CN118141067A - Processing method for improving hot air drying quality of jujube slices - Google Patents
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- 238000001035 drying Methods 0.000 claims abstract description 81
- 238000010438 heat treatment Methods 0.000 claims abstract description 30
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Abstract
The invention relates to the technical field of food processing, in particular to a processing method for improving hot air drying quality of jujube slices, which aims at the defects of low efficiency, poor quality and color and luster and the like of the prior art that the jujube slices are dried by natural airing or single hot air, and the invention provides the following scheme that fresh jujube is processed according to the following steps: the method comprises the steps of (1) selecting fresh jujube, cleaning, removing cores, slicing, (2) adopting high-temperature and high-speed hot air for drying in the early stage of drying, (3) reducing the hot air temperature and wind speed in the middle stage of drying, simultaneously applying continuous radio frequency heat treatment to assist hot air drying, (4) adopting intermittent radio frequency treatment in the later stage of drying, further reducing the hot air temperature and wind speed until the drying is finished, and (5) cooling and packaging jujube slices. Compared with the prior art, the invention has the characteristics of high processing efficiency, good quality of the processed jujube slice hot air drying product, good color maintenance, good volume and structure maintenance and the like.
Description
Technical Field
The invention relates to the technical field of food processing, in particular to a processing method for improving hot air drying quality of jujube slices.
Background
The radio frequency is used as a high-frequency dielectric heating technology, can penetrate into the material to cause oscillation migration of polar molecules and charged ions in the material, rub each other and convert electromagnetic energy into heat energy, so that the aim of drying is fulfilled. The radio frequency heating is different from the traditional hot air drying, because the radio frequency heating generates heat in the material, moisture gradually migrates to the surface of the material from the inside of the material, and then evaporates from the surface, thereby being beneficial to improving the drying rate and the drying uniformity of food.
At present, the jujube slices are mainly dried by natural airing, hot air drying, infrared assisted hot air drying, microwave assisted hot air drying and the like. Natural airing and single hot air drying methods are difficult to further improve the drying rate and quality of jujube slices and even other fruit and vegetable materials; the infrared drying has higher requirements on materials, mainly acts on the surfaces of the materials and the near surfaces, and has weaker penetrating power; compared with microwaves (300 MHz-30000 MHz), the radio frequency (3 kHz-300 MHz) has the advantages of low frequency, long wavelength and strong penetrating power.
Chinese patent CN113142518a discloses a processing method of crisp fruit and vegetable slices and a three-stage belt type infrared dryer suitable for the method, the method adopts three-stage drying, no additional cooling sterilization links are required, the processing period is shortened, but infrared drying is adopted, and the penetrating power is weak; chinese patent CN112450397a discloses a method for producing gray jujube slices by combining instantaneous ejection steam explosion and vacuum microwave, which adopts instantaneous ejection steam explosion pretreatment and microwave vacuum drying to jointly produce gray jujube slices, which is beneficial to release of aroma components of gray jujube slices, but the method has no universality and high cost; chinese patent CN110463942a discloses a method and apparatus for processing red jujube slices, which realizes batch processing of red jujube, but adopts traditional hot air drying in heating mode, and the processing time is longer.
The hot air drying can effectively remove the surface moisture of the jujube slices, and the radio frequency heating rapidly diffuses the moisture in the jujube slices to the surface due to the unique pressure gradient, so that the influence of edge effect in the material drying process can be reduced when the radio frequency technology is applied to the hot air drying process of the jujube slices, the problems of low hot air drying efficiency, poor drying quality and the like can be improved, the advantages of the two can be fully brought into play, the simultaneous heating of the inside and the outside of the jujube slices is realized, the drying rate of the jujube slices is improved, the shrinkage deformation of the internal structure is slowed down, and the texture and the shrinkage characteristic of the jujube slices are further improved.
Disclosure of Invention
Aiming at the defects and shortcomings of the existing hot air drying processing method of the jujube slices, the invention aims to provide the processing method for improving the hot air drying quality of the jujube slices, which has high processing efficiency, so that the obtained hot air drying product of the jujube slices has good quality, better color and shrinkage rate are reserved, and the product quality of the dried jujube slices can be effectively improved.
In order to achieve the aim and other advantages of the present invention, a processing method for improving hot air drying quality of jujube slices is provided, comprising:
(1) Selecting fresh jujube, cleaning, removing core and slicing: selecting fresh jujube with uniform size and undamaged epidermis, cleaning, wiping and stoning, and cutting into jujube slices with similar thickness of 5-10mm, wherein the moisture content of the wet base of the fresh jujube slices is 60% -75%;
(2) The drying early stage adopts higher temperature and high-speed hot air drying: uniformly spreading the processed jujube slices on a material tray in a single layer, placing the material tray into a drying cavity, setting the air temperature of a hot air convection heating device to be 70-80 ℃, the air speed to be 3-5m/s and the drying time to be 0.5-1.5h. The fresh jujube slices in the earlier stage of drying have higher moisture content and mainly remove most of free water, and the stage adopts higher-temperature and high-speed hot air drying to quickly remove the free water;
(3) The hot air temperature and the wind speed are reduced in the middle drying stage, and continuous radio frequency heat treatment is applied to assist hot air drying: applying continuous radio frequency auxiliary hot air treatment, and simultaneously reducing the hot air temperature to 60-70 ℃ and the air speed to 1.5-3m/s, and the drying time to 0.5-2h. The continuous radio frequency heat treatment is applied at the stage, so that water molecules in the jujube slices vibrate at high frequency under a radio frequency field, the temperature in the jujube slices rises rapidly, a micro pore structure is maintained and formed, and the phenomenon of surface hardening and crusting is avoided;
(4) Intermittent radio frequency treatment is adopted in the later drying stage, so that the air temperature and the air speed of hot air are further reduced until the drying is finished: setting the interval time of the radio frequency heat treatment to be 5-20min and the application time to be 1-5min each time, further reducing the hot air temperature to be 50-60 ℃ and the wind speed to be 0.5-1m/s, and stopping drying when the moisture content of the wet base of the jujube slices is lower than 10%. Intermittent radio frequency is adopted at the stage, the wind temperature and the wind speed are reduced, the energy consumption is reduced while the micro pore structure in the jujube slices is maintained, and the bound water in the jujube slices is removed until the drying is finished;
(5) Cooling and packaging jujube slices: and cooling and sterilizing the dried jujube slices, and then filling nitrogen, packaging and storing.
Preferably, according to the processing method for improving the hot air drying quality of the jujube slices, the preferable frequency band applied by the radio frequency heat treatment under the hot air drying condition is 27.12MHz, and the distance between the upper polar plate and the lower polar plate is limited to 100-500mm according to the height of the material layer.
Preferably, according to the processing method for improving the hot air drying quality of the jujube slices, the radio frequency is applied to have the characteristic of high penetrability, the materials can be dried in multiple layers in the drying process, the material tray is designed to be of a net-shaped ventilation structure, a hot air passage of 1-3cm is reserved between layers, and the height of the material layer is adjustable within a distance of 10-50 cm.
Preferably, according to the processing method for improving the hot air drying quality of the jujube slices, the hot air flow direction in the drying process is parallel to the material layer and perpendicular to the radio frequency field.
The invention at least comprises the following beneficial effects:
Compared with single hot air drying, the method provided by the invention has the advantages that the application of radio frequency heat treatment is beneficial to migration and diffusion of moisture in the jujube slices in the drying process, meanwhile, the variable process parameter drying is adopted, the phenomenon of hardening and crusting on the surfaces of the jujube slices can be effectively avoided by adjusting the hot air temperature, the wind speed and the radio frequency application mode according to different stages of drying, the microstructure morphology of the jujube slices is well maintained, the microstructure of the microstructure is regularly arranged, the dried jujube slices have higher elasticity and cohesiveness, the volume and structure of the jujube slice samples are well maintained, the drying efficiency is remarkably improved, the color degree is maintained, and the application prospect is good.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. Drawings
FIG. 1 is a flow chart of the method of the present invention.
FIG. 2 is a schematic drying diagram of the present invention.
FIG. 3 is a scanning electron microscope image of jujube slices dried with hot air (comparative example 1).
Fig. 4 is a scanning electron microscope image of jujube slices dried by using radio frequency assisted hot air (example 1).
Detailed description of the preferred embodiments
The present invention is described in further detail below with reference to examples to enable those skilled in the art to practice the invention by reference to the specification.
The experimental methods described in the following embodiments are conventional methods unless otherwise indicated, and the reagents and materials are commercially available.
Example 1]
A processing method for improving hot air drying quality of winter jujube slices is carried out according to the following steps:
(1) Selecting winter jujubes, cleaning, removing cores and slicing: selecting winter jujube with uniform size (with the longitudinal diameter of 29+/-2 mm and the transverse diameter of 25+/-2 mm), red and green jujube peels alternately without damage, cleaning, wiping and stoning, and cutting into jujube slices with the thickness of 8-10mm and the like, wherein the moisture content of the wet base of the fresh jujube slices is 65% -75%;
(2) The drying early stage adopts higher temperature and high-speed hot air drying: uniformly spreading the treated jujube slices on a material tray in a single layer, placing the material tray into a drying cavity, setting the air temperature of a hot air convection heating device to be 75 ℃, the air speed to be 4m/s and the drying time to be 1h;
(3) The hot air temperature and the wind speed are reduced in the middle drying stage, and continuous radio frequency heat treatment is applied to assist hot air drying: setting the plate spacing of the upper plate and the lower plate to be 110mm, reducing the hot air temperature to be 60 ℃, the air speed to be 2m/s, and the drying time to be 1.5h;
(4) Intermittent radio frequency treatment is adopted in the later drying stage, so that the air temperature and the air speed of hot air are further reduced until the drying is finished: setting the interval time of the radio frequency heat treatment to be 10min and the time of each application to be 3min, further reducing the hot air temperature to be 50 ℃ and the air speed to be 1m/s, and stopping drying when the moisture content of the wet base of the jujube slices is lower than 10%;
(5) Cooling and packaging jujube slices: and cooling and sterilizing the dried jujube slices, and then filling nitrogen, packaging and storing.
Example 2]
A processing method for improving hot air drying quality of jun jujube slices comprises the following steps:
(1) Selecting jun jujubes, cleaning, removing cores and slicing: selecting winter jujube with uniform size (45+/-2 mm in longitudinal diameter and 33+/-2 mm in transverse diameter) and red and green jujube peel without damage, cleaning, wiping, removing cores, cutting into jujube slices with similar thickness of 5-7mm, wherein the moisture content of the wet base of the fresh jujube slices is 60% -70%;
(2) The drying early stage adopts higher temperature and high-speed hot air drying: uniformly spreading the treated jujube slices on a material tray in a single layer, placing the material tray into a drying cavity, setting the air temperature of a hot air convection heating device to be 70 ℃, the air speed to be 3m/s and the drying time to be 1h;
(3) The hot air temperature and the wind speed are reduced in the middle drying stage, and continuous radio frequency heat treatment is applied to assist hot air drying: setting the plate spacing of the upper plate and the lower plate to be 120mm, reducing the hot air temperature to 55 ℃, the wind speed to 2m/s and the drying time to 1.5h;
(4) Intermittent radio frequency treatment is adopted in the later drying stage, so that the air temperature and the air speed of hot air are further reduced until the drying is finished: setting the interval time of the radio frequency heat treatment to be 10min and the time of each application to be 3min, further reducing the hot air temperature to be 50 ℃ and the air speed to be 1m/s, and stopping drying when the moisture content of the wet base of the jujube slices is lower than 10%;
(5) Cooling and packaging jujube slices: and cooling and sterilizing the dried jujube slices, and then filling nitrogen, packaging and storing.
Example 3 ]
A processing method for improving hot air drying quality of winter jujube slices comprises the following steps:
(1) Selecting fresh jujube, cleaning, removing core and slicing: selecting winter jujube with uniform size (longitudinal diameter (29+ -2) mm, transverse diameter (25+ -2) mm), red and green jujube peel, cleaning, wiping, removing core, and cutting into jujube slices with similar thickness of 8-10 mm;
(2) The drying early stage adopts higher temperature and high-speed hot air drying: uniformly spreading the processed jujube slices on 5 layers of trays, reserving 1-3cm hot air passages between layers, setting the air temperature of a hot air convection heating device to 80 ℃, the air speed to 5m/s and the drying time to 1.5h;
(3) The hot air temperature and the wind speed are reduced in the middle drying stage, and continuous radio frequency heat treatment is applied to assist hot air drying: setting the plate spacing of the upper plate and the lower plate to be 500mm, reducing the hot air temperature to be 70 ℃, the wind speed to be 3m/s and the drying time to be 2h;
(4) Intermittent radio frequency treatment is adopted in the later drying stage, so that the air temperature and the air speed of hot air are further reduced until the drying is finished: setting the interval time of the radio frequency heat treatment to be 20min and the time of each application to be 5min, further reducing the hot air temperature to be 60 ℃ and the air speed to be 1m/s, and stopping drying when the moisture content of the wet base of the jujube slices is lower than 10%;
(5) Cooling and packaging jujube slices: and cooling and sterilizing the dried jujube slices, and then filling nitrogen, packaging and storing.
Comparative example 1]
A method for drying winter jujube slices, which is substantially the same as in example 1, except that no radio frequency is applied in steps (3) (4).
Comparative example 2]
A process for drying a Jun jujube slice is substantially the same as in example 2, except that no RF is applied in steps (3) (4).
Comparative example 3 ]
A method for drying winter jujube slices is basically the same as that in example 1, except that no radio frequency is applied in the drying process and the hot air temperature and wind speed are constant.
Detection and analysis:
The texture, color and shrinkage characteristics of the jujube slices prepared in examples 1 to 3 and comparative examples 1 to 3 were measured, and the results are shown in tables 1, 2 and 3, specifically:
(1) The texture of the jujube slices is subjected to multi-surface analysis by using a texture analyzer, and 3 texture characteristic indexes of the jujube slice sample, namely brittleness, hardness and chewiness, can be obtained through further analysis of the obtained TPA curve. The test parameters were set as follows: the P/50 probe is used, the speed before measurement is 1mm/s, the measuring speed is 0.5mm/s, the upward speed after measurement is 1mm/s, the compression deformation of the jujube slices is 50%, the two compression pause time is 5s, each sample is measured 3 times, and the average value is obtained.
(2) Using a color difference meter, the values of L * (lightness), a * (red-green index) and b * (Huang Lanzhi) were measured, and the average value was taken as the test result (L * value indicates also light and dark, positive value indicates bright and negative value indicates dark; a * value indicates red-green, positive value indicates red, negative value indicates green, b * value indicates yellow-blue, positive value indicates yellow and negative value indicates blue), and the color difference value calculation formula was:
(3) And acquiring a two-dimensional image of the jujube slices by adopting a camera with a fixed focal length, and acquiring shrinkage parameters of the jujube slice samples.
The area shrinkage of the jujube slices is calculated as follows:
the area of the sample from the drying time to the time t is the initial area of the sample.
The calculation formula of the perimeter shrinkage is as follows:
Where the circumference of the sample dried to time t is the initial circumference of the sample.
Roundness (Roundness, R) refers to the degree to which the cross section of the jujube slices is close to a circle, the roundness ranges from 0 to 1, the bigger the numerical value is, the more round the jujube slices is, and the roundness calculation formula is as follows:
TABLE 1 chroma values of jujube slices under different embodiments
| Group of | L* | a* | b* | ∆E |
| Example 1 | 75.25±1.21 | -8.74±0.11 | 21.79±0.47 | 9.19±0.34 |
| Example 2 | 75.46±1.02 | -8.65±0.16 | 22.23±0.63 | 9.21±0.31 |
| Example 3 | 75.48±1.09 | -7.32±0.032 | 24.24±0.66 | 9.59±1.34 |
| Comparative example 1 | 73.93±2.34 | -5.72±0.14 | 25.62±1.11 | 11.58±1.50 |
| Comparative example 2 | 72.34±1.45 | -5.67±0.20 | 25.45±0.84 | 11.67±1.15 |
| Comparative example 3 | 72.45±0.96 | -6.65±0.297 | 25.28±0.24 | 11.79±0.98 |
As can be seen from Table 1, examples 1 to 3 were dried by using a radio frequency assisted hot air, and at the end of drying, examples 1 to 3 had a better color than comparative examples 1 to 3, and the obtained jujube pieces had a maximum L * (brightness value) of 75.48, a * (red-green value) of-8.74, b * (Huang Lanzhi) of 21.79, and E (color difference) of 9.19. The drying time of the whole of comparative examples 1 to 3 was long, and the reducing sugar reacted with free amino groups of amino acid residues on free amino acids or protein chains, i.e., maillard reaction, to cause browning of jujube pieces, and the pigment was gradually degraded with drying temperature, resulting in a decrease in L * value, an increase in a *、b* and an increase in E value. By comparing the different drying modes of the winter jujubes in the example 1 and the comparative example 1 with the different drying modes of the junjujubes in the example 2 and the comparative example 2, different jujube types are applicable to the processing method.
TABLE 2 texture Property index of jujube slices under different embodiments
| Group of | Brittleness (N) | Hardness (N) | Chewing nature (N) |
| Example 1 | 79±0.95 | 124±0.58 | 28±0.27 |
| Example 2 | 78±0.26 | 124±0.19 | 28±0.81 |
| Example 3 | 83±0.68 | 135±1.10 | 29±0.13 |
| Comparative example 1 | 96±0.79 | 145±0.21 | 30±0.42 |
| Comparative example 2 | 98±1.23 | 158±0.69 | 31±0.39 |
| Comparative example 3 | 117.6±0.61 | 154±0.62 | 32±0.82 |
As can be seen from Table 2, the date slices processed by the methods of examples 1 to 3 have different degrees of brittleness, hardness and chewiness reduced compared with the date slices processed by the methods of comparative examples 1 to 3, the application of the radio frequency heat treatment is favorable for the migration and diffusion of moisture in the date slices in the drying process, the microstructure morphology of the date slices is well maintained, and the loose and porous internal structure is the main reason that the hot air dried date slices are lower in hardness and better in crunchiness after being dried by the methods of examples 1 to 3. The lower hardness and friability values of examples 1-3 indicate that the date pieces treated by this method are easier to chew. In example 3, compared with comparative example 1, brittleness, hardness and chewiness are respectively reduced by 13.5%, 6.9% and 6.5%, which shows that under the condition of radio frequency assisted hot air drying, the quality of the hot air dried structure of the jujube slices can be effectively improved by adopting the multi-layer drying.
TABLE 3 shrinkage parameters of jujube slices under different embodiments
| Group of | Area shrinkage rate | Circumference shrinkage rate | Roundness of |
| Example 1 | 0.54±0.01b | 0.82±0.01b | 0.81±0.01b |
| Example 2 | 0.50±0.01c | 0.80±0.01b | 0.74±0.01b |
| Example 3 | 0.53±0.01b | 0.81±0.02b | 0.79±0.02b |
| Comparative example 1 | 0.47±0.014d | 0.77±0.012c | 0.75±0.01c |
| Comparative example 2 | 0.45±0.01b | 0.75±0.01b | 0.72±0.02b |
| Comparative example 3 | 0.43±0.01e | 0.78±0.018bc | 0.69±0.01d |
As can be seen from Table 3, the area shrinkage of the jujube sheets dried by the methods of examples 1 to 3 was increased by 9.3 to 16.3%, the circumference shrinkage was increased by 5.1 to 14.5%, and the roundness was increased by 2.6 to 6.3%, as compared with the jujube sheets dried by the methods of comparative examples 1 to 3. The area shrinkage of the jujube slices dried by the method of examples 1-3 is significantly greater than that of the jujube slices dried by the method of comparative examples 1-3 (p < 0.05), because the radio frequency heating can reduce the surface shrinkage (expansion effect due to rapid outward exudation of moisture) and produce a loose porous structure (expansion effect), and the radio frequency assisted hot air drives away the combination of internal and external heating, so that the volume and structure of the jujube slice sample can be better maintained.
The technical scheme is not a simple superposition of two drying modes, and the comparison of the data of the embodiment 1 and the comparative examples 1 and 3 shows that the product obtained by adopting constant-temperature drying has poorer color, texture characteristics and shrinkage, which indicates that the product is dried by adopting variable process parameters, and the drying quality of the jujube slices is improved by adjusting the hot air temperature, the wind speed and the radio frequency application mode according to different stages of drying.
Although embodiments of the present invention have been disclosed above, it is not limited to the details and embodiments shown, it is well suited to various fields of use for which the invention is suited, and further modifications may be readily made by one skilled in the art, and the invention is therefore not to be limited to the particular details and examples shown and described herein, without departing from the general concepts defined by the claims and the equivalents thereof.
Claims (4)
1. A processing method for improving hot air drying quality of jujube slices is characterized by comprising the following steps:
(1) Selecting fresh jujube, cleaning, removing core and slicing: selecting fresh jujube with uniform size and undamaged epidermis, cleaning, wiping and stoning, and cutting into jujube slices with similar thickness of 5-10mm, wherein the moisture content of the wet base of the fresh jujube slices is 60% -75%;
(2) The drying early stage adopts higher temperature and high-speed hot air drying: uniformly spreading the processed jujube slices on a material tray in a single layer, placing the material tray into a drying cavity, setting the air temperature of a hot air convection heating device to be 70-80 ℃, the air speed to be 3-5m/s and the drying time to be 0.5-1.5h. The fresh jujube slices in the earlier stage of drying have higher moisture content and mainly remove most of free water, and the stage adopts higher-temperature and high-speed hot air drying to quickly remove the free water;
(3) The hot air temperature and the wind speed are reduced in the middle drying stage, and continuous radio frequency heat treatment is applied to assist hot air drying: applying continuous radio frequency auxiliary hot air treatment, and simultaneously reducing the hot air temperature to 60-70 ℃ and the air speed to 1.5-3m/s, and the drying time to 0.5-2h. The continuous radio frequency heat treatment is applied at the stage, so that water molecules in the jujube slices vibrate at high frequency under a radio frequency field, the temperature in the jujube slices rises rapidly, a micro pore structure is maintained and formed, and the phenomenon of surface hardening and crusting is avoided;
(4) Intermittent radio frequency treatment is adopted in the later drying stage, so that the air temperature and the air speed of hot air are further reduced until the drying is finished: setting the interval time of the radio frequency heat treatment to be 5-20min and the application time to be 1-5min each time, further reducing the hot air temperature to be 50-60 ℃ and the wind speed to be 0.5-1m/s, and stopping drying when the moisture content of the wet base of the jujube slices is lower than 10%. Intermittent radio frequency is adopted at the stage, the wind temperature and the wind speed are reduced, the energy consumption is reduced while the micro pore structure in the jujube slices is maintained, and the bound water in the jujube slices is removed until the drying is finished;
(5) Cooling and packaging jujube slices: and cooling and sterilizing the dried jujube slices, and then filling nitrogen, packaging and storing.
2. The processing method for improving the hot air drying quality of jujube slices according to claim 1, wherein the preferable frequency band applied by the radio frequency heat treatment under the hot air drying condition is 27.12MHz, and the distance between the upper polar plate and the lower polar plate is defined to be 100-500mm according to the height of the material layer.
3. The processing method for improving the hot air drying quality of jujube slices according to claim 1, wherein the radio frequency has the characteristic of high penetrability, the materials can be dried in multiple layers in the drying process, the material tray is designed into a net-shaped ventilation structure, a hot air passage of 1-3cm is reserved between the layers, and the height of the material layer is adjustable within a distance of 10-50 cm.
4. The process for improving the hot air drying quality of jujube slices according to claim 1, wherein the hot air flows in parallel with the material layer and is perpendicular to the radio frequency field in the drying process.
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