Normal-temperature fresh-keeping method for green-peel-removed walnuts

Abstract

The invention relates to a normal-temperature fresh-keeping method for walnuts without green husks, which belongs to the field of fresh-keeping processing and comprises the following steps: (1) pretreating fresh walnuts; (2) preparing a preservative A, putting the pretreated walnuts into the preservative A, and wrapping walnut seed holes and suture lines; (3) taking out the walnuts obtained in the step (2), and rapidly immersing the walnuts in a calcium chloride solution; (4) taking out the walnuts after immersing, and drying the walnuts in a drying oven at 40 DEG C for 1 hour; (5) preparing a preservative B, immersing the walnuts taken out in the step (4) in the preservative B, taking out the walnuts, and drying the walnuts in a drying oven at 40 DEG C for 1 hour; (6) taking out the dried walnuts, spraying a preservative B on the whole walnuts, and drying the walnuts in the drying oven at 40 DEG C again; and (7) taking the fresh walnuts out of the oven, cooling to normal temperature, and performing vacuum packaging. According to the method, the fresh walnuts can be preserved for 60 days at normal temperature, the fresh, crisp and sweet taste of the walnuts is kept, the operation is simple and rapid, the cost is low, and industrial popularization is facilitated.

Description

Technical Field

[0001] The invention relates to the technical field of fresh-keeping processing, and in particular to a room-temperature fresh-keeping method for peeled walnuts. Background Art

[0002] Walnut is one of the four major nuts in the world. Fresh walnuts have a sweet taste and are rich in nutrients such as protein, fatty acids, and amino acids. Compared with dry walnuts, they can minimize the loss of walnut nutrients, so they are deeply loved by consumers and are gradually becoming a consumer fashion in recent years. However, due to their high water content, fresh walnuts are very easy to breed harmful microorganisms and mold during storage. Although the existing freezing and preservation technology can largely solve the problem of fresh walnut mold, long-term freezing will cause the free water in the walnut kernel to freeze and cause cell dehydration when it returns to room temperature and melts, affecting the taste, quality, and nutrition of fresh walnuts.

[0003] The existing walnut preservation solutions include low temperature, irradiation, high voltage static electricity, nitrogen packaging, preservative modified packaging materials, etc. The low temperature preservation effect is limited and the warehouse application has high requirements for facilities and equipment. Irradiation preservation will cause vitamin loss, and the high voltage static electricity preservation operation procedure is complicated. Nitrogen packaging and preservative modified packaging materials need to be used in conjunction with low temperature methods. Moreover, the above methods are all preservation solutions for green-skinned walnuts, and may not be suitable for the preservation of green-skinned walnuts. For example, Chinese patent document CN112868756A provides a normal temperature logistics preservation method for peeled and shelled fresh wet walnuts. The method first performs hydrogen shock preservation treatment on peeled and shelled fresh walnuts, and then innovatively adds a three-dimensional passivation process to the peeled and shelled fresh wet walnuts after hydrogen shock preservation treatment, and puts them into a new mixed atmosphere fresh-keeping packaging to solve the technical problems of fresh walnuts in the later storage period, such as water backflow, browning of walnut kernels, and mold, but it can only be kept fresh at room temperature for 15 days, the operation is complicated, and the preservation time is short. Therefore, it is necessary to provide a room-temperature preservation method for peeled green-shelled walnuts, which can prolong the room-temperature preservation time of the peeled fresh walnuts and is simple and quick to operate. Summary of the invention

[0004] In order to overcome the problems existing in the background technology, the present invention provides a room-temperature preservation method for peeled walnuts, which can achieve room-temperature preservation of fresh walnuts for 60 days and keep the walnut kernels fresh, crispy and sweet. The operation is simple and fast, the cost is low, and it is conducive to industrial promotion.

[0005] To achieve the above object, the present invention is implemented through the following technical solutions: The present invention provides a method for preserving peeled walnuts at room temperature, which specifically comprises the following steps: (1) Pretreatment of fresh walnuts; (2) preparing preservative A, mixing sodium alginate, potassium sorbate, sodium diacetate and water in proportion, stirring the mixture thoroughly to obtain preservative A, placing the pretreated walnuts into the preservative A, and wrapping the seed holes and sutures of the walnuts; (3) taking out the walnuts obtained in step (2) and quickly immersing them in a calcium chloride solution; (4) After immersion, take out the walnuts and bake them in an oven at 40°C for 1 h; (5) preparing preservative B: potassium sorbate, sodium diacetate, food-grade liquid wax and water are mixed in proportion, stirred evenly to obtain preservative B, and the walnuts taken out in step (4) are immersed in preservative B, taken out and placed in a 40° C. oven for 1 h; (6) taking out the walnuts baked in step (5), spraying the preservative B on the whole walnuts, and drying them in a 40° C. oven again; (7) After the fresh walnuts are taken out of the oven, they are cooled to room temperature and vacuum packed.

[0006] In the above technical solution, the pretreatment of fresh walnuts in step (1) is as follows: peeling the fresh walnuts and brushing off the residual fibers and residues on the shell surface.

[0007] In the above technical solution, the preservative A in step (2) contains 10-50 g of sodium alginate, 1-50 g of potassium sorbate, 0.1-20 g of sodium diacetate per liter, and the balance is water.

[0008] In the above technical solution, the concentration of the calcium chloride solution in step (3) is 0.1 mol / L.

[0009] In the above technical solution, in step (3), the fresh walnuts are immersed in the calcium chloride solution for ≥5 seconds.

[0010] In the above technical solution, the preservative B in step (5) contains 1-50 g potassium sorbate, 0.1-20 g sodium diacetate, 70-100 ml food-grade liquid wax per liter, and the balance is water.

[0011] In the above technical solution, the time of immersion in the preservative B in step (5) is 5-10 seconds.

[0012] In the above technical solution, the drying time in step (6) is 0.5 h.

[0013] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention first peels fresh walnuts, and uses preservative A to wrap, calcium chloride solution to immerse, and preservative B to immerse, and then sprays preservative B again after drying, and then cools to room temperature after drying, and vacuum packs, so as to provide a room-temperature preservation technology for fresh walnuts, and can preserve the fresh walnuts at room temperature for 60 days, thereby extending the room-temperature preservation time of the fresh walnuts. The walnut flesh is full, the taste is fresh and tender, and there is no peculiar smell. The auxiliary reagents involved meet the requirements of the national food safety standards, ensure that the fresh walnuts maintain their green food attributes, solve the limitations of the existing cold chain preservation technology such as transportation distance and storage place, and reduce the storage and transportation costs of the fresh walnuts.

[0014] 2. The present invention is easy and quick to operate, and the whole process can be completed within 2 hours, which is conducive to industrial promotion.

[0015] 3. The present invention forms a film on the surface of walnuts by preservatives A and B to maintain its moisture and nutrients, and inhibit the growth of microorganisms on the surface of walnuts and walnut kernels, thereby effectively extending the shelf life of walnuts and preventing them from becoming moldy. The film can not only effectively isolate external air and moisture, but also reduce oxidation reactions and prevent the rancidity and deterioration of walnut kernels. Through the protection of the film, walnuts can maintain good color and taste during storage, and greatly reduce the risk of decay and mildew, thereby achieving long-term preservation. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0017] Figure 1 It is a comparison chart of walnuts in shell preserved at low temperature for 60 days by the traditional method and preserved at room temperature for 60 days by the method of the present invention; Figure 2 It is a comparison chart of walnut kernels preserved at low temperature for 60 days by the traditional method and preserved at room temperature for 60 days by the method of the present invention. DETAILED DESCRIPTION

[0018] In order to make the objectives, technical solutions and advantages of the present invention more clear, the following part will further describe the embodiments of the present application in detail in conjunction with the accompanying drawings.

[0019] When the following description refers to the drawings, unless otherwise indicated, the same numerals in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention.

[0020] In the description of the present invention, it should be understood that the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances. In addition, in the description of the present invention, unless otherwise specified, "plurality" refers to two or more. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. The character " / " generally indicates that the previously associated objects are in an "or" relationship.

[0021] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in this specification are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0022] like Figure 1-2 As shown, the embodiment of the present application proposes a method for preserving peeled walnuts at room temperature, which specifically includes the following steps: (1) Peel the green skin of fresh walnuts and brush off any remaining fiber and debris on the shell surface.

[0023] (2) Preservative A is prepared in a ratio of 10-50 g of sodium alginate, 1-50 g of potassium sorbate, 0.1-20 g of sodium diacetate, and the balance of water per liter of preservative A. The preservative A is fully stirred to obtain preservative A. The pretreated walnuts are placed in the preservative A to cover the seed holes and sutures of the walnuts.

[0024] (3) taking out the walnuts obtained in step (2) and quickly immersing them in a 0.1 mol / L calcium chloride solution for a time of ≥ 5 s; (4) After immersion, take out the walnuts and bake them in an oven at 40°C for 1 hour.

[0025] (5) Preservative B is prepared in a ratio of 1-50 g potassium sorbate, 0.1-20 g sodium diacetate, 70-100 ml food-grade liquid wax, and the balance water per liter of preservative B. The preservative B is obtained after being stirred evenly. The walnuts taken out in step (4) are immersed in the preservative B for 5-10 seconds, and then taken out and placed in a 40° C. oven for 1 hour.

[0026] (6) Take out the walnuts baked in step (5), spray the preservative B on the whole walnuts, and bake them again in a 40°C oven for 0.5 h.

[0027] (7) After the fresh walnuts are taken out of the oven, they are cooled to room temperature and vacuum packed.

[0028] When the method of the present invention is used to process the peeled fresh walnuts, the walnuts still have a fresh and crisp taste and full flesh after being placed at room temperature for 60 days. Compared with the traditional technology, the preservation time is prolonged, the time for the walnut kernel to turn brown and moldy is prolonged, the fresh taste and rich nutrition of the fresh walnuts are maintained, the color of the walnut kernels is maintained unchanged, the operation is simple and convenient, the whole process is completed within 2 hours, is not restricted by the transportation distance, the storage place, etc., does not rely on the low temperature environment, reduces the storage and transportation cost of the fresh walnuts, and is conducive to industrial promotion.

[0029] Example 1 A method for preserving peeled walnuts at room temperature specifically comprises the following steps: (1) Peel the green skin of fresh walnuts and brush off any remaining fiber and debris on the shell surface.

[0030] (2) Prepare preservative A by adding 10 g of sodium alginate, 1 g of potassium sorbate, 0.2 g of sodium diacetate and the remainder of water per liter of preservative A, and stir the mixture thoroughly to obtain preservative A. Place the pretreated walnuts into the preservative A to wrap the seed holes and sutures of the walnuts.

[0031] (3) taking out the walnuts obtained in step (2) and quickly immersing them in a 0.1 mol / L calcium chloride solution for a time of ≥ 5 s; (4) After immersion, take out the walnuts and bake them in an oven at 40°C for 1 hour.

[0032] (5) Prepare preservative B by adding 1 g of potassium sorbate, 0.1 g of sodium diacetate, 70 ml of food-grade liquid wax and the balance of water per liter of preservative B, and stir evenly to obtain preservative B. Immerse the walnuts taken out in step (4) in preservative B for 5 seconds, take them out, and bake them in a 40° C. oven for 1 hour.

[0033] (6) Take out the walnuts baked in step (5), spray the preservative B on the whole walnuts, and bake them again in a 40°C oven for 0.5 h.

[0034] (7) After the fresh walnuts are taken out of the oven, they are cooled to room temperature and vacuum packed.

[0035] After being placed at room temperature for 60 days, the walnut shell and walnut kernel did not turn brown or moldy, the flesh was plump, tasted fresh and tender, and had no peculiar smell.

[0036] Example 2 A method for preserving peeled walnuts at room temperature specifically comprises the following steps: (1) Peel the green skin of fresh walnuts and brush off any remaining fiber and debris on the shell surface.

[0037] (2) Prepare preservative A by adding 30 g of sodium alginate, 10 g of potassium sorbate, 0.3 g of sodium diacetate and the remainder of water per liter of preservative A, and stir the mixture thoroughly to obtain preservative A. Place the pretreated walnuts into the preservative A to wrap the seed holes and sutures of the walnuts.

[0038] (3) taking out the walnuts obtained in step (2) and quickly immersing them in a 0.1 ml / L calcium chloride solution for ≥5 s; (4) After immersion, take out the walnuts and bake them in an oven at 40°C for 1 hour.

[0039] (5) Prepare preservative B by adding 10 g of potassium sorbate, 0.3 g of sodium diacetate, 70 ml of food-grade liquid wax and the balance of water per liter of preservative B, and stir evenly to obtain preservative B. Immerse the walnuts taken out in step (4) in preservative B for 5 seconds, take them out, and bake them in a 40° C. oven for 1 hour.

[0040] (6) Take out the walnuts baked in step (5), spray the preservative B on the whole walnuts, and bake them again in a 40°C oven for 0.5 h.

[0041] (7) After the fresh walnuts are taken out of the oven, they are cooled to room temperature and vacuum packed.

[0042] After being placed at room temperature for 60 days, the walnut shell and walnut kernel did not turn brown or moldy, the flesh was plump, tasted fresh and tender, and had no peculiar smell.

[0043] Example 3 A method for preserving peeled walnuts at room temperature specifically comprises the following steps: (1) Peel the green skin of fresh walnuts and brush off any remaining fiber and debris on the shell surface.

[0044] (2) Prepare preservative A by adding 40 g of sodium alginate, 30 g of potassium sorbate, 10 g of sodium diacetate and the remainder of water per liter of preservative A, and stir the mixture thoroughly to obtain preservative A. Place the pretreated walnuts into the preservative A to wrap the seed holes and sutures of the walnuts.

[0045] (3) taking out the walnuts obtained in step (2) and quickly immersing them in a 0.1 ml / L calcium chloride solution for ≥5 s; (4) After immersion, take out the walnuts and bake them in an oven at 40°C for 1 hour.

[0046] (5) Prepare preservative B by adding 20 g of potassium sorbate, 10 g of sodium diacetate, 80 ml of food-grade liquid wax and the balance of water per liter of preservative B, and stir evenly to obtain preservative B. Immerse the walnuts taken out in step (4) in preservative B for 8 seconds, take them out, and bake them in a 40° C. oven for 1 hour.

[0047] (6) Take out the walnuts baked in step (5), spray the preservative B on the whole walnuts, and bake them again in a 40°C oven for 0.5 h.

[0048] (7) After the fresh walnuts are taken out of the oven, they are cooled to room temperature and vacuum packed.

[0049] After being placed at room temperature for 60 days, the walnut shell and walnut kernel did not turn brown or moldy, the flesh was plump, tasted fresh and tender, and had no peculiar smell.

[0050] Example 4 A method for preserving peeled walnuts at room temperature specifically comprises the following steps: (1) Peel the green skin of fresh walnuts and brush off any remaining fiber and debris on the shell surface.

[0051] (2) Prepare preservative A by adding 40 g of sodium alginate, 20 g of potassium sorbate, 10 g of sodium diacetate and the remainder of water per liter of preservative A, and stir the mixture thoroughly to obtain preservative A. Place the pretreated walnuts into the preservative A to wrap the seed holes and sutures of the walnuts.

[0052] (3) taking out the walnuts obtained in step (2) and quickly immersing them in a 0.1 ml / L calcium chloride solution for ≥5 s; (4) After immersion, take out the walnuts and bake them in an oven at 40°C for 1 hour.

[0053] (5) Prepare preservative B by adding 30 g of potassium sorbate, 10 g of sodium diacetate, 90 ml of food-grade liquid wax and the balance of water per liter of preservative B, and stir evenly to obtain preservative B. Immerse the walnuts taken out in step (4) in preservative B for 8 seconds, take them out, and bake them in a 40° C. oven for 1 hour.

[0054] (6) Take out the walnuts baked in step (5), spray the preservative B on the whole walnuts, and bake them again in a 40°C oven for 0.5 h.

[0055] (7) After the fresh walnuts are taken out of the oven, they are cooled to room temperature and vacuum packed.

[0056] After being placed at room temperature for 60 days, the walnut shell and walnut kernel did not turn brown or moldy, the flesh was plump, tasted fresh and tender, and had no peculiar smell.

[0057] Example 5 A method for preserving peeled walnuts at room temperature specifically comprises the following steps: (1) Peel the green skin of fresh walnuts and brush off any remaining fiber and debris on the shell surface.

[0058] (2) Prepare preservative A by adding 50 g of sodium alginate, 50 g of potassium sorbate, 20 g of sodium diacetate and the remainder of water per liter of preservative A, and stir the mixture thoroughly to obtain preservative A. Place the pretreated walnuts into the preservative A to wrap the seed holes and sutures of the walnuts.

[0059] (3) taking out the walnuts obtained in step (2) and quickly immersing them in a 0.1 ml / L calcium chloride solution for ≥5 s; (4) After immersion, take out the walnuts and bake them in an oven at 40°C for 1 hour.

[0060] (5) Prepare preservative B by adding 50 g of potassium sorbate, 20 g of sodium diacetate, 100 ml of food-grade liquid wax and the balance of water per liter of preservative B, and stir evenly to obtain preservative B. Immerse the walnuts taken out in step (4) in preservative B for 10 seconds, take them out, and bake them in a 40° C. oven for 1 hour.

[0061] (6) Take out the walnuts baked in step (5), spray the preservative B on the whole walnuts, and bake them again in a 40°C oven for 0.5 h.

[0062] (7) After the fresh walnuts are taken out of the oven, they are cooled to room temperature and vacuum packed.

[0063] After being placed at room temperature for 60 days, the walnut shell and walnut kernel did not turn brown or moldy, the flesh was plump, tasted fresh and tender, and had no peculiar smell.

[0064] After 60 days of storage at room temperature, the peeled fresh walnuts obtained in Examples 3-5 of the method of the present invention are relatively fresh, have a better taste, a pure flavor, and better preserved nutritional value. Compared with the traditional method of low-temperature storage, they show better effects. The specific results are shown in Tables 1 and 2.

[0065] Table 1 Comparison of the quality of peeled walnuts preserved at low temperature for 60 days by the traditional method and preserved at room temperature for 60 days by the method of the present invention According to the national standard GB19300-2014, the peroxide value (g / 100g) of nuts should be ≤0.08 and the acid value (mg / g) should be ≤3; according to the national standard GB / T 20398-2021, the moldy fruit rate of walnuts of grade 1 should be ≤0.5%. The peeled fresh walnuts treated by the technology of the present invention meet the above indicators of the national standard after being stored at room temperature for 60 days, and the above indicators are similar to those of freshly picked walnuts.

[0066] Table 2 Sensory evaluation of walnuts preserved at low temperature for 60 days by the traditional method and preserved at room temperature for 60 days by the method of the present invention during storage like Figure 1-2As shown in Table 1-2, after 60 days of low-temperature preservation by the traditional method, the kernels grew mold and had a distinct odor. Although its physical and chemical indicators such as peroxide value, acid value, saponification value, and iodine value were not much different from those of freshly picked fresh-eating walnuts, its moldy fruit rate was as high as 72%, which was quite different from the moldy fruit rate of 60 days of room temperature preservation by the method of the present invention, and did not meet the national standard GB / T 20398-2021, walnuts of excellent grade 1 requirements; while the peeled fresh walnuts preserved by the method of the present invention had plump kernels and good taste after being placed at room temperature for 60 days. Its physical and chemical indicators such as peroxide value, acid value, saponification value, and iodine value were similar to those of freshly picked fresh-eating walnuts, and the moldy fruit rate was only 0.5%, which met the national standard GB / T 20398-2021, walnuts of excellent grade 1 requirements, and the operation was simple and quick. The reagents used met the national food safety standards, maintained the green food attributes of fresh-eating walnuts, did not rely on a low-temperature environment, reduced the storage and transportation costs of fresh-eating walnuts, and were conducive to industrial promotion.

[0067] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A method for preserving peeled walnuts at room temperature, characterized in that: The specific steps include: (1) Pretreatment of fresh walnuts; (2) preparing preservative A, mixing sodium alginate, potassium sorbate, sodium diacetate and water in proportion, stirring the mixture thoroughly to obtain preservative A, placing the pretreated walnuts into the preservative A, and wrapping the seed holes and sutures of the walnuts; (3) taking out the walnuts obtained in step (2) and quickly immersing them in a calcium chloride solution; (4) After immersion, take out the walnuts and bake them in an oven at 40°C for 1 h; (5) preparing preservative B: potassium sorbate, sodium diacetate, food-grade liquid wax and water are mixed in proportion, stirred evenly to obtain preservative B, and the walnuts taken out in step (4) are immersed in preservative B, taken out and placed in a 40° C. oven for 1 h; (6) taking out the walnuts baked in step (5), spraying the preservative B on the whole walnuts, and drying them in a 40° C. oven again; (7) After the fresh walnuts are taken out of the oven, they are cooled to room temperature and vacuum packed.

2. The method for preserving peeled walnuts at room temperature according to claim 1, characterized in that: The pretreatment of fresh walnuts in step (1) comprises: removing the green skin of the fresh walnuts and brushing off the residual fibers and residues on the shell surface.

3. The method for preserving peeled walnuts at room temperature according to claim 1, characterized in that: In step (2), each liter of the preservative A contains 10-50 g of sodium alginate, 1-50 g of potassium sorbate, 0.1-20 g of sodium diacetate, and the balance is water.

4. The method for preserving peeled walnuts at room temperature according to claim 1, characterized in that: The concentration of the calcium chloride solution in step (3) is 0.1 mol / L.

5. A method for preserving peeled walnuts at room temperature according to any one of claims 1 or 4, characterized in that: In step (3), the fresh walnuts are immersed in the calcium chloride solution for ≥5 seconds.

6. The method for preserving peeled walnuts at room temperature according to claim 1, characterized in that: In step (5), each liter of the preservative B contains 1-50 g of potassium sorbate, 0.1-20 g of sodium diacetate, 70-100 ml of food-grade liquid wax, and the balance is water.

7. The method for preserving peeled walnuts at room temperature according to claim 1, characterized in that: The time of immersion in the preservative B in step (5) is 5-10 seconds.

8. The method for preserving peeled walnuts at room temperature according to claim 1, characterized in that: The drying time in step (6) is 0.5 h.

Images