CN106070550B - Composite color protection liquid for longan drying and drying method - Google Patents

Abstract

The invention discloses a composite color-protecting liquid for drying longan and a drying method. The color-protecting liquid is composed of the following components by mass percentage: ascorbic acid 0.05%-0.15%, malic acid 0.06%-0.10%, calcium chloride 0.10% to 0.30%, 0.10% to 0.30% of sodium bicarbonate, and the balance is water; the drying method is: pruning, selecting and grading fresh longan, blanching the graded fresh longan to inactivate enzymes, and blanching the fresh longan. The longan is put into the color-protecting solution for color-protection treatment, and the longan after the color-protection treatment is subjected to hot air drying. The composite color-protecting liquid for drying longan can effectively inhibit the browning reaction in the drying process of longan, reduce the loss of nutrients in the drying process of longan, and has good color-protecting effect, no toxicity, high safety and convenient operation. .

Description

A kind of composite color protecting liquid for longan drying and drying method

technical field

The invention belongs to the technical field of fruit and vegetable processing, and in particular relates to a composite color-protecting liquid used for drying longan, and also relates to a method for drying longan.

Background technique

Longan (Dimocarpus longan Lour.) is a fruit tree of the Sapinaceae family, and its fruit is rich in carbohydrates, amino acids and vitamins. Longan is picked in the high temperature season, and the post-harvest physiological metabolism is strong, it is very easy to spoil and rot, and loses its edible value. In order to reduce the economic loss caused by the extremely perishable longan and increase the edible value of the longan, the drying method is currently used to make the fresh longan into dried longan (longan). In recent years, the drying technology of longan has developed rapidly. There are many studies on vacuum freeze drying, infrared drying, microwave drying and combined drying. However, in actual production, hot air drying and superheated steam drying methods are still used, which require less equipment. main. Longan is prone to browning during the drying process, which reduces the sensory quality of longan and affects the commercial value of longan.

Browning is the main reason that causes longan to deteriorate and lose its edible value. According to the different browning mechanisms, it can be divided into two categories: enzymatic browning and non-enzymatic browning. Enzymatic browning is the destruction of the outer shell of longan under the influence of external heating and drying conditions or mechanical damage, and a large amount of oxygen entering the tissue activates the function of enzymes, catalyzing the oxidation of phenolic substances in the tissue to form quinones, and the repolymerization of quinones leads to the formation of quinones. Tissue discolored brown substance. In intact longan tissue cells, phenolic substances, which are respiratory transmission substances, maintain a dynamic balance between phenol-quinones. Once the longan shell is damaged, the air can directly contact the pulp, the polyphenols are oxidized to o-quinone in the presence of oxygen and the catalysis of enzymes, and the trihydroxy compound is oxidized to hydroxyquinone under the strong oxidizing ability of o-quinone. , the red hydroxyquinone turns brown after polymerization, and then turns dark brown, resulting in browning and discoloration of longan pulp. Longan color protection treatment before drying can effectively inhibit the occurrence of browning and reduce the deformation and shrinkage of longan pulp.

The commonly used color protection solution is mainly for the color protection treatment of longan pulp, which needs to be peeled for longan and other longan. And the commonly used color protection solution is divided into two kinds, the first one contains SO ₂ salts, such as sodium sulfite, sodium metabisulfite and sodium bisulfite, etc. are a kind of commonly used preservatives, which can inhibit enzyme activity at lower concentrations, thereby Inhibiting enzymatic browning, SO ₂ can combine with oxygen in organic peroxides so that hydrogen peroxide will not be generated, then peroxidase POD will lose its oxidation effect, and at the same time SO ₂ can combine with the ketone group of tannin, The tannin is not oxidized and the PPO and POD lose their substrates, thereby preventing enzymatic browning. In addition, the dilute acid environment generated by bisulfite makes the carbonyl ammonia condensation product of the Maillard reaction easy to hydrolyze, thereby inhibiting the use of the United States. Nonenzymatic browning caused by the Rad reaction. However, the residue of SO ₂ poses a potential safety hazard to human health; the second is sulfur-free color protection. This color protection method commonly uses citric acid, ascorbic acid, malic acid, etc. as color protection ingredients, mainly acting on polyphenol oxidase, while improving fruits and vegetables. The sensory quality, but the color protection effect is not obvious.

SUMMARY OF THE INVENTION

In view of this, the present invention aims at the above-mentioned problems, and provides a kind of composite color protection liquid and drying method for longan drying, which can effectively suppress the browning reaction in the drying process of longan, and reduce the nutrients in the drying process of longan. It has good color protection effect, non-toxic, high safety and convenient operation.

In order to solve the above-mentioned technical problems, the present invention discloses a composite color-protecting liquid for drying longan, which is composed of the following components according to mass percentage: ascorbic acid 0.05%-0.15%, malic acid 0.06%-0.10%, calcium chloride 0.10% %～0.30%, sodium bicarbonate 0.10%～0.30%, and the balance is water.

Preferably, it is composed of the following components by mass percentage: ascorbic acid 0.1%, malic acid 0.08%, calcium chloride 0.3%, sodium bicarbonate 0.1%, and the balance is water.

The invention also discloses a method for drying longan, comprising the following steps:

The fresh longan is pruned, selected and graded, the graded fresh longan is blanched to inactivate enzymes, the blanched longan is put into a color-protecting solution for color-protection treatment, and the color-protected longan is subjected to hot air drying; The color liquid is composed of the following components in percentage by mass: ascorbic acid 0.05%-0.15%, malic acid 0.06%-0.10%, calcium chloride 0.10%-0.30%, sodium bicarbonate 0.10%-0.30%, and the balance is water.

Further, the color protection solution is composed of the following components by mass percentage: ascorbic acid 0.1%, malic acid 0.08%, calcium chloride 0.3%, sodium bicarbonate 0.1%, and the balance is water.

Further, the pruning and selecting and grading are specifically as follows: selecting fresh longan with similar fruit maturity, healthy and pest-free, selecting those without external mechanical damage, pruning and leaving the stem about 0.5cm for grading, selecting fresh longan with moderate and uniform size. Longan is ready to use.

Further, the blanching inactivating enzyme is specifically: immersing the fresh longan after classification in 100° C. hot water for 3 minutes, and cooling at room temperature.

Further, the time of the color protection treatment is 30min, and the solid-liquid ratio is 1:1.5.

Further, the hot air drying adopts a staged drying method: the drying temperature in the first stage is 65°C, the drying time is 6h, and the hot air velocity is 1.5m/s, and the drying temperature in the second stage is 75°C, the drying time is 12h, and the hot air velocity is 1.5m. /s, the drying temperature of the third stage is 70°C, the drying time is 6h, and the hot air velocity is 1.5m/s.

Further, the hot air drying adopts two layers of longan to bake.

Compared with the prior art, the present invention can obtain the following technical effects:

(1) Ascorbic acid in each component of the present invention can be combined with nascent quinone substances, can complex the prosthetic group of polyphenol oxidase, directly act on the enzyme, and prevent the occurrence of enzymatic browning. At the same time, ascorbic acid has reducing properties, which can prevent The coloring substances in the pulp are oxidized; calcium chloride can maintain the brittleness of fruits and vegetables, prevent the shrinkage and deformation of fruits and vegetables during processing, and can also be used as a color-retaining agent to inhibit the browning of fruits and vegetables; malic acid and sodium bicarbonate are combined with ascorbic acid and When used together with calcium chloride, etc., it has a beneficial effect on the inhibition of browning, thereby effectively inhibiting the browning reaction in the drying process of longan, reducing the loss of nutrients in the drying process of longan, and extending the shelf life of dried longan;

(2) using the color-protecting liquid of the present invention to carry out color-protecting treatment on longan, the color and luster of dried longan pulp is obviously improved, and the browning degree of dried longan is effectively reduced, and the loss of nutrients such as soluble protein and sugar is reduced simultaneously , has a passivation effect on PPO and POD;

(3) The color protection liquid has the characteristics of good comprehensive color protection effect, non-toxic, high safety and convenient operation.

Of course, any product implementing the present invention does not necessarily need to achieve all the above-mentioned technical effects at the same time.

Description of drawings

The accompanying drawings described herein are used to provide further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the attached image:

Fig. 1 is the comparison chart of browning degree of longan pulp according to the embodiment of the present invention;

Fig. 2 is the color difference contrast diagram of longan pulp according to the embodiment of the present invention;

Fig. 3 is the soluble protein content comparison diagram in the longan pulp of the embodiment of the present invention;

Fig. 4 is the comparison diagram of reducing sugar content in the pulp of longan according to the embodiment of the present invention;

Fig. 5 is the PPO enzyme activity contrast figure in the longan pulp of the embodiment of the present invention;

Fig. 6 is the comparison diagram of POD enzyme activity in the pulp of longan according to the embodiment of the present invention.

Detailed ways

The embodiments of the present invention will be described in detail with the following examples, so as to fully understand and implement the implementation process of how to apply technical means to solve technical problems and achieve technical effects of the present invention.

The present invention is a composite color protection solution for drying longan, which is composed of the following components according to mass percentage: ascorbic acid 0.05%-0.15%, malic acid 0.06%-0.10%, calcium chloride 0.10%-0.30%, sodium bicarbonate 0.10%～0.30%, the balance is water.

Preferably, it is composed of the following components by mass percentage: ascorbic acid 0.1%, malic acid 0.08%, calcium chloride 0.3%, sodium bicarbonate 0.1%, and the balance is water.

The highest values of the above-mentioned components are all within the scope of use limited by the national standard 2760, which meets the standards for the use of additives; secondly, through the test, it is known that within the range of the above components, the drying and color protection effect of longan with shells is relatively optimal. ; Finally, considering the production cost, if the concentration is increased, the usage of each component will increase, that is, the cost will increase. Therefore, considering the above considerations, the content range of each component is the above-mentioned value range.

This color protection solution is used to protect the color of the longan before drying. It does not need to dehull the longan to ensure the integrity of the dried fruit. By adding ascorbic acid, malic acid, calcium chloride, sodium bicarbonate, etc. as color-protecting components, ascorbic acid can complex the prosthetic group of polyphenol oxidase and act directly on the enzyme to prevent the occurrence of enzymatic browning At the same time, ascorbic acid has reducing properties, which can prevent the coloring substances in the pulp from being oxidized; calcium chloride is a commonly used hardener, which can maintain the brittleness of fruits and vegetables, prevent the shrinkage and deformation of fruits and vegetables during processing, and can also be used as a protective agent. A colorant to inhibit the browning of fruits and vegetables. The use of malic acid and sodium bicarbonate in combination with ascorbic acid and calcium chloride has a beneficial effect on browning inhibition.

A method for drying longan, comprising the following steps:

S01, pruning and selection and grading

Select fresh longan with similar fruit maturity, healthy and pest-free, select those with no external mechanical damage, prune branches and leave stalks about 0.5 cm before grading, and select fresh longan with moderate and uniform size for use;

S02, blanching blunt enzymes

Immerse the graded fresh longan in 100°C hot water for 3 minutes and cool at room temperature;

S03, color protection treatment

The blanched longan is placed in a color-protecting solution for color-protecting treatment, and after the treatment, it is drained at room temperature; the color-protecting solution is composed of the following components by mass percentage: ascorbic acid 0.05%-0.15%, malic acid 0.06%-0.10%, Calcium chloride is 0.10% to 0.30%, sodium bicarbonate is 0.10% to 0.30%, and the balance is water.

Preferably, the color protection solution is composed of the following components by mass percentage: ascorbic acid 0.1%, malic acid 0.08%, calcium chloride 0.3%, sodium bicarbonate 0.1%, and the balance is water.

Further, the time of the color protection treatment is 30min, and the solid-liquid ratio is 1:1.5.

The color protection time is 30 minutes. The reason is that the color-protected longan has not been shelled. If the soaking time is too short, the color-protecting liquid will not be able to penetrate deep into the fruit to dye the pulp. If the soaking time is too long, the longan husk will be too weak. damaged. When the solid-liquid ratio is lower than 1:1.5, the longan cannot be completely immersed in the color-protecting liquid, which affects the color-protecting effect; when the material-liquid ratio is higher than 1:1.5, it is easy to cause too much color-protecting liquid to cause waste and increase the economic cost. Therefore, the ratio of solid to liquid is 1:1.5.

S04, hot air drying

Dry the longan with hot air after the color protection treatment.

Further, the hot air drying adopts a staged drying method: the drying temperature in the first stage is 65°C, the drying time is 6h, and the hot air velocity is 1.5m/s, and the drying temperature in the second stage is 75°C, the drying time is 12h, and the hot air velocity is 1.5m. /s, the drying temperature of the third stage is 70°C, the drying time is 6h, and the hot air velocity is 1.5m/s.

The drying process is mainly divided into three steps. The first stage is heated at a lower temperature, so that during the drying process of longan, the evaporation rate of water is lower than the migration rate of internal water, so as to prevent the surface of the longan from drying too strongly and the longan shell will be damaged. The formation of a layer of dry hard film causes most of the residual moisture to be blocked in the longan shell, resulting in the phenomenon that the outside is hard, the inside is soft and soft, and the drying rate drops sharply; the second stage is dried at a higher temperature to improve the drying efficiency; the third stage of heating It is designed to supplement the heating of longan with large fruit, thick flesh or not up to the drying standard due to high air humidity.

Further, the hot air drying adopts two layers of longan baking, and this method does not need to be turned during the drying process.

S05, cooling

Store the dried longan after cooling.

Using the color protection solution of the invention to treat longan can effectively inhibit the browning reaction in the drying process of longan, reduce the loss of nutrients in the drying process of longan, reduce the activities of polyphenol oxidase and peroxidase, and thus have the advantages of It is beneficial to prolong the shelf life of dried longan.

Example

Select fresh longan with similar fruit maturity, healthy and pest-free, select those with no external mechanical damage, prune branches and leave stalks about 0.5 cm before grading, and select fresh longans of moderate and uniform size for later use; The enzyme was immersed in hot water at 100°C and blanched for 3 minutes, and cooled at room temperature; the blanched longan was placed in a color-protecting solution for 30 minutes, and the material-to-liquid ratio was 1:1.5. The ratio of the color-protecting solution is shown in Table 1. , Table 1 enumerates the color protection solution of different ratios and the color protection solution ratio of the comparative example, and the remainder is water; the longan after the color protection treatment is dried by hot air, and the hot air drying adopts a segmented drying method: the first The drying temperature of the first stage is 65°C, the drying time is 6h, and the hot air velocity is 1.5m/s. The drying temperature of the second stage is 75°C, the drying time is 12h, and the hot air velocity is 1.5m/s. 6h, hot air velocity 1.5m/s.

Table 1 Color protection solution ratio

The comparative example without color protection treatment and the dried longan after color protection treatment according to the color protection solution ratio in Table 1 and tested:

1. Evaluation indicators and measurement methods:

(1) Determination of browning degree

Weigh 2g of de-pitted pulp samples, grind them fully, add 20mL of 2% (v/v) acetic acid solution, mix well, centrifuge at 8000r·min ^-1 for 10min, and suck the supernatant. 20 mL of acetone was added to the supernatant, mixed evenly, centrifuged at 8000 r·min ^-1 for 10 min, and the supernatant was aspirated. Its optical density was measured at a wavelength of 420 nm, and the result was expressed as D _{420 nm} .

(2) Measurement of color difference

The color difference of the dried longan pulp was measured by a colorimeter, 5 times for each sample, and 3 different angles were taken each time.

(3) Determination of reducing sugar content

The reducing sugar content was determined by 3,5-dinitrosalicylic acid colorimetric method (Wang Xuekui. Principles and Techniques of Plant Physiological and Biochemical Experiments [M]. Beijing: Higher Education Press, 2006: 202-205.).

(4) Determination of soluble protein content

Soluble protein content was determined by Bradford method (Bradford MM. A rapid and sensitive method for the quantification of microgram qualities of proteins utilizing the principle of protein-dye binding [J]. Analytical Biochemistry, 1976, 72: 248-254.).

(5) Determination of POD and PPO activity

Take about 2g dried longan pulp, chop it, put it in a mortar, add an appropriate amount of phosphate buffer (pH=6.8) and grind it into a homogenate in an ice bath environment. Refrigerate and centrifuge for 20 min at the speed of min, and store at low temperature for future use.

The reaction system for measuring POD enzyme activity included 1.8 mL of 0.05 mol.L ^-1 phosphate buffer (pH=6.8), 1.0 mL of 2% H ₂ O ₂ solution, 1.0 mL of 0.05 mol. L ^-1 guaiacol solution and 0.2 mL enzyme solution. Taking the enzyme solution heated in boiling water for 5 min as the control, three groups of repetitions were made. The reaction system was timed after the enzyme solution was added, and was immediately placed in the sample chamber of the UV spectrophotometer, and the absorbance was measured every 0.5 min with a wavelength of 470 nm. The change in absorbance per gram of sample per minute was increased by 1 as a unit of peroxidase activity, ΔOD ₄₇₀ /min.g. The calculation refers to formula 1.

In the formula, ΔOD: the change of the absorbance value of the sample at 470 nm per minute; V: the total volume of the sample extract, mL; V _s : the volume of the sample extract taken during the measurement, mL; m: the sample mass in g.

The preparation of the enzyme solution in the determination of PPO activity is the same as the treatment method for the determination of POD, and the buffer solution is changed to phosphate buffered saline with pH=5.8. The reaction system for measuring enzyme activity includes 1.5 mL of 0.05 mol.L ^-1 phosphate buffer solution (pH=7), 1.0 mL of 0.05 mol.L ^-1 catechol solution and 0.5 mL of enzyme solution. The enzyme solution heated in boiling water for 5 min was used as the control, and three groups were repeated. The reaction system was timed after the enzyme solution was added, and was immediately placed in the sample chamber of the UV spectrophotometer, and the absorbance was measured every 0.5 min with a wavelength of 470 nm. Calculate the specific activity of PPO of dried longan pulp according to formula 1.

2. Test results:

(1) Changes in browning degree and color difference of pulp

The browning degree of longan treated with different compound color protection solution after hot air drying is shown in Figure 1 (different lowercase letters in the figure indicate significant differences between different treatments, p<0.05, the same below), it can be seen that longan is drying The color protection treatment before making can reduce the browning reaction in the drying process. The browning degree of Example 5 is 0.046D _420nm , which is much lower than other examples. Statistical analysis of the new multiple range shows that there is a significant difference between Example 5 and Example 1, 2, and 3 (P<0.05), and there is no significant difference between Example 1, 2, 3, and 7 groups (P>0.05) .

For dried longan, the smaller the color difference, the closer the color of the dried longan flesh is to the fresh longan. The effect of different compound color-protecting liquids on the pulp color of dried longan is as shown in Figure 2, and the numerical difference between each component is not big, and the statistical analysis of the new complex range shows: there is no significant difference between the comparative example and Example 8 ( P>0.05).

(2) Changes in soluble protein and reducing sugar content

The effects of different color-protecting solution treatments on the soluble protein content of longan after drying are shown in Figure 3. As shown in Figure 3, the soluble protein content of dried longan in Example 6 is the highest. Statistical analysis of the new multiple range shows that: there is no significant difference between Example 6 and Example 3, 4, 5, 7, and 9 groups (P>0.05), Example 6 and Comparative Examples, Examples 1, 2, 8 There was a significant difference between the groups (P<0.05), and there was also a significant difference (P<0.05) between Example 5 and the comparative example and Example 2.

The effect of different color-protecting liquid treatments on the reducing sugar content of longan after drying is shown in Figure 4. As shown in Figure 4, Example 5 has the highest reducing sugar content after drying. Statistical analysis of the new multiple range shows that there is a significant difference between Example 5 and Comparative Example and Example 4 (P<0.05), and there is also a significant difference between Comparative Example and Examples 3 and 9 (P<0.05).

(3) Changes in the activity of PPO and POD

Generally speaking, peroxidase and polyphenol oxidase are the key enzymes that cause browning of fruits and vegetables. The higher the enzyme activities of PPO and POD, the faster the browning speed of longan during the drying process.

Figure 5 shows the results of PPO enzyme activity assay, and the new multiple range statistical analysis results are as follows: there is a significant difference (P<0.05) between Example 5 and Comparative Examples, Examples 7 and 9, and there is no significant difference between Examples 9 and 7 Sex difference (P>0.05). Figure 6 shows the results of POD enzyme activity assay, and the new complex range statistical analysis results are as follows: There is no significant difference between Examples 5 and 3 (P>0.05), and the POD enzyme activities of Examples 5 and 3 are significantly lower than those of other examples. Group. It can be seen from Figure 5 and Figure 6 that the PPO and POD of Example 5 are both the lowest, the PPO enzyme activity of the dried longan after treatment with this color protection solution is 0.088ΔOD ₄₇₀ /(min·g), and the POD enzyme activity is 3.181ΔOD ₄₇₀ / (min·g), significantly lower than other examples.

The color protection treatment of longan by using the color protection solution of the invention significantly improves the color and luster of dried longan pulp, effectively reduces the degree of browning of dried longan, and reduces the loss of nutrients such as soluble protein and sugar at the same time. It has a passivation effect with POD. When the compound color protection solution contains 0.10% ascorbic acid, 0.08% malic acid, 0.30% calcium chloride, 0.10% sodium bicarbonate, the quality of dried longan is better, and the browning degree of longan after this color protection solution is 0.046D At _{420 nm} , the PPO enzyme activity was 0.088ΔOD ₄₇₀ /(min·g), and the POD enzyme activity was 3.181ΔOD ₄₇₀ /(min·g).

As certain terms are used in the specification and claims to refer to particular components or methods. It should be understood by those skilled in the art that different regions may use different nouns to refer to the same ingredient. The description and claims do not use differences in names as a way of distinguishing components. As mentioned in the entire specification and claims, "comprising" is an open-ended term, so it should be interpreted as "including but not limited to". "Approximately" means that within an acceptable error range, those skilled in the art can solve the technical problem within a certain error range, and basically achieve the technical effect. Subsequent descriptions in the specification are preferred embodiments for implementing the present invention, however, the descriptions are for the purpose of illustrating the general principles of the present invention and are not intended to limit the scope of the present invention. The scope of protection of the present invention should be determined by the appended claims.

It should also be noted that the terms "comprising", "comprising" or any other variation thereof are intended to encompass non-exclusive inclusion, such that a commodity or system comprising a list of elements includes not only those elements, but also includes not explicitly listed other elements, or elements inherent to the commodity or system. Without further limitation, an element defined by the phrase "comprising a..." does not preclude the presence of additional identical elements in the article or system that includes the element.

The foregoing specification illustrates and describes several preferred embodiments of the invention, but as previously mentioned, it should be understood that the invention is not limited to the form disclosed herein and should not be construed as an exclusion of other embodiments, but may be used in a variety of other Combinations, modifications and environments are possible within the scope of the inventive concepts described herein, from the above teachings or from skill or knowledge in the relevant fields. However, modifications and changes made by those skilled in the art do not depart from the spirit and scope of the invention, and should all fall within the protection scope of the appended claims of the invention.

Claims (5)

1. a longan drying method, is characterized in that, comprises the following steps: The fresh longan is pruned, selected and graded, the graded fresh longan is blanched to inactivate enzymes, the blanched longan is put into a color-protecting solution for color-protection treatment, and the color-protected longan is subjected to hot air drying; The color liquid is composed of the following components according to the mass percentage: ascorbic acid 0.05%-0.15%, malic acid 0.06%-0.10%, calcium chloride 0.10%-0.30%, sodium bicarbonate 0.10%-0.30%, and the balance is water; The hot air drying adopts a staged drying method: the drying temperature of the first stage is 65°C, the drying time is 6h, and the hot air velocity is 1.5m/s; The drying temperature of the third stage is 70℃, the drying time is 6h, and the hot air velocity is 1.5m/s; The time of the color protection treatment is 30min, and the ratio of solid to liquid is 1:1.5. 2. longan drying method as claimed in claim 1, is characterized in that, described color protection liquid is made up of following components by mass percentage: ascorbic acid 0.1%, malic acid 0.08%, calcium chloride 0.3%, sodium bicarbonate 0.1% %, the balance is water. 3. longan drying method as claimed in claim 1, it is characterized in that, described pruning and selection and classification are specially: select fruit ripeness to be close, the fresh longan of health and no insect damage, select person without external mechanical damage, pruning leaves. The stalks are about 0.5cm long for grading, and fresh longan of moderate and uniform size is selected for use. 4. longan drying method as claimed in claim 1, is characterized in that, described blanching inactivating enzyme is specifically: immersing fresh longan after classification in 100 ℃ of hot water blanching 3min, room temperature cooling. 5. longan drying method as claimed in claim 1 is characterized in that, described hot air drying adopts two layers of longan to bake.

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