Production method of half-dry fruit slices

Abstract

The invention relates to the technical field of food processing, and particularly provides a production method of half-dry fruit slices. According to the method, vacuum freeze drying equipment with a cold trap is adopted, uniform dehydration of fruits is achieved by accurately controlling the vacuum degree, the temperature and a drying curve, and it is ensured that the product has the soft and glutinous texture, the natural flavor and the good rehydration property. The technological process comprises the steps of cleaning, peeling, denucleating, cutting, color protecting, vacuum drying, moisture balancing, grading, detecting, sub-packaging, storing and delivering. The dehydration process is completed through a single drying technology, material transfer is effectively reduced, and quality fluctuation caused by unstable conversion points in a traditional composite drying mode is avoided. In addition, oxygen is isolated in the vacuum drying process, browning is remarkably reduced, and the sensory quality is improved. The additive-free production process is insisted, and the moisture balance point is accurately controlled, so that the product is cured, the natural flavor and nutritional ingredients of the product are maintained, and the storage stability is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of food processing, and more particularly, to a production method of fruit semi-dried slices. Background Art

[0002] In recent years, with the continuous increase in consumers' demand for natural and healthy foods, semi-dried fruit and vegetable products have gradually become a hot topic in the market due to their retention of natural nutrients and good palatability. However, in the drying process of high-moisture fruit and vegetable products, there are still technical bottlenecks such as unstable texture control, poor coordination of process parameters, and inevitable component modification, which directly affect the taste, nutritional value, and industrial feasibility of the products.

[0003] CN111920039A discloses a vacuum drying process for instant Pleurotus eryngii chips. Although it can shorten the drying cycle, when switching the drying method at the critical point where the moisture content of the material reaches 48%, due to the instability of the phase change process, the cell wall rupture rate is as high as 32% to 45%, which is more obvious in the case of Pleurotus eryngii. In addition, this moisture range is in the sensitive area of the glass transition temperature of saccharide substances, and the Tg value drops to -15 to -20 degrees Celsius. At this time, the thermal stress generated by hot air drying will cause the porosity of the material to drop suddenly by 56%, and finally the rehydration rate drops from 3.2 times to 1.8 times, significantly reducing the product quality.

[0004] CN115553442A discloses a processing method for sub-frozen vacuum-dried strawberry products, which realizes section protection through sugar powder coating. Although the drying rate can be increased by 18%, the forced introduction of exogenous sugar increases the total sugar content of the product passively by 23% to 28%, severely restricting the development of products suitable for diabetics. In addition, the barrier effect of sugar crystals inhibits the redistribution of pectin, causing the texture of the final product to deviate from the soft and glutinous characteristics of natural fruits, and the hardness value exceeds 1800 g·mm, affecting the taste experience of consumers.

[0005] CN108464343A proposes a combined drying method for apple semi-dried slices, which uses the synergistic effect of gas jet impingement and vacuum microwave to improve the shrinkage problem. However, the stage conversion of this process depends on empirical time parameters, with an error range of plus or minus 15 minutes, resulting in a moisture gradient difference between batches as high as 4.7% to 6.3%, which is particularly obvious in the case of apple slices. A more prominent problem is that the coupling effect of microwave field strength and gas flow rate is likely to cause local overheating, with a hot spot temperature difference exceeding 8 degrees Celsius, resulting in an increase in the production amount of melanoidins by 35 mg / kg, directly affecting the color stability of the product, and the ΔE value fluctuates by more than 3.5, reducing the market acceptance.

[0006] It can be seen that the industrial production of current semi-dried fruit and vegetable products generally faces the contradiction among texture stability, processing efficiency, and ingredient purity. The drying process in the high moisture content range is difficult to accurately control, and the material is prone to uncontrollable collapse during drying, resulting in the collapse of the organizational structure and affecting the final taste. In addition, the existing process has a high dependence on additives, which causes the product ingredients to be passively modified during processing, not meeting the requirements of the healthy food market for additive-free and natural products.

[0007] At the same time, the parameter matching of the combined drying process is poor, resulting in large fluctuations in quality between production batches, restricting the feasibility of large-scale promotion. These key problems have severely limited the industrialization process of high-value-added semi-dried fruit products, and there is an urgent need for a drying technology that can balance texture stability, avoid additional additives, and have good industrial adaptability. Summary of the Invention

[0008] A production method of semi-dried fruit slices includes a vacuum drying step, and the vacuum drying step is to use a vacuum freeze-drying device with a cold trap to achieve fruit drying by controlling the vacuum degree, temperature, and drying curve.

[0009] Preferably, the drying speed is controlled to be 1 - 1.1 times the moisture escape speed.

[0010] Preferably, the vacuum drying step includes the following steps:

[0011] S1 Equipment preparation: Use a vacuum freeze-drying device equipped with a cold trap and a drying chamber;

[0012] S2 Material placement: Evenly spread the processed fruit raw materials on the trays in the drying chamber, and the initial temperature of the fruit raw materials is normal temperature;

[0013] S3 Vacuum drying:

[0014] S31 Close the door of the drying chamber and evacuate to 100 - 150 Pa;

[0015] S32 Start heating, set the drying temperature to 55 - 65 °C and dry for 2 - 6 hours, then reduce it to 40 - 50 °C and dry for another 2 - 6 hours until the terminal moisture content of the material reaches 12 - 18 wt%; during the drying process, capture the evaporated moisture through the cold trap to keep the vacuum degree stable.

[0016] Preferably, the fruit is at least one of apple, strawberry, mango, kiwifruit, banana, cherry, blueberry, pineapple, peach, plum, fig, persimmon, loquat, apricot, prune, coconut meat, passion fruit, grape, mulberry, and longan.

[0017] Preferably, the production method of the fruit semi-dried slices includes: washing / peeling / pitting → drying → moisture balancing.

[0018] Preferably, the production method of the fruit semi-dried slices includes: washing / peeling / pitting → slicing → color protection → drying → moisture balancing.

[0019] Preferably, the moisture balancing step is: placing the dried material above in a sealed container and standing at room temperature for 24 - 72 h. The moisture in the center of the material will be higher than that on the surface of the material. At this time, the moisture will naturally transfer from the high point to the low point, and the moisture balance can be achieved after standing at room temperature.

[0020] The present invention adopts a vacuum drying chamber with a cold trap, which effectively reduces the direct discharge of moisture through the vacuum pump, improves the vacuum degree stability of high-moisture fruits during the drying process, and thus optimizes the drying environment. By precisely controlling the balance between the vaporization speed on the surface of the material and the moisture escape speed inside, the collapse of high-moisture fruits after drying can be controlled, enabling the final product to have an ideal soft and glutinous texture. At the same time, the vacuum drying process isolates oxygen, and compared with the ordinary oxygen-containing drying method, it effectively reduces the browning rate of the product and significantly improves the sensory quality. In addition, the present invention adopts a method of sealing and balancing moisture, which not only simplifies the operation process but also ensures the stability of the product quality, providing a reliable guarantee for the industrial production of high-value-added fruit semi-dried products. Description of the Drawings

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required to be used in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0022] Figure 1 It is the process flow chart of the production method of the fruit semi-dried slices in Example 1;

[0023] Figure 2 It is the physical picture of the product finally prepared by using the production method of the fruit semi-dried slices of the present invention in Example 1. Detailed Embodiments

[0024] 1. Process Flow / Method Steps

[0025] Apple raw material → washing / peeling / pitting → slicing → color protection → drying → moisture balancing → grading → metal detection / X-ray detection → packaging → storage and shipment

[0026] 2. Condition Parameters

[0027] 2.1 Raw Material: Fuji Apple

[0028] 2.2 Cleaning, peeling, and pitting

[0029] 2.3 Slicing: 10 - 14 mm thick, sliced randomly

[0030] 2.4 Color protection steps:

[0031] Hot steam enzyme inactivation method: Lay the apples flat on a nylon tray, place them in an industrial steamer at 85 - 95 °C, turn on the steam, quickly raise the temperature of the apple material to 85 - 95 °C, and maintain for 1 - 5 minutes to inactivate the polyphenol oxidase in the apples.

[0032] Or, chemical enzyme inactivation method: Place the sliced apples in a mixed aqueous solution of ascorbic acid and citric acid and let them stand at room temperature to inactivate the polyphenol oxidase in the apples.

[0033] 2.5 Drying

[0034] Ordinary vacuum drying is mainly composed of a drying chamber and a vacuum pump. Since the moisture in the material becomes water vapor and is discharged through the vacuum pump during drying, when encountering products with high moisture content, more water vapor will be discharged through the vacuum pump. At this time, the sealing system of the vacuum pump is under pressure, and the vacuum degree will be lower than before, which is not conducive to the drying quality of the product; vacuum freeze-drying requires freezing the material temperature below the eutectic point temperature, and then transferring the material to the vacuum drying chamber. After sublimation and desorption, the product maintains its original shape and forms a honeycomb-like tissue structure.

[0035] In the drying stage of the present invention, the advantages of vacuum freeze-drying are combined, and the disadvantages of vacuum drying are avoided, so as to achieve the process of producing high-moisture fruit products with a soft and glutinous tissue structure. The specific method is as follows:

[0036] For the equipment using vacuum freeze-drying, a cold trap must be configured to capture the water vapor vaporized during the drying process.

[0037] Place the processed material on the drying tray, lay the apples flat on the aluminum tray in the drying chamber. Different from freeze-drying, it does not go through the quick-freezing process and directly enters the drying chamber. At this time, the temperature of the material is at room temperature.

[0038] Dry at 55 - 65 °C for 2 - 6 hours, then reduce the temperature to 40 - 50 °C and dry for another 2 - 6 hours until the terminal moisture content of the material reaches 12 - 18 wt%; during the drying process, capture the evaporated water through the cold trap to keep the vacuum degree stable.

[0039] After closing the hatch, a vacuum pumping process is carried out. After the vacuum degree reaches 100 - 150 Pa, heating can be started. The setting criterion for the drying curve is that the drying speed = 1 - 1.1 times the moisture escape speed. Taking the drying of apples with a sliced thickness of 10 - 14 mm as an example, the drying temperature is set at 55 - 65 °C for 2 - 6 hours and then reduced to 40 - 50 °C for another 2 - 6 hours until the terminal moisture content of the material reaches 12 - 18 wt%. The purpose of setting the drying curve in this way is to reduce the expansion of the pores in the material caused by too fast drying speed, so as to maintain the original pore structure to the greatest extent.

[0040] The present invention is a vacuum drying process equipped with a cold trap. The evaporated moisture is collected by the cold trap in a timely manner, so the vacuum system is relatively stable. The vacuum degree during the whole drying process is relatively stable, and the speed difference of moisture from the inside to the outside of the material is further reduced, thereby reducing the moisture difference between the inside and outside of the material.

[0041] During the drying process, the material will slowly collapse, forming a collapse ratio between freeze-drying and hot air drying. The sugar in the apple will adhere more evenly to the moisture escape channels, forming a soft texture characteristic.

[0042] In the drying process of the present invention, the situation of uneven moisture content inside and outside will also occur, so it is necessary to further balance the moisture content.

[0043] 2.6 Moisture balance

[0044] Taking the above-mentioned dried material as an example of apples, take it out of the drying bin and place it in a transparent or opaque food-grade PE bag and seal it. Let it stand at room temperature for 24 - 72 h. The moisture in the center of the material will be higher than that on the surface of the material. At this time, the moisture will naturally transfer from the high point to the low point, and the purpose of moisture balance can be achieved after 24 - 72 h.

[0045] 2.7 Grading, metal detection, X-ray detection, packaging, storage and shipment. This step is a conventional step in this industry and will not be described in detail.

[0046] The key of the present invention lies in the selection of drying equipment and the optimization of drying process. A vacuum freeze-drying equipment is adopted, and its cold trap is used to capture the water vaporized during the drying process, so as to stabilize the vacuum degree and improve the controllability of the drying environment. Different from the traditional freeze-drying process, the present invention does not require pre-freezing treatment of fruits. Instead, the pretreated fruits are directly sent into the drying chamber at room temperature, and the water is removed under vacuum environment by using the principle of vaporization drying, and the final moisture content is controlled within a range. During the drying process, through precise regulation, the water evaporation rate is made equal to or slightly higher than the rate of internal water migrating to the surface, so as to avoid surface hardening or uneven internal residual moisture, and ensure the stability of the product texture. After the drying is completed, further moisture balance treatment is carried out to make the moisture content of the product tend to be uniform and improve the quality stability of the final product.

[0047] Example 1

[0048] 1. Raw material pretreatment

[0049] Cleaning: A circulating water spray cleaning system is adopted, the water temperature is controlled at 20°C, and the cleaning time is 3 minutes to ensure the removal of surface sediment and pesticide residues.

[0050] Peeling and pitting: Use a mechanical rotary peeling machine.

[0051] Slicing: A double-axis slicing machine (rotation speed: 30 r / min) is adopted, and the slicing thickness is strictly controlled at 12 mm. After slicing, it is immediately transferred to the color protection process to reduce oxidative browning.

[0052] 2. Color protection step

[0053] Hot steam enzyme inactivation method:

[0054] Equipment: Industrial steam sterilization cabinet, steam pressure 0.15 MPa.

[0055] Operation: Spread the apple slices on a food-grade nylon mesh tray, quickly introduce steam to raise the center temperature of the material to 90°C within 90 seconds, maintain for 3 minutes and then immediately take it out and cool to room temperature.

[0056] 3. Key parameters of vacuum drying

[0057] Equipment: Vacuum freeze-dryer.

[0058] Drying curve:

[0059] The first stage: Dry at 60°C for 4 hours, and maintain the vacuum degree at 120 Pa.

[0060] The second stage: Dry at 50°C for 4 hours, and maintain the vacuum degree at 150 Pa.

[0061] Drying speed control: The infrared moisture analyzer (accuracy ±0.1%) is used to monitor the moisture evaporation rate in real time, and the heating power is dynamically adjusted to ensure that the drying speed is stable at 1.05 times the moisture escape speed.

[0062] Function of the cold trap:

[0063] Defrost once per hour (hot air purge for 30 seconds) to ensure that the trapping efficiency ≥ 99% and the water vapor content at the inlet of the vacuum pump ≤ 0.02 g / m 3 .

[0064] 4. Equilibrium moisture

[0065] Sealed container: Use a food-grade PE material sealed bag (thickness 0.1 mm, oxygen permeability 5 cm 3 / m 2 ·24h·atm).

[0066] Environmental conditions: Equilibrium temperature 25 ± 1°C, relative humidity 60 ± 5%.

[0067] Initial moisture distribution after drying: Surface moisture 13.5%, central moisture 16.2%.

[0068] Moisture uniformity after equilibrium: The moisture difference of the whole batch of samples ≤ 0.5% (CV value < 1%).

[0069] 5. Quality inspection data

[0070] Test items Example 1 Traditional hot air drying Hardness (g·mm-1) 850±50 1500±80 Rehydration ratio (times) 2.8±0.2 1.5±0.1 Porosity (%) 32±2 18±3 Browning index (ΔE) 2.1±0.3 5.8±0.5

[0071] Example 2:

[0072] The difference from Example 1 is that the 2.4 color protection step is: After placing the sliced apples in an aqueous solution of 2 wt% ascorbic acid and 0.5 wt% citric acid and standing at room temperature for 30 min, wash them once with clean water.

[0073] The present invention uses a vacuum freeze-drying equipment with a cold trap to complete the dehydration process with a single drying process, effectively reducing material transfer and avoiding unstable factors caused by the conversion of drying methods. At the same time, the present invention adheres to a production process without additives, and realizes the solidification of the product by precisely controlling the moisture balance point, ensuring the quality stability and the retention of natural flavor.

[0074] Obviously, the above examples are only for clearly illustrating the examples and are not intended to limit the implementation methods. For those of ordinary skill in the art, other different forms of changes or variations can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. And the obvious changes or variations derived therefrom are still within the protection scope of the present invention.

Claims

1. A production method of fruit semi-dried slices, including a vacuum drying step, characterized in that, The vacuum drying step is as follows: Using a vacuum freeze-drying equipment with a cold trap, the fruit drying is achieved by controlling the vacuum degree, temperature and drying curve.

2. A production method of semi-dried fruit slices, characterized in that, Control the drying speed to be 1 - 1.1 times the water evaporation speed.

3. The production method according to claim 1, characterized in that, The vacuum drying step includes: Equipment preparation: Use a vacuum freeze-drying equipment equipped with a cold trap and a drying chamber; Material placement: Evenly lay the processed fruit raw materials on the trays in the drying chamber, and the initial temperature is normal temperature; Vacuum drying: Close the door of the drying chamber, evacuate the vacuum to 100 - 150 Pa; Start heating, set the drying temperature to 55 - 65 °C and dry for 2 - 6 hours, then reduce it to 40 - 50 °C and dry for another 2 - 6 hours until the terminal moisture content of the material reaches 12 - 18 wt%.

4. The production method according to any one of claims 1 to 3, characterized in that, The fruit is at least one of apple, strawberry, mango, kiwifruit, banana, cherry, blueberry, pineapple, peach, plum, fig, persimmon, loquat, apricot, prune, coconut meat, passion fruit, grape, mulberry and longan.

5. The production method according to any one of claims 1-3, characterized in that, The production method of the fruit semi-dried slices includes: washing / peeling / pitting → drying → moisture balancing.

6. The production method according to any one of claims 1 to 3, characterized in that, The production method of the fruit semi-dried slices includes: washing / peeling / pitting → slicing → color protection → drying → moisture balancing.

7. The production method according to claim 6, characterized in that, The color protection step is the hot steam enzyme inactivation method.

8. The production method according to claim 6, characterized in that, The color protection step is: Place the sliced fruits in a mixed aqueous solution of ascorbic acid and citric acid and let it stand at room temperature.

9. The production method according to claim 5, characterized in that, The moisture balancing step is: Place the dried material in a sealed container and let it stand at normal temperature for 24 - 72 h.

10. The production method according to claim 6, characterized in that, The moisture balancing step is: Place the dried material in a sealed container and let it stand at normal temperature for 24 - 72 h.

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