Dried shelled walnut with skin and preparation method thereof

Abstract

This invention discloses a method for preparing dried walnuts with their shells intact, belonging to the field of food processing technology. The dried walnuts with their shells intact include the following steps: First, harvesting the walnuts when the green husk begins to turn from green to yellow; Second, breaking down the surface layer of the green husk by abrasion or hot air heating to break down the waxy layer on the surface of the walnut shell; Third, dehydrating the green husk by rapidly dehydrating it at a temperature above 120℃, causing the green husk to dry on the surface of the walnut, forming a tough protective layer; Fourth, drying the walnuts by natural sun drying or using drying equipment. This invention solves the problems of short shelf life after drying walnuts and environmental pollution caused by large amounts of green walnut shells. It not only extends the shelf life of dried walnuts but also improves their flavor, increases their nutritional value, and reduces environmental pollution caused by green walnut shells.

Description

Technical Field

[0001] This application relates to the field of food preparation technology, and in particular to a dried walnut with skin and its preparation method. Background Technology

[0002] Walnuts are rich in nutrients. Every 100g of walnuts contains 50-64g of fat, of which linoleic acid accounts for 71% and linolenic acid for 12%, 15-20g of protein, and 10g of carbohydrates. In addition, they contain elements such as calcium, phosphorus, and iron, as well as carotene, riboflavin, vitamin B6, vitamin E, phospholipids, and tannins, all beneficial to the human body. Drying is a crucial step in the post-harvest processing of walnuts. The traditional walnut drying method is harvesting → removing the green husk → washing → drying. This process generates a large amount of green husk and wastewater from washing the walnuts, causing environmental pollution. In particular, the removal of the green husk often requires the addition of plant hormones such as ethephon, and the potential environmental and biological hazards are still unclear. Furthermore, walnuts produced using this process have a shelf life of only about six months at room temperature in drier northern climates, and an even shorter shelf life in hot and humid southern regions. They often become infested with insects, develop rancid oils, and develop an unpleasant odor, causing problems for walnut processing and consumers, and resulting in resource waste. On the other hand, the green husk of walnuts, also known as "green dragon skin," has a pungent and bitter taste, and is warm and neutral in nature. Traditional Chinese medicine uses it for its heat-clearing and detoxifying, wind-dispelling and tinea-treating, pain-relieving and dysentery-relieving effects. Modern pharmacological research shows that green dragon skin has strong analgesic, anti-inflammatory, and anti-tumor effects; its alcohol and water extracts both exhibit good cytotoxic activity. Walnut green husks contain various secondary metabolites, including phenols, flavonoids, coumarins, terpenes, sterols, and organic acids, which have good preservation, antibacterial, and insecticidal effects. A 5% ethanol extract of walnut green husks not only preserves figs but also maintains their quality and flavor. In traditional walnut drying processes, processing plants often produce 4-5 times the amount of green husks found in dried walnuts, resulting in a significant quantity. Walnut husks contain a variety of substances. When walnut husks piled up in the wild are soaked by rainwater, the leachate flows into channels, rivers (lakes), and lakes, causing serious environmental pollution. Therefore, reducing the environmental pollution caused by walnut husks and extending the shelf life of walnuts have become two major issues in walnut drying. Summary of the Invention

[0003] This invention provides a method for preparing dried walnuts with the peel on, which can solve the problems of short storage period after drying walnuts and environmental pollution caused by a large amount of green walnut peel. It not only extends the storage period after drying walnuts, but also improves the flavor of walnuts, increases the nutritional value of walnuts, and reduces the environmental pollution caused by green walnut peel.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A method for preparing dried walnuts with the skin on includes the following steps:

[0006] Step 1: Harvesting walnuts. Harvest the walnuts when the green husks begin to turn yellow.

[0007] Step 2: Damage the surface of the green husk by using friction or hot air heating to break down the waxy layer on the surface of the walnut's green husk;

[0008] Step 3: Dehydration of green husk. The green husk is rapidly dehydrated at a temperature above 120℃, causing the green husk of the walnut to dry on the surface of the walnut and form a tough protective layer.

[0009] Step 4: Dry the walnuts by sun-drying or using drying equipment.

[0010] The second step involves heating with hot air at a temperature of 50-60℃ and a wind speed of 5-20m / s.

[0011] The fourth step is drying. Depending on the requirements, dry the walnuts to different moisture levels. For dried walnuts: moisture content is 5.5-6.0%, store at room temperature; for semi-fresh walnuts: moisture content is 12-14%, seal in packaging, store at a temperature below 20℃; for fresh walnuts: moisture content is between 15-23%, seal and refrigerate at a temperature below 3℃.

[0012] After the first harvest, the plants are screened, destoned, and magnetically separated.

[0013] The screening process involves using a drum machine to perform strong air screening on the dehydrated walnuts to remove weeds, which takes 4-6 seconds.

[0014] The stone removal process uses a stone removal machine to remove soil, sand, and gravel mixed in with the dehydrated walnuts, which takes 4-6 seconds.

[0015] The magnetic separation process uses a magnetic separator to remove iron filings mixed in with the dehydrated walnuts.

[0016] The beneficial effects of this invention are:

[0017] Compared with traditional walnut drying and processing techniques, the walnut drying and processing method of this invention has fewer steps, is simpler to operate, and ensures quality. It produces walnuts with different moisture contents according to consumption or processing needs. Moreover, it does not remove the green husk, so it does not cause solid or liquid pollution to the environment, nor does it use plant hormones, so it does not pollute the walnut fruit. It effectively extends the shelf life, and the flavor substances obtained from the dried walnuts are richer than those of traditional dried walnuts, making them more appealing to consumers. The retention rates of polyphenols, flavonoids, and unsaturated fatty acids are much higher with extended storage than traditional drying methods, which is conducive to promotion and use. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0019] Figure 1 This is a product image of dried walnuts with skin prepared in Example 1.

[0020] Figure 2 This is a comparison of the peroxide value of walnut kernels during storage between conventionally dried walnuts (blank) in Comparative Example 1 and dried walnuts with skin (sample) in Example 1.

[0021] Figure 3 This study compares the acid value of walnut kernels during storage between conventionally dried walnuts (blank) in Comparative Example 1 and dried walnuts (sample) in Example 1. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1

[0024] A method for preparing dried walnuts with the skin on includes the following steps:

[0025] Step 1: Harvesting walnuts. Harvest the walnuts when the green husks begin to turn yellow.

[0026] Step 2: Screening. A drum machine is used to screen the dehydrated walnuts with strong air to remove weeds. The time is 5 seconds.

[0027] Step 3: De-stone removal. Use a de-stone machine to remove the soil, sand, and gravel mixed in with the dehydrated walnuts. The process takes 5 seconds.

[0028] Step 4: Magnetic separation, using a magnetic separator to remove iron filings mixed in with the dehydrated walnuts;

[0029] Step 5: Damage the surface of the green husk by rubbing to break down the waxy layer on the surface of the walnut's green husk;

[0030] Step 6: Dehydration of green husk. Hot air is used at 130℃ to quickly dehydrate the green husk, so that the green husk of the walnut dries on the surface of the walnut and forms a tough protective layer.

[0031] Step 7: Drying the walnuts. Use natural sun drying to prepare dried walnuts with a moisture content of 5.8%, and store at room temperature.

[0032] Example 2

[0033] A method for preparing dried walnuts with the skin on includes the following steps:

[0034] Step 1: Harvesting walnuts. Harvest the walnuts when the green husks begin to turn yellow.

[0035] Step 2: Screening. A drum machine is used to screen the dehydrated walnuts with strong air to remove weeds. The time is 4 seconds.

[0036] Step 3: De-stone removal. Use a de-stone machine to remove the soil, sand, and gravel mixed in with the dehydrated walnuts. The process takes 6 seconds.

[0037] Step 4: Magnetic separation, using a magnetic separator to remove iron filings mixed in with the dehydrated walnuts;

[0038] Step 5: Destroying the outer layer of the green husk. Hot air is used to destroy the waxy layer on the surface of the green husk of the walnut. The hot air is heated at 65℃ and the wind speed is 20m / s for 9 hours.

[0039] Step 6: Dehydration of the green husk. Hot air is used at 150℃ to quickly dehydrate the green husk, so that the green husk of the walnut dries on the surface of the walnut and forms a tough protective layer.

[0040] Step 7: Drying the walnuts. Use drying equipment to dry them to prepare semi-fresh walnuts with a moisture content of 14%. Seal them in packaging and store them at a temperature below 18℃.

[0041] Comparative Example 1

[0042] Traditional dried walnuts are prepared by removing the green husk using traditional machinery or manual methods and then directly sun-drying them.

[0043] Experimental results:

[0044] 1. Comparison of storage periods

[0045] Figure 2 This is a comparison of the peroxide value of walnut kernels during storage between conventionally dried walnuts (blank) in Comparative Example 1 and dried walnuts with shells (sample) in Example 1. Figure 1As can be seen, the peroxide value of traditionally dried walnut kernels increases sharply with the extension of storage time, accelerating spoilage. However, the peroxide value of dried walnut kernels with skin in Example 1 increases slowly with the extension of storage time. After 3 months, the peroxide value of Comparative Example 1 is 1.08 mg / 100g, while the peroxide value of Example 1 is 0.3 mg / 100g, showing a significant difference between the two.

[0046] Figure 3 This study compares the acid value of walnut kernels during storage between conventionally dried walnuts (blank) and dried walnuts (sample) from Example 1. Figure 2 As can be seen, after 3 months, the acid value of Comparative Example 1 was 4.5 mg / 100g, and the acid value of Example 1 was 1.3 mg / 100g.

[0047] This demonstrates that the dried walnuts prepared by the method of the present invention have a longer storage period.

[0048] 2. Comparison of nutrients

[0049] Table 1 below shows the retention rates of polyphenols, flavonoids, and polyunsaturated fatty acids in the kernels of traditionally dried walnuts (Comparative Example 1) and dried walnuts with shells (Example 1) during storage. Table 1 shows that the retention rates of polyphenols, flavonoids, and polyunsaturated fatty acids in the kernels of the dried walnuts prepared according to this invention are significantly higher than those of traditional drying methods as the storage period increases.

[0050] Table 1. Retention rates of polyphenols, flavonoids, and polyunsaturated fatty acids in walnut kernels during storage.

[0051]

[0052] 2. Comparison of flavor compounds

[0053] Flavor compounds were determined using GC-IMS. Tables 2-3 below show the flavor compounds in conventionally dried walnuts (Comparative Example 1) and dried walnuts with shells (Example 1), respectively. The comparison in Tables 2 and 3 demonstrates that the dried walnuts with shells prepared according to this invention contain a richer variety of flavor compounds than conventionally dried walnuts, and are more appealing to consumers.

[0054] Table 2 Flavor compounds in traditionally dried walnuts

[0055]

[0056]

[0057] Table 3. Flavor compounds in dried walnuts with skin

[0058]

[0059]

[0060] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0061] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method of preparing a skin-on-dry walnut, characterized by, The method comprises the following steps: First step: walnut picking, picking when the green color of walnut green skin begins to change to yellow; Second step: green skin surface layer damage, using friction or hot air heating method to make walnut green skin surface layer wax layer damage; the hot air heating method is: using hot air with temperature of 50-60℃ and wind speed of 5-20m / s to treat for 8-12 hours; Third step: green skin dehydration, rapid dehydration of green skin at temperature above 120℃, making walnut green skin dry on the surface of walnut, forming a layer of tough protective layer; Fourth step: walnut drying, using natural drying or drying equipment to dry.

2. The method of preparing skin-on dry roasted walnut according to claim 1, wherein, The fourth step drying is dried to different moisture according to requirements, wherein, dry walnut: moisture content is 5.5-6.0%, stored at room temperature; semi-fresh-eating walnut: moisture content is 12-14%, sealed packaging, storage temperature is lower than 20℃; fresh-eating walnut: moisture content is between 15-23%, sealed cold storage, storage temperature is lower than 3℃.

3. The method of preparing skin-on dry roasted walnut according to claim 1, wherein, Screening, stone removal and magnetic separation are carried out after the first step picking.

4. The method of preparing skin-on dry roasted walnut according to claim 3, characterized in that, The screening uses a drum machine to remove weeds from the dehydrated walnut by strong wind screening for 4-6 seconds.

5. The method of preparing skin-on dry roasted walnut according to claim 3, wherein, The stone removal uses a stone removal machine to remove the soil, sand and stone blocks mixed in the dehydrated walnut for 4-6 seconds.

6. The method of preparing skin-on dry roasted walnut according to claim 3, wherein, The magnetic separation uses a magnetic separator to remove the iron filings mixed in the dehydrated walnut.

7. The dried walnut with skin prepared by the preparation method according to any one of claims 1-6.

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