Method for freezing and refrigerating chestnut kernels

Abstract

The present invention relates to a method for freezing and refrigerating chestnut kernels for preservation, and the specific method includes: sterilizing the chestnut kernels with a composite specific bactericide in coordination with slightly acidic electrolyzed water after pre-treatment of the chestnut kernels, then color-protecting the chestnut kernels with L-cysteine ​​in combination with cold shock treatment, and finally slightly freezing and air conditioning after treating the chestnut kernels with chitosan coating. The present invention uses a specific bactericide needle combined with the synergistic effect of slightly acidic electrolyzed water to completely kill the pathogenic bacteria of chestnuts during storage; L-cys is used to change the molecular spatial structure of PPO that causes browning during chestnut kernel storage, thereby achieving the purpose of inhibiting PPO activity; a microenvironment with high CO2 and low O2 is formed on the surface of the fruit by using a chitosan coating treatment method, and combined with cold shock treatment, the respiration intensity can be reduced to inhibit the activity of PPO polyphenol oxidase and POD peroxidase, while also inhibiting the activity of PAL phenylalanine ammonia lyase, thereby reducing the synthesis of phenolic substances.

Description

Technical Field

[0001] The invention belongs to the field of agricultural product processing and relates to agricultural product preservation technology, in particular to a chestnut kernel freezing and refrigeration preservation method. Background Art

[0002] Chestnut kernels carry insect eggs after being harvested. If they are not sterilized before preservation, they are prone to infection, aging and mildew. Chestnut kernels are rich in starch and other polysaccharides. During storage, starch is hydrolyzed into sugars, which makes chestnuts very easy to brown during preservation. In addition, chestnut kernels have strong respiration and enzyme activity during storage, and are very easy to lose water and dry. In other words, microbial infection, browning and water loss are the key technical issues affecting chestnut kernel preservation.

[0003] In the prior art, chestnut kernels are usually preserved by vacuum air packaging combined with preservatives. The following patent documents are found by searching the published patent documents:

[0004] 1. A plastic packaging preservation method for extending the shelf life of fresh chestnut kernels (CN107455461A). The disclosed technology uses coating preservation combined with silicon window modified atmosphere packaging for fresh chestnut kernels. The technology does not sterilize the chestnut kernels before storage, and the chestnut kernels are easily invaded by microorganisms and cause diseases during storage. In addition, the technology does not perform anti-browning treatment, and the chestnut kernels are prone to browning during storage.

[0005] 2. A method for extending the shelf life of shelled fresh chestnut kernels (CN105532868A). The disclosed technology involves shelling chestnuts, treating them with the natural preservative nisin, and using special packaging bags for spontaneous atmosphere treatment. The technology also does not use color preservatives or color preservative liquids to protect the chestnut kernels, and does not solve the technical problem that chestnuts are prone to browning during storage.

[0006] 3. A method for safe preservation and storage of chestnuts (CN1561765A). This disclosed technology removes the deteriorated or worm-egg-infected chestnut shells before storage, and allows the color-protecting liquid to contact the surface of the chestnut kernels, thereby achieving the purpose of color protection and sterilization. At the same time, ultraviolet sterilization and inert gas-filled refrigerated chestnut kernels are used to preserve the chestnut kernels. However, this technology ignores the hidden pathogenic bacteria infection of chestnut kernels, which are easily invaded by microorganisms during storage and cause diseases. It also does not effectively solve the technical problem of chestnut kernel browning. Summary of the invention

[0007] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method of using slightly acidic electrolyzed water in combination with a bactericide to sterilize + L-cysteine ​​combined with cold shock treatment to protect the color of chestnut kernels + chitosan coating in combination with micro-freezing and controlled atmosphere preservation to effectively solve the technical problems of microbial infection, water loss and browning in chestnut kernel preservation, effectively extend the storage and preservation time of chestnut kernels, and improve the storage quality of chestnut kernels.

[0008] The present invention solves the technical problem by adopting the following technical solutions:

[0009] The method for freezing and refrigerating chestnut kernels is to sterilize the chestnut kernels with composite specific fungicides and slightly acidic electrolyzed water after pre-treatment, then use L-cysteine ​​and cold shock treatment to protect the color of the chestnut kernels, and finally use chitosan coating to treat the chestnut kernels and then slightly freeze and store them in controlled atmosphere. The whole process includes: harvesting → fruit selection → shelling → sterilization → anti-browning treatment → chitosan coating → controlled atmosphere storage. The specific method steps are as follows:

[0010] (1) The harvested chestnuts are shelled to obtain chestnut kernels, which are graded according to color and size, and the chestnut kernels with spots and substandard are selected. The qualified chestnut kernels are washed in batches in running clean water, and the kernels are selected and removed again during the washing process.

[0011] (2) Select shelled chestnut kernels of uniform size and no disease, soak them in a composite specific fungicide for 5 minutes to specifically sterilize the main pathogenic bacteria, and then soak them in slightly acidic electrolyzed water for 3 minutes for sterilization.

[0012] The composite specific fungicide comprises beta-aminobutyric acid, benzyl isothiocyanate BITC and surfactant mannose erythritol lipid, wherein in each mL of the composite specific fungicide, beta-aminobutyric acid: benzyl isothiocyanate BITC: surfactant mannose erythritol lipid = 0.125 g: 0.75 μL: 0.5 μL.

[0013] The preparation method of the composite specific fungicide comprises: using water as a solvent, adding mannose erythritol lipid as a surfactant to improve the fungicidal effect, slowly adding β-aminobutyric acid and benzyl isothiocyanate BITC respectively during stirring after fully dissolving, and continuing stirring until completely dissolved.

[0014] The effective chlorine content of slightly acidic electrolyzed water is 85-90 mg / L and the pH is 5-6.5.

[0015] (3) Soak the chestnut kernels obtained in step (2) in a 1.5:1=g:kg L-cys solution for 100s.

[0016] (4) The chestnut kernels obtained in step (3) are subjected to cold shock treatment for 30-40 minutes at a temperature of 0-1°C.

[0017] (5) Soak the chestnut kernels obtained in step (4) in the chitosan composite solution for 5 minutes and then take them out to complete the coating process.

[0018] The chitosan composite solution preparation method comprises: using 1% acetic acid as a solvent, stirring chitosan until it is dissolved, cooling to room temperature, continuing to stir and slowly adding sodium alginate and total saponin of polygonatum with a mass ratio of 1:3, and continuing to stir until it is completely dissolved.

[0019] (6) The chestnut kernels obtained in step (5) are placed in batches in a cold storage at a temperature of -2.5-0°C and a relative humidity of RH93%-97% for partial freezing storage, and the chestnut kernels are preserved by adjusting the gas composition of the cold storage to accurately maintain the volume percentage of O2 in the cold storage gas at 2%-5%, the volume percentage of CO2 at 2%-4%, and the rest being nitrogen.

[0020] The chestnut kernel preservation process of the present invention adopts the steps of primary selection, classification, shelling, selection, sterilization, anti-browning treatment, chitosan coating, gas conditioning and refrigeration, etc., which can significantly extend the preservation time of chestnut kernels. Multiple processes are used during the impregnation, which respectively have the effects of sterilization, color protection and inhibition of cell respiration. The chestnut kernels stored by this process have no obvious difference in color, taste and nutrition from fresh chestnuts, and the original color and taste of the chestnut kernels are maintained. The process is widely applicable to the chestnut processing industry.

[0021] The advantages and positive effects of the present invention are:

[0022] 1. The effective chlorine component in slightly acidic electrolyzed water can destroy the bacterial cell membrane structure, causing a large amount of intracellular substances to overflow and deoxyribonucleic acid to denature. By inhibiting the action of some oxidases, the active oxygen in the cells accumulates, destroying intracellular nucleic acids, proteins, lipids and other substances, and promoting cell death, thereby achieving the effect of killing microorganisms. Composite specific fungicides are used to specifically sterilize the pathogens anthracnose and penicillium that cause chestnut storage diseases. Among the composite specific fungicides, β-aminobutyric acid inhibitors can significantly inhibit the mycelial growth, spore germination and germ tube elongation of penicillium under the synergistic effect of a slightly acidic environment, increase the relative conductivity of the mycelium and the leakage of proteins and sugars, and effectively kill the main chestnut pathogen Penicillium under the synergistic effect of slightly acidic electrolyzed water; BITC can change the integrity of the bacterial biological oxidation system of anthracnose, affect the production of ATP, and hinder a series of important chemical reactions of coenzymes involved in hydrogen ion transfer in the respiratory chain. It can effectively kill the anthracnose hidden in chestnut kernels with the bactericidal effect of acidic electrolyzed water.

[0023] 2. L-cys can change the spatial structure of PPO molecules to achieve the purpose of inhibiting PPO activity. PPO is an oligomeric enzyme with a complete quaternary structure, and it can only show the strongest catalytic effect when the structure is complete. When its molecular structure is destroyed (loss of hydrophobic interactions, salt bonds, hydrogen bonds, etc.), the subunits separate, and even the structure of the active center changes, resulting in changes in enzyme activity. Cold shock treatment can reduce the respiratory intensity and inhibit the activity of PPO (polyphenol oxidase) and POD (peroxidase), while also inhibiting the activity of PAL (phenylalanine ammonia lyase) and reducing the synthesis of phenolic substances. L-cys pretreatment combined with cold shock treatment can effectively reduce the impact of high enzyme activity on the quality of chestnut kernels and greatly reduce the browning in the subsequent flour making process.

[0024] 3. Aiming at the problem of strong self-respiration of chestnut kernels during storage, the present invention adopts a chitosan coating treatment method. The chitosan film can form a microenvironment with high CO2 and low O2 on the surface of the fruit, while inhibiting the release of ethylene gas, significantly reducing the chestnut respiration intensity and decay rate. Aiming at the problem of high α-amylase activity, the total saponin of Polygonatum sibiricum is added to inhibit the activity of amylase in chestnuts, reduce starch degradation, and maintain the quality of chestnut kernels. At the same time, in view of the shortcomings of chitosan being brittle and easy to crack, the mechanical properties of the chitosan composite film are improved by adding sodium alginate. Micro-freezing can inhibit deterioration reactions such as biochemical degradation in biological tissues and the growth and reproduction of microorganisms, and prolong the storage period. In addition, a small amount of ice crystals formed on the surface or inside of the tissue can be used as a refrigerant to temporarily maintain the storage temperature balance. Atmosphere conditioning can maintain the stability of the gas composition in the cold storage, reduce the respiration of chestnut kernels during storage, and reduce quality loss. It has a significant synergistic and complementary effect, enhances the storage effect of chestnut kernels, and improves the quality of chestnut kernels.

[0025] 4. The present invention is scientifically and reasonably designed, and provides a composite preservation method for extending the shelf life of fresh chestnut kernels. The use of specific fungicides to destroy the physiological processes of anthrax and penicillium, which cause diseases during chestnut storage, and the synergistic effect of slightly acidic electrolyzed water can completely kill the pathogenic bacteria of chestnuts during storage, which can effectively solve the problem that chestnuts carry eggs after picking, are easy to be infested with insects and other microorganisms and rot and deteriorate. By using the method of chitosan coating treatment, a microenvironment with high CO2 and low O2 is formed on the surface of the fruit, while the release of ethylene gas is inhibited, the respiratory intensity and decay rate of chestnuts are significantly reduced, and the addition of total saponins of polygonatum to the chitosan coating inhibits the activity of amylase in chestnuts, reduces starch degradation, and maintains the quality of chestnut kernels. At the same time, the shortcomings of chitosan being brittle and easy to crack are solved. L-cys is used to change the molecular spatial structure of PPO, which causes browning during chestnut kernel storage, to achieve the purpose of inhibiting PPO activity. Combined with cold shock treatment, the respiration intensity can be reduced to inhibit the activity of PPO polyphenol oxidase and POD peroxidase, and the activity of PAL phenylalanine ammonia lyase can also be inhibited, reducing the synthesis of phenolic substances. It can effectively inhibit the browning of chestnut kernels during storage, maintain the original color of chestnut kernels, improve the quality of chestnut kernels, and retain the nutritional value and economic value of chestnuts. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a comparison result of the PPO activity of chestnut kernels stored by the method of the present invention and the PPD activity of the CK control group;

[0027] Figure 2 This is a comparison result of the PPO activity of chestnut kernels stored by the method of the present invention and the PPO activity of the CK control group;

[0028] Figure 3 This is a graph comparing the PPO activity of chestnut kernels stored by the method of the present invention and the starch content of the CK control group. DETAILED DESCRIPTION

[0029] The present invention is further described in detail below through specific examples. The following examples are only illustrative and not restrictive, and the protection scope of the present invention cannot be limited thereto.

[0030] Example 1

[0031] The method for freezing and refrigerating chestnut kernels is as follows:

[0032] (1) The harvested chestnuts are shelled to obtain chestnut kernels, which are graded according to color and size, and the chestnut kernels with spots and substandard are selected. The qualified chestnut kernels are washed in batches in running clean water, and the kernels are selected and removed again during the washing process.

[0033] (2) Select shelled chestnut kernels of uniform size and no disease, soak them in a composite specific fungicide for 5 minutes to specifically sterilize the main pathogenic bacteria, and then soak them in slightly acidic electrolyzed water for 3 minutes for sterilization.

[0034] The composite specific fungicide comprises beta-aminobutyric acid: benzyl isothiocyanate BITC: surfactant mannose erythritol lipid = 0.25 g: 0.15 μL: 0.1 μL.

[0035] The preparation method of the composite specific fungicide comprises: using water as a solvent, adding mannose erythritol lipid as a surfactant to improve the fungicidal effect, slowly adding β-aminobutyric acid and benzyl isothiocyanate BITC respectively during stirring after fully dissolving, and continuing stirring until completely dissolved.

[0036] The effective chlorine content of slightly acidic electrolyzed water is 85 mg / L and the pH is 5.

[0037] (3) Soak the chestnut kernels obtained in step (2) in a 0.3:0.2=g:kg L-cys solution for 100s.

[0038] (4) The chestnut kernels obtained in step (3) are subjected to cold shock treatment for 30 minutes at a temperature of 0-1°C.

[0039] (5) Soak the chestnut kernels obtained in step (4) in the chitosan composite solution for 5 minutes and then take them out to complete the coating process.

[0040] Example 2

[0041] The method for freezing and refrigerating chestnut kernels is as follows:

[0042] (1) The harvested chestnuts are shelled to obtain chestnut kernels, which are graded according to color and size, and the chestnut kernels with spots and substandard are selected. The qualified chestnut kernels are washed in batches in running clean water, and the kernels are selected and removed again during the washing process.

[0043] (2) Select shelled chestnut kernels of uniform size and no disease, soak them in a composite specific fungicide for 5 minutes to specifically sterilize the main pathogenic bacteria, and then soak them in slightly acidic electrolyzed water for 3 minutes for sterilization.

[0044] The composite specific fungicide comprises beta-aminobutyric acid: benzyl isothiocyanate BITC: surfactant mannose erythritol lipid = 0.125 g: 0.75 μL: 0.5 μL.

[0045] The preparation method of the composite specific fungicide comprises: using water as a solvent, adding mannose erythritol lipid as a surfactant to improve the fungicidal effect, slowly adding β-aminobutyric acid and benzyl isothiocyanate BITC respectively during stirring after fully dissolving, and continuing stirring until completely dissolved.

[0046] The effective chlorine content of slightly acidic electrolyzed water is 87 mg / L and the pH is 5.5.

[0047] (3) Soak the chestnut kernels obtained in step (2) in a 1.5:1=g:kg L-cys solution for 100s.

[0048] (4) The chestnut kernels obtained in step (3) were subjected to cold shock treatment for 35 minutes at a temperature of 0-1°C.

[0049] (5) Soak the chestnut kernels obtained in step (4) in the chitosan composite solution for 5 minutes and then take them out to complete the coating process.

[0050] Example 3

[0051] The method for freezing and refrigerating chestnut kernels is as follows:

[0052] (1) The harvested chestnuts are shelled to obtain chestnut kernels, which are graded according to color and size, and the chestnut kernels with spots and substandard are selected. The qualified chestnut kernels are washed in batches in running clean water, and the kernels are selected and removed again during the washing process.

[0053] (2) Select shelled chestnut kernels of uniform size and no disease, soak them in a composite specific fungicide for 5 minutes to specifically sterilize the main pathogenic bacteria, and then soak them in slightly acidic electrolyzed water for 3 minutes for sterilization.

[0054] The composite specific fungicide comprises beta-aminobutyric acid: benzyl isothiocyanate BITC: surfactant mannose erythritol lipid = 0.625 g: 0.75 μL: 0.5 μL.

[0055] The preparation method of the composite specific fungicide comprises: using water as a solvent, adding mannose erythritol lipid as a surfactant to improve the fungicidal effect, slowly adding β-aminobutyric acid and benzyl isothiocyanate BITC respectively during stirring after fully dissolving, and continuing stirring until completely dissolved.

[0056] The effective chlorine content of slightly acidic electrolyzed water is 90 mg / L and the pH is 6.5.

[0057] (3) Soak the chestnut kernels obtained in step (2) in a 7.5:5=g:kg L-cys solution for 100s.

[0058] (4) The chestnut kernels obtained in step (3) are subjected to cold shock treatment for 30 minutes at a temperature of 0-1°C.

[0059] (5) Soak the chestnut kernels obtained in step (4) in the chitosan composite solution for 5 minutes and then take them out to complete the coating process.

[0060] Experimental Results and Discussion

[0061] Figure 1 This is a comparison chart of the PPO activity of chestnut kernels stored by the method of the present invention and the PPD activity of the CK control group. As shown in the figure, the POD activity of the chestnut kernels treated by the experiment in the later stage of storage is significantly lower than that of the CK control group, indicating that the POD activity of the treated chestnut kernels is low and the preservation effect is better.

[0062] Figure 2 This is a comparison chart of the PPO activity of chestnut kernels stored by the method of the present invention and the PPO activity of the CK control group. As shown in the figure, the polyphenol oxidase activity of the chestnut kernels after the experimental treatment is significantly lower than that of the CK control group, and the enzyme activity peak is later, indicating that the treated chestnut kernels have strong anti-browning ability, higher nutritional value and better preservation effect.

[0063] Figure 3 This is a comparison chart of the PPO activity of chestnut kernels stored by the method of the present invention and the starch content of the CK control group. As shown in the figure, the starch content of the chestnut kernels treated by the experiment in the later stage of storage is significantly higher than that of the CK control group, indicating that the starch degradation rate of the treated chestnut kernels is low and the preservation effect is better.

[0064] Although the embodiments of the present invention are disclosed for illustrative purposes, those skilled in the art will appreciate that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments.

Claims

1. A method for preserving chestnut kernels, characterized in that: After the chestnut kernels are pre-treated, the chestnut kernels are sterilized with a composite specific fungicide in cooperation with slightly acidic electrolyzed water, and then the chestnut kernels are color-protected with L-cysteine ​​in cooperation with cold shock treatment, and finally the chestnut kernels are treated with chitosan coating and then slightly frozen and atmosphere-conditioned for preservation. The composite specific fungicide in cooperation with slightly acidic electrolyzed water sterilizes the chestnut kernels, including: soaking the qualified chestnut kernels in the composite specific fungicide for 5 minutes, and then soaking them in slightly acidic electrolyzed water for 3 minutes for sterilization, wherein the composite specific fungicide includes β-aminobutyric acid, benzyl isothiocyanate BITC and surfactant The compound specific fungicide contains β-aminobutyric acid, benzyl isothiocyanate BITC, and surfactant mannose erythritol lipid = 0.125g: 0.75μL: 0.5μL in each mL of the compound specific fungicide. The preparation method of the compound specific fungicide comprises: using water as a solvent, adding mannose erythritol lipid as a surfactant to improve the bactericidal effect, and slowly adding β-aminobutyric acid and benzyl isothiocyanate BITC during stirring after fully dissolving, and continuing to stir until completely dissolved. The effective chlorine content of the slightly acidic electrolyzed water is 85-90mg / L and the pH is 5-6.

5. The method for protecting the color of chestnut kernels by using L-cysteine ​​in combination with cold shock treatment includes: soaking the chestnut kernels sterilized by composite specific fungicide and slightly acidic electrolyzed water in a 1.5g:1kg L-cys solution for 100s, then cold shocking for 30-40min, controlling the temperature at 0-1℃, and coating the chestnut kernels with chitosan for micro-freezing and atmosphere conditioning. The method for preserving the color of chestnut kernels by using L-cysteine ​​in combination with cold shock treatment includes: soaking the chestnut kernels in a chitosan composite solution for 5min and then taking them out, completing the coating treatment, and placing the coated chestnut kernels in batches. The chitosan composite solution is prepared by slightly freezing and storing in a cold storage at a temperature of -2.5-0°C and a relative humidity of RH93%-97%, and the chestnut kernels are kept fresh by regulating the gas composition of the cold storage. The preparation method of the chitosan composite solution comprises: using acetic acid with a mass fraction of 1% as a solvent, stirring the chitosan until it is dissolved, cooling it to room temperature, continuing to stir and slowly adding sodium alginate and total saponin of polygonatum with a mass ratio of 1:3, and continuing to stir until it is completely dissolved. The conditions for the controlled atmosphere preservation are that the volume percentage of O2 in the cold storage gas is 2%-5%, the volume percentage of CO2 is 2%-4%, and the rest is nitrogen.

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