Asparagus based on superheated steam drying and preparation method and application thereof

Abstract

The invention provides asparagus based on superheated steam drying and a preparation method and application thereof, and belongs to the technical field of food processing. The method comprises the following steps: ultrasonically cleaning asparagus, deactivating enzymes, cooling, and performing subsection drying by adopting superheated steam and far infrared rays to obtain the dried asparagus. The asparagus segments prepared by the method have good rehydration rate and color recovery rate, are emerald green in color, high in nutrition retention rate and good in taste, and can improve the quality of the dried asparagus. The asparagus segments prepared by the method can be used for development and utilization of instant food such as premade vegetables, and the market competitiveness of asparagus processed products is improved.

Description

Technical Field

[0001] The invention relates to the technical field of food processing, and in particular to asparagus dried based on superheated steam and a preparation method and application thereof. Background Art

[0002] Asparagus is the seedling of Asparagus officinalis L., Asparagaceae, and is known as the "king of vegetables". The tender stems of asparagus are delicate, low in fiber, rich in amino acids, proteins, vitamins and various trace elements, and have the effects of regulating body metabolism and improving immunity. Regular consumption has certain beneficial effects on heart disease, hypertension, cardiovascular disease, liver dysfunction, etc. Therefore, it has good nutritional value and health value.

[0003] The moisture content of asparagus is generally above 90% when it is just harvested. However, the asparagus tissue is young and tender after harvest, and the water retention capacity of the epidermal tissue is poor. In addition, the tender stems of asparagus breathe vigorously after harvest, and the water is easily evaporated and lost, resulting in weight loss of the tender stems. At the same time, asparagus still carries out various physiological metabolic activities after harvest and is prone to lignification, which greatly affects the edibility of the asparagus after harvest and causes asparagus waste.

[0004] Drying asparagus and preserving it is a feasible means to solve the problems of short edible period of asparagus and waste of asparagus after harvest. At present, the main method of drying asparagus is oven drying, but the dried asparagus obtained by oven drying suffers from serious nutrient loss, has a poor taste after rehydration, and has a darker color. The market competitiveness of dried asparagus is low.

[0005] Therefore, it is necessary to provide a new asparagus drying method, which can inhibit various physiological metabolic activities of asparagus after harvesting, ensure the taste and nutritional value of asparagus, and improve the market competitiveness of dried asparagus. Summary of the invention

[0006] The purpose of the present invention is to provide an asparagus dried based on superheated steam and a preparation method and application thereof, so as to solve the technical problems that asparagus is easily wasted due to lignification after harvest and the quality of dried asparagus obtained by the existing asparagus drying method is poor.

[0007] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0008] The invention provides a method for drying asparagus based on superheated steam. The method comprises the steps of ultrasonically cleaning the asparagus, killing the green part of the asparagus, cooling the asparagus, and drying the asparagus in sections by superheated steam and far infrared to obtain dried asparagus.

[0009] Preferably, the water used in ultrasonic cleaning is saline with a concentration of 1 to 3%, the power of the ultrasound is 300 to 500 W, and the time is 10 to 20 minutes.

[0010] Preferably, the temperature during the fixing is 100-120° C., and the time is 20-40 min.

[0011] Preferably, the asparagus is cooled to 20-40°C after being blanched.

[0012] Preferably, the superheated steam and far-infrared staged drying are performed at 85-90° C., 100-110° C., and 85-90° C. for 50-70 min respectively.

[0013] Preferably, the humidity during baking is 25-35%.

[0014] Preferably, the obtained dried asparagus is cut into sections and packaged.

[0015] Preferably, the length of the cut segments is 1 to 10 cm, and the packaging is vacuum packaging.

[0016] The invention also provides dried asparagus prepared according to the method.

[0017] The present invention further provides an application of the dried asparagus in preparing instant food.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] 1. The present invention puts fresh asparagus into salt water with a concentration of 1-3% and washes it under ultrasonic conditions, which can partially dehydrate the asparagus, which is beneficial to the protection of the asparagus color. The prepared asparagus is more emerald green in color and has a crisp taste.

[0020] 2. The present invention adopts superheated steam and far-infrared segmented method to dry asparagus, which can quickly dehydrate the asparagus and is beneficial to the retention of nutrients in the asparagus. Compared with microwave vacuum drying and oven drying methods, it is more conducive to killing microorganisms in the asparagus segments and is beneficial to extending the shelf life of asparagus.

[0021] 3. The asparagus segments prepared by the present invention have good rehydration rate and color recovery rate, are emerald green in color, have high nutrient retention rate, and have good taste, and can improve the quality of dried asparagus. The asparagus segments prepared by the present invention can be used for the development and utilization of convenient foods such as pre-prepared dishes, and improve the market competitiveness of asparagus processed products. DETAILED DESCRIPTION

[0022] The invention provides a method for drying asparagus based on superheated steam. The method comprises the steps of ultrasonically cleaning the asparagus, killing the green part of the asparagus, cooling the asparagus, and drying the asparagus in sections by superheated steam and far infrared to obtain dried asparagus.

[0023] In the present invention, the water used for ultrasonic cleaning is saline with a concentration of 1 to 3%, preferably saline with a concentration of 1.5 to 2.5%, and more preferably saline with a concentration of 2%. The power of the ultrasound is 300 to 500 W, preferably 350 to 450 W, more preferably 380 to 420 W, and more preferably 400 W. The time is 10 to 20 min, preferably 12 to 18 min, more preferably 14 to 16 min, and more preferably 15 min.

[0024] The invention ultrasonically cleans the asparagus in salt water, and can remove impurities on the asparagus and partially dehydrate the asparagus, so that the prepared asparagus is crisper.

[0025] In the present invention, the temperature during the fixing is 100-120°C, preferably 105-115°C, more preferably 108-112°C, more preferably 110°C, and the time is 20-40min, preferably 22-38min, more preferably 25-35min, more preferably 30min.

[0026] In the present invention, after the asparagus is withered, it is cooled to 20 to 40°C, preferably 22 to 38°C, more preferably 25 to 35°C, and even more preferably 30°C.

[0027] In the present invention, superheated steam and far-infrared staged drying are respectively baked at 85-90°C, 100-110°C, and 85-90°C for 50-70 min, preferably at 86-89°C, 102-108°C, and 86-89°C for 54-66 min, further preferably at 87-88°C, 104-106°C, and 87-88°C for 58-62 min, more preferably at 88°C, 105°C, and 88°C for 60 min.

[0028] In the present invention, the humidity during baking is 25 to 35%, preferably 26 to 34%, more preferably 28 to 32%, and even more preferably 30%.

[0029] In the present invention, the obtained dried asparagus is cut into sections and packaged.

[0030] In the present invention, the length of the cut segments is 1 to 10 cm, preferably 1 to 5 cm, more preferably 1 to 3 cm, and more preferably 2 cm, and the packaging is vacuum packaging.

[0031] The invention also provides dried asparagus prepared according to the method.

[0032] The present invention further provides an application of the dried asparagus in preparing instant food.

[0033] In the present invention, the instant food includes pre-prepared dishes.

[0034] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0035] Example 1

[0036] A method for drying asparagus based on superheated steam, the steps are as follows:

[0037] (1) Select fresh asparagus with a bottom diameter of about 1 cm, weigh them, and place them in 1% saline (the saline covers the asparagus), and treat them ultrasonically at a power of 300 W for 10 minutes to obtain pretreated asparagus;

[0038] (2) placing the pretreated asparagus obtained in step (1) in hot water at a temperature of 100° C. for 20 minutes to obtain blanched asparagus;

[0039] (3) When the blanched asparagus obtained in step (2) is cooled to 30° C., superheated steam and far infrared drying are performed in stages, firstly baking at a temperature of 85° C. and a humidity of 25% for 50 min, then baking at a temperature of 100° C. and a humidity of 25% for 50 min, and finally baking at a temperature of 85° C. and a humidity of 25% for 50 min, to obtain dried asparagus;

[0040] (4) shaping and cutting the dried asparagus obtained in step (3) into small segments of 2 cm in length, and vacuum packaging the segments to obtain finished asparagus segments.

[0041] Example 2

[0042] A method for drying asparagus based on superheated steam, the steps are as follows:

[0043] (1) fresh asparagus with a bottom diameter of about 1 cm was selected, weighed, and placed in 3% saline (the saline covered the asparagus), and ultrasonically treated for 20 min at a power of 500 W to obtain pretreated asparagus;

[0044] (2) placing the pretreated asparagus obtained in step (1) in hot water at a temperature of 120° C. for 40 minutes to obtain blanched asparagus;

[0045] (3) When the blanched asparagus obtained in step (2) is cooled to 30° C., superheated steam and far infrared drying are performed in stages, firstly baking at a temperature of 90° C. and a humidity of 35% for 70 min, then baking at a temperature of 110° C. and a humidity of 35% for 70 min, and finally baking at a temperature of 90° C. and a humidity of 35% for 70 min, to obtain dried asparagus;

[0046] (4) shaping and cutting the dried asparagus obtained in step (3) into small segments of 2 cm in length, and vacuum packaging the segments to obtain finished asparagus segments.

[0047] Example 3

[0048] A method for drying asparagus based on superheated steam, the steps are as follows:

[0049] (1) Select fresh asparagus with a bottom diameter of about 1 cm, weigh them, and place them in 1% saline (the saline covers the asparagus), and treat them ultrasonically at a power of 300 W for 10 minutes to obtain pretreated asparagus;

[0050] (2) placing the pretreated asparagus obtained in step (1) in hot water at a temperature of 100° C. for 20 minutes to obtain blanched asparagus;

[0051] (3) When the blanched asparagus obtained in step (2) is cooled to 20° C., superheated steam and far infrared drying are performed in stages, firstly baking at a temperature of 88° C. and a humidity of 30% for 60 min, then baking at a temperature of 105° C. and a humidity of 30% for 60 min, and finally baking at a temperature of 88° C. and a humidity of 30% for 60 min, to obtain dried asparagus;

[0052] (4) shaping and cutting the dried asparagus obtained in step (3) into small segments of 2 cm in length, and vacuum packaging the segments to obtain finished asparagus segments.

[0053] Comparative Example 1

[0054] The difference between this comparative example and Example 3 is that the preparation method of pre-treated asparagus in step (1) is different. In this comparative example, fresh asparagus with a bottom diameter of about 1 cm is selected, weighed, placed in saturated brine (the brine covers the asparagus), and ultrasonically treated for 10 minutes at a power of 300 W to obtain pre-treated asparagus. The remaining steps are the same as in Example 3.

[0055] Comparative Example 2

[0056] The difference between this comparative example and Example 3 is that the preparation method of the pretreated asparagus in step (1) is different. In this comparative example, fresh asparagus with a bottom diameter of about 1 cm is selected, weighed, placed in clean water (the water covers the asparagus), and ultrasonically treated for 10 minutes at a power of 300 W to obtain pretreated asparagus. The remaining steps are the same as in Example 3.

[0057] Comparative Example 3

[0058] The difference between this comparative example and Example 3 is that the drying method in step (3) is different. In this comparative example, when the blanched asparagus is cooled to 20° C., superheated steam and far infrared drying are used, and the asparagus is baked at a temperature of 105° C. and a humidity of 30% for 3 hours to obtain dried asparagus. The remaining steps are the same as in Example 3.

[0059] Comparative Example 4

[0060] The difference between this comparative example and Example 3 is that step (3) and step (4) are different. In this comparative example, when the blanched asparagus is cooled to 20° C., it is cut into thin slices with a length of 2 cm and a thickness of about 5 mm, and then laid flat and subjected to a microwave vacuum drying method, and treated for 8 hours under the conditions of a microwave power density of 1.5 W / g, a vacuum degree of 0.08 MPa, and a temperature of 60° C., and vacuum-packed to obtain finished asparagus segments. The remaining steps are the same as those in Example 3.

[0061] Comparative Example 5

[0062] A method for drying asparagus, comprising the following steps:

[0063] Select fresh asparagus with a bottom diameter of about 1 cm, wash with clean water, dry and weigh, put the weighed asparagus in 100°C boiling water for 20 minutes, dry again and cut into small pieces with a length of 2 cm, put into an oven, dry at 120°C for 20 hours, and vacuum pack to obtain finished asparagus segments.

[0064] Test example

[0065] 1. Determination of rehydration rate

[0066] The finished asparagus segments prepared in Examples 1 to 3 and Comparative Examples 1 to 5 were respectively immersed in 25° C. pure water, taken out every 5 minutes, and the surface moisture was wiped dry and weighed. When the weight no longer changed, the weight of the saturated asparagus segments was recorded, and the rehydration rate was calculated. The calculation results are shown in Table 1.

[0067] Rehydration rate = weight of saturated asparagus segment / weight of fresh asparagus × 100%

[0068] Table 1 Determination results of rehydration rate of asparagus segments in each treatment group

[0069] Rehydration rate (%) Example 1 88.53 Example 2 91.85 Example 3 92.36 Comparative Example 1 76.94 Comparative Example 2 74.26 Comparative Example 3 82.57 Comparative Example 4 61.33 Comparative Example 5 58.96

[0070] It can be seen from Table 1 that the rehydration rate of the asparagus segments in the treatment groups of Examples 1 to 3 reached 88.53 to 92.36%, which is significantly higher than that of Comparative Examples 1 to 5, indicating that the state of the asparagus segments prepared by the method of the present invention after rehydration is closer to that of fresh asparagus, and the asparagus segments have a better taste after rehydration.

[0071] 2. Color difference measurement

[0072] The total color difference ΔE of the finished asparagus segments prepared in Examples 1 to 3 and Comparative Examples 1 to 5 under saturated conditions was measured using a colorimeter. The measurement results are shown in Table 2.

[0073]

[0074] Among them, L and L* represent the brightness of the tested asparagus and the fresh asparagus, a and a* represent the red and green values ​​of the tested asparagus and the fresh asparagus, b and b* represent the yellow and blue values ​​of the tested asparagus and the fresh asparagus, respectively.

[0075] Table 2 Total color difference of asparagus segments in each treatment group under saturated state

[0076]

[0077]

[0078] As shown in Table 2, the total color difference between the asparagus segments of Examples 1 to 3 in the saturated state and the fresh asparagus is between 0.86 and 1.21, and the total color difference value is small, indicating that the color of the asparagus segments prepared by the present invention after rehydration is close to that of fresh asparagus, and has a good color recovery rate.

[0079] 3. Determination of vitamin C content

[0080] The vitamin C contents of fresh asparagus, asparagus segments prepared in Examples 1 to 3 and Comparative Examples 1 to 5 at saturated state were determined by 2,6-dichloroindophenol titration. The results are shown in Table 3.

[0081] Table 3 Determination results of vitamin C content in asparagus segments of each treatment group

[0082] Vitamin C content (mg / 100g) Example 1 36.7 Example 2 35.8 Example 3 36.5 Comparative Example 1 32.4 Comparative Example 2 34.1 Comparative Example 3 35.3 Comparative Example 4 31.6 Comparative Example 5 28.9 Fresh asparagus 42.1

[0083] It can be seen from Table 3 that the vitamin content of the asparagus segments in Examples 1 to 3 under saturated conditions is between 35.8 and 36.7 mg / 100 g, which is significantly higher than that of Comparative Examples 1 to 5, indicating that the nutrient retention rate of the asparagus segments obtained by the method of the present invention is relatively high.

[0084] 4. Determination of colony count

[0085] The colony counts of fresh asparagus, finished asparagus segments prepared in Examples 1 to 3 and Comparative Examples 1 to 5 were determined in a saturated state by referring to the method specified in the national standard GB4789.2-2022 "National Food Safety Standard Food Microbiological Examination Colony Count Determination", and the results are shown in Table 4.

[0086] Table 4 Colony counts of asparagus segments in each treatment group

[0087] Colony count (CFU / g) Example 1 53 Example 2 50 Example 3 49 Comparative Example 1 46 Comparative Example 2 67 Comparative Example 3 55 Comparative Example 4 64 Comparative Example 5 89 Fresh asparagus 203

[0088] As shown in Table 4, the colony counts of the asparagus segments of Examples 1 to 3 under saturated conditions are between 49 and 53 CFU / g, which are lower than those of Comparative Examples 2 to 5 and fresh asparagus. It can be seen that the method of the present invention can effectively kill microorganisms in asparagus, which is beneficial to improving the preservation effect of asparagus and extending the shelf life.

[0089] As can be seen from the above embodiments, the present invention provides a method for drying asparagus based on superheated steam, which can significantly improve the rehydration rate and color recovery rate of asparagus, and the prepared asparagus has a emerald green color after rehydration, a high nutrient retention rate, and a good taste. The asparagus segments prepared by the present invention can be used for the development and application of convenience foods such as pre-prepared dishes.

[0090] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for drying asparagus based on superheated steam, characterized in that: The asparagus is ultrasonically cleaned, then withered, cooled, and dried in sections using superheated steam and far infrared to obtain dried asparagus.

2. The method according to claim 1, characterized in that The water used in ultrasonic cleaning is saline with a concentration of 1-3%, the power of the ultrasound is 300-500W, and the time is 10-20 minutes.

3. The method according to claim 2, characterized in that The temperature during the fixing is 100-120° C., and the time is 20-40 minutes.

4. The method according to claim 3, characterized in that After killing the green asparagus, cool it to 20-40℃.

5. The method according to claim 4, characterized in that When superheated steam and far infrared staged drying are used, baking is performed at 85-90°C, 100-110°C and 85-90°C for 50-70 minutes respectively.

6. The method according to claim 5, characterized in that The humidity during baking is 25-35%.

7. The method according to any one of claims 1 to 6, characterized in that: The resulting dried asparagus is also cut into sections and packaged.

8. The method according to claim 7, characterized in that The length of the cut segments is 1 to 10 cm, and the packaging is vacuum packaging.

9. Dried asparagus prepared according to the method according to any one of claims 1 to 8.

10. Use of the dried asparagus according to claim 9 in preparing instant food.

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