Fruit and vegetable product quality guarantee storage method based on cold storage long shelf life

Abstract

The invention discloses a quality-guaranteeing storage method for fruit and vegetable products based on a cold storage long shelf life, and belongs to the technical field of fruit and vegetable product preservation. The method mainly comprises the following steps: pretreating fruit and vegetable products, preparing Zn / N-doped carbon quantum dots and a thin film, performing electrostatic field and magnetic field treatment, performing carbon quantum dot thin film packaging, performing modified atmosphere packaging, and finally performing refrigeration at 0-4 DEG C. The method can effectively maintain the texture and sense of the fruit and vegetable products, control the microbial growth rate of the fruit and vegetable products, and realize long-shelf-life quality-guaranteeing storage.

Description

Technical Field

[0001] The present invention belongs to the technical field of preservation of fruit and vegetable products, and particularly relates to a method for quality preservation and storage of fruit and vegetable products with a long shelf life based on refrigeration. Background Art

[0002] Fruit and vegetable products are foods made mainly from fruits and vegetables through processing methods such as drying, pickling, canning, freezing, or juicing. They are widely popular due to their convenience, deliciousness, and rich nutrition. They can make up for the deficiencies of fresh fruits and vegetables in terms of storage and portability, providing diverse dietary options for modern fast-paced life and becoming an important source for many people to supplement vitamins, minerals, and dietary fiber. However, fruit and vegetable products also have some drawbacks. For example, some products are prone to spoilage, bacteria may grow if the sanitary conditions during processing are not up to standard, and some processing methods may cause nutrient loss. Some products may add additives such as preservatives and pigments to extend the shelf life or improve the taste, and long-term consumption may be harmful to health. Therefore, it is necessary to find a method that enables fruit and vegetable products to be stored with a long shelf life under refrigeration conditions.

[0003] Ni Haifeng et al. (Publication No.: CN117426415A) disclosed a fruit and vegetable preservative. The specific composition of each component of the preservative is as follows: whey fermentation powder 15 - 25%, polylysine hydrochloride 5 - 15%, nisin 5 - 15%, glycerol monooctanoate 5 - 15%, rosemary extract 5 - 10%, green tea extract 5 - 10%, Chinese prickly ash extract 5 - 15%, and modified starch 25 - 35%. Under this condition, the preservative has a better antibacterial effect, and the antioxidant performance of fruit and vegetable products has increased by 20%. However, this preservative acts directly on fruit and vegetable products and may have an unnecessary impact on their flavor.

[0004] Liu Shengtao et al. (Publication No.: CN111763484A) disclosed a fruit and vegetable preservation gum and its preparation method. The preservation gum contains 70 - 90 parts by weight of preservation powder, 350 - 450 parts by weight of starch, 2 - 4 parts by weight of borax, 3.5 - 5.5 parts by weight of caustic soda, 7 - 9 parts by weight of binder, 3.4 - 5.5 parts by weight of stabilizer, and 450 - 650 parts by weight of water. Under this method, the total number of colonies of fruit and vegetable products has decreased by more than 50%. However, this method is only a packaging technology, and its action form is relatively single, and its effect on fruit and vegetable products is limited.

[0005] Li Suyun et al. (Application No.: CN202210097038.X) disclosed a composite preservative loaded with carbon quantum dots, a preparation method thereof, and an application thereof in the preservation of fresh-cut fruits and vegetables. The invention prepared a composite preservative loaded with carbon quantum dots, and its raw material composition is 2.5% - 4.5% of carrot carbon quantum dots, 1% - 2% of gluten, 1% - 1.5% of chitosan, 1% - 3% of ascorbic acid, 2% - 3% of glycerol, 3% - 5% of absolute ethanol, and the balance is acetic acid buffer solution. This method has good effects in aspects such as anti-browning, water retention, sterilization, and anti-rot. This method uses the immersion method for preservation, and it may leave a part of the preservative on the fruits and vegetables, which will have a certain impact on the safety of fruit and vegetable products.

[0006] Yang Yaling et al. (Application No.: CN201810560029.3) disclosed a zinc-doped carbon quantum dot-coated fruit preservative and its preparation and use methods. The film solution prepared by this method contains 0.1 - 0.5% of zinc-doped carbon quantum dots, konjac gum, chitosan, zinc sulfate, citric acid, ascorbic acid, calcium chloride, and inositol. It has good antibacterial effects and quality preservation functions for fruits such as citrus and litchi. However, the range of fruit and vegetable products applicable to this method is relatively narrow, and the characteristic of easy residue of the coating reduces the safety of fruit and vegetable products.

[0007] Zhang Min et al. (Application No.: CN202011361791.2) disclosed a method for controlling bacteria and improving the quality of special soy products by combining orange carbon quantum dots with microwave-radio frequency treatment. This method first selects high-quality special soy products and puts them into a cooking bag; secondly, mixes orange carbon quantum dots into the seasoning liquid, pours the mixed seasoning liquid into the cooking bag containing special soy products, and performs vacuum packaging; subjects the packaged samples to microwave sterilization, then radio frequency sterilization, and finally performs the second-stage microwave sterilization to obtain special soy products with controlled bacteria and improved quality. This method is economical and effective, and the minimum bactericidal concentration is higher than 100 μg / mL. However, fruit and vegetable products do not have the ability to absorb carbon quantum dots.

[0008] Feng Simin et al. (Application No.: CN202111536168.0) disclosed a preparation method of potato carbon quantum dots and a biodegradable preservative film with high antibacterial activity. This method uses potatoes as raw materials, and through shearing, heating, centrifugation, and filtration, a solution containing carbon quantum dots is obtained. The prepared carbon quantum dot solution is added as a component to a preservative film solution based on green components such as chitosan and polyvinyl alcohol, and after ultrasonic degassing, it is cast on a substrate by a casting method, allowed to stand and cool, and peeled off after drying to obtain a film with strong antibacterial effects. This method can be used to extend the shelf life of fruit and vegetable products, but the action form is relatively single and there is still room for improvement. Summary of the Invention

[0009] The object of the present invention is to provide a method for quality preservation and storage of fruit and vegetable products with a long refrigerated shelf life. By means of Zn / N-doped carbon quantum dots, combined with high-efficiency physical fields and modified atmosphere packaging technology, the growth of microorganisms is inhibited and the starch aging is delayed, enabling fruit and vegetable products to maintain texture, sensory and nutritional values under the condition of 0-4 °C, so as to achieve the purpose of quality preservation and storage with a long shelf life.

[0010] The technical solution of the present invention:

[0011] A method for quality preservation and storage of fruit and vegetable products with a long refrigerated shelf life mainly includes the following steps:

[0012] (1) Pretreatment of fruit and vegetable products: Select newly prepared solid fruit and vegetable products and put them into a sterilized cooking bag for waiting to be processed;

[0013] (2) Synthesis of Zn / N-doped carbon quantum dots: After pulverizing the residue or inferior fruits of yacon, mix them with histidine, zinc acetate and ultrapure water, place them in a hydrothermal reactor, carry out high-temperature reaction in a muffle furnace, after the reaction ends, carry out centrifugal separation on the product, take the supernatant for filtration, and carry out dialysis purification on the filtered liquid, and finally obtain nanoscale Zn / N-doped carbon quantum dots by freeze-drying the supernatant;

[0014] (3) Preparation of carbon quantum dot film: Use carboxymethyl chitosan, gelatin, glycerol, citric acid and Zn / N-doped carbon quantum dots as raw materials to prepare a carbon quantum dot film with specific functions;

[0015] (4) Electrostatic field treatment: Treat the fruit and vegetable products pretreated in step (1) together with the cooking bag in a high-voltage electric field environment;

[0016] (5) Magnetic field treatment: Treat the fruits and vegetables after electrostatic field treatment in step (4) together with the cooking bag in a magnetic field environment;

[0017] (6) Packaging with carbon quantum dot film: Take out the fruits and vegetables after magnetic field treatment in step (5) from the cooking bag, put them into a carbon quantum dot film packaging bag for film packaging, and the carbon quantum dot film packaging bag needs to be in full contact with and closely fit the product surface;

[0018] (7) Modified atmosphere packaging: Put the fruit and vegetable products packaged with carbon quantum dot film in step (6) into a polyethylene packaging bag, fill it with gas with a modified atmosphere packaging machine, and seal it with a heat sealer;

[0019] (8) Storage: Store the fruit and vegetable products packaged with modified atmosphere in step (7) under the condition of 0-4 °C by refrigeration.

[0020] Furthermore, the fruit and vegetable products in step (1) are solid fruit and vegetable products such as dried fruits and vegetables, pickled / pickled vegetables, frozen fruits and vegetables, etc.

[0021] Further, the sterilization treatment of the cooking bag in step (1) needs to go through the following processes: place the cooking bag in boiling water for 15 - 20 minutes of sterilization treatment, and then transfer it to a sterile oven and dry it until there is no moisture on the surface before it can be used.

[0022] Further, in the preparation process of Zn / N - doped carbon quantum dots in step (2), the raw material ratios are as follows: the mass fraction of yacon is 15% - 25%, the mass fraction of histidine is 3% - 5%, the mass fraction of zinc acetate is 1% - 3%, the mass fraction of ultrapure water is 70% - 78%, and the sum of the mass fractions of each component is 100%.

[0023] Further, in the preparation process of Zn / N - doped carbon quantum dots in step (2), the conditions for the centrifugation operation are: the centrifuge speed is set at 8000 rpm, and the centrifugation time is 25 - 35 minutes; the filtration operation uses a microfiltration membrane with a pore size of 200 nm; the dialysis operation uses a dialysis bag with a cut - off molecular weight of 500 D, and the dialysis time is 48 - 72 hours.

[0024] Further, the raw material composition of the carbon quantum dot film in step (3) is as follows: the mass fraction of carboxymethyl chitosan is 1.8% - 2.2%, the mass fraction of gelatin is 1% - 1.4%, the mass fraction of glycerol is 0.4% - 0.8%, the mass fraction of citric acid is 0.1% - 0.3%, and the mass fraction of carbon quantum dots is 0.1% - 0.3%.

[0025] Further, in step (4), the electric field strength range for the electrostatic field treatment is 30 kV / m - 40 kV / m.

[0026] Further, in step (5), the magnetic field strength range for the magnetic field treatment is 6 mT - 8 mT.

[0027] Further, in step (7), the gas composition filled by the modified atmosphere packaging machine is: the volume fraction of O2 is 4% - 6%, the volume fraction of CO2 is 75% - 85%, the volume fraction of N2 is 15% - 25%, and the sum of the volume fractions of the three gases is 100%.

[0028] Further, the density range of the polyethylene film used in step (7) is 0.92 g / cm3 to 0.96 g / cm 3 .

[0029] The beneficial effects of the present invention compared with the prior art are as follows:

[0030] (1) The present invention uses the residual fruits and substandard fruits of yacon as raw materials for carbon dots. Yacon is rich in fructooligosaccharides and cellulose, which can greatly improve the yield of carbon quantum dots. Using residual fruits and substandard fruits can make full use of waste, being more environmentally friendly while reducing costs. Compared with traditional carbon quantum dots, the carbon quantum dots used in the present invention are doped with histidine as the nitrogen source and chelated with zinc acetate as the zinc ion source. Among them, the mass fraction of yacon is 15%-25%, the proportion of histidine is 3%-5%, and the proportion of zinc acetate is 1%-3%. The raw materials are non-toxic and more friendly to food safety. Compared with unmodified carbon quantum dots, the addition of N element can significantly enhance the antibacterial activity of carbon quantum dots. The reason may be that the N-containing groups can promote the reaction between hydroxyl radicals in carbon quantum dots and the cell wall of bacteria, thus killing bacteria more effectively. The addition of Zn not only enhances the antibacterial effect, but also makes the carbon quantum dots have stronger antioxidant effect due to its strong reducibility, further improving the functional properties of carbon quantum dots.

[0031] (2) The film in the present invention is prepared from carbon quantum dots, carboxymethyl chitosan, gelatin, and citric acid. Carboxymethyl chitosan is a chemically modified product formed by introducing carboxymethyl groups onto the chitosan molecule. After the introduction of carboxymethyl groups, the polarity and hydrophilicity of carboxymethyl chitosan are enhanced, so it has better water solubility. Compared with chitosan, carboxymethyl chitosan has lower crystallinity. Since the crosslinking degree of the molecular chain decreases after the introduction of carboxymethyl groups, the molecular spacing increases and the looseness between molecules is enhanced. Therefore, carboxymethyl chitosan is more superior to chitosan in rheological properties. Therefore, after replacing chitosan with carboxymethyl chitosan, it is no longer necessary to adjust the pH value of the solution during the preparation of the film solution, the operation is more convenient, and the film-forming properties are also better. Gelatin, as a plasticizer, greatly improves the tensile properties of the film. Citric acid, as a new crosslinking agent, improves the uniformity and mechanical properties of the film to a certain extent.

[0032] (3) The two high-efficiency physical fields of high-voltage electrostatic field and magnetic field have better preservation effects through synergistic action. Among them, the electric field intensity of the high-voltage electric field is 30 kV / m - 40 kV / m, and the magnetic field intensity of the magnetic field is 6 mT - 8 mT. The high-voltage electrostatic field technology acts through an externally applied electric field, making the medium around the fruit and vegetable products generate ions and photoelectrons. By contacting the surface of bacteria, the cell membrane of bacteria gradually becomes thinner and finally disintegrates and dies, thus achieving the purpose of sterilization, with the advantages of short time consumption, no radiation, no pollution, and low energy consumption. The magnetic field sterilizes bacteria by generating induced current in the bacteria themselves. When the induced current reaches a certain threshold, it will interfere with the charge distribution of the bacterial cell membrane. This interference will affect the process of substances entering and leaving the cell, resulting in the imbalance of the exchange of substances inside and outside the cell, thus achieving the sterilization effect.

[0033] (4) In the modified atmosphere fresh-keeping method provided by the present invention, a filling gas is composed of a specific proportion of O2, CO2, and N2. Among them, the volume ratio of O2 is 4% - 6%, CO2 is 75% - 85%, and N2 is 15% - 25%. Compared with the traditional filling of pure N2 or pure CO2, the gas filling ratio of this method can better inhibit the growth of microorganisms, and on the basis of the existing sterilization technology, the present invention has a better sterilization effect.

[0034] (5) The present invention uses a Zn / N-carbon quantum dot film, combined with the synergistic effect of a high-efficiency physical field and modified atmosphere, to preserve fruit and vegetable products. It makes up for the deficiency that the carbon quantum dot film and modified atmosphere packaging cannot reduce the microbial content of fruit and vegetable products at the initial stage, and also improves the defect that the high-efficiency physical field cannot control the whole process of the storage process of fruit and vegetable products. It can not only reduce the microbial content of fruit and vegetable products, but also maintain the sensory characteristics of fruit and vegetable products, so as to achieve the purpose of long shelf-life preservation under refrigerated conditions.

[0035] The carbon quantum dots used in the present invention are not only doped with N, but also chelated with Zn ions. Compared with the original carbon quantum dots, there are significant improvements in antibacterial and antioxidant properties. Carboxymethyl chitosan has stronger water solubility and rheology, making the film-making process more convenient. Gelatin as a plasticizer and citric acid as a cross-linking agent also make the film-forming properties of the film better. The synergistic effect of the two high-efficiency physical fields can significantly reduce the microbial content of fruit and vegetable products at the initial stage of storage. Modified atmosphere packaging further ensures the quality of fruit and vegetable products during storage.

[0036] The present invention uses a Zn / N-doped carbon quantum dot film, combined with a high-efficiency physical field and modified atmosphere packaging, to carry out quality preservation storage of fruit and vegetable products based on long shelf-life under refrigeration. Sterilize the fruit and vegetable products before storage through a high-efficiency physical field. Continuously sterilize the fruit and vegetable products during storage through a Zn / N-doped carbon quantum dot film. Delay the deterioration of the quality of fruit and vegetable products through modified atmosphere packaging, maintain the moisture content of fruit and vegetable products, and maintain the sensory characteristics of fruit and vegetable products. Detailed implementation mode

[0037] In order to make the purpose, technical solution and advantages of the present invention clearer, the following examples are used to further explain the present invention in detail. It should be understood that the specific examples described here are only used to explain the present invention and are not used to limit the present invention.

[0038] In the following examples of the present invention, the storage environment is a 4°C refrigerator. The samples are all freshly steamed fruit and vegetable products.

[0039] Example 1

[0040] A low-temperature fresh-keeping method for dried apples combining a nano-film and an electromagnetic field mainly includes the following steps:

[0041] (1)Slice fresh apples, freeze them to -30 °C and then freeze-dry them. Select apple chips that are of appropriate size, uniform texture, have no abnormal color, and a dry surface;

[0042] (2)Preparation of Zn / N carbon quantum dot-carboxymethyl chitosan-gelatin blend film: Mix crushed yacon waste fruits / substandard fruits, histidine, zinc acetate, and ultrapure water, place them in a hydrothermal reactor, and carry out a high-temperature reaction in a muffle furnace. Centrifuge, filter, dialyze, and freeze-dry the obtained product to obtain nanoscale Zn / N-doped carbon quantum dots; Prepare a carbon quantum dot film using carboxymethyl chitosan, gelatin, glycerol, citric acid, and Zn / N-doped carbon quantum dots;

[0043] (2)Synthesis of Zn / N-doped carbon quantum dots: After crushing yacon waste fruits or substandard fruits, mix them with histidine, zinc acetate, and ultrapure water, place them in a hydrothermal reactor, and carry out a high-temperature reaction in a muffle furnace. After the reaction, centrifuge the product, take the supernatant for dialysis purification, and finally obtain nanoscale Zn / N-doped carbon quantum dots through a freeze-drying process; Use carboxymethyl chitosan, gelatin, glycerol, citric acid, and Zn / N-doped carbon quantum dots as raw materials to prepare a carbon quantum dot film with specific functions;

[0044] (3)Electrostatic field treatment: Treat the apple chips in a high-voltage electric field environment with an electric field strength of 30 kV / m;

[0045] (4)Magnetic field treatment: Treat the apple chips processed in step (3) in a magnetic field environment with a magnetic field strength of 6 mT;

[0046] (5)Take out the apple chips processed in step (4) from the packaging bag and put them into a packaging bag of the carbon quantum dot film for film packaging. The preparation process of the Zn / N carbon quantum dot-carboxymethyl chitosan-gelatin blend film is as follows: Mix crushed yacon waste fruits / substandard fruits, histidine, zinc acetate, and ultrapure water according to the proportions of 20%, 4%, 2%, and 74% respectively, place them in a hydrothermal reactor, and carry out a high-temperature reaction in a muffle furnace. Centrifuge, filter, dialyze, and freeze-dry the obtained product to obtain nanoscale Zn / N-doped carbon quantum dots; Prepare a carbon quantum dot film using carboxymethyl chitosan, gelatin, glycerol, citric acid, and Zn / N-doped carbon quantum dots;

[0047] (6)Modified atmosphere packaging: Put the apple chips packaged in film in step (5) into a polyethylene packaging bag, fill it with gas using a modified atmosphere packaging machine, and seal it with a heat sealer;

[0048] (7)Storage: Store the apple chips packaged in step (6) under refrigeration at 4 °C.

[0049] Measure the total number of colonies, color difference, and texture changes of the above-prepared rice cakes within 0 - 14 days to analyze their quality changes.

[0050] Example 2

[0051] A low-temperature preservation method for Chinese jujubes by combining nano-film with electromagnetic field mainly includes the following steps:

[0052] (1) After hardening, blanching, and pickling the Chinese jujubes, they are dried by hot air to make pickled Chinese jujube candies. Select pickled Chinese jujube candies with appropriate size, uniform texture, and round and complete appearance;

[0053] (2) Synthesis of Zn / N-doped carbon quantum dots: After crushing the residue or inferior fruits of yacon, mix them with histidine, zinc acetate, and ultrapure water, place them in a hydrothermal reactor, and carry out high-temperature reaction in a muffle furnace. After the reaction, centrifuge the product, take the supernatant for dialysis purification, and finally obtain nano-scale Zn / N-doped carbon quantum dots through freeze-drying process; Using carboxymethyl chitosan, gelatin, glycerol, citric acid, and Zn / N-doped carbon quantum dots as raw materials, prepare a carbon quantum dot film with specific functions;

[0054] (3) Electrostatic field treatment: Treat the pickled Chinese jujube candies in a high-voltage electric field environment with an electric field strength of 40 kV / m;

[0055] (4) Magnetic field treatment: Treat the pickled Chinese jujube candies processed in step (3) in a magnetic field environment with a magnetic field strength of 8 mT;

[0056] (5) Put the pickled Chinese jujube candies processed in step (4) into a carbon quantum dot film packaging bag for film packaging. The preparation process of the Zn / N carbon quantum dot-carboxymethyl chitosan-gelatin blend film is as follows: Mix the crushed residue / inferior fruits of yacon, histidine, zinc acetate, and ultrapure water according to the proportions of 20%, 4%, 2%, and 74% respectively, place them in a hydrothermal reactor, carry out high-temperature reaction in a muffle furnace, and centrifuge, filter, dialyze, and freeze-dry the obtained product to obtain nano-scale Zn / N-doped carbon quantum dots; Prepare a carbon quantum dot film using carboxymethyl chitosan, gelatin, glycerol, citric acid, and Zn / N-doped carbon quantum dots;

[0057] (6) Modified atmosphere packaging: Put the pickled Chinese jujube candies packaged in film in step (5) into a polyethylene packaging bag, fill it with gas using a modified atmosphere packaging machine, and seal it with a heat sealer;

[0058] (7) Storage: Store the pickled Chinese jujube candies packaged in step (6) under refrigeration at 4°C.

[0059] Measure the total number of colonies, color difference, and texture changes of the pickled Chinese jujube candies prepared above within 0 - 14 days to analyze their quality changes.

[0060] Comparative examples 1 - 4: Comparative experiments taking whether to add a carbon quantum dot film and use a high-voltage electric field and a magnetic field as examples.

[0061] Comparative Example 1:

[0062] Compared with Example 1, in this comparative example, steps (2), (3), (4), and (5) were not carried out, and only the dried apples were subjected to modified atmosphere packaging and storage.

[0063] Comparative Example 2:

[0064] Compared with Example 1, in this comparative example, steps (2) and (5) were not carried out, and only the dried apples were subjected to the action of high-voltage electric field and magnetic field, modified atmosphere packaging and storage.

[0065] Comparative Example 3:

[0066] Compared with Example 2, in this comparative example, steps (2), (3), (4), and (5) were not carried out, and only the candied dates were subjected to modified atmosphere packaging and storage.

[0067] Comparative Example 4:

[0068] Compared with Example 2, in this comparative example, steps (2) and (5) were not carried out, and only the candied dates were subjected to the action of high-voltage electric field and magnetic field, modified atmosphere packaging and storage.

[0069] As can be seen from Table 1, compared with Comparative Example 1 and Comparative Example 2, the total number of colonies of the dried apples in Example 1 decreased from 3.41±0.22×10 4 CFU / g to 1.01±0.1×10 4 CFU / g on the 14th day, with an overall decrease of about 70%. Compared with Comparative Example 1, the total number of colonies of the dried apples in Comparative Example 2 decreased by about 17% on the 14th day. It shows that the dried apples after the action of Comparative Example 2 and Example 1 can be stored for a longer time.

[0070] Table 1 Total number of colonies of dried apples under different treatment methods

[0071] Number of months 0 1 2 3 4 5 6 7 Comparative Example 1 5.32±0.24*10^1a 9.32±0.17*10^1a 4.56±0.31*10^2a 8.73±0.41*10^2a 2.32±0.35*10^3a 5.8±0.45*10^3a 9.31±0.12*10^3a 3.41±0.22*10^4a Comparative Example 2 5.32±0.24*10^1a 8.77±0.14*10^1a 4.37±0.29*10^2a 7.32±0.3*10^2a 1.18±0.12*10^3b 4.33±0.28*10^3b 7.34±0.2*10^3b 2.83±0.14*10^4b Example 1 5.32±0.24*10^1a 8.62±0.21*10^1a 3.16±0.1*10^2b 5.73±0.28*10^2b 9.21±0.17*10^2b 2.98±0.32*10^3c 4.71±0.13*10^3c 1.01±0,1*10^4c

[0072] As can be seen from Table 2, the values of L*, a*, and b* of the dried apples in Example 1 decreased more slowly. Compared with Comparative Example 1, the L*, a*, and b* of the dried apples in Comparative Example 2 decreased slowly, but the decreasing speed was faster than that of Example 1, which indicates that the carbon quantum dot film significantly acts on maintaining the stability of the appearance of the dried apples.

[0073] Table 2 Color difference of dried apples under different treatment methods

[0074]

[0075]

[0076] As can be seen from Table 3, the apple chips of Example 1 have a higher degree of retention of hardness and elasticity than those of Comparative Example 1 and Comparative Example 2. The degree of hardness decrease is reduced by 10.4% and 9.6% respectively, and the degree of elasticity decrease is reduced by 4.3% and 4.1% respectively. It shows that the apple chips after the treatment of Example 1 can maintain better texture characteristics.

[0077] Table 3 Texture of apple chips under different treatment methods

[0078]

[0079] As can be seen from Table 4, compared with Comparative Example 3 and Comparative Example 4, the total number of colonies of the processed candied dates on the 14th day decreased from 3.41±0.22×10 4 CFU / g to 6.00±0.31×10 3 CFU / g, with an overall decrease of about 82%. Compared with Comparative Example 3, the total number of colonies of the candied dates in Comparative Example 4 decreased by about 56% on the 14th day. It shows that the candied dates after the treatment of Comparative Example 4 and Example 2 can be stored for a longer time.

[0080] Table 4 Total number of colonies of candied dates under different treatment methods

[0081] Number of months 0 1 2 3 4 5 6 7 Comparative Example 3 3.41±0.16*10^1a 8.77±0.72*10^1a 5.89±0.55*10^2a 9.76±0.41*10^2a 5.54±0.22*10^3a 7.84±0.98*10^3a 1.65±0.27*10^4a 5.20±0.27*10^4a Comparative Example 4 3.41±0.16*10^1a 7.51±0.23*10^1a 1.09±0.12*10^2b 3.33±0.19*10^2b 8.23±0.52*10^2b 2.67±0.31*10^3b 4.27±0.43*10^3b 2.29±0.51*10^4b Example 2 3.41±0.16*10^1a 6.25±0.2*10^1a 8.09±0.33*10^1b 2.75±0.12*10^2b 5.08±0.49*10^2b 8.91±0.15*10^2c 1.44±0.1*10^3c 6.00±0.31*10^3c

[0082] As can be seen from Table 5, the values of L*, a*, and b* of the candied dates after the treatment of Example 2 decreased more slowly. Compared with Comparative Example 3, there were significant differences in L*, a*, and b* of the candied dates in Comparative Example 4, and the difference value was less than that of Example 2. This shows that the candied dates treated with Example 2 have better appearance stability, and the carbon quantum dot film significantly acts on maintaining the appearance stability of the candied dates.

[0083] Table 5 Color difference of candied dates under different treatment methods

[0084] Number of months 0 1 2 3 4 5 6 7 Comparative Example 3 L* 41.27±0.3a 40.21±0.22a 38.02±1.65a 37.00±0.77a 35.75±0.41a 34.2±1.13a 31.95±0.21a 30.01±0.89a Comparative Example 3 a* 12.90±0.44a 11.45±0.33a 10.88±0.29a 10.46±0.28a 9.82±0.078a 9.56±0.36a 8.58±0.71a 8.43±0.077a Comparative Example 3 b* 3.01±0.60a 2.98±0.33a 2.93±0.50a 2.86±0.37a 2.78±0.24a 2.63±0.049a 2.59±0.20a 2.29±0.09a Comparative Example 4 L* 41.27±0.3a 40.24±1.21a 39.13±0.44a 37.24±0.17a 36.55±1.29b 34.34±0.84a 33.37±2.03ab 32.36±0.25b Comparative Example 4 a* 12.90±0.44a 11.90±0.32a 11.43±0.21b 11.28±0.11b 10.86±0.16b 10.32±0.1b 9.74±0.098b 9.61±0.075b Comparative Example 4 b* 3.01±0.60a 2.98±0.27a 2.95±0.24a 2.91±0.88a 2.85±0.43a 2.73±0.051ab 2.68±0.21a 2.40±0.092b Example 2 L* 41.27±0.3a 40.25±1.61a 38.92±0.29a 37.09±2.90a 36.34±1.48b 34.27±1.95a 34.19±2.23b 33.27±1.96c Example 2 a* 12.90±0.44a 12.30±0.12b 11.79±0.78b 11.44±0.13b 10.87±0.25b 10.76±0.80b 10.77±0.092c 10.63±0.11b Example 2 b* 3.01±0.60a 2.99±0.25a 2.96±0.34a 2.93±0.78a 2.89±0.13a 2.84±0.11b 2.79±0.09b 2.71±0.021c

[0085] As can be seen from Table 6, the degrees of retention of hardness, elasticity, and chewiness of the processed candied dates are all higher than those of Comparative Example 3 and Comparative Example 4. The degree of hardness decrease is reduced by 6.1% and 4.2% respectively. The degree of elasticity decrease is reduced by 9.1% and 3.9% respectively.

[0086] Table 6 Texture of candied dates under different treatment methods

[0087]

[0088] In summary, as an auxiliary fresh-keeping means for carbon quantum dot films, the efficient physical field plays a significant role in reducing the microbial content. As a new type of carbon quantum dot film, the Zn / N-doped carbon quantum dot film is of great significance for maintaining the appearance and texture of fruit and vegetable products, and even the microbial content.

[0089] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention.

Claims

1. A method for quality preservation storage of fruit and vegetable products based on refrigeration and long shelf life, characterized in that, It mainly includes the following steps: (1) Pretreatment of fruit and vegetable products: Select newly prepared solid fruit and vegetable products and put them into a sterilized cooking bag for waiting treatment. (2) Synthesis of Zn / N-doped carbon quantum dots: After crushing the residual or inferior yacon fruits, mix them with histidine, zinc acetate and ultrapure water, place them in a hydrothermal reactor, and conduct a high-temperature reaction in a muffle furnace. After the reaction, perform centrifugal separation on the product, take the supernatant for filtration, and purify the filtered liquid by dialysis. Finally, obtain nanoscale Zn / N-doped carbon quantum dots by freeze-drying the supernatant. (3) Preparation of carbon quantum dot film: Use carboxymethyl chitosan, gelatin, glycerol, citric acid and Zn / N-doped carbon quantum dots as raw materials to prepare a carbon quantum dot film with specific functions. (4) Electrostatic field treatment: Treat the fruit and vegetable products pretreated in step (1) together with the cooking bag in a high-voltage electric field environment. (5) Magnetic field treatment: Treat the fruits and vegetables after electrostatic field treatment in step (4) together with the cooking bag in a magnetic field environment. (6) Packaging with carbon quantum dot film: Take out the fruits and vegetables after magnetic field treatment in step (5) from the cooking bag, put them into a carbon quantum dot film packaging bag for film packaging. The carbon quantum dot film packaging bag needs to be in full contact with and closely fit the product surface. (7) Modified atmosphere packaging: Put the fruit and vegetable products packaged with carbon quantum dot film in step (6) into a polyethylene packaging bag, fill it with gas using a modified atmosphere packaging machine, and seal it with a heat sealer. (8) Storage: Store the fruit and vegetable products packaged with modified atmosphere in step (7) under the condition of 0-4°C.

2. The method for quality-preserving storage of fruit and vegetable products with a long refrigerated shelf life according to claim 1, characterized in that, The fruit and vegetable products in step (1) are solid fruit and vegetable products such as dried fruits and vegetables, pickled / pickled vegetables, frozen fruits and vegetables, etc.

3. A method for preserving and storing fruit and vegetable products with a long refrigerated shelf life according to claim 1, characterized in that, The sterilization treatment of the cooking bag in step (1) needs to go through the following treatment: Place the cooking bag in boiling water for 15-20 minutes of sterilization treatment, and then transfer it to a sterile oven and dry it until there is no moisture on the surface before it can be used.

4. A method for quality preservation storage of fruit and vegetable products based on cold storage with a long shelf life according to claim 1, characterized in that, In the preparation process of Zn / N-doped carbon quantum dots in step (2), the raw material ratio is as follows: the mass fraction of yacon is 15%-25%, the mass fraction of histidine is 3%-5%, the mass fraction of zinc acetate is 1%-3%, and the mass fraction of ultrapure water is 70%-78%. The sum of the mass fractions of each component is 100%.

5. A method for preserving and storing fruit and vegetable products with a long refrigerated shelf life according to claim 1, characterized in that, In the preparation process of Zn / N-doped carbon quantum dots in step (2), the conditions for centrifugation operation are: the centrifuge speed is set at 8000 rpm, and the centrifugation time is 25-35 minutes; the filtration operation uses a microfiltration membrane with a pore size of 200 nm; the dialysis operation uses a dialysis bag with a cut-off molecular weight of 500 D, and the dialysis time is 48-72 hours.

6. A method for quality preservation storage of fruit and vegetable products based on cold storage with a long shelf life according to claim 1, characterized in that, In step (3), the raw material composition of the carbon quantum dot film is as follows: the mass fraction of carboxymethyl chitosan is 1.8%-2.2%, the mass fraction of gelatin is 1%-1.4%, the mass fraction of glycerol is 0.4%-0.8%, the mass fraction of citric acid is 0.1%-0.3%, and the mass fraction of carbon quantum dots is 0.1%-0.3%.

7. A method for quality-preserving storage of fruit and vegetable products with a long refrigerated shelf life according to claim 1, characterized in that, In step (4), the electric field strength range for electrostatic field treatment is 30 kV / m - 40 kV / m.

8. A method for quality preservation storage of fruit and vegetable products based on refrigeration and long shelf life according to claim 1, characterized in that, In step (5), the magnetic field strength range for magnetic field treatment is 6 mT - 8 mT.

9. A method for preserving and storing fruits and vegetable products with a long refrigerated shelf life according to claim 1, characterized in that, The gas composition filled by the modified atmosphere packaging machine in step (7) is as follows: the volume fraction of O2 is 4% - 6%, the volume fraction of CO2 is 75% - 85%, and the volume fraction of N2 is 15% - 25%. The sum of the volume fractions of the three gases is 100%.

10. A method for preserving and storing fruits and vegetable products with a long refrigerated shelf life according to claim 1, characterized in that, The density range of the polyethylene film used in step (7) is 0.92 g / cm 3 to 0.96 g / cm 3 .

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