A method of vacuum freeze-drying of fresh berry centrifugation-enhanced penetration

Abstract

A kind of fresh berry centrifugal strengthening penetration vacuum freeze-drying method relates to a kind of fresh berry vacuum freeze-drying method. To solve the problem of low water removal efficiency, high energy consumption, easy to collapse, poor quality of freeze-dried product of fresh berry vacuum freeze-drying method. Method: the fresh berry is quick frozen, and the quick frozen berry is placed in multi-element high-efficiency penetration liquid for centrifugal auxiliary strengthening penetration dehydration;Finally, vacuum freeze-drying is carried out. The temperature control of the present application in the drying process of berry is lower, and the pretreatment method before vacuum freeze-drying is less damaged to the microstructure of berry, so that the dried berry product can keep the original cell skeleton and morphology, effectively reduce the bound water content of berry, save the time of vacuum freeze-drying, thereby save energy consumption, improve the glass transition temperature of berry, improve the drying efficiency, avoid the product collapse, product porous loose, with good taste, long shelf life.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for vacuum freeze-drying of fresh berries. BACKGROUND

[0002] With the improvement of people's living standards, energy saving and food quality have become increasingly concerned issues. In the season with high humidity, berries are prone to be infected by microorganisms or other mechanical damage after picking, resulting in quality deterioration, thus not being resistant to storage, short shelf life, and serious postharvest loss. Processing berries into freeze-dried products can effectively prolong their shelf life, while better preserving the nutrients of berries.

[0003] In recent years, in view of the high energy consumption and long time consumption of the vacuum freeze-drying process of berries, different types of vacuum freeze-drying processes have been developed at home and abroad. Among them, the processing mode of "hot air drying + osmotic dehydration + vacuum freeze-drying" can shorten the drying time and reduce the energy consumption of drying, but it has problems such as hard freeze-dried skin of berries after hot air drying treatment, low degree of crispness, and loss of heat-sensitive nutrients, which reduces the quality of freeze-dried berry food.

[0004] In addition, in the process of drying berries containing a waxy layer, the surface of the berries contains a waxy layer, which hinders the transportation of water from the inside to the surface of the berries, resulting in poor dehydration effect. Osmotic dehydration is often used as a drying pretreatment method to promote mass transfer, but it has the problems of low dehydration efficiency, which leads to long soaking time, resulting in deterioration of the original cell skeleton and morphology of the berries, causing the product to collapse in the subsequent vacuum freeze-drying process, affecting the sensory and nutritional quality of the berries, and increasing the probability of microbial contamination. Therefore, it is very important to improve the existing pretreatment method and use efficient osmotic dehydration solution for the osmotic dehydration process of berries containing a waxy layer.

[0005] The traditional vacuum freeze-drying has the problems of long drying time, high energy consumption, and inability to effectively solve the problem of collapse of freeze-dried products during the vacuum freeze-drying process of berries. The vacuum freeze-drying process has two stages, namely the sublimation drying stage and the desorption drying stage. The traditional vacuum freeze-drying has the problem of difficulty in removing combined water in the desorption drying stage, which requires a long time to remove a small amount of combined water, greatly increasing the energy consumption, and being unable to ensure the quality of freeze-dried products while reducing the processing time. During the vacuum freeze-drying process, when the temperature of the dried product is higher than its glass transition temperature, the product changes from a glassy state to a rubbery state, the internal porous structure becomes less rigid, and the viscosity decreases. The porous structure of the object collapses due to the decrease in viscosity of the solid, so improper control of the drying temperature will cause the freeze-dried berry product to collapse.

[0006] Therefore, the existing fresh berry freeze-drying method has the problems of long drying period, high energy consumption, low bound water removal efficiency, and easy collapse of the berry. SUMMARY

[0007] The present application provides a fresh berry centrifugal enhanced penetration vacuum freeze-drying method to solve the problems of long drying period, high energy consumption, low bound water removal efficiency, and easy collapse of the berry in the existing fresh berry freeze-drying method.

[0008] The fresh berry centrifugal enhanced penetration freeze-drying method according to the present application is performed according to the following steps:

[0009] First, the fresh berry is placed in a quick-freezing device to obtain quick-frozen berries.

[0010] Second, the quick-frozen berries are placed in a multi-element high-efficiency penetration liquid for centrifugal auxiliary enhanced penetration dehydration.

[0011] The temperature of the centrifugal auxiliary enhanced penetration dehydration is 10-20℃, the centrifugal rotation speed is 200r / min-400r / min, and the time is 4-5h.

[0012] The preparation method of the multi-element high-efficiency penetration liquid is performed according to the following steps:

[0013] ①, the sugar alcohol, potassium carbonate, calcium chloride and water are mixed to obtain a mixed solution;

[0014] The potassium carbonate, sugar alcohol and calcium chloride are food grade;

[0015] The mass fraction of potassium carbonate in the mixed solution is 1-2%, the mass fraction of sugar alcohol is 40-55%, and the mass fraction of calcium chloride is 3-7%;

[0016] The sugar alcohol is one of xylitol, sorbitol and maltitol;

[0017] ②, the oleic acid and ethanol are placed in a reflux flask with magnetic stirring and oil bath heating, then a catalyst is added, heated and refluxed at 120-130℃ for 4-4.5h, then cooled to obtain a reaction liquid, dried with anhydrous calcium chloride to obtain a dehydrated ethyl oleate reaction liquid, and the dehydrated ethyl oleate reaction liquid is subjected to vacuum distillation to obtain an ethyl oleate liquid;

[0018] The oleic acid and ethanol are food grade, the mass ratio of oleic acid to ethanol is 1:2-3, and the catalyst is 0.5-1.5% of the total mass of oleic acid and ethanol;

[0019] The catalyst is mesoporous molecular sieve B-SBA-15;

[0020] ③, the ethyl oleate liquid obtained in step 2 is cooled and sterilized;

[0021] ④, the ethyl oleate obtained in step 3 is added to the mixed solution in step 1 to obtain a multi-component high-efficiency penetrating solution; the mass fraction of ethyl oleate in the multi-component high-efficiency penetrating solution is 0.5%-1%;

[0022] III. The berry treated in step II is washed with water and dried with a water-absorbing paper to remove surface moisture, and then is placed in a vacuum freeze dryer for vacuum freeze drying to obtain a freeze-dried berry food, i.e. the process is completed.

[0023] The process of vacuum freeze drying in step III is as follows: first, pre-freezing at a temperature of-50℃ to-40℃ for 180-240 min; then sublimation drying at a temperature of 10℃ to 15℃ and a vacuum degree of 30 pa for 500-600 min; finally, desorption drying at a temperature of 25℃ to 30℃ and a vacuum degree of 30 pa for 280-500 min.

[0024] The principles and beneficial effects of the present application are as follows:

[0025] 1. The method of the present application is suitable for drying berries which are not easy to be cut into slices and have a high water content. The present application does not use the pretreatment method of hot air drying, but performs centrifugal penetration dehydration at a low temperature of 10-20℃, thereby solving the problems of the "hot air drying+penetration dehydration+vacuum freeze drying" process, such as the over-hardness of the freeze-dried skin of the berry, the low degree of crispness and the loss of heat-sensitive nutrients, etc. caused by high-temperature hot air in the drying process, and realizing the penetration dehydration of the berry in a low-temperature environment.

[0026] 2. After the treatment of "quick freezing+centrifugal auxiliary penetration dehydration+vacuum freeze drying", the present application solves the problem of the difficulty in removing bound water in the desorption drying stage of the vacuum freeze drying process of the berry. The bound water existing in the cell wall of the berry is combined closely with the structural materials such as cell wall polysaccharides, and is also affected by the water-fiber interaction and the water-gel interaction, and it is difficult to be removed in the conventional vacuum freeze drying process. The berry after quick freezing, centrifugal auxiliary strengthening and penetration dehydration by the multi-component high-efficiency solution in the present application mainly removes a small amount of bound water in the desorption drying stage, thereby greatly shortening the constant-temperature time of the desorption drying and reducing a large amount of energy consumption in the vacuum freeze drying process due to the removal of the bound water. And the present application has a small damage to the microstructure of the berry, the dried berry product can maintain the original cell skeleton and morphology, and the glass transition temperature of the berry is improved (in the vacuum freeze drying stage, with the temperature rising, the material changes from glass state to rubber state, and the corresponding transition temperature is the glass transition temperature), the drying rate is improved, and the product collapse is avoided.

[0027] 3. In this invention, the alkaline ethyl oleate and sodium carbonate in the multi-component high-efficiency permeation solution enhance the permeation dehydration effect. Sodium carbonate enhances the permeability of the epidermis, while ethyl oleate separates the waxy platelets on the berry epidermis, removes the surface wax layer, and improves the water permeability of the peel, thus improving the permeation dehydration effect, which is superior to conventional binary permeation dehydration solutions (such as sucrose / water). By performing quick-freezing and centrifugation-assisted permeation dehydration before vacuum freeze-drying of the berries, and by using the multi-component high-efficiency permeation solution to effectively reduce the bound water content of the berries, the water loss rate of the berries can be improved more effectively.

[0028] 4. The sugar alcohols in the multi-component high-efficiency permeation solution of this invention effectively reduce the sugar content in dehydrated berries, ensuring the taste of freeze-dried berries while increasing the health benefits of berries for diabetic patients.

[0029] In summary, this invention achieves lower osmotic dehydration temperature control during berry drying, minimizing damage to the berry's microstructure. The dried berry product retains its original cellular framework and morphology, effectively reducing the bound water content of the berries. This significantly saves vacuum freeze-drying time and energy, increases the glass transition temperature, and keeps the shelf temperature throughout the vacuum freeze-drying process as low as possible below the product's glass transition temperature, thereby improving the drying rate, preventing product collapse, resulting in a porous and loose product with a better taste and a longer shelf life. Detailed Implementation

[0030] The technical solution of the present invention is not limited to the specific embodiments listed below, but also includes any reasonable combination of the specific embodiments.

[0031] Specific Implementation Method 1: The freeze-drying method for enhanced centrifugation and osmosis of fresh berries in this implementation method is carried out according to the following steps:

[0032] First, place the fresh berries in a quick-freezing device to quick-freeze them, thus obtaining quick-frozen berries;

[0033] 2. Place the quick-frozen berries in a multi-component high-efficiency osmotic solution and centrifuge to enhance osmotic dehydration;

[0034] The centrifugation-assisted enhanced osmotic dehydration is carried out at a temperature of 10-20℃, a centrifugation speed of 200r / min-400r / min, and a time of 4-5h.

[0035] The preparation method of the multi-component high-efficiency permeation solution is carried out according to the following steps:

[0036] ① Mix sugar alcohol, potassium carbonate, calcium chloride and water to obtain a mixture;

[0037] The potassium carbonate, sugar alcohol, and calcium chloride are food grade.

[0038] The mass fraction of potassium carbonate in the mixed solution is 1-2%, the mass fraction of sugar alcohol is 40-55%, and the mass fraction of calcium chloride is 3-7%;

[0039] The sugar alcohol is one of xylitol, sorbitol and maltitol;

[0040] ②, the oleic acid and ethanol are put into a refluxing flask with magnetic stirring and oil bath heating, then a catalyst is added, and heating reflux is carried out at 120-130 DEG C for 4-4.5 h, then the reaction solution is cooled to obtain a reaction solution, which is dried by anhydrous calcium chloride to obtain the dehydrated ethyl oleate reaction solution, and the dehydrated ethyl oleate reaction solution is subjected to reduced pressure distillation to obtain ethyl oleate liquid;

[0041] The oleic acid and ethanol are food grade, and the mass ratio of the oleic acid to the ethanol is 1:2-3, and the catalyst is 0.5-1.5% of the total mass of the oleic acid and the ethanol;

[0042] The catalyst is mesoporous molecular sieve B-SBA-15;

[0043] ③, the ethyl oleate liquid obtained in step ② is cooled and sterilized;

[0044] ④, the ethyl oleate obtained in step ③ is added to the mixed solution in step ① to obtain a multi-component efficient penetration solution; the mass fraction of ethyl oleate in the multi-component efficient penetration solution is 0.5%-1%;

[0045] III, the treated berry is taken out, washed with water, dried with a water-absorbing paper to remove surface water, and then put into a vacuum freeze dryer for vacuum freeze drying to obtain a berry freeze-dried food, and the process is completed;

[0046] The process of vacuum freeze drying in step three is as follows: firstly, pre-freezing at a temperature of-50 DEG C to-40 DEG C for 180-240 min; then sublimation drying at a temperature of 10 DEG C to 15 DEG C and a vacuum degree of 30 pa for 500-600 min; finally, desorption drying at a temperature of 25 DEG C to 30 DEG C and a vacuum degree of 30 pa for 280-500 min.

[0047] 1, the method of the embodiment is suitable for drying berries which are not easy to be cut into slices and have high water content. The embodiment does not use the pretreatment method of hot air drying, but carries out centrifugal osmotic dehydration at a low temperature of 10-20 DEG C, which solves the problems of hard surface of berry freeze-dried skin, low crispness and loss of heat-sensitive nutrients caused by high temperature of hot air in the drying process of "hot air drying + osmotic dehydration + vacuum freeze drying", and realizes the osmotic dehydration of berries in a low temperature environment.

[0048] 2、The embodiment solves the problem of difficulty in removing bound water in the analysis drying stage in the process of vacuum freeze drying of berries after the treatment of "quick freezing + centrifugal auxiliary osmotic dehydration + vacuum freeze drying". The bound water in the cell wall of berries is closely combined with structural materials such as cell wall polysaccharides, and is also affected by the interaction of water-flesh fiber and water-gelatin, so it is difficult to be removed in the conventional vacuum freeze drying process. The berries after quick freezing, centrifugal auxiliary strengthening and multi-element efficient solution osmotic dehydration in the embodiment mainly remove a small amount of bound water in the analysis drying stage, thereby greatly shortening the analysis drying constant temperature time and reducing a large amount of energy consumption generated in the process of removing bound water in the vacuum freeze drying process. And the microstructure of the berries is less damaged after the treatment of the embodiment, the dried berry products can maintain the original cell skeleton and morphology, and the glass transition temperature of the berries is improved (in the vacuum freeze drying stage, as the temperature rises, the material changes from glass state to rubber state, and the corresponding transition temperature is the glass transition temperature), the drying rate is improved, and the product collapse is avoided.

[0049] 3、In the embodiment, the alkaline ethyl oleate and sodium carbonate in the multi-element efficient penetration solution enhance the osmotic dehydration effect, the sodium carbonate enhances the permeability of the epidermis, the ethyl oleate separates the wax platelets of the berry epidermis, removes the surface wax layer, improves the water permeability of the pericarp, and improves the osmotic dehydration effect, which is better than the conventional binary osmotic dehydration solution (such as sucrose / water); the quick freezing and centrifugal auxiliary osmotic dehydration before the vacuum freeze drying of the berries, and the use of the multi-element efficient penetration solution effectively reduce the bound water content of the berries, which can more effectively improve the water loss rate of the berries.

[0050] 4、The sugar alcohol in the multi-element efficient penetration solution in the embodiment effectively reduces the sugar content in the dehydrated berries, ensures the taste of the freeze-dried berries, and increases the health care effect of the berries on diabetic patients.

[0051] In summary, the osmotic dehydration temperature in the drying process of the berries in the embodiment is relatively low, the microstructure of the berries is less damaged, the dried berry products can maintain the original cell skeleton and morphology, the bound water content of the berries is effectively reduced, thereby greatly saving the time of vacuum freeze drying, saving energy consumption, improving the glass transition temperature, making the shelf temperature in the whole vacuum freeze drying process be maximized below the glass transition temperature of the product, improving the drying rate, avoiding the product collapse problem, the product is porous and loose, has good taste, and has a long shelf life.

[0052] Specific implementation method two: The difference between the embodiment and the specific implementation method one is that the quick freezing temperature in step one is -70℃ to -40℃, and the time is 30min to 35min.

[0053] Specific embodiment three: the difference between this embodiment and specific embodiment one or two is that: the berry in step one is a berry containing a waxy layer; the berry containing a waxy layer is blueberry, grape, goji, carambola, plum, loquat, currant, ginseng fruit, passion fruit, lingonberry or cherry.

[0054] Specific embodiment four: the difference between this embodiment and one of specific embodiments one to three is that: the volume ratio of the quick-frozen berry to the penetration solution in step two is 1-1.1:10.

[0055] Specific embodiment five: the difference between this embodiment and one of specific embodiments one to four is that: the process of vacuum freeze-drying in step three is: first pre-freeze for 180 min at a temperature of-50℃ to-40℃; then sublimate dry for 500 min at a temperature of 10℃ to 15℃ and a vacuum degree of 30 pa; finally, desorption dry for 280 min at a temperature of 25℃ to 30℃ and a vacuum degree of 30 pa.

[0056] Example 1:

[0057] The fresh berry centrifugal strengthening penetration freeze-drying method of this embodiment is carried out according to the following steps:

[0058] I. First, the fresh berry is placed in a quick-freezing device for quick-freezing to obtain quick-frozen berries;

[0059] The quick-freezing temperature is-40℃, and the time is 30 min;

[0060] The berry is a berry containing a waxy layer; the berry containing a waxy layer is blueberry;

[0061] II. The quick-frozen berries are placed in a multi-element high-efficiency penetration solution for centrifugal auxiliary strengthening penetration dehydration;

[0062] The volume ratio of the quick-frozen berries to the penetration solution is 1:10;

[0063] The temperature of the centrifugal auxiliary strengthening penetration dehydration is 20℃, the centrifugal rotation speed is 400 r / min, and the time is 5 h;

[0064] The preparation method of the multi-element high-efficiency penetration solution is carried out according to the following steps:

[0065] ①, mix sugar alcohol, potassium carbonate, calcium chloride and water to obtain a mixed solution;

[0066] The potassium carbonate, sugar alcohol and calcium chloride are food grade;

[0067] The mass fraction of potassium carbonate in the mixed solution is 2%, the mass fraction of sugar alcohol is 50%, and the mass fraction of calcium chloride is 5%;

[0068] The sugar alcohol in the multi-element high-efficiency penetration solution is xylitol;

[0069] ②, the oleic acid and ethanol into the magnetic stirring and oil bath heating reflux flask, then add catalyst, heated to 120 ℃ under the condition of reflux 4h, then cooling to obtain the reaction liquid, using anhydrous calcium chloride drying, to obtain the dehydrated ethyl oleate reaction liquid, the dehydrated ethyl oleate reaction liquid is distilled under reduced pressure, intercept ethyl oleate fraction, to obtain ethyl oleate liquid;

[0070] The oleic acid and ethanol are food grade, the mass ratio of oleic acid and ethanol is 1:2.5, and the mass of the catalyst is 1% of the total mass of the oleic acid and ethanol;

[0071] The catalyst is mesoporous molecular sieve B-SBA-15;

[0072] ③, the step ② obtained grade ethyl oleate liquid cooling, sterilization treatment;

[0073] ④, the step ③ grade ethyl oleate is added to the mixed liquid in step ①, to obtain a multi efficient penetration solution; the mass fraction of grade ethyl oleate in the multi efficient penetration solution is 1%;

[0074] III, the step two treated berry, washed with water and dried with water absorption paper to remove surface moisture, then put into vacuum freeze dryer, vacuum freeze drying, to obtain the berry freeze dried food;

[0075] The process of vacuum freeze drying is: first, pre-freezing at a temperature of-40 ℃ for 180 min; then sublimation drying at a temperature of 10 ℃ and a vacuum degree of 30 pa for 500 min; finally, desorption drying at a temperature of 30 ℃ and a vacuum degree of 30 pa for 280 min.

[0076] Comparative example 1:

[0077] The osmotic dehydration of fresh berries in this example is carried out according to the following steps:

[0078] I, first, the fresh berries are placed in a quick freezing device to obtain quick frozen berries;

[0079] The quick freezing temperature is-40 ℃, and the time is 30 min;

[0080] The berries are berries containing waxy layer; the berries containing waxy layer are blueberries;

[0081] II, the quick frozen berries are placed in a multi efficient penetration solution for centrifugal assisted enhanced osmotic dehydration;

[0082] The volume ratio of the quick frozen berries to the penetration solution is 1:10;

[0083] The temperature of the centrifugal auxiliary reinforced penetration dehydration is 20℃, the centrifugal rotation speed is 400r / min, and the time is 5h;

[0084] The preparation method of the multi-element high-efficiency penetration solution is carried out according to the following steps:

[0085] ①, the sugar alcohol, potassium carbonate, calcium chloride and water are mixed to obtain a mixed solution;

[0086] The potassium carbonate, sugar alcohol and calcium chloride are food grade;

[0087] The mass fraction of potassium carbonate in the mixed solution is 2%, the mass fraction of sugar alcohol is 50%, and the mass fraction of calcium chloride is 5%;

[0088] The sugar alcohol in the multi-element high-efficiency penetration solution is xylitol;

[0089] ②, the oleic acid and ethanol are put into a refluxing flask with magnetic stirring and oil bath heating, then a catalyst is added, heated and refluxed at 120℃ for 4h, then cooled to obtain a reaction solution, dried with anhydrous calcium chloride to obtain a dehydrated ethyl oleate reaction solution, and the dehydrated ethyl oleate reaction solution is subjected to vacuum distillation to obtain an ethyl oleate liquid;

[0090] The oleic acid and ethanol are food grade, the mass ratio of oleic acid to ethanol is 1:2.5, and the mass of the catalyst is 1% of the total mass of oleic acid and ethanol;

[0091] The catalyst is mesoporous molecular sieve B-SBA-15;

[0092] ③, the ethyl oleate liquid obtained in step ② is cooled and sterilized;

[0093] ④, the ethyl oleate obtained in step ③ is added to the mixed solution in step ① to obtain a multi-element high-efficiency penetration solution; the mass fraction of ethyl oleate in the multi-element high-efficiency penetration solution is 1%.

[0094] Comparative example 2:

[0095] The fresh berry penetration dehydration method of this embodiment is carried out according to the following steps:

[0096] I. First, the fresh berries are placed in a quick freezing device to obtain quick frozen berries;

[0097] The quick freezing temperature is-40℃, and the time is 30min;

[0098] The berries are berries containing a waxy layer; the berries containing a waxy layer are blueberries;

[0099] II. The quick frozen berries are placed in a sucrose / water penetration solution and subjected to centrifugal auxiliary reinforced penetration dehydration;

[0100] the volume ratio of the quick-frozen berry to the penetrating solution is 1:10;

[0101] the temperature of the centrifugal-assisted reinforced penetration dehydration is 20℃, the centrifugal speed is 400r / min, and the time is 5h;

[0102] the mass fraction of sucrose in the sucrose / water penetrating solution is 50%.

[0103] Comparative Example 3:

[0104] The penetration dehydration of the fresh berry in this example is carried out according to the following steps:

[0105] the berry (fresh blueberry) is placed in the multi-element high-efficiency penetrating solution for centrifugal-assisted reinforced penetration dehydration;

[0106] the volume ratio of the quick-frozen berry to the penetrating solution is 1:10;

[0107] the temperature of the centrifugal-assisted reinforced penetration dehydration is 20℃, the centrifugal speed is 400r / min, and the time is 5h;

[0108] the preparation method of the multi-element high-efficiency penetrating solution is carried out according to the following steps:

[0109] ①, the sugar alcohol, potassium carbonate, calcium chloride and water are mixed to obtain a mixed solution;

[0110] the potassium carbonate, sugar alcohol and calcium chloride are food grade;

[0111] the mass fraction of potassium carbonate in the mixed solution is 2%, the mass fraction of sugar alcohol is 50%, and the mass fraction of calcium chloride is 5%;

[0112] the sugar alcohol in the multi-element high-efficiency penetrating solution is xylitol;

[0113] ②, the oleic acid and ethanol are placed in a refluxing flask with magnetic stirring and oil bath heating, then a catalyst is added, heated and refluxed at 120℃ for 4h, then cooled to obtain a reaction solution, dried with anhydrous calcium chloride to obtain a dehydrated ethyl oleate reaction solution, and the dehydrated ethyl oleate reaction solution is subjected to reduced pressure distillation to obtain an ethyl oleate liquid;

[0114] the oleic acid and ethanol are food grade, the mass ratio of oleic acid to ethanol is 1:2.5, and the mass of the catalyst is 1% of the total mass of oleic acid and ethanol;

[0115] the catalyst is mesoporous molecular sieve B-SBA-15;

[0116] ③, the ethyl oleate liquid obtained in step ② is cooled and sterilized;

[0117] IV. The ethyl oleate obtained in step III is added to the mixture in step I to obtain a multi-component high-efficiency penetrating solution; the mass fraction of the ethyl oleate in the multi-component high-efficiency penetrating solution is 1%.

[0118] Comparative Example 4

[0119] The osmotic dehydration of the fresh berries in this example is carried out according to the following steps: the berries (fresh blueberries) are placed in a multi-component high-efficiency penetrating solution for osmotic dehydration; the volume ratio of the quick-frozen berries to the multi-component high-efficiency penetrating solution is 1:10; the osmotic dehydration temperature is 20°C, and the osmotic dehydration time is 5h;

[0120] The preparation method of the multi-component high-efficiency penetrating solution is carried out according to the following steps:

[0121] I. Sugar alcohol, potassium carbonate, calcium chloride and water are mixed to obtain a mixture;

[0122] The potassium carbonate, sugar alcohol and calcium chloride are food grade;

[0123] The mass fraction of the potassium carbonate in the mixture is 2%, the mass fraction of the sugar alcohol is 50%, and the mass fraction of the calcium chloride is 5%;

[0124] The sugar alcohol in the multi-component high-efficiency penetrating solution is xylitol;

[0125] II. Oleic acid and ethanol are placed in a refluxing flask with magnetic stirring and oil bath heating, and then a catalyst is added. The mixture is heated and refluxed at 120°C for 4h, and then cooled to obtain a reaction liquid. The reaction liquid is dried with anhydrous calcium chloride to obtain a dehydrated ethyl oleate reaction liquid. The dehydrated ethyl oleate reaction liquid is subjected to vacuum distillation, and the ethyl oleate fraction is collected to obtain an ethyl oleate liquid;

[0126] The oleic acid and ethanol are food grade, the mass ratio of the oleic acid to the ethanol is 1:2.5, and the mass of the catalyst is 1% of the total mass of the oleic acid and the ethanol;

[0127] The catalyst is mesoporous molecular sieve B-SBA-15;

[0128] III. The ethyl oleate liquid obtained in step II is cooled and sterilized;

[0129] IV. The ethyl oleate obtained in step III is added to the mixture in step I to obtain a multi-component high-efficiency penetrating solution; the mass fraction of the ethyl oleate in the multi-component high-efficiency penetrating solution is 1%.

[0130] Table 1

[0131] Experiment Rate of water loss g / g Rate of solid increase g / g Peak area of bound water Moisture content Fresh blueberry 0 0 1793.52 85.70％ Comparative Example 1 0.34 0.13 812.46 71.50％ Comparative Example 2 0.16 0.08 1261.78 79.01％ Comparative Example 3 0.20 0.09 1583.79 77.39％ Comparative Example 4 0.08 0.01 1696.38 82.13％

[0132] As can be seen from Table 1, before the vacuum freeze-drying of the berries, the water content of the quick-frozen + centrifugal-assisted osmotic dehydration (multi-element high-efficiency osmotic solution) is the lowest compared with other pretreatment methods, indicating that the osmotic dehydration effect of the treatment method of the application is the best, and the multi-element high-efficiency osmotic solution of the application is superior to the conventional binary osmotic dehydration solution (such as sucrose / water), and the combined water content of the dehydrated berries is the lowest.

[0133] Comparative Example 5:

[0134] The drying method of the fresh berries of the present comparative example is carried out according to the following steps:

[0135] I. First, the fresh berries are dried in a hot air drying device to obtain pre-dried berries;

[0136] The drying temperature is 52℃, the hot air speed is 1.2m / s, and the time is 55min;

[0137] The berries are berries containing a waxy layer; the berries containing a waxy layer are blueberries;

[0138] II. The pre-dried berries are placed in a multi-element high-efficiency osmotic solution for osmotic dehydration;

[0139] The volume ratio of the quick-frozen berries to the multi-element high-efficiency osmotic solution is 1:10;

[0140] The osmotic dehydration temperature is 20℃, and the osmotic dehydration time is 5h;

[0141] The preparation method of the multi-element high-efficiency osmotic solution is carried out according to the following steps:

[0142] ①, mixing sugar alcohol, potassium carbonate, calcium chloride and water to obtain a mixed solution;

[0143] The potassium carbonate, sugar alcohol and calcium chloride are food grade;

[0144] The mass fraction of potassium carbonate in the mixed solution is 2%, the mass fraction of sugar alcohol is 50%, and the mass fraction of calcium chloride is 5%;

[0145] The sugar alcohol in the multi-element high-efficiency osmotic solution is xylitol;

[0146] ②, put oleic acid and ethanol into a reflux flask with magnetic stirring and oil bath heating, then add a catalyst, heat under the condition of 120℃ for 4h, then cool to obtain a reaction liquid, dry with anhydrous calcium chloride to obtain a dehydrated ethyl oleate reaction liquid, and perform vacuum distillation on the dehydrated ethyl oleate reaction liquid, intercept the ethyl oleate fraction to obtain an ethyl oleate liquid;

[0147] The oleic acid and the ethanol are food grade, the mass ratio of the oleic acid and the ethanol is 1:2.5, and the mass of the catalyst is 1% of the total mass of the oleic acid and the ethanol;

[0148] The catalyst is mesoporous molecular sieve B-SBA-15;

[0149] ③, cooling and sterilizing the ethyl oleate liquid obtained in step ②;

[0150] ④, adding the ethyl oleate obtained in step ③ into the mixed solution in step ① to obtain a multi-component efficient penetration solution; the mass fraction of the ethyl oleate in the multi-component efficient penetration solution is 1%;

[0151] III. After the treatment in step II, the berries are washed with water and dried with a water-absorbing paper to remove surface water, and then the dehydrated berries are placed in a vacuum freeze dryer for vacuum freeze drying to obtain a freeze-dried berry food;

[0152] The process of the vacuum freeze drying is: first, pre-freezing at a temperature of -40℃ for 180 min; then sublimation drying at a temperature of 10℃ and a vacuum degree of 30 pa for 520 min; finally, desorption drying at a temperature of 30℃ and a vacuum degree of 30 pa for 360 min.

[0153] Comparative Example 6:

[0154] The drying method of the fresh berries in this comparative example is carried out according to the following steps:

[0155] I. First, the fresh berries are placed in a multi-component efficient penetration solution for osmotic dehydration;

[0156] The berries are berries containing a waxy layer; the berries containing a waxy layer are blueberries;

[0157] The volume ratio of the quick-frozen berries to the penetration solution is 1:10;

[0158] The osmotic dehydration temperature is 20℃, and the osmotic dehydration time is 5h;

[0159] The preparation method of the multi-component efficient penetration solution is carried out according to the following steps:

[0160] ①, mixing sugar alcohol, potassium carbonate, calcium chloride and water to obtain a mixed solution;

[0161] The potassium carbonate, sugar alcohol and calcium chloride are food grade;

[0162] The mass fraction of potassium carbonate in the mixed solution is 2%, the mass fraction of sugar alcohol is 50%, and the mass fraction of calcium chloride is 5%;

[0163] The sugar alcohol in the multi-component efficient penetration solution is xylitol;

[0164] ②, put oleic acid and ethanol into a refluxing flask with magnetic stirring and oil bath heating, then add catalyst, heat under reflux at 120℃ for 4h, then cool to obtain reaction liquid, dry with anhydrous calcium chloride to obtain dehydrated ethyl oleate reaction liquid, distill the ethyl oleate reaction liquid under reduced pressure, and intercept the ethyl oleate fraction to obtain ethyl oleate liquid;

[0165] The oleic acid and ethanol are food grade, and the mass ratio of the oleic acid to the ethanol is 1:2.5, and the mass of the catalyst is 1% of the total mass of the oleic acid and the ethanol;

[0166] The catalyst is mesoporous molecular sieve B-SBA-15;

[0167] ③, cool the ethyl oleate liquid obtained in step ② and sterilize it;

[0168] ④, add the ethyl oleate obtained in step ③ to the mixed liquid in step ① to obtain a multi-component high-efficiency penetrating solution; the mass fraction of ethyl oleate in the multi-component high-efficiency penetrating solution is 1%;

[0169] III. Take out the berry treated in step II, rinse with water, dry with a water-absorbing paper to remove surface moisture, and put the dehydrated berry into a vacuum freeze dryer for vacuum freeze drying to obtain a berry freeze-dried food;

[0170] The process of vacuum freeze drying is: first pre-freeze at a temperature of -40℃ for 180min; then sublimate dry at a temperature of 10℃ and a vacuum degree of 30pa for 570min; finally, desorption dry at a temperature of 30℃ and a vacuum degree of 30pa for 430min.

[0171] Comparative Example 7:

[0172] The drying method of the fresh berry in this comparative example is carried out according to the following steps:

[0173] I. First, rinse the fresh berry with water, dry it with a water-absorbing paper to remove surface moisture, and put the berry into a vacuum freeze dryer for vacuum freeze drying to obtain a berry freeze-dried food;

[0174] The berry is a berry containing a waxy layer; the berry containing a waxy layer is blueberry;

[0175] The process of vacuum freeze drying is: first pre-freeze at a temperature of -40℃ for 180min; then sublimate dry at a temperature of 10℃ and a vacuum degree of 30pa for 600min; finally, desorption dry at a temperature of 30℃ and a vacuum degree of 30pa for 450min.

[0176] Table 2

[0177] Experiment Hardness / gf Chewiness / gf Elasticity Freeze-drying time / min Example 1 774.53 98.68 0.45 960 Comparative Example 5 3240.21 196.43 0.30 1060 Comparative Example 6 1196.82 118.65 0.39 1180 Comparative Example 7 1913.31 120.58 0.33 1230

[0178] From Table 2, it can be seen that the freeze-drying time of the method of Example 1 of the present application is the least, the vacuum freeze-drying time is shortened by 270 min compared with the traditional vacuum freezing, and the vacuum freeze-drying time is saved by 22% of time. Since the method of the present application effectively removes the water content of the berry, a large amount of time spent in the desorption drying process due to the removal of the bound water is reduced, thereby reducing the freeze-drying time. The hardness of the berry freeze-dried food treated by "hot air + osmotic dehydration + vacuum freeze-drying" (Comparative Example 5) is the largest, which is mainly caused by the hot air pretreatment process. After the treatment of the freeze-drying centrifugal enhanced osmotic dehydration vacuum freeze-drying, the hardness and chewiness of the berry freeze-dried food are the lowest, indicating that the freeze-dried food is crispier and has the best taste.

[0179] The above test indexes and determination methods are as follows:

[0180] 1. Moisture state is determined by low-field nuclear magnetic resonance technology, and a CPMG (Carr-Purcell-Meiboom-Gill) pulse sequence is used for signal acquisition of transverse relaxation time of the sample; the acquisition parameters are 90° pulse time P1 = 6 μs, 180° pulse time P2 = 12 μs, repetition time 4000 ms, echo time 0.15 ms, echo number 16000, and the number of accumulated sampling times is 16, and 3 signals are collected each time to ensure the stability of the signal amplitude; the transverse relaxation time signal collected is obtained by inversion software to obtain the transverse relaxation time inversion spectrum, and then the area curve of the relaxation component is obtained, so as to calculate the peak area of each component.

[0181] 2. Calculation of water loss rate and solid increase rate

[0182] (1) Water loss rate

[0183]

[0184] Wherein, WL is the water loss rate of blueberry osmotic dehydration, dry basis g / g; M O is the initial mass of the fresh blueberry sample at the initial moment of osmotic dehydration, g; M t is the mass of the blueberry sample at the moment t of osmotic dehydration treatment, g; m o is the mass of the fresh blueberry after drying, g; m t is the mass of the blueberry sample after drying at the moment t of osmotic dehydration treatment, g;

[0185] (2) Solid increase rate

[0186]

[0187] Wherein, SG is the solid increase rate of blueberry osmotic dehydration, dry basis g / g; m oFresh blueberry dried quality, g; m t Penetrated dehydration treatment t time blueberry sample dried quality, g. The ratio of water loss rate and solid increase rate.

[0188] 3. The hardness and chewiness of blueberry pulp were determined and analyzed by texture analyzer.

[0189] 4. Determination of blueberry moisture content.

[0190] The moisture content of blueberry was determined according to the "National Food Safety Standard Determination of Moisture in Food" GB 5009.3-2016, as shown in the formula.

[0191] The moisture content of blueberry is:

[0192] In the formula: WC - the moisture content of blueberry at t time of penetration treatment, wet basis %;

[0193] M t - blueberry sample quality at t time of penetration treatment, g;

[0194] m t - blueberry solid quality at t time of penetration treatment, g.

[0195] Materials and equipment Blueberry "blue abundance" in this example was purchased from Harbin fruit wholesale market and stored in a 4℃ refrigerator. The moisture content of fresh blueberry was 85.37%. Low-field nuclear magnetic resonance equipment PQ-001 Shanghai Nuami Science and Technology Co., Ltd., quick-freezing equipment DW-86W100 China Haier, high-precision electronic analytical balance XS105DU Switzerland Mettler Toledo Company, medical low-temperature storage box DW-86W100 J Qingdao Haier Biomedical Co., Ltd., air drying oven GZX-9030MBE Shanghai Boxun Industrial Co., Ltd. Medical Equipment Factory, high-precision food thermometer WT-1B Jiangsu Jingchuang Electrical Co., Ltd., low-temperature constant-temperature tank RH-DC-V30-R20 Nanjing Hongrun Company, constant-temperature incubation shaker THZ-100B Shanghai Yiheng Scientific Instruments Co., Ltd., full-temperature incubation constant-temperature shaker HYM-100D Shanghai Shangyueming Scientific Instruments Co., Ltd., vacuum freeze dryer LGJ-30G Beijing Sihuan Furuike Instrument Technology Development Company, texture analyzer Universal TA Shanghai Tengbu Instrument Technology Co., Ltd.

Claims

1. A vacuum freeze-drying method for fresh berries using centrifugation-enhanced osmosis, characterized in that: The vacuum freeze-drying method for enhancing the osmosis of fresh berries by centrifugation is carried out according to the following steps: First, place the fresh berries in a quick-freezing device to quick-freeze them, thus obtaining quick-frozen berries; 2. Place the quick-frozen berries in a multi-component high-efficiency osmotic solution and centrifuge to enhance osmotic dehydration; The centrifugation-assisted enhanced osmotic dehydration is carried out at a temperature of 10-20℃, a centrifugation speed of 200r / min-400r / min, and a time of 4-5h. The preparation method of the multi-component high-efficiency permeation solution is carried out according to the following steps: ① Mix sugar alcohol, potassium carbonate, calcium chloride and water to obtain a mixture; The potassium carbonate, sugar alcohol, and calcium chloride are food grade. The mixture contains 1-2% potassium carbonate, 40-55% sugar alcohol, and 3-7% calcium chloride by mass. The sugar alcohol is one of xylitol, sorbitol, and maltitol; ② Place oleic acid and ethanol into a reflux flask equipped with magnetic stirring and oil bath heating, add catalyst, and heat under reflux at 120-130℃ for 4-4.5 hours. Then cool to obtain a reaction solution, dry with anhydrous calcium chloride to obtain a dehydrated ethyl oleate reaction solution. Perform vacuum distillation on the dehydrated ethyl oleate reaction solution, and collect the ethyl oleate fraction to obtain liquid ethyl oleate. The oleic acid and ethanol are food grade, the mass ratio of oleic acid to ethanol is 1:2 to 3, and the catalyst is 0.5 to 1.5% of the total mass of oleic acid and ethanol. The catalyst is mesoporous molecular sieve B-SBA-15; ③ Cool and sterilize the ethyl oleate liquid obtained in step ②; ④ Add the ethyl oleate obtained in step ③ to the mixture in step ① to obtain a multi-component high-efficiency permeation solution; the mass fraction of ethyl oleate in the multi-component high-efficiency permeation solution is 0.5% to 1%; 3. Take out the berries processed in step 2, rinse them with water and dry them with absorbent paper to remove surface moisture, and then put them into a vacuum freeze dryer for vacuum freeze drying to obtain freeze-dried berry food, which is complete. The vacuum freeze-drying process described in step three is as follows: first, pre-freeze at a temperature of -50℃ to -40℃ for 180-240 min; then sublimate and dry at a temperature of 10℃ to 15℃ and a vacuum of 30 Pa for 500-600 min; finally, desorption and dry at a temperature of 25℃ to 30℃ and a vacuum of 30 Pa for 280-500 min.

2. The vacuum freeze-drying method for enhancing the permeation of fresh berries by centrifugation according to claim 1, characterized in that: The quick-freezing temperature in step one is -70℃ to -40℃, and the time is 30 min to 35 min.

3. The vacuum freeze-drying method for enhancing the permeation of fresh berries by centrifugation according to claim 1, characterized in that: The berries mentioned in step one are berries containing a waxy layer; berries containing a waxy layer include blueberries, grapes, goji berries, star fruit, plums, loquats, currants, ginseng fruit, passion fruit, blueberries, or cherries.

4. The vacuum freeze-drying method for enhancing the permeation of fresh berries by centrifugation according to claim 1, characterized in that: The volume ratio of quick-frozen berries to permeation solution in step two is 1 to 1.1:

10.

5. The vacuum freeze-drying method for enhancing the permeation of fresh berries by centrifugation according to claim 1, characterized in that: The vacuum freeze-drying process described in step three is as follows: first, pre-freeze at a temperature of -50℃ to -40℃ for 180 minutes; then sublimate and dry at a temperature of 10℃ to 15℃ and a vacuum of 30 Pa for 500 minutes; finally, desorption and dry at a temperature of 25℃ to 30℃ and a vacuum of 30 Pa for 280 minutes.

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