Vegetable preservation method based on ultralow-temperature quick-freezing technology

Abstract

The invention relates to the technical field of food preservation, in particular to a vegetable preservation method based on an ultralow-temperature quick-freezing technology. Comprising the following steps: carrying out cleaning and impurity removal treatment on vegetables to be preserved; rapidly cooling the treated vegetables to a temperature ranging from-40 DEG C to-78 DEG C by using an ultra-low temperature technology for not less than 10 minutes; putting the quick-frozen vegetables into a vacuum package, and keeping the freshness of the vegetables in a low-oxygen environment; a natural antioxidant is added in the packaging process, so that the storage life of the vegetables is further prolonged. According to the vegetable fresh-keeping method based on the ultralow-temperature quick-freezing technology, the freezing technology and packaging materials are optimized, so that the storage time of the vegetables is effectively prolonged, and meanwhile, the original color, texture and nutritional ingredients of the vegetables are kept.

Description

Technical Field

[0001] The invention relates to the technical field of food preservation, and in particular to a vegetable preservation method based on ultra-low temperature quick freezing technology. Background Art

[0002] Vegetables are an indispensable part of human daily diet, rich in vitamins, minerals and dietary fiber, and are very important for human health. However, after harvesting, vegetables are easily invaded by microorganisms and affected by their own metabolic processes, causing them to spoil quickly.

[0003] At present, the common vegetable preservation methods on the market are mainly the following:

[0004] (1) Refrigeration: The most commonly used method for preserving vegetables is to slow down the growth of microorganisms and the respiration of vegetables by lowering the temperature. However, simple refrigeration has limited effect on some vegetables with high water content, has a short shelf life, and is prone to frostbite.

[0005] (2) Controlled atmosphere preservation: By adjusting and controlling the gas composition in the package, such as reducing the oxygen concentration and increasing the carbon dioxide concentration, the respiration of vegetables and the growth of microorganisms are slowed down. However, controlled atmosphere preservation equipment is expensive, complicated to operate, and has limited preservation effect on some vegetables.

[0006] (3) Chemical preservation: Use preservatives or antioxidants to treat vegetables to extend their shelf life. However, the use of chemical substances poses certain safety risks and may have a negative impact on the environment.

[0007] (4) Film preservation: A layer of plastic wrap is applied on the surface of vegetables to reduce water evaporation and microbial invasion. However, film preservation is not effective for some high-moisture vegetables, and there are certain limitations in the selection and use of film materials. Summary of the invention

[0008] The present invention provides a vegetable preservation method based on ultra-low temperature quick freezing technology, which effectively prolongs the storage time of vegetables while maintaining their original color, texture and nutritional components by optimizing the freezing process and packaging materials.

[0009] The technical solution adopted by the present invention is: a vegetable preservation method based on ultra-low temperature quick freezing technology, comprising the following steps:

[0010] Step 1: Wash and remove impurities from the vegetables to be preserved;

[0011] Step 2: Use ultra-low temperature technology to quickly cool the processed vegetables to a temperature between -40°C and -78°C for at least 10 minutes;

[0012] Step 3: Place the quick-frozen vegetables in vacuum packaging and use a low-oxygen environment to maintain their freshness;

[0013] Step 4: Add natural antioxidants during the packaging process to further extend the shelf life of the vegetables.

[0014] As a further improvement of the present invention, during the ultra-low temperature quick freezing process, the temperature change rate is reduced by 5° C. to 10° C. per minute.

[0015] As a further improvement of the present invention, the natural antioxidant is a mixture of vitamin C and vitamin E, wherein the mass ratio of vitamin C to vitamin E is 1-4:1.

[0016] As a further improvement of the present invention, the vacuum packaging material is a biodegradable material and the moisture permeability of the packaging material is lower than 0.1 g / m 2 day, oxygen permeability is less than 0.1ml / m 2 ·day.

[0017] As a further improvement of the present invention, the biodegradable material is made of a composite material consisting of polylactic acid, chitosan and nanocellulose to improve the mechanical properties and barrier properties of the material.

[0018] As a further improvement of the present invention, after the vacuum packaging is completed, the vegetables are placed in a refrigerated environment at -18°C to -25°C for long-term storage.

[0019] As a further improvement of the present invention, the ultra-low temperature quick freezing further includes a step of precooling the vegetables, wherein the precooling temperature is controlled at 5° C. to 10° C., and the precooling time is 30-60 minutes.

[0020] Beneficial effects of the present invention: The present invention not only significantly extends the shelf life of vegetables, but also effectively maintains the quality and nutritional components of vegetables by optimizing the ultra-low temperature quick-freezing process and using environmentally friendly vacuum packaging materials, and has high practical value and market prospects.

[0021] Prolonging the shelf life of vegetables: (1) The present invention uses ultra-low temperature quick freezing technology to quickly cool vegetables to -40°C to -78°C, with a temperature change rate of 5°C to 10°C per minute. This rapid freezing method can minimize the formation of ice crystals and avoid damage to the cell structure caused by large ice crystals, thereby significantly extending the shelf life of vegetables. (2) The present invention performs a pre-cooling treatment before quick freezing, reducing the temperature of vegetables to 5°C to 10°C and continuing for 30 to 60 minutes. The pre-cooling treatment can reduce the water activity in the vegetable cells, reduce the formation of ice crystals during the quick freezing process, further improve the freezing effect, and extend the shelf life of vegetables.

[0022] Maintaining vegetable quality: (1) The present invention reduces the formation and growth of ice crystals through rapid freezing, effectively protects the cell structure of vegetables, avoids the rupture of cell walls and the loss of cell fluid, and enables vegetables to maintain their original color and texture after thawing, with a better taste. (2) A mixture of vitamin C and vitamin E is added during the vacuum packaging process as a natural antioxidant, wherein the mass ratio of vitamin C to vitamin E is 1-4:1, which can effectively prevent oxidation reactions, inhibit the growth of microorganisms, and further maintain the freshness and nutritional content of vegetables. (3) Placing the quick-frozen vegetables in a vacuum package and using a low-oxygen environment to maintain their freshness can effectively slow down the respiration of vegetables and the reproduction of microorganisms, thereby maintaining the high quality of vegetables. DETAILED DESCRIPTION

[0023] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application more clearly understood, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0024] The present invention provides a vegetable preservation method based on ultra-low temperature quick freezing technology, comprising the following steps:

[0025] Step 1: Wash and remove impurities from the vegetables to be preserved, and pre-cool the vegetables. The pre-cooling temperature is controlled at 5°C to 10°C, and the pre-cooling time is 30-60 minutes;

[0026] Step 2: Use ultra-low temperature technology to quickly cool the processed vegetables to a temperature range of -40°C to -78°C for no less than 10 minutes, with a temperature change rate of 5°C to 10°C per minute;

[0027] Step 3: Place the quick-frozen vegetables in vacuum packaging, use a low-oxygen environment to maintain their freshness, and store the vegetables in a cold storage environment at -18°C to -25°C for a long time;

[0028] Step 4: Add natural antioxidants during the packaging process. The natural antioxidants are a mixture of vitamin C and vitamin E, where the mass ratio of vitamin C to vitamin E is 1-4:1, to further extend the shelf life of the vegetables.

[0029] The vacuum packaging material of the present invention is a biodegradable material and the moisture permeability of the packaging material is lower than 0.1g / m 2 day, oxygen permeability is less than 0.1ml / m 2 ·day, the biodegradable material is made of a composite material consisting of polylactic acid, chitosan and nanocellulose to improve the mechanical properties and barrier properties of the material.

[0030] Embodiment 1:

[0031] 1. Experimental materials and equipment

[0032] (1) Vegetables: fresh spinach; (2) Cleaning equipment: high-pressure spray cleaning machine; (3) Precooling equipment: precooling room; (4) Quick freezing equipment: liquid nitrogen quick freezing machine;

[0033] (5) Vacuum packaging machine; (6) Low temperature cold storage;

[0034] (7) Natural antioxidants: a mixture of vitamin C and vitamin E (the mass ratio of vitamin C to vitamin E is 2:1);

[0035] (8) Packaging material: A composite material consisting of polylactic acid (PLA), chitosan and nanocellulose, with a moisture permeability of less than 0.1 g / m 2 day, oxygen permeability is less than 0.1ml / m 2 ·day.

[0036] (II) Experimental steps

[0037] (1) Cleaning and impurity removal: Clean the fresh spinach with a high-pressure spray cleaning machine to remove surface dirt and impurities, and then remove the outer rough part of the spinach.

[0038] (2) Precooling treatment: The cleaned and impurity-free spinach is placed in a precooling room. The precooling temperature is controlled at 7°C for 45 minutes.

[0039] (3) Ultra-low temperature quick freezing: The pre-cooled spinach is quickly placed in a liquid nitrogen quick freezer, the quick freezing temperature is set to -60°C, the temperature change rate is reduced by 7°C per minute, and the quick freezing duration is 15 minutes.

[0040] (4) Vacuum packaging: Place the quick-frozen spinach into a vacuum packaging bag made of a composite material of polylactic acid, chitosan and nanocellulose, and use a vacuum packaging machine to evacuate the bag to ensure a low-oxygen environment inside.

[0041] (5) Adding natural antioxidants: During the packaging process, a mixture of vitamin C and vitamin E is added, wherein the mass ratio of vitamin C to vitamin E is 2:1, and 0.1 gram of antioxidant is added to every 100 grams of spinach.

[0042] (6) Refrigerated storage: Place the vacuum-packed spinach in a -20°C cold storage for long-term storage.

[0043] (III) Experimental results

[0044] After being stored in a -20℃ cold storage for 3 months, the spinach was taken out for thawing and its quality was tested. The results showed that the color of the spinach was well maintained, the texture was fresh and tender, and the retention rate of nutrients (such as vitamin C and chlorophyll) was as high as over 85%.

[0045] In contrast, spinach not processed by the method of the present invention has a storage time of only one month, and obvious yellowing and softening phenomena occur during storage, resulting in serious loss of nutrients.

[0046] Embodiment 2:

[0047] 1. Experimental materials and equipment

[0048] (1) Vegetables: fresh lettuce; (2) Cleaning equipment: sink; (3) Precooling equipment: precooling; (4) Quick freezing equipment: liquid nitrogen quick freezing;

[0049] (5) Vacuum packaging machine; (6) Low temperature cold storage;

[0050] (7) Natural antioxidants: a mixture of vitamin C and vitamin E (the mass ratio of vitamin C to vitamin E is 3:1);

[0051] (8) Packaging material: A composite material consisting of polylactic acid (PLA), chitosan and nanocellulose, with a moisture permeability of less than 0.1 g / m 2 day, oxygen permeability is less than 0.1ml / m 2 ·day.

[0052] (II) Experimental steps

[0053] (1) Cleaning and impurity removal: Clean the fresh lettuce in a sink with running water to remove dirt and impurities on the surface; then manually remove the outer old leaves and roots of the lettuce.

[0054] (2) Precooling treatment: The washed and impurity-free lettuce is placed in a precooling box, the precooling temperature is controlled at 8°C, and the precooling time lasts for 50 minutes.

[0055] (3) Ultra-low temperature quick freezing: The pre-cooled lettuce is quickly placed in a liquid nitrogen quick freezer, the quick freezing temperature is set to -50°C, the temperature change rate is 8°C per minute, and the quick freezing duration is 12 minutes.

[0056] (4) Vacuum packaging: Place the quick-frozen lettuce into a vacuum packaging bag made of a composite material of polylactic acid, chitosan and nanocellulose, and use a vacuum packaging machine to evacuate the bag to ensure a low-oxygen environment inside.

[0057] (5) Adding natural antioxidants: During the packaging process, a mixture of vitamin C and vitamin E is added, wherein the mass ratio of vitamin C to vitamin E is 3:1, and 0.15 grams of antioxidants are added to every 100 grams of lettuce.

[0058] (6) Refrigerated storage: The vacuum-packed lettuce is placed in a -22°C cold storage for long-term storage.

[0059] (III) Experimental results

[0060] After being stored in a -22°C freezer for 4 months, the lettuce was taken out for thawing and its quality was tested. The results showed that the color of the lettuce was well maintained, the texture was fresh and tender, and the retention rate of nutrients (such as vitamin C and chlorophyll) was as high as over 80%.

[0061] In contrast, the lettuce not prepared by the method of the present invention has a storage time of only one month, and obvious yellowing and softening phenomena occur during the storage period, resulting in serious loss of nutrients.

[0062] Embodiment 3:

[0063] 1. Experimental materials and equipment

[0064] (1) Vegetables: fresh green beans; (2) Cleaning equipment: high-pressure spray cleaning machine; (3) Precooling equipment: precooling room; (4) Quick freezing equipment: liquid nitrogen quick freezing machine;

[0065] (5) Vacuum packaging machine; (6) Low temperature cold storage;

[0066] (7) Natural antioxidants: a mixture of vitamin C and vitamin E (the mass ratio of vitamin C to vitamin E is 4:1);

[0067] (8) Packaging material: A composite material consisting of polylactic acid (PLA), chitosan and nanocellulose, with a moisture permeability of less than 0.1 g / m 2 day, oxygen permeability is less than 0.1ml / m 2 ·day.

[0068] (II) Experimental steps

[0069] (1) Cleaning and impurity removal: Clean the fresh green beans with a high-pressure spray cleaning machine to remove surface dirt and impurities.

[0070] (2) Precooling treatment: Place the cleaned green beans in a precooling room, control the precooling temperature at 5°C, and precooling for 60 minutes.

[0071] (3) Ultra-low temperature quick freezing: The pre-cooled green beans are quickly placed in a liquid nitrogen quick freezer, the quick freezing temperature is set to 70°C, the temperature change rate is reduced by 10°C per minute, and the quick freezing duration is 10 minutes.

[0072] (4) Vacuum packaging: The quick-frozen green beans are placed in a vacuum packaging bag made of a composite material of polylactic acid, chitosan and nanocellulose, and the packaging bag is evacuated using a vacuum packaging machine to ensure a low-oxygen environment inside.

[0073] (5) Adding natural antioxidants: During the packaging process, a mixture of vitamin C and vitamin E is added, wherein the mass ratio of vitamin C to vitamin E is 4:1, and 0.2 grams of antioxidants are added to every 100 grams of green beans.

[0074] (6) Refrigerated storage: Place the vacuum-packed green beans in a low-temperature refrigerator at 25°C for long-term storage.

[0075] (III) Experimental results

[0076] After being stored in a low-temperature refrigerator at 25°C for 6 months, the green beans were taken out for thawing and their quality was tested. The results showed that the green beans maintained good color, tender texture, and the retention rate of nutrients (such as vitamin C and protein) was as high as over 88%.

[0077] Compared with green beans not prepared by the method of the present invention, the storage time is only 1.5 months, and obvious yellowing and softening phenomena occur during the storage period, and the nutritional components are seriously lost.

[0078] In summary, it can be seen from the experimental results of the above embodiments 1-3 that the vegetable preservation method based on ultra-low temperature quick freezing technology provided by the present invention can indeed significantly prolong the storage time of vegetables and maintain their high quality and nutritional content.

[0079] Specifically: (1) Ultra-low temperature quick freezing technology: Quick freezing effectively reduces the formation of ice crystals, protects the cell structure of vegetables, avoids damage to cells caused by large ice crystals, and enables vegetables to maintain their original color and texture after thawing. (2) Pre-cooling treatment: Pre-cooling treatment reduces the water activity of vegetables, reduces the formation of ice crystals during the quick freezing process, and further improves the freezing effect. (3) Vacuum packaging and natural antioxidants: Vacuum packaging and the addition of natural antioxidants effectively inhibit the growth of microorganisms and oxidation reactions, ensuring the long-term preservation of vegetables in a low-temperature refrigerated environment.

[0080] Therefore, the vegetable preservation method based on the ultra-low temperature quick freezing technology of the present invention has high practical value and market prospects, and is suitable for various types of vegetables with high moisture content and easy to rot.

[0081] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A vegetable preservation method based on ultra-low temperature quick freezing technology, characterized in that: The following steps are involved: Step 1: Wash and remove impurities from the vegetables to be preserved; Step 2: Use ultra-low temperature technology to quickly cool the processed vegetables to a temperature between -40°C and -78°C for at least 10 minutes; Step 3: Place the quick-frozen vegetables in vacuum packaging and use a low-oxygen environment to maintain their freshness; Step 4: Add natural antioxidants during the packaging process to further extend the shelf life of the vegetables.

2. The vegetable preservation method based on ultra-low temperature quick freezing technology according to claim 1, characterized in that: During the ultra-low temperature quick freezing process, the temperature change rate is 5° C. to 10° C. per minute.

3. The vegetable preservation method based on ultra-low temperature quick freezing technology according to claim 1, characterized in that: The natural antioxidant is a mixture of vitamin C and vitamin E, wherein the mass ratio of vitamin C to vitamin E is 1-4:

1.

4. The vegetable preservation method based on ultra-low temperature quick freezing technology according to claim 1, characterized in that: The vacuum packaging material is a biodegradable material and the moisture permeability of the packaging material is lower than 0.1 g / m 2 day, oxygen permeability is less than 0.1ml / m 2 ·day.

5. The vegetable preservation method based on ultra-low temperature quick freezing technology according to claim 4, characterized in that: The biodegradable material is made of a composite material consisting of polylactic acid, chitosan and nanocellulose to improve the mechanical properties and barrier properties of the material.

6. The vegetable preservation method based on ultra-low temperature quick freezing technology according to claim 1, characterized in that: After the vacuum packaging is completed, the vegetables are placed in a refrigerated environment at -18°C to -25°C for long-term storage.

7. The vegetable preservation method based on ultra-low temperature quick freezing technology according to claim 1, characterized in that: The method also includes precooling the vegetables before ultra-low temperature quick freezing, wherein the precooling temperature is controlled at 5° C. to 10° C. and the precooling time is 30-60 minutes.