepared by mixing composite sugar and water in a ratio of 1:1.5 to 2; the composite sugar of the composite sugar liquid comprises maltose and granulated sugar, and the mass ratio of maltose to granulated sugar is 1:9 to 3:7; the mass of the color-protecting agent is 0.3% to 0.5% of the mass of the composite sugar liquid, and the mass of the hardener is 0.01% to 0.03% of the mass of the composite sugar liquid; 4) placing the vacuumed fruits and vegetables and the color-protecting and hardened complex sugar in a sugar infiltration device for a first low-temperature sugar infiltration treatment to obtain a complex of the first low-temperature infiltration candied fruit and complex sugar solution; the temperature of the first low-temperature sugar infiltration treatment is -2 to 0°C; 5) adding complex sugar to the complex of the first low-temperature infiltration sugared preserved fruit and the complex sugar solution until the mass concentration of the sugar solution in the sugar infiltration device reaches 40% to 45%, and then filling the sugar infiltration device with carbon dioxide and sealing it for a second low-temperature infiltration sugar treatment to obtain a complex of the second low-temperature infiltration sugared preserved fruit and the complex sugar solution; the temperature of the second low-temperature infiltration sugar treatment is -5 to -2°C; 6) adding complex sugar to the complex of the second low-temperature infiltration sugared preserved fruit and the complex sugar solution until the sugar solution concentration in the sugar infiltration device reaches 55% to 60%, and then filling the sugar infiltration device with carbon dioxide and sealing it for a third low-temperature infiltration sugar treatment to obtain a complex of the third low-temperature infiltration sugared preserved fruit and the complex sugar solution; the temperature of the third low-temperature infiltration sugar treatment is -8 to -5°C; 7) The preserved fruits are taken out from the complex of the preserved fruits and the composite sugar solution after the third low-temperature infiltration, and the sugar solution is drained and then dried to obtain the cold-infused preserved fruits.

2. The method for processing cold-soaked preserved fruits according to claim 1, characterized in that: The dehydration method includes room temperature airflow dehydration and hot air dehydration. The temperature of the room temperature airflow dehydration is 15-35°C, and the temperature of the hot air dehydration is 30-50°C.

3. The method for processing cold-soaked preserved fruits according to claim 1, characterized in that: The color protecting agent comprises phytic acid, ascorbic acid and citric acid, wherein the mass ratio of the phytic acid, ascorbic acid and citric acid is 3:3:4; the hardening agent comprises organic acid calcium or inorganic calcium salt.

4. The method for processing cold-soaked preserved fruits according to claim 1, characterized in that: Step 3) The mass ratio of the partially dehydrated fruits and vegetables to the color-protecting and hardened composite sugar solution is 1:1 to 1:

2.

5. The cold-soaked preserved fruit processing method according to claim 1 or 4, characterized in that: Step 3) The vacuum treatment pressure is ≤15 kPa and the time is 20 to 30 minutes.

6. The method for processing cold-soaked preserved fruits according to claim 1, characterized in that: The duration of the first low-temperature sugar infiltration treatment in step 4) is 3 to 15 days.

7. The method for processing cold-soaked preserved fruits according to claim 1, characterized in that: Step 5) The duration of the second low-temperature sugar infiltration treatment is 5 to 30 days.

8. The method for processing cold-soaked preserved fruits according to claim 1, characterized in that: Step 6) The duration of the third low-temperature sugar infiltration treatment is 10 to 300 days.

9. The method for processing cold-soaked preserved fruits according to claim 1, characterized in that: Step 7) The drying method is air flow drying, the air flow drying temperature is 15 to 50° C., and the time is 12 to 36 hours.

10. The method for processing cold-soaked preserved fruits according to claim 1, characterized in that: The fruits and vegetables include fruits and vegetables; the fruits include one or more of apricots, dates, apples, crabapples and melons.

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