Water chestnut drying method capable of improving rehydration rate

Abstract

The invention provides a water chestnut drying preservation method capable of improving the rehydration rate. The water chestnut drying preservation method comprises the following steps: (1) cleaning fresh water chestnuts, peeling, and cutting into water chestnut slices with a certain thickness; and (2) performing drying treatment on the cut water chestnut slices under different conditions until the weight is constant to obtain dried water chestnut slices, and preserving the dried water chestnut slices in a cool and dry place. The different drying conditions comprise hot air drying treatment, vacuum drying treatment, microwave differential pressure drying treatment and vacuum freeze drying treatment. According to the water chestnut drying and fresh-keeping method for improving the rehydration rate, after vacuum drying, the rehydration rate of the water chestnuts is optimal, the texture characteristics of the water chestnuts are not changed, the transportation cost of the water chestnuts dried through the method can be reduced, the texture characteristics of the water chestnuts after rehydration are similar to those of the water chestnuts before drying, and the water chestnuts can be used as food processing raw materials.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of fruit and vegetable food processing, and particularly relates to a dry preservation method for improving the rehydration rate of Chinese water chestnut. BACKGROUND

[0002] Chinese water chestnut (Eleocharis tuberosa) is also known as "horse's hoof", and belongs to the shallow water herbaceous plants of sedge family. Chinese water chestnut is rich in nutrients, sweet and juicy, and has the reputation of "underground snow pear" and "Jiangnan ginseng". The cultivation area of Chinese water chestnut in China is about 30,000 mu, and the yield accounts for more than 95% of the world. Guangxi ranks first in the country in terms of Chinese water chestnut planting area and total yield, among which Hezhou and Guilin are the "Chinese water chestnut hometown", with more than 400,000 mu of Chinese water chestnut planting area and more than 800,000 tons of yield, accounting for more than 70% of the total yield in China. Fresh-cut Chinese water chestnut is favored by consumers due to its rich nutrition, safety and convenience, and is the key processing product of Guangxi Chinese water chestnut industry. Scientific research shows that fresh-cut Chinese water chestnut has both enzymatic browning and non-enzymatic browning, and the activity of microorganisms also aggravates the browning degree of Chinese water chestnut. The storage of fresh-cut Chinese water chestnut cannot achieve good results. The problem of flesh browning seriously restricts the sales and promotion of fresh-cut Chinese water chestnut. There have been relevant research reports on the inhibitory effect of heat treatment on the browning of fresh-cut Chinese water chestnut, but the heat treatment is carried out after peeling. This heat treatment method will cause the loss of nutrients and other adverse effects on the quality of fresh-cut Chinese water chestnut, and the flesh is easily damaged during heat treatment, which is not conducive to prolonging the shelf life.

[0003] The prior art CN 106359568 A discloses a fresh-cut Chinese water chestnut preservation method, which can reduce the browning degree and weight loss rate of fresh-cut Chinese water chestnut during storage, has little effect on the taste of Chinese water chestnut, and can be stored for more than 40 days under the storage condition of 4℃, basically meeting the needs of long-distance transportation and sales. However, the fresh-cut Chinese water chestnut treated by this method has a high water content, and the number of fresh-cut Chinese water chestnut loaded per vehicle is limited by the vehicle load during transportation. In addition, the unit price of fresh-cut Chinese water chestnut is low, and the transportation cost per ton of fresh-cut Chinese water chestnut is higher than the price difference between the fresh-cut Chinese water chestnut in the rich production area and the poor production area during long-distance transportation, which limits the long-distance transportation of fresh-cut Chinese water chestnut in the rich production area. SUMMARY

[0004] Considering that Chinese water chestnut is a seasonal and regional product, the processing of Chinese water chestnut products using fresh Chinese water chestnut as raw material is limited by seasonality and differences in Chinese water chestnut raw materials. The present application dries Chinese water chestnut moderately, then transports the dried Chinese water chestnut over a long distance to reduce transportation costs, and rehydrates the dried Chinese water chestnut into fresh-cut Chinese water chestnut after arriving at the destination, which can effectively solve the problem of high cost of long-distance transportation of fresh Chinese water chestnut. The present application explores a product processing path based on dried raw materials and provides a dry preservation method for improving the rehydration rate of Chinese water chestnut.

[0005] In order to achieve the above object, the technical scheme adopted by the present application is as follows: A dry preservation method for improving the rehydration rate of Chinese water chestnut, comprising the following steps: (1) washing fresh Chinese water chestnut, peeling, and cutting into Chinese water chestnut slices with a certain thickness; (2) drying the cut Chinese water chestnut slices under different conditions until constant weight to obtain dried Chinese water chestnut slices, which are stored in a cool and dry place.

[0006] Further, the thickness of the Chinese water chestnut slices in step (1) is 3-5 mm.

[0007] Further, the different conditions in step (2) include hot air drying treatment, vacuum drying treatment, microwave pressure difference drying treatment, and vacuum freeze drying treatment.

[0008] Further, the hot air drying treatment in step (2) includes hot air 50℃ treatment, hot air 60℃ treatment, and hot air 70℃ treatment, and the vacuum drying treatment includes vacuum 50℃ treatment, vacuum 60℃ treatment, and vacuum 70℃ treatment.

[0009] Further, the drying condition in step (2) is vacuum drying treatment.

[0010] Further, the vacuum drying in step (2) is carried out at 50℃.

[0011] The present application also provides a preparation method for rehydrating dried Chinese water chestnut based on the above-mentioned preservation method, comprising the following steps: (1) washing fresh Chinese water chestnut, peeling, and cutting into Chinese water chestnut slices with a certain thickness; (2) drying the cut Chinese water chestnut slices under different conditions until constant weight to obtain dried Chinese water chestnut slices, which are stored in a cool and dry place; and (3) soaking the dried Chinese water chestnut slices obtained in the above step in water at room temperature to obtain rehydrated Chinese water chestnut slices.

[0012] Compared with the prior art, the present application has the following beneficial effects: The present application selects the preparation process conditions for rehydrating dried Chinese water chestnut under different drying conditions, and obtains a dry preservation method for improving the rehydration rate of Chinese water chestnut, which does not change the texture characteristics of Chinese water chestnut. The dried Chinese water chestnut prepared by the method of the present application can reduce transportation costs, and the texture characteristics after rehydration are similar to those before drying.

[0013] The dried water chestnut has more uses, and can be used as a pastry and a stuffing: mixed into steamed stuffed buns, dumplings, shumai, wonton stuffing, to improve the crispness and water retention of the stuffing, and reduce the greasy feeling; can also be used as a dessert and a sweet water: added to Hong Kong-style desserts (such as water chestnut crisp, water chestnut cake, sweet water) or jelly / budding type desserts, to highlight the sweet and transparent taste; can also be used as a beverage / cold drink ingredient: small Ding as a tea, milk tea, fruit tea ingredient (similar to "crispy boba" "crispy fruit particles"), or made into frozen "crispy fruit particles" and added to ice cream. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 The drying rate and rehydration rate of fresh-cut water chestnut slices under different drying conditions; Figure 2 The color difference of the rehydrated water chestnut slices obtained after rehydration treatment of the dried water chestnut slices under different drying conditions; Figure 3 The texture index analysis of the rehydrated water chestnut slices obtained after rehydration treatment of the dried water chestnut slices under different drying conditions; Figure 4 The sensory evaluation of the rehydrated water chestnut slices obtained after rehydration treatment of the dried water chestnut slices under different drying conditions. DETAILED DESCRIPTION

[0015] The application will be further described in detail below in combination with examples.

[0016] The raw materials used in each preparation example and embodiment of the application are commercially available, except for the special description below.

[0017] The products obtained in each preparation example and embodiment of the application are subjected to drying rate, rehydration rate, texture test, color difference test and sensory evaluation, and the specific methods are as follows: I. Drying rate The dried water chestnut dried to a constant weight in different ways, and the proportion of the dried water chestnut to the fresh sample, i.e. the drying rate.

[0018] II. Rehydration rate The dried water chestnut is soaked in water at room temperature to obtain rehydrated water chestnut, and the percentage of the rehydrated water chestnut to the fresh sample weight, i.e. the rehydration rate.

[0019] III. Texture The texture properties of the rehydrated water chestnut are determined by a texture analyzer (TA-XT Plus) TPA program, and hardness, brittleness, chewiness, etc. are selected as the analysis indexes of the water chestnut texture. The test parameters are: probe P / 36R, pre-test speed 3 mm / s, test speed 5 mm / s, post-test speed 3 mm / s, compression ratio is the sample deformation degree is 40%, compression trigger force is 5g, 6 parallel test experiments are carried out for each sample. The instrument records the "force-displacement" curve in real time, and then the software automatically gives: Hardness = the maximum force (gf) on the curve.

[0020] Fracturability = the force at which the first significant "break" in the curve occurs; if there is no break, take the same value as the hardness.

[0021] Chewiness = Hardness x Cohesiveness x Springiness (all calculated from the area or slope of the curve), in gf.

[0022] Four, color difference The JZ-300 universal colorimeter was used to detect the surface color difference L * value, a * value, b * value of fresh-cut eelgrass. Among them, L * is the brightness value; a * positive value indicates red, a * negative value indicates green; b * positive value indicates yellow, b * negative value indicates blue. Each group of samples was measured 10 times and the average value was taken.

[0023] Five, sensory evaluation Ten food professional postgraduates (5 boys and 5 girls, aged 22-25, from Hubei) were invited to be group members after training to conduct sensory evaluation. The sensory evaluation standard is shown in Table 1.

[0024] Table 1 Sensory evaluation standard: Example 1 A dried preservation method for improving the rehydration rate of eelgrass, comprising the following preparation steps: (1) Fresh eelgrass is washed clean, peeled, and cut into eelgrass slices with a thickness of 3-5 mm; (2) The cut eelgrass slices are dried by different conditions until the constant weight; (3) The dried eelgrass slices in the previous step are soaked in clean water at room temperature to obtain rehydrated eelgrass slices.

[0025] In the above steps, the drying conditions of step (2) include hot air drying treatment, vacuum drying treatment, microwave differential pressure drying treatment and vacuum freeze drying treatment; wherein the hot air drying treatment includes hot air 50℃ treatment, hot air 60℃ treatment, hot air 70℃ treatment, vacuum drying treatment includes vacuum 50℃ treatment, vacuum 60℃ treatment, vacuum 70℃ treatment, a total of 8 drying conditions.

[0026] I. Test content: First, the drying rate of the samples treated by different drying conditions in step (2) is determined; Then, the rehydration yield of rehydrated water chestnut slices after being treated with different drying conditions in step (3) was tested.

[0027] Finally, the texture characteristics of the rehydrated water chestnut slices were measured using a texture analyzer (TA-XT Plus) with a TPA program. Hardness, crispness (elasticity) and chewiness were selected as evaluation indicators, and sensory evaluation was conducted according to Table 1.

[0028] II. Test Results 1. The drying yield and rehydration yield of fresh-cut water chestnut slices under different drying conditions in step (2) are shown in Table 2 below. Figure 1 As shown.

[0029] Table 2. Drying and rehydration of dried water chestnut slices under different drying conditions. Depend on Figure 1 As shown in Table 2, the drying yields of fresh-cut water chestnut slices treated with different temperatures (50℃, 60℃, 70℃) for hot air drying, different temperatures (50℃, 60℃, 70℃) for vacuum drying, microwave pressure difference drying, and vacuum freeze-drying, from lowest to highest, are as follows: freeze-drying < vacuum 70℃ < hot air 70℃ < microwave pressure difference < hot air 50℃ < hot air 60℃ < vacuum 50℃ < vacuum 60℃. Among them, the freeze-drying group had the lowest drying yield, showing a significant difference from other treatment groups. This was followed by the vacuum 70℃ and hot air 70℃ drying groups. There were no significant differences in drying yields among the microwave pressure difference, hot air 50℃, and hot air 60℃ groups.

[0030] A lower drying yield indicates a lower moisture content in the dried sample, which is more conducive to storage and preservation. This shows that vacuum drying at 70℃ and freeze-drying are both effective methods. A higher rehydration yield indicates a stronger ability of the dried sample to be restored to a fresh state. Conversely, a lower rehydration yield indicates that the cell structure in the sample is damaged and cannot be restored to a fresh state.

[0031] This is because the freeze-drying process involves two steps: first, rapid freezing to below -80°C, followed by direct sublimation of the ice under vacuum. The sublimation driving force is high, and the vacuum level is high, resulting in a final residual moisture content of 1%–10%, far lower than that of hot air (5%–15%) or microwave (4%–15%). In the freeze-drying process, the less solids remain in the dry substrate, the lower the yield. Therefore, the freeze-drying yield of 12% indicates that it achieves the most thorough dehydration and the lowest drying yield.

[0032] During rehydration, the freeze-dried cells may experience a significant reduction in water retention due to the formation of needle-like ice crystals within the cells, which can puncture the cell walls. Sublimation leaves behind numerous irreversible micropores and cracks, allowing water molecules to freely enter and exit. However, the cells have lost their original "elastic sponge" structure and cannot retain large amounts of water through osmotic pressure and hydrocolloids like fresh cells. Macroscopically, this manifests as: slow water absorption; water content at equilibrium significantly lower than in fresh samples; and a rehydration yield of only 47%. In contrast, while hot air or vacuum drying also damages cells, the degree of damage is less than with freeze-drying. Rehydration in these cells retains more water-holding space, achieving a rehydration yield of 80%–87%.

[0033] Therefore, as Figure 1 As shown in the evaluation of drying and rehydration yields, hot air drying at 50℃, hot air drying at 60℃, and microwave pressure difference drying yielded the best rehydration rate for fresh water chestnut slices. The texture characteristics of the rehydrated water chestnuts are likely closer to those of the original fresh water chestnuts. Vacuum drying at 50℃, 60℃, and 70℃ yielded the next best rehydration rates. However, there were no significant differences in drying yield among the treatment groups using microwave pressure difference, hot air drying at 50℃, hot air drying at 60℃, vacuum drying at 50℃, and vacuum drying at 60℃. The rehydration effects were all good, and the rehydration rates were all not less than 80%.

[0034] 2. The color difference measurement results of the rehydrated water chestnut slices obtained by rehydrating the dried water chestnut slices obtained under different drying conditions in step (3) are shown in Table 3 below. Figure 2 As shown.

[0035] Table 3. Color difference of dried water chestnut slices after rehydration under different drying conditions In the table above, the L* value represents brightness, ranging from 0 to 100. The higher the value, the brighter the color; the lower the value, the darker the color.

[0036] The a* value indicates the color's position on the red-green axis, reflecting its red-green tendency. a* > 0 (positive value): indicates the color leans towards red. The larger the value, the more pronounced the red. a* < 0 (negative value): indicates the color leans towards green. The larger the absolute value, the more pronounced the green. a* = 0 indicates that under standard observation conditions, the color is neither red nor green, and lies on the neutral axis.

[0037] The b* value indicates the color's position on the yellow-blue axis, reflecting its yellow-blue tendency. b* > 0 (positive value): indicates the color leans towards yellow. The larger the value, the more pronounced the yellow. b* < 0 (negative value): indicates the color leans towards blue. The larger the absolute value, the more pronounced the blue. b* = 0 indicates that under standard observation conditions, the color is neither yellow nor blue, and lies on the neutral axis.

[0038] In assessing the difference between two color samples (e.g., a standard and a test sample), the L1*, a1*, b1* and L2*, a2*, b2* values are measured for each sample. The difference between them is quantified by calculating the differences (ΔL*, Δa*, Δb*) and the total color difference (ΔE): ΔL* = L2* - L1*: A positive value indicates that the test sample is lighter than the standard sample, and a negative value indicates that it is darker.

[0039] Δa* = a2* - a1*: A positive value indicates that the test sample is more red (or more reddish) than the standard sample, and a negative value indicates that it is more green.

[0040] Δb* = b2* - b1*: A positive value indicates that the test sample is more yellow (or more yellowish) than the standard sample, and a negative value indicates that it is more blue.

[0041] The formula for calculating the total color difference ΔE is: ΔE = [(ΔL*) 2 + (Δa*) 2 + (Δb*) 2 ] 1 / 2 The larger the value of ΔE, the greater the overall difference between the two colors.

[0042] In the above table, the total color difference (ΔE) of the fresh sample is the value obtained after whiteboard correction.

[0043] From Table 3 and Figure 2 we can see the changes in L*, a*, b* and ΔE after drying and rehydrating the samples.

[0044] Among them, ΔE as the total color difference, freeze-drying is the smallest (14.05), the color is relatively white; vacuum 50°C treatment, vacuum 60°C treatment is second (≈18), the difference is small; while hot air 60°C, hot air 70°C and vacuum 70°C ΔE > 26, the naked eye is obvious discoloration.

[0045] L* value (lightness), the results are freeze-drying treatment > vacuum 60°C ≈ vacuum 50°C > fresh sample > hot air treatment group, indicating that the freeze-dried lotus root slice is the "brightest white", and the lotus root slice treated by hot air at 70°C is the "darkest". Reason: High temperature heat load of hot air / vacuum 70°C promotes non-enzymatic browning (Maillard, caramelization), generating melanoidins, and reducing brightness.

[0046] a* value (red-green), the results are that the a* value of freeze-dried treatment is the lowest (1.69), with the least green tone, and the visual is more "white"; the a* value of hot air 70°C increases to 8.10, which is obviously reddish brown, also caused by non-enzymatic browning.

[0047] b* value (yellow-blue), the b* value of hot air 70℃ was the highest (18.96), yellow / brown was the heaviest; the b* value of freeze-drying was the lowest (7.37), blue / green was less, further strengthening the "white" appearance.

[0048] From the above data results, it can be seen that the drying temperature has a significant effect on the color of the dried water chestnut slices. As the drying temperature increases, the brightness decreases, and the brightness of the vacuum freeze-dried dried water chestnut is the highest. When the temperature is at 50℃ and 60℃, the rehydration browning degree of the vacuum dried dried water chestnut is smaller, and the color is lighter. a* (redness) and b* (yellowness): vacuum freeze-drying is the lowest, and 70℃ hot air drying is the highest. ΔE (total color difference): the color difference of 70℃ hot air drying is the largest, indicating that the color shifts to red and yellow, showing brown. Vacuum freeze-drying is the smallest, indicating that the color after vacuum freeze-drying is closest to the fresh sample.

[0049] Conclusion: Freeze-drying, ΔE < 15, L* high, a*, b* low, "color retention is best", almost maintains the fresh white, the disadvantage is high cost and low rehydration rate. Second, vacuum drying, among which vacuum 50 / 60℃ treatment, ΔE ≈ 18, L* slightly increased, a*, b* changed little, so the color retention is only second to freeze-drying. Hot air 50℃ treatment, ΔE ≈ 20, the color is acceptable, but the brightness has started to decline; hot air / vacuum 70℃, ΔE > 26, obvious browning occurs, and the dried and rehydrated water chestnut is easily perceived as not fresh.

[0050] 3. The rehydrated water chestnut slices obtained by rehydrating the dried water chestnut slices obtained under different drying conditions in step (3) were subjected to texture determination, and the results are shown in Table 4 and Figure 3 .

[0051] Table 4 Texture of rehydrated water chestnut under different drying conditions Note: The same column of lowercase letters indicates significant difference (P < 0.05).

[0052] From Table 4 and Figure 3 , it can be seen that there are obvious differences between hardness, brittleness and chewiness indexes of dried water chestnut slices obtained under different drying conditions after rehydration. The closer the three values to the fresh sample, the more like fresh water chestnut in taste; too high, too hard to chew; too low, too soft without crispness.

[0053] Freeze-drying, all three indexes decreased sharply (deviation ≈ 85%), the rehydrated taste was the softest, losing the unique crispness of water chestnut, which can be considered as the worst texture. In microwave pressure difference and hot air 50℃ treatment, the hardness of the two was only 57% and 59% of the fresh sample respectively, and the chewiness was only 45% and 48% respectively, although better than freeze-drying, but still significantly softer.

[0054] Vacuum 50℃, vacuum 70℃, hot air 60℃, hardness retention 65%~88%, chewiness 35%~57%, "medium hardness", acceptable taste.

[0055] Hot air 70℃, hardness higher than fresh sample 7%, chewiness decreased only 19%, indicating that high temperature caused excessive shrinkage of cell wall and excessive hardening of pectin, resulting in "dry outside and tough inside" negative taste.

[0056] Comprehensive ranking (closer to fresh sample is better), vacuum 50℃≈vacuum 70℃>hot air 60℃>vacuum 60℃>hot air 50℃≈microwave pressure difference>hot air 70℃>freeze-drying.

[0057] Compared with the fresh sample group, the hardness value of the hot air 70℃ drying treatment sample was higher than that of the fresh sample group, followed by vacuum 50℃ and vacuum 70℃. Among them, the three texture indexes of the rehydrated water chestnut slices treated by vacuum 50℃ and vacuum 70℃ were closer to the texture indexes of fresh samples compared with hot air 60℃ treatment conditions.

[0058] Conclusion: Freeze-drying treatment has the best color and the worst taste; hot air 70℃ treatment has the worst color and the hardest taste; vacuum 50℃ and vacuum 70℃ are closest to fresh samples in texture, and combined with the color difference results, vacuum drying is the best drying scheme.

[0059] 4. The rehydrated water chestnut slices obtained by rehydrating the dried water chestnut slices obtained under different drying conditions in step (3) were subjected to sensory evaluation, and the results are shown in Table 5 and Figure 4 .

[0060] Table 5 Sensory evaluation of fresh-cut water chestnut slices dried under different drying conditions after rehydration In Table 5, the same column of lowercase letters indicates significant difference (P<0.05).

[0061] As shown in Table 5 and Figure 4 , the sensory evaluation of samples treated by different drying conditions and then rehydrated was significantly lower than that of fresh samples. Among the treatment groups, the drying sensory score of 60℃ vacuum treatment was the highest, followed by 50℃ vacuum, 70℃ vacuum and freeze-drying, while the hot air drying sensory score was generally low.

[0062] From the above analysis of various indicators, the change of each treatment group in different indicators is inconsistent. Among the above indicators, the rehydration yield of various drying methods has a large difference. The rehydration yield of hot air 70℃ treatment group and freeze-drying treatment group is lower, which shows that the cell structure of fresh water chestnut slices treated by high temperature is damaged to some extent and it is difficult to recover to the degree of fresh water chestnut after rehydration. There is no significant difference in the rest of the groups. Moreover, in the color difference index, the hot air drying treatment with higher temperature (hot air 70℃) and the vacuum drying treatment with higher temperature (vacuum 70℃) have obvious browning compared with other drying treatments, and the water chestnut obtained after drying and rehydration is easy to perceive as not fresh. Therefore, the water chestnut treated by vacuum drying, lower temperature (50℃) hot air drying and microwave pressure difference drying has less difference from fresh sample after rehydration.

[0063] In the texture analysis of rehydrated water chestnut, the effect of freeze-drying treatment is the worst. The effects of microwave pressure difference and hot air 50℃ treatment are also not ideal. In contrast, the hardness / brittleness of vacuum 50℃ and vacuum 70℃ treatment groups is higher, and the chewiness of hot air 60 / 70℃ and vacuum 70℃ treatment is better. Moreover, the results of texture test are consistent with the results of sensory evaluation. In general, the advantage of vacuum drying is more obvious.

[0064] In summary, by comparing the results of different indicators of water chestnut obtained under different drying conditions, it can be concluded that vacuum drying is a better drying condition. When only vacuum heating is used to treat water chestnut, the drying yield is low and the rehydration yield is high compared with other drying methods. In the color difference test, ΔE (total color difference) and L, a, b change little, which is not much different from fresh water chestnut, close to fresh sample.

[0065] The water chestnut dried by the above vacuum drying method has a wider range of uses, which can be used as pastry and filling: mixed into steamed buns, dumplings, shumai and wonton filling to improve the crispness and water retention of the filling and reduce the greasy feeling; it can also be used as dessert and syrup: added to Hong Kong-style desserts (such as horse chestnut crisp, horse chestnut cake, syrup) or jelly / budding dessert to highlight the sweet and transparent taste; it can also be used as beverage / cold drink ingredients: small Ding as tea, milk tea, fruit tea ingredients (similar to "crispy Bobo" and "crispy fruit particles"), or made into frozen "crispy fruit particles" and added to ice cream.

[0066] The above specific embodiments are only an explanation of the present application, which is not a limitation of the present application. Those skilled in the art can make modifications to the embodiments without creative contribution after reading the specification, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. A method for drying and preserving water chestnuts to improve rehydration rate, characterized in that, Includes the following steps: (1) Clean the fresh water chestnuts, peel them, and cut them into slices of a certain thickness; (2) The sliced ​​water chestnuts are dried under different conditions until they reach a constant weight, and then dried water chestnut slices are stored in a cool and dry place for later use.

2. The method for improving the rehydration rate of dried water chestnuts according to claim 1, characterized in that, The thickness of the water chestnut slices in step (1) is 3~5mm.

3. The method for improving the rehydration rate of dried water chestnuts according to claim 1, characterized in that, The different conditions in step (2) include hot air drying, vacuum drying, microwave differential pressure drying and vacuum freeze drying.

4. The method for improving the rehydration rate of dried water chestnuts according to claim 3, characterized in that, The hot air drying process in step (2) includes hot air drying at 50°C, hot air drying at 60°C, and hot air drying at 70°C, and the vacuum drying process includes vacuum drying at 50°C, vacuum drying at 60°C, and vacuum drying at 70°C.

5. The method for improving the rehydration rate of dried water chestnuts according to claim 4, characterized in that, The drying conditions in step (2) are vacuum drying.

6. The method for improving the rehydration rate of dried water chestnuts according to claim 5, characterized in that, The vacuum drying in step (2) is carried out at 50℃-70℃.

7. A method for preparing water chestnuts obtained by the preservation method according to any one of claims 1-6, which is then dried and rehydrated, characterized in that... The process includes step (3) after step (2), in which the dried water chestnut slices obtained in the previous step are soaked in water at room temperature to obtain rehydrated water chestnut slices.

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