Fruit and vegetable preservation methods

Abstract

The present invention relates to the field of fresh-keeping and discloses a method for preserving fruits and vegetables. The method comprises: immersing the fruits and vegetables in a preservative solution containing a preservative at a concentration of 0.1-8.5 wt% at 22-32°C under microwave conditions; the preservative is selected from at least one of chitosan, glycerol, curcumin, chitosan oligosaccharide, nisin, and zein; and the microwave power is 5-30 W / g of fruit and vegetable. This method can better inhibit bacterial growth and significantly extend the shelf life of fruits and vegetables.

Description

Technical Field

[0001] The present invention relates to the field of fresh-keeping, and in particular to a method for preserving fruits and vegetables. Background Art

[0002] Due to physiological and biochemical processes such as maturation and aging, fruits and vegetables gradually soften and lose firmness after harvest, reducing their quality and nutritional value. This not only complicates transportation but also weakens their resistance to bacteria. Therefore, fruit and vegetable preservation has long been a focus of public attention. Berries like strawberries, for example, are beloved for their vibrant color, juicy texture, sweet and sour flavor, and rich nutrition. However, due to their high water content and thin, unprotected skin, strawberries are susceptible to mechanical damage and microbial contamination during harvesting, storage, and transportation, leading to rot and deterioration. After just one to three days at room temperature, they will discolor, lose flavor, and begin to rot, losing their commercial value. This severely impacts their sales and processing, and in turn hinders the development of the strawberry industry.

[0003] Currently, the main storage and preservation methods for fruits and vegetables, such as strawberries, include low-temperature refrigeration, heat treatment, irradiation, controlled atmosphere storage, and chemical preservatives. However, these methods all have limitations, such as a short shelf life and susceptibility to microbial contamination and deterioration. Therefore, there is an urgent need to develop a green preservation method that can better inhibit bacterial growth, significantly reduce decay, and significantly extend the shelf life of fruits and vegetables. Summary of the Invention

[0004] The purpose of the present invention is to overcome the above-mentioned problems existing in the prior art and to provide a method for preserving fruits and vegetables, which can better inhibit the growth of bacteria and more significantly extend the shelf life of fruits and vegetables.

[0005] To achieve the above object, the present invention provides a method for preserving fruits and vegetables, comprising: immersing the fruits and vegetables in a preservative solution having a preservative concentration of 0.1-8.5 wt% at 22-32°C under microwave conditions;

[0006] Wherein, the preservative is selected from at least one of chitosan, glycerol, curcumin, chitosan oligosaccharide, nisin and zein;

[0007] Wherein, the power of the microwave is 5-30W / g fruits and vegetables.

[0008] The method provided by the present invention can better inhibit bacterial growth, significantly extend the shelf life, and significantly improve the color, hardness and other qualities of fruits and vegetables during the shelf life, thereby increasing their commercial value. It is a green and efficient storage and preservation technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 The microbial growth of fruits and vegetables in Example 2 and Comparative Examples 2-4 is taken as an example;

[0010] Figure 2 The results of the inhibition zone test on gray mold of the fresh-keeping solutions of Example 2, Comparative Example 1, Comparative Example 2 and Comparative Example 4 are shown;

[0011] Figure 3 These are the results of the inhibition zone experiments on Escherichia coli of the fresh-keeping solutions of Example 2, Comparative Example 1, Comparative Example 2, and Comparative Example 4. DETAILED DESCRIPTION

[0012] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0013] The present invention provides a method for preserving fruits and vegetables, comprising: immersing the fruits and vegetables in a preservative liquid with a preservative concentration of 0.1-8.5 wt% (for example, 0.1 wt%, 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 8.5 wt%, and a range formed by any two of the above values ​​or a value within the range) at 22-32° C. (for example, 22° C., 23° C., 24° C., 25° C., 26° C., 27° C., 28° C., 29° C., 30° C., 31° C., 32° C., and a range formed by any two of the above values ​​or a value within the range) under microwave conditions;

[0014] Wherein, the preservative is selected from at least one of chitosan, glycerol, curcumin, chitosan oligosaccharide, nisin and zein;

[0015] The power of the microwave is 5-30 W / g of fruits and vegetables (for example, it can be 5 W / g of fruits and vegetables, 8 W / g of fruits and vegetables, 10 W / g of fruits and vegetables, 13 W / g of fruits and vegetables, 15 W / g of fruits and vegetables, 18 W / g of fruits and vegetables, 20 W / g of fruits and vegetables, 22 W / g of fruits and vegetables, 25 W / g of fruits and vegetables, 28 W / g of fruits and vegetables, 30 W / g of fruits and vegetables, and the range formed by any two of the above values ​​and the value within the range).

[0016] The inventors of the present invention have discovered through research that, by using the above-mentioned method, after immersing fruits and vegetables in a preservative liquid of a specific concentration under specific temperature and microwave conditions, the original quality of the fruits and vegetables (such as hardness, appearance and color, etc.) can be maintained without being significantly affected, while significantly inhibiting the growth of bacteria (especially the inhibition of gray mold and Escherichia coli is more obvious), thereby significantly extending the shelf life of fruits and vegetables.

[0017] Among them, the molecular weight of chitosan oligosaccharide can be 2000-3200Da.

[0018] According to the present invention, preferably, the power of the microwave is 10-20 W / g fruit and vegetable.

[0019] According to the present invention, preferably, the frequency of the microwave is 300-600 MHz (for example, it can be 300 MHz, 350 MHz, 400 MHz, 420 MHz, 450 MHz, 480 MHz, 500 MHz, 550 MHz, 600 MHz, and the range formed by any two of the above values, and values ​​within the range), more preferably 400-500 MHz.

[0020] Under the above conditions, it can be further ensured that the growth of bacteria is further inhibited while the quality of fruits and vegetables is not significantly affected.

[0021] Among them, intermittent microwave equipment with an automatic temperature control device can be used. When the temperature exceeds the specified range, the automatic temperature control device temporarily stops the microwave and automatically turns on the microwave again after the temperature drops. The automatic temperature control device can control the temperature within a relatively small range.

[0022] According to the present invention, preferably, the amount of the preservative liquid used is 1.8-3 L, more preferably 2-2.5 (for example, 2, 2.1, 2.2, 2.3, 2.4, 2.5) L relative to 1 kg of fruits and vegetables.

[0023] The method of the present invention is particularly suitable for preserving strawberries. Therefore, preferably, the fruits and vegetables are selected from strawberries.

[0024] According to the present invention, the solvent of the fresh-keeping liquid is preferably selected from at least one of a C1-C5 alcohol and water, more preferably water. It is understood that the water is preferably sterile water, which can generally be obtained by sterilizing distilled water in an autoclave at 104-137.3 kPa and 121-126°C for 15-30 minutes.

[0025] According to the present invention, preferably, the preservative is chitosan, glycerol and curcumin. The inventors of the present invention further discovered that when the preservative contains the three ingredients mentioned above, it can better cooperate with microwaves to inhibit bacteria and can still better inhibit bacteria during long-term storage.

[0026] According to the present invention, preferably, in the fresh-keeping solution, the concentration of chitosan is 0.1-3wt% (for example, it can be 0.1wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%), the concentration of glycerol is 0.5-5wt% (for example, it can be 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%), the concentration of curcumin is 0.05-0.15wt% (for example, it can be 0.05wt%, 0.06wt%, 0.07wt%, 0.08wt%, 0.09wt%, 0.1wt%, 0.11wt%, 0.12wt%, 0.13wt%, 0.14wt%, 0.15wt%), and the balance is solvent water. The inventors of the present invention have also found that within the above range, the antibacterial effect can be fully guaranteed at a low cost.

[0027] According to the present invention, preferably, the weight average molecular weight of the chitosan is 0.5-15,000 g / mol (for example, 0.5,000 g / mol, 0.8,000 g / mol, 10,000 g / mol, 12,000 g / mol, 13,000 g / mol, or 15,000 g / mol).

[0028] According to the present invention, preferably, the immersion time is 5-8 minutes, more preferably 6-7 minutes.

[0029] According to the present invention, preferably, the immersion temperature is 25-30°C.

[0030] According to the present invention, preferably, after dipping, the fruits and vegetables are taken out, dried and stored at 4-15° C. It is understood that the fruits and vegetables are generally dried naturally until there are no obvious droplets on the surface.

[0031] The present invention will be described in detail below through examples.

[0032] The discontinuous microwave equipment used in the following examples was purchased from Qingdao Mikeway Microwave Innovation Technology Co., Ltd., model MKZ-M2B, which has an automatic temperature control device.

[0033] In the following examples, sterile water was obtained by sterilizing distilled water in an autoclave at 110 kPa and 124° C. for 20 min.

[0034] The strawberries used in the following examples and comparative examples were freshly picked from the same batch.

[0035] Example 1

[0036] A fresh-keeping solution containing chitosan (weight average molecular weight of 10,000 g / mol), glycerol and curcumin was prepared, wherein the concentration of chitosan was 0.1 wt %, the concentration of glycerol was 4.8 wt %, the concentration of curcumin was 0.15 wt %, and the rest was solvent sterile water.

[0037] In an intermittent microwave device, the microwave temperature was set at 25-30°C, the microwave power was 10W / g strawberry, and the microwave frequency was 400MHz. Under these conditions, freshly picked strawberries were immersed in the preservative solution for 6 minutes, and the amount of preservative solution used was 2L relative to 1kg of fruits and vegetables.

[0038] After the soaking is completed, take out the strawberries and dry them naturally until there are no obvious droplets on the surface, and then store them in a refrigerator at 10°C.

[0039] Example 2

[0040] A fresh-keeping solution containing chitosan (weight average molecular weight of 5,000 g / mol), glycerol and curcumin was prepared, wherein the concentration of chitosan was 2 wt %, the concentration of glycerol was 1.8 wt %, the concentration of curcumin was 0.1 wt %, and the rest was solvent sterile water.

[0041] In an intermittent microwave device, the microwave temperature was set at 25-30°C, the microwave power was 15W / g strawberry, and the microwave frequency was 400MHz. Under these conditions, freshly picked strawberries were immersed in the preservative solution for 6.5 minutes, and the amount of preservative solution used was 2.2L per 1kg of fruit and vegetables.

[0042] After the soaking is completed, take out the strawberries and dry them naturally until there are no obvious droplets on the surface, and then store them in a refrigerator at 15°C.

[0043] Example 3

[0044] A fresh-keeping solution containing chitosan (weight average molecular weight of 15,000 g / mol), glycerol and curcumin was prepared, wherein the concentration of chitosan was 3 wt %, the concentration of glycerol was 0.5 wt %, the concentration of curcumin was 0.05 wt %, and the rest was solvent sterile water.

[0045] In an intermittent microwave device, the microwave temperature was set at 25-30°C, the microwave power was 20W / g strawberry, and the microwave frequency was 400MHz. Under these conditions, freshly picked strawberries were immersed in the preservative solution for 7 minutes, and the amount of preservative solution used was 2.5L per 1kg of fruit and vegetables.

[0046] After the soaking is completed, take out the strawberries and dry them naturally until there are no obvious droplets on the surface, and then store them in a refrigerator at 5°C.

[0047] Example 4

[0048] The method of Example 2 was followed, except that in the preservative solution, the concentration of chitosan was 0.05 wt %, the concentration of glycerol was 0.3 wt %, the concentration of curcumin was 3.55 wt %, and the rest was the solvent, sterile water.

[0049] Example 5

[0050] The method of Example 2 was followed, except that the concentration of chitosan in the preservative solution was 3.9 wt %, glycerol and curcumin were not included, and the rest was sterile water.

[0051] Example 6

[0052] The method of Example 2 was followed, except that the concentration of glycerol in the preservative solution was 3.9 wt %, chitosan and curcumin were not included, and the rest was sterile water.

[0053] Example 7

[0054] The method of Example 2 was followed, except that the concentration of curcumin in the preservative solution was 3.9 wt %, chitosan and glycerol were not included, and the rest was sterile water.

[0055] Example 8

[0056] The method of Example 2 was followed, except that the microwave power was 30 W / g strawberry, and the temperature of the microwave equipment was set at 32-35°C.

[0057] Example 9

[0058] The method of Example 2 was followed, except that the immersion time was 10 min.

[0059] Example 10

[0060] The method of Example 2 was followed, except that the preservative in the preservative solution was zein (with a concentration of 3.9 wt%).

[0061] Comparative Example 1

[0062] The method of Example 2 is followed, except that the microwave is turned off throughout the process.

[0063] Comparative Example 2

[0064] The method of Example 2 was followed, except that no preservative solution was used and the strawberries were placed in the intermittent microwave apparatus for 6.5 minutes, but the set temperature, power and frequency of the microwave apparatus remained unchanged.

[0065] Comparative Example 3

[0066] The method of Example 11 is followed, except that the microwave is turned off throughout the process.

[0067] Comparative Example 4

[0068] Take freshly picked strawberries and store them directly in a refrigerator at 15℃.

[0069] Test Example 1

[0070] For the fruits and vegetables treated in each of the above examples and comparative examples, the freshness time was recorded (starting from the time they were placed in the refrigerator) during storage at the respective storage temperatures. The freshness time was determined by testing with a texture analyzer (TA.XTPLUS, purchased from Stable MicroSystems, UK). Strawberries with a hardness less than 150g were considered spoiled (bacterial growth is generally accompanied by a decrease in hardness, and hardness is often used in the preservation field as a measure of preservation effectiveness).

[0071] Table 1

[0072] Example Shelf life (days) Example 1 27 Example 2 26 Example 3 25 Example 4 23 Example 5 22 Example 6 21 Example 7 19 Example 8 18 Example 9 23 Example 10 11 Comparative Example 1 7 Comparative Example 2 6 Comparative Example 3 8 Comparative Example 4 4

[0073] Among them, during the storage in the refrigerator, the number of microorganisms of fruits and vegetables in each embodiment or comparative example is measured and recorded every day. The measurement method is as follows: crush the strawberry sample, dilute and mix it with a strawberry: sterile water mass ratio of 1:500 to obtain a diluted sample liquid, take a certain amount of the diluted sample liquid and apply it on a plate, and after cultivation, each single cell grows and reproduces to form a colony visible to the naked eye, that is, a single colony should represent a single cell in the original sample; count the number of colonies, and the number of microorganisms in the sample can be converted according to its dilution multiple and the sampling inoculation amount. Taking the microbial growth of Example 2 and Comparative Examples 2-4 as an example, the results are shown in FIG. Figure 1 .

[0074] Test Example 2

[0075] The inhibition zone experiment was carried out, and the experimental steps were as follows:

[0076] Take the same batch of freshly picked strawberries as in the example, and isolate microorganisms (including gray mold and Escherichia coli, etc.) from them. Take the inhibition zone experiment of gray mold as an example. The experimental method is as follows: the isolated gray mold is made into a bacterial concentration of 10 6 cfu / ml of bacterial solution, evenly spread on the sterilized plate, select filter paper with uniform texture, use a punch to punch into discs of the same diameter, sterilize and dry, soak in the preservation solution of Example 2, Comparative Examples 1, 2 and 4 respectively, and then place in the test plate to culture for a period of time and measure the size of the inhibition zone. Taking the inhibition zone test on gray mold and the inhibition zone test on Escherichia coli as examples, the results are shown in Figure 2 (Botrytis cinerea) and Figure 3 (Escherichia coli).

[0077] The size of the inhibition zone indicates the growth status of microorganisms. The inventors of the present invention also found that when the preservation solutions of Examples 1 and 3 were used in the inhibition zone experiment, the results were similar to those of Example 2.

[0078] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A method for preserving fruits and vegetables, characterized in that: The method comprises: immersing fruits and vegetables in a preservative liquid containing a preservative at 22-32°C under microwave conditions; Wherein, the preservatives are chitosan, glycerol and curcumin; Wherein, in the preservative solution, the concentration of chitosan is 0.1-3wt%, the concentration of glycerol is 0.5-4.8wt%, the concentration of curcumin is 0.05-0.15wt%, and the balance is solvent water; Wherein, the power of the microwave is 5-30W / g fruit and vegetable; Wherein, the fruits and vegetables are selected from strawberries.

2. The method according to claim 1, wherein The power of the microwave is 10-20W / g fruit and vegetable; And / or, the frequency of the microwave is 300 MHz to 600 MHz.

3. The method according to claim 2, wherein: The frequency of the microwave is 400 MHz-500 MHz.

4. The method according to claim 1 or 2, wherein: For 1kg of fruits and vegetables, the amount of preservative liquid used is 1.8-3L.

5. The method according to claim 4, wherein For 1kg of fruits and vegetables, the amount of preservative liquid used is 2-2.5L.

6. The method according to claim 1, wherein The weight average molecular weight of the chitosan is 0.5-15,000 g / mol.

7. The method according to claim 1, wherein The dipping time is 5-8 minutes; And / or, the immersion temperature is 25-30°C.

8. The method according to claim 7, wherein: The dipping time is 6-7 minutes.

9. The method according to claim 1 or 6, wherein: The method further comprises: after the soaking, taking out the fruits and vegetables, drying them and storing them at 4-15°C.

10. Use of the method according to any one of claims 1 to 9 for inhibiting the growth of gray mold and Escherichia coli in strawberries and improving the firmness of strawberries during shelf life.

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