DRIED FRESH JUJUBE SLICES AND ENERGY-SAVING PROCESS TECHNOLOGY FOR DIFFERENTIAL PRESSURE EXPANSION DRYING

Abstract

A method for processing dried fresh jujube slices includes the following steps: preparing jujube slices, coring and removing stems, quick-freezing and retaining freshness of the jujube slices, thawing frozen jujube slices, protecting color treatment, expanding jujube slices under differential pressure, preparing superfine mixed seasoning powder, and coating of the superfine mixed seasoning powder. For one hand, this method solves problems that the dried fresh jujube slices will be deeply oxidized and brown when dried by the hot air at a high temperature of 90-110 C., the jujube slices with compacted cells will become harder and be difficult to chew because of 6-8 h rapid dehydration. On the other hand, it solves problems that exist in freeze drying at a vacuum degree of 1.3-13 Pa, and at a low temperature of 10-50 C., such as high energy consumption, long processing cycle, high equipment investment, small size of slices, and poor taste.

Claims

1. A method for processing dried fresh jujube slices, comprising the following steps: 1) preparing jujube slices by washing and classify fresh jujubes, performing anti-cracking treatment to the jujubes, and blanching the jujubes at a temperature of 50-60 C. for sterilization; 2) coring and removing stems by cutting off both ends of the jujubes, drilling an opening with a depth of 1-1.2 cm at a center of one of the cutting end surfaces formed, when drilling, keeping a driller vibrating at the same time to core, cutting the cored jujubes into slices of 3-5 mm thickness, classifying the slices, and removing irregular slices; 3) quick-freezing and retaining freshness of the jujube slices by quick-freezing fresh jujube slices at a temperature of 40 C. for 2-5 min, and then retaining at a temperature of 18 C. for standby application; 4) thawing frozen fresh jujube slices by spraying frozen jujube slices from two sides thereof with a steam at a temperature of 110 C. and at a pressure of 0.1-0.15 Mpa, wherein the sprayed steam contains 3-5 wt % of phytic acid, and the steam is sprayed onto a surface of the slices for 1-2 min; 5) protecting color treatment by impregnating thawed jujube slices in color protecting solution for 30-50 min, wherein the color protecting solution is adjusted to pH 8 with NaHCO.sub.3 and contains one or more of zinc gluconate, calcium gluconate, zinc oxide, calcium sulfate, and selenium gluconate; 6) expanding jujube slices under differential pressure by turning on an electromagnetic valve to connect a steam generator and an expansion tank, superheated steam transported by the steam generator heating the expansion tank to raise a temperature in the expansion tank to 102-104 C., and turning off the electromagnetic valve; opening an intake valve to connect an air compressor and the expansion tank, introducing non-condensing gas nitrogen to rise a pressure in the expansion tank from 0.1 MPa to 0.6 MPa in 15-20 min, and closing the intake valve; turning on a vacuum pump and vacuuming a vacuum tank to 0.08 MPa; opening a pressure-relief valve to connect the expansion tank and the vacuum tank, which makes raw materials expanding instantaneously, so that a large amount of water in the expansion tank is taken away; introducing cooling water into cooling tubes quickly to lower a temperature in the expansion tank to 90 C. required for vacuum drying; vacuum drying for 220-250 min, assisting with supersonic during vacuum drying process at a supersonic intensity of 500-800 W, when a moisture content in the raw materials being lower than 5%, closing the pressure-relief valve, and stopping vacuuming; and introducing cooling water to lower the temperature to 25-35 C., opening a ventilating valve, taking out products after the pressure returns to atmospheric pressure; 7) preparing superfine seasoning powder by mixing uniformly 15-25 parts of hawthorn fruit powder, 35-50 parts of cocoa powder, 10-20 parts of cocoa butter, 15-25 parts of coconut powder, and 15-25 parts of jujube powder calculated by total weight, wherein all powders are ultrafine powders with a diameter less than 5-10 m; and 8) coating of the superfine mixed seasoning powder by spraying the prepared superfine seasoning powder on an outer surface of the expanded jujube slices, and then packaging after completely cooling.

2. The method accoring to claim 1, wherein a method for preparing the hawthorn fruit powder comprises: pretreating hawthorns by washing the hawthorns, heating and color protecting, beating and sieving, enzymolysis treatment, blending, and spray drying; first step: adding a compound color protecting agent with total mass fraction of 0.05-0.1% into 20-30 parts of corded and stem-removed hawthorns, and boiling in hot water at a temperature of 80-90 C.; second step: putting preprocessed hawthorns into a beating machine, beating a mixture containing water and hawthorn with a volume ratio of 1:3, sieving the beaten mixture with a sieve, adding Ca(OH).sub.2 to adjust pH to 3.5-4.0, and obtaining a hawthorn pulp; third step: enzymolysis by adding 0.1%-0.2% cellulose complex enzyme, 0.05%-0.1% hawthorn pulp enzyme, 0.1%-0.2% pectinase and 0.10%-0.15% tannase to hydrolyze supersonically the hawthorn pulp obtained in the second step for 3 h at a power of 200-300 W and at a temperature of 50-55 C., and then inactivating enzymes; fourth step: blending the hawthorn pulp in a blender; and fifth step: spray drying by putting the hawthorn pulp into a centrifugal spray drying tower, an inlet temperature of the centrifugal spray drying tower being 180-185 C., a flowing rate in a peristaltic pump being controlled at 14 r/min, a rotating speed of a nozzle of the centrifugal spray drying tower being 6400-8000 r/min, after the centrifugal spray drying tower is completely cooled, collecting the produced hawthorn powder for standby application.

Description

DESCRIPTION OF THE DRAWINGS

[0043] FIG. 1 is a diagram showing comparison between qualities of jujube slices under different pressures.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0044] The present disclosure will now be further described in details with reference to embodiments. The embodiments below are only illustrative, but not restrictive, and the scope of the disclosure should not be limited to the embodiments described.

[0045] A method for processing dried fresh jujube slices, comprises the following steps:

[0046] Treatments after picking: treating jujube with 20-50 mg/kg ethephon for 10-12 h at room temperature of 15-20 C. immediately after picked, wherein the time is actually equal to an interval between harvest and cleaning, classifying, and cutting process at the next day. While washing jujubes, a supersonic will synergize to make the mass and the water content uniform, which is equivalent to shuffle and re-license.

[0047] 1) preparing jujube slices by washing and classify fresh jujubes, performing anti-cracking treatment to the jujubes, and blanching the jujubes at a temperature of 50-60 C. for sterilization, wherein the blanching treatment at the temperature of 50-60 C. can realize the object of sterilization, on the other hand, it can also soften the jujube to prevent damage to the integrity of the jujube during the subsequent coring process;

[0048] 2) coring and removing stems by cutting off both ends of the jujubes, drilling an opening with a depth of 1-1.2 cm at a center of one of the cutting end surfaces formed, when drilling, keeping a driller vibrating at the same time to core, cutting the cored jujubes into slices of 3-5 mm thickness, classifying the slices, and removing irregular slices, wherein the vibrating during opening can preliminarily separate a jujube core from the jujube flesh to prevent a sudden separation of the jujube core during the coring process and damage the jujube flesh in a large area, so as to effectively improve the yield;

[0049] 3) quick-freezing and retaining freshness of the jujube slices by quick-freezing fresh jujube slices at a temperature of 40 C. for 2-5 min, and then retaining at a temperature of 18 C. for standby application; wherein the principles of freeze-thawing pretreatment for many times are that water in the tissue of the fruit and vegetable is present in a combined state and a free state, when the temperature is lowered than the freezing point, water that is weakly bound to the hydrophilic colloid or mainly in the intercellular space forms ice crystals firstly, as a result, the concentration of the solution near the ice crystal is increased and an osmotic pressure is formed to drive intracellular juice, and an extrusion will be formed from ice crystals to cells, so that the moisture inside the cells will continuously spread to the outer side of the cell and accumulate around the ice crystals, at the same time, when the water vapor pressure formed by the intracellular juice is greater than that of the ice crystals, these moistures will continuously spread to the outer side of the cells and surround the ice crystals, thus partial dehydration of the cells will be caused, and at the same time, during the freezing process, the cell tissue is further subjected to temperature shock and dehydration is more thorough;

[0050] 4) thawing frozen fresh jujube slices by spraying frozen jujube slices from two sides thereof with a steam at a temperature of 110 C. and at a pressure of 0.1-0.15 Mpa, wherein the sprayed steam contains 3-5 wt % of phytic acid, and the steam is sprayed onto a surface of the slices for 1-2 min by adopting a fluidized bed continuous spraying, the steam contains 3-5% phytic acid, the phytic acid can form a film which can help to form pressure when expanding, and the internal expanded pores can be increased by about 10% with the rise of the pressure, so that the dried jujube slices taste more brittle;

[0051] 5) protecting color treatment by impregnating thawed jujube slices in a color protecting solution for 30-50 min, wherein the solution is adjusted to pH 8 with NaHCO.sub.3 and contains one or more of zinc gluconate, calcium gluconate, zinc oxide, calcium sulfate, and selenium gluconate, the concentration of the color protecting solution is 0.05-0.1%, all components of the color protecting solution are nutrients, metal ions have high nutritional value, they can increase the brittleness and further supplement the nutrition of the jujube slices; color of fresh jujube slices are emerald green, and the color is easily discolored after being expanded at a high temperature, so the color protection treatment is performed in a step before the expansion;

[0052] 6) pretreating hawthorns by washing hawthorns.fwdarw.heating and color protecting.fwdarw.beating and sieving.fwdarw.enzymolysis treatment.fwdarw.blending.fwdarw.spray drying;

[0053] first step: adding a compound color protecting agent which contains 0.01-0.05 wt % L-cysteine, 0.05-0.1 wt % phytic acid and 0.05-0.1wt % lemon into 20-30 parts of corded and stem-removed hawthorns, and boiling in hot water at a temperature of 80-90 C.;

[0054] second step: putting preprocessed hawthorns into a beating machine, beating a mixture containing water and hawthorn with a volume ratio of 1:3, sieving the beaten mixture with a sieve, adding Ca(OH).sub.2 to adjust pH to 3.5-4.0, and obtaining a hawthorn pulp;

[0055] third step: enzymolysis by adding 0.1%-0.2% cellulose complex enzyme, 0.05%-0.1% hawthorn pulp enzyme, 0.1%-0.2% pectinase and 0.10%-0.15% tannase to hydrolyze supersonically the hawthorn pulp obtained in the second step for 3 h at a power of 200-300 W and at a temperature of 50-55 C.; wherein under the action of tannase, the ester bond, phenolic bond and glycosidic bond in the tannin molecule of hawthorn are broken and catalyzed to form the corresponding depsipeptide and polyol, and they will continue to be degraded into phloroglucinol and resorcinol under the action of enzymes, and finally are degraded into small molecular substances such as 3-hydroxy-5-oxo-hexanoic acid and 5-oxo-6-hexanoic acid methyl ester, thus the bitterness is reduced;

[0056] fourth step: blending, blending the hawthorn pulp in a blender; and

[0057] fifth step: spray drying by putting the hawthorn pulp into a centrifugal spray drying tower, an inlet temperature of the centrifugal spray drying tower being 180-185 C., a flowing rate in a peristaltic pump being controlled at 14 r/min, a rotating speed of a nozzle of the centrifugal spray drying tower being 6400-8000 r/min, after the centrifugal spray drying tower is completely cooled, collecting the produced hawthorn powder for standby application;

[0058] 7) expanding jujube slices under differential pressure by turning on an electromagnetic valve to connect a steam generator and an expansion tank, superheated steam generated by the steam generator heating the expansion tank to raise a temperature in the expansion tank to 102-104 C., and turning off the electromagnetic valve; opening an intake valve to connect an air compressor and the expansion tank, introducing non-condensing gas nitrogen to raise a pressure in the expansion tank from 0.1 MPa to 0.6 MPa in 15-20 min, and closing the intake valve; turning on a vacuum pump and vacuuming a vacuum tank to 0.08 MPa; opening a pressure-relief valve to connect the expansion tank and the vacuum tank, which makes raw materials expanding instantaneously, so that a large amount of water in the expansion tank is taken away; introducing cooling water into cooling tubes quickly to lower a temperature in the expansion tank to 90 C. required for vacuum drying; vacuum drying for 220-250 min, assisting with supersonic during vacuum drying process at a supersonic intensity of 500-800 W, when a moisture content in the raw materials being lower than 5%, closing the pressure-relief valve and stopping vacuuming; and introducing cooling water to lower temperature to 25-35 C., opening a ventilating valve, taking out products after the pressure return to atmospheric pressure; and

[0059] 8) preparing superfine seasoning powder by mixing uniformly 15-25 parts of hawthorn fruit powder, 35-50 parts of cocoa powder, 10-20 parts of cocoa butter, 15-25 parts of coconut powder, 15-25 parts of jujube powder,wherein all powders are ultrafine powder with a diameter less than 5-10 m; and

[0060] 9) coating of the superfine mixed seasoning powder by spraying the prepared superfine seasoning powder on an outer surface of the expanded jujube slices, and then packaging after completely cooling.

[0061] By adopting the method of the present disclosure, a porosity of the jujube slices is increased by 20%, an internal color of the fresh jujube is pale green, and the ultrafine powder is sprayed on the outside of the jujube slices, and the taste of the jujube slices is crispy and changeable, the jujube slices is a new type of snack food with good taste and rich nutrition that has never appeared temporarily in the market.

[0062] The relevant parameters and results of the test for jujube skin are described below.

TABLE-US-00001 TABLE 1 Effect of expansion temperature on the quality of expanded slices Expansion temperature ( C.) Moisture (%) Hardness (g) Brittleness (N/S) 70 32.76 1231.01 120.23 80 18.51 1836.56 252.01 90 7.36 2798.32 425.12 100 5.11 2786.23 456.89 110 4.89 2741.89 445.23

TABLE-US-00002 TABLE 2 Effect of vacuum temperature on the quality of expanded slices Vacuuming temperature ( C.) Moisture (%) Hardness (g) Brittleness (N/S) 60 27.76 1331.01 132.83 70 23.51 1936.56 272.01 80 7.36 2898.32 417.12 90 5.52 2786.23 442.80 100 5.13 2748.89 435.23

[0063] With the increase of vacuum temperature, the moisture content of the slices is significantly reduced, while the hardness and brittleness are significantly increased. When the temperature is above 90 C., the moisture content changes slowly, and the moisture content, hardness and brittleness of the product are good. Considering comprehensively, the vacuum temperature is preferably 90 C.

TABLE-US-00003 TABLE 3 Effect of vacuuming time on the quality of expanded slices Vacuuming time (min) Moisture (%) Hardness (g) Brittleness (N/S) 150 29.26 1446.81 142.23 180 9.51 2896.56 476.01 210 5.16 2998.32 455.12 240 4.98 4286.73 556.89 270 4.77 4848.19 545.23

[0064] With the extension of the vacuuming time, the moisture content of the slices is significantly reduced. However, when the moisture content is reduced to a certain extent, it is difficult to transfer the water again, so there is no significant difference between the products with a vacuum time more than 240 min, and the moisture content has already been lower than 7%; the hardness and the brittleness are increase sharply between 210-240 min, and the change was not obvious after 240 min. Considering comprehensively, the vacuuming time is preferably 240 minutes.

TABLE-US-00004 TABLE 4 Effect of differential pressure on the quality of puffed slices Differential pressure (MPa) Moisture (%) Hardness (g) Brittleness (N/S) 0.2 5.76 2853.01 410.23 0.4 5.51 2836.56 452.01 0.6 4.96 3798.32 525.12 0.8 4.53 3886.23 556.89 1.0 4.21 3941.89 623.23

[0065] There is no significant difference in moisture content, hardness and brittleness between the treatments of 0.2-0.4 MPa, and these sense scores are higher. There is no significant difference in moisture content, hardness and brittleness between the treatments of 0.8-1.0 MP, but the differential pressures are too large, causing the slice to crack and the sense quality to drop. Considering comprehensively, the expansion pressure of 0.6 MPa should be selected.

TABLE-US-00005 TABLE 5 Comparison of the color of different drying methods Drying method L a* b* AD 52.18 12.36 19.63 FD 82.35 5.36 27.89 EFD 69.32 8.32 22.36

[0066] Referring to Table 5, the three drying method values are put in order from high to low, that is, the color is from shallow to deep, freeze drying, expansion drying, and hot air drying. The drying method has a significant effect on the color of the dehydrated jujube slices. The color of the freeze drying samples is the best, and the color of the jujube slices prepared by the differential pressure expansion drying is better than that of hot air drying. This result may be related to a vacuum state of the material. During the freeze drying process, the material is always in a freezing vacuum state. During the expansion drying process, the materials are mostly in a vacuum state, while in the hot air drying process, the materials are in a atmospheric pressure state. Jujube slices are more stable under vacuum state.

[0067] The rehydration rate of freeze drying is the best, and the equilibrium is reached after rehydration for 20 min, the variable temperature and differential pressure expansion drying ranks the second. This is because the freeze-dried product and the variable temperature differential pressure expansion drying product have a porous structure; the rehydration rate of hot air drying product is relatively lower. According to the rehydration rate of jujube slices, the solubility and the modulability of the silty products can be predicted. It can be predicted that the freeze-dried jujube powder and the variable temperature differential pressure expansion drying jujube powder have better solubility and adjustability.