Method and product for improving shelf life quality of fresh-cut vegetables based on green cold sterilization

Abstract

The present invention relates to a method for improving the shelf life quality of fresh-cut vegetables based on green cold sterilization and a product thereof, belonging to the technical field of antibacterial preservation of fresh fruits and vegetables. The method comprises placing fresh-cut vegetables in a solution containing slightly acidic electrolyzed water (SAEW), nisin, zinc gluconate / ferrous gluconate (C 12 H 22 O 14 Zn / C 12 H 22 FeO 14 ) and micro-nano ultrasonic technology for treatment, combined with dehydration, packaging and refrigeration steps, effectively delaying the browning of fresh-cut vegetables and inhibiting the growth of microorganisms, significantly improving the shelf life quality. Preferably, the effective chlorine content of SAEW is 50mg / L, the mass concentration of nisin is 300mg / L, the micro-nano ultrasonic treatment frequency is 20‑40kHz, the power density is 100‑300W / L, and the treatment time is 5min. The experimental results show that when the method is stored at 10±1°C for the 8th day, the browning index and the total number of microbial colonies of fresh-cut vegetables are significantly reduced, and a high color, chlorophyll content and taste quality are maintained, while the growth of Acidovorax and Plectosphaerella is inhibited. The present invention has broad application prospects in the field of fresh-cut vegetable preservation, especially in extending the shelf life, improving quality and reducing energy consumption. Excellent effects are shown.

Description

Technical Field

[0001] The invention belongs to the technical field of antibacterial and fresh-keeping of fresh fruits and vegetables, and more specifically relates to a method and a product for improving the shelf life quality of fresh-cut vegetables based on green cold sterilization. Background Art

[0002] With the improvement of residents' living standards and the acceleration of the pace of life, pre-packaged vegetable salads have gradually become the favorite choice of consumers due to their freshness, nutrition, health and convenience. However, during the processing, transportation, storage and sales of pre-packaged vegetable salads, they are easily affected by multiple factors such as mechanical damage, physiological metabolism, microbial contamination and temperature fluctuations, resulting in a series of adverse phenomena such as tissue softening, enzymatic browning, and loss of nutrients, which significantly shortens the shelf life of the product. In order to ensure that consumers can enjoy fresh and safe fresh-cut vegetables for a longer period of time, extending their shelf life has become a technical problem that the vegetable industry needs to solve urgently.

[0003] Traditional preservation technologies usually rely on low-temperature refrigeration, modified atmosphere packaging, chemical preservatives and other means. Although these technologies can slow down the quality deterioration of fresh-cut vegetables to a certain extent, they often face some limitations. Patent publication CN113180213B reports a preservation method for extending the shelf life of fresh-cut asparagus, which adopts different cleaning methods combined with cinnamon essential oil fumigation for fresh-cut asparagus preservation. This method can effectively inhibit the growth of microorganisms, delay the aging of fresh-cut asparagus and the degradation of chlorophyll, delay the increase of lignin content, maintain nutritional quality, and maintain the good sensory quality of fresh-cut asparagus, thereby achieving the purpose of extending its shelf life. Patent publication CN108967521A reports a composite antioxidant fresh-cut vegetable preservative and its preparation method and application, wherein the active ingredients of the fresh-cut vegetable preservative include 0.05% to 0.5% of bamboo leaf antioxidants and 0.5% to 1.5% of calcium ascorbate. A certain amount of fresh-cut vegetables are soaked in the preservative at room temperature for a certain period of time, and then packaged and refrigerated. Although the above technologies provide some ideas for sterilizing and preserving fresh-cut vegetables, they lack effective solutions for anti-oxidation, scavenging free radicals and inhibiting browning. In addition, the existing cold chain transportation and shelf conditions cannot guarantee the stability of conditions at around 4°C. Frequent high temperature fluctuations accelerate the deterioration of vegetable quality, including browning, softening, dehydration and excessive microorganisms, which greatly reduce the commodity value during the shelf life and make it difficult to meet the demand of modern consumers for high-quality food. Summary of the invention

[0004] In view of the above technical problems, the present invention provides a method and product for improving the shelf life quality of fresh-cut vegetables by cold sterilization. By combining slightly acidic electrolyzed water SAEW, nisin, zinc gluconate and / or ferrous gluconate and micro-nano ultrasonic treatment technology for pre-packaged vegetable salad preservation at 10°C, the browning of fresh-cut vegetables and microorganisms are effectively inhibited, the texture and appearance quality are maintained, the shelf life quality and commodity value are extended, and the people's increasingly diversified and healthy food needs are met.

[0005] To achieve the above objectives, in a first aspect, the present invention provides a method for improving the shelf life quality of fresh-cut vegetables based on green cold sterilization, comprising the following steps:

[0006] Precooling: Put the purchased fresh vegetables in the refrigerator to precool for about 12 hours;

[0007] Raw material preparation: remove the damaged parts of the pre-cooled fresh vegetables, select vegetables with bright colors and uniform sizes, wash them and set aside;

[0008] Cutting: Take the washed vegetable raw materials and cut the vegetables separately with a sterilized kitchen knife to obtain fresh-cut vegetables;

[0009] Soaking: placing the fresh-cut vegetables in a composite treatment system comprising slightly acidic electrolyzed water, nisin, zinc gluconate and / or ferrous gluconate, and a micro-nano ultrasonic device for treatment;

[0010] Dehydration: using a vegetable drying machine to dry the fresh-cut vegetables for 30 to 60 seconds to obtain fresh-cut vegetables to be packaged;

[0011] Packaging: Packing the fresh-cut vegetables to be packaged, wherein each bag has a weight of 70 to 80 g, and sealing and packaging with a sealing machine to obtain fresh-cut vegetable products;

[0012] Storage: The fresh-cut vegetable products are stored at 4-10°C.

[0013] The effective chlorine content (ACC) of the slightly acidic electrolyzed water is 10-70 mg L-1, the mass concentration of nisin is 100-500 mg L-1, and the zinc gluconate C 12 H 22 O 14 The concentration of Zn solution is 0~2.4mg L-1, and the concentration of ferrous gluconate C 12 H 22 FeO 14 The concentration of the solution is 0 to 15 mg L-1.

[0014] In the method for improving the shelf life quality of fresh-cut vegetables based on green cold sterilization of the present invention, the fresh-cut vegetables can be mixed and immersed in an immersion solution composed of slightly acidic electrolyzed water, nisin, zinc gluconate and / or ferrous gluconate, wherein slightly acidic electrolyzed water and nisin are necessary, and one of zinc gluconate and ferrous gluconate or both are included; the fresh-cut vegetables can also be immersed in sections, that is, first immersed in slightly acidic electrolyzed water for a certain period of time, and then immersed in a composite solution of nisin and zinc gluconate and / or ferrous gluconate solution.

[0015] Preferably, the temperature of the composite treatment system is 4-10°C, and the oxidation-reduction potential (ORP) of the slightly acidic electrolyzed water is greater than or equal to 850mV, and the pH value is 5-6.5. The higher oxidation-reduction potential of slightly acidic electrolyzed water can enhance its oxidative capacity, help destroy the cell structure of microorganisms, and achieve a bactericidal effect; and within the pH range of 5-6.5, the bactericidal components such as hypochlorous acid in slightly acidic electrolyzed water can remain stable and exert the best bactericidal effect.

[0016] In some embodiments, the micro-nano ultrasonic device is an ultrasonic rod or an ultrasonic preparation device. When the amount of fresh-cut vegetables to be soaked is relatively small, a good ultrasonic treatment effect can be achieved by selecting an ultrasonic rod. When the amount of fresh-cut vegetables to be soaked is large, an ultrasonic preparation device such as ultrasonic waves can be used. Optionally, the length and diameter of the ultrasonic rod are 42 cm and 4 cm respectively, the water level is 5 to 10 cm, the treatment frequency is 20 to 40 kHz, the power density is 100 to 300 W / L, the treatment time is 2 to 10 min, and during the treatment process, the zinc gluconate and / or ferrous gluconate solution is used together with nisin. Within the above-mentioned treatment frequency, power density and treatment time range, the tiny bubbles and strong shock waves generated by the cavitation effect of ultrasonic waves in the liquid are used to accelerate the rapid action of the solute effective components on the surface of the vegetables, and destroy the cell walls of the surface microorganisms, thereby improving the sterilization effect.

[0017] Preferably, the effective chlorine content ACC of the slightly acidic electrolyzed water is not less than 50 mg L-1, and the mass concentration of nisin is 300 mg L-1.

[0018] More preferably, the "immersion" step comprises the following operations:

[0019] The fresh-cut vegetables are first soaked in slightly acidic electrolyzed water for 5 to 20 minutes to obtain pretreated fresh-cut vegetables;

[0020] The pretreated fresh-cut vegetables are transferred into a composite solution containing nisin and zinc gluconate and / or ferrous gluconate solution and soaked for 5 to 20 minutes;

[0021] Wherein, the slightly acidic electrolyzed water and the composite liquid containing nisin and zinc gluconate and / or ferrous gluconate solution are first treated with a micro-nano ultrasonic device for 2 to 10 minutes before being used to soak the fresh-cut vegetables and the pre-treated fresh-cut vegetables respectively. With such a setting, the effective ingredients in the slightly acidic electrolyzed water and the composite liquid containing nisin and zinc gluconate and / or ferrous gluconate solution will be distributed more evenly, and the soaking effect of fresh-cut vegetables or pre-treated fresh-cut vegetables will be better. Moreover, the slightly acidic electrolyzed water first kills the bacteria and microorganisms in the fresh-cut vegetables, and then nisin with broad-spectrum antibacterial activity and zinc gluconate with color protection and antioxidant properties are used. 12 H 22 O 14 Zn / Fe(II) Gluconate C 12 H 22 FeO 14 Further kill residual bacteria and effectively inhibit bacteria and protect color, achieving excellent bactericidal, antibacterial and color-protecting effects.

[0022] Slightly acidic electrolyzed water (SAEW) has become a natural bactericidal preservative with great potential in the field of food processing due to its green, safe and low toxicity characteristics. Slightly acidic electrolyzed water generates hypochlorous acid through electrolysis of water, which has a strong antibacterial effect, can effectively inhibit the growth of microorganisms and delay the spoilage process of food. In addition, the antimicrobial peptide Nisin, as a natural preservative, has been widely used in processed foods. It has a significant antibacterial effect and is harmless to the human body. Although the application of Nisin in processed foods is relatively mature, research in the field of fresh-cut vegetable preservation is still relatively limited. Zinc / iron, as an important metal element, has a strong antioxidant effect. It removes free radicals and reduces oxidative stress by activating antioxidant enzymes (such as SOD), and can directly capture free radicals, stabilize cell membranes, and thus protect cells from oxidative damage. In addition, zinc / iron also participates in the protection mechanism of chlorophyll, promotes chlorophyll synthesis, and delays chlorophyll degradation, thereby effectively maintaining the color and freshness of fresh-cut vegetables. Therefore, the addition of zinc / iron not only helps to improve the antioxidant capacity of vegetables, but also helps to protect chlorophyll, delay browning, and improve the quality of fresh-cut vegetables.

[0023] In addition, as a new physical sterilization method, micro-nano ultrasonic technology uses the cavitation effect of ultrasound in liquid to generate tiny bubbles and strong shock waves to accelerate the rapid action of solute effective components on the surface of vegetables and destroy the cell walls of surface microorganisms to improve the sterilization effect. The application of micro-nano ultrasonic technology in food preservation, especially in the treatment of agricultural products such as vegetables and fruits, has shown excellent results. Compared with traditional chemical treatment, micro-nano ultrasonic technology is more green and has fewer side effects.

[0024] Preferably, the fresh-cut vegetable products can be stored at 10±1°C or other refrigerated temperature conditions below this temperature condition. Storing fresh-cut vegetable products at 10±1°C requires lower refrigeration capacity of refrigeration equipment than at 4°C, thereby reducing energy consumption and costs. However, the traditional practice of storing fresh-cut vegetable products at 10±1°C also has some hidden dangers. For example, generally higher temperatures (10±1°C compared to 4°C) will accelerate the metabolism of vegetables and the growth of microorganisms, thereby shortening their shelf life, and the risk of quality deterioration may increase. The technical solution of the present invention can fully take into account the production and operation needs of sterilizing and preserving fresh-cut vegetables, long-term antibacterial and extending the shelf life quality, as well as energy saving and consumption reduction during the storage period.

[0025] In a more preferred embodiment, the micro-nano ultrasonic treatment is performed intermittently, with each treatment lasting 2 minutes and an interval of 1 minute, for a total of no more than 10 minutes. Continuous ultrasonic treatment may cause the structure of fresh-cut vegetables to be destroyed, and intermittent operation and interval time are conducive to dissipating the energy accumulated by ultrasound and maintaining the integrity, taste and flavor of fresh-cut vegetables.

[0026] The second object of the present invention is to provide fresh-cut vegetables obtained by the method described in the first aspect of the present invention.

[0027] Preferably, when the shelf life of the fresh-cut vegetables is less than or equal to 5 days, the browning degree is less than or equal to 1.53ΔOD410nm / g, and the total number of colonies is less than or equal to 1.2×10 5 CFU / g. Browning index is a quantitative indicator of the degree of color change caused by oxidation, enzymatic reaction and heat treatment during storage and processing of food. Browning index is one of the important indicators for measuring the quality of fresh-cut vegetables. The lower the browning index, the better the quality of the vegetables during storage and processing, the brighter the color and the higher the nutritional value. A browning index less than or equal to 1.53ΔOD410nm / g reflects that the browning degree of fresh-cut vegetables is controlled at a low level during the shelf life, maintaining good quality and color.

[0028] Preferably, when the shelf life of the fresh-cut vegetables is less than or equal to 5 days, the total number of colonies is less than or equal to 1.2×10 5 CFU / g. The total number of colonies can directly reflect the effect of sterilization treatment. If the sterilization treatment is proper, the number of microorganisms on fresh-cut vegetables will be effectively controlled and the total number of colonies will be kept at a low level. Under the above given conditions, by controlling the total number of colonies at a low level - less than or equal to 1.2×10 5 CFU / g, which can effectively extend the shelf life of fresh-cut vegetables and maintain their quality.

[0029] More preferably, when the shelf life of the fresh-cut vegetables is less than or equal to 3 days, bacteria associated with plant decay, such as Acidovorax and Plectosphaerella, are effectively inhibited.

[0030] The third object of the present invention is to provide an application of the method of the first aspect of the present invention in improving the quality of fresh-cut vegetables.

[0031] Compared with the prior art, the present invention combines SAEW, nisin, zinc gluconate C 12 H 22 O 14 Zn / Fe(II) Gluconate C 12 H 22 FeO 14 The solution and micro-nano ultrasonic treatment technology effectively delayed the browning of fresh-cut lettuce and inhibited the growth of microorganisms, and significantly improved its shelf life quality. The experimental results showed that when using 50mg / L SAEW, 300mg / L nisin, zinc gluconate C 12 H 22 O 14 Zn / Fe(II) Gluconate C 12 H 22 FeO 14 The effect of reducing browning in the treatment groups of solution and micro-nano ultrasonic treatment (labeled as S+N) was significantly better than that in other treatment groups. On the eighth day of storage, the browning index of the S+N group was 78.0% lower than that of the control group (labeled as Control). In addition, the combination significantly reduced the browning index, browning degree, a* and b* values, total colony count, weight loss rate and the activity of browning-related enzymes (SOD, PPO, POD and PAL), while maintaining a high L* value, vitamin C and chlorophyll content and texture (hardness, chewiness, and crispness). In addition, it also effectively reduced the total phenolic and MDA contents in fresh-cut lettuce during storage. Overall, SAEW, nisin, zinc gluconate C 12 H 22 O 14 Zn / Fe(II) Gluconate C 12 H 22 FeO 14 The combined use of solution and micro-nano ultrasonic treatment technology performs well in delaying browning, inhibiting microorganisms and extending shelf life. It is better than existing technologies in maintaining the shelf life quality, taste, flavor and color of fresh-cut vegetables, and shows good prospects in the practical application of fresh-cut lettuce preservation.

[0032] The above-mentioned records related to the invention content are only an overview of the technical solution of the present application. In order to enable ordinary technicians in the field to more clearly understand the technical solution of the present application, and then implement it according to the text of the specification and the contents recorded in the drawings, and to make the above-mentioned purpose and other purposes, features and advantages of the present application easier to understand, the following is an explanation in combination with the specific implementation mode and drawings of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The drawings are only used to illustrate the principles, implementation methods, applications, characteristics and effects of the specific embodiments of the present application and other related contents, and shall not be considered as limitations of the present application.

[0034] In the drawings of the specification:

[0035] Figure 1 This is a data comparison chart of the change of browning index of each fresh-cut lettuce sample over the storage time;

[0036] Figure 2 This is a data comparison chart of the browning degree change of each fresh-cut lettuce sample over the storage time;

[0037] Figure 3 This is a data comparison chart of the change in chlorophyll content of each fresh-cut lettuce sample over time;

[0038] Figure 4 This is a data comparison chart of the change of total phenolic content of each fresh-cut lettuce sample over the storage time;

[0039] Figure 5 This is a data comparison chart of the changes in vitamin C content of each fresh-cut lettuce sample over time;

[0040] Figure 6 This is a data comparison chart of the weight loss rate of each fresh-cut lettuce sample over time;

[0041] Figure 7 This is a data comparison chart of the changes in L* value content of each fresh-cut lettuce sample over storage time;

[0042] Figure 8 This is a data comparison chart of the changes in a* value content of each fresh-cut lettuce sample over time;

[0043] Fig. 9 This is a data comparison chart of the changes in the b* value content of each fresh-cut lettuce sample over time;

[0044] Fig.10 This is a data comparison chart of the hardness change of each fresh-cut lettuce sample over the storage time;

[0045] Fig.11 This is a data comparison chart of the change in chewiness of each fresh-cut lettuce sample over storage time;

[0046] Fig.12 This is a data comparison chart of the change in the crispness of each fresh-cut lettuce sample over time;

[0047] Fig.13 This is a data comparison chart of the changes in the total bacterial count content of each fresh-cut lettuce sample over the storage time;

[0048] Fig.14 The sensory evaluation of each fresh-cut lettuce sample over the storage time;

[0049] Fig.15 This is a data comparison chart of the changes in malondialdehyde (MDA) content in each fresh-cut lettuce sample over storage time;

[0050] Fig.16 This is a data comparison chart of the changes in superoxide dismutase (SOD) content in each fresh-cut lettuce sample over storage time;

[0051] Fig.17 This is a data comparison chart of the changes in polyphenol oxidase (PPO) content in each fresh-cut lettuce sample over storage time;

[0052] Fig.18 This is a data comparison chart of the changes in peroxidase (POD) content of each fresh-cut lettuce sample over storage time;

[0053] Fig.19 This is a data comparison chart of the changes in phenylalanine ammonia lyase (PAL) content in each fresh-cut lettuce sample over storage time;

[0054] Fig. 20 This is a stacked diagram of species distribution at each level (16S), with bacteria in the figure;

[0055] Fig.21 This is the stacked map (ITS) of species distribution at each level, and the figure shows fungi;

[0056] Fig. 22 Diagram of the possible mechanism of S+N treatment inhibiting browning of fresh-cut lettuce and microorganisms. DETAILED DESCRIPTION

[0057] In order to explain in detail the possible application scenarios, technical principles, specific schemes that can be implemented, and the purposes and effects that can be achieved, the following is a detailed description of the specific embodiments listed in conjunction with the accompanying drawings. The embodiments described herein are only used to more clearly illustrate the technical solutions of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0058] Reference to "embodiment" herein means that the specific features, structures or characteristics described in conjunction with the embodiment may be included in at least one embodiment of the present application. The term "embodiment" appearing in various places in the specification does not necessarily refer to the same embodiment, nor does it particularly limit its independence or association with other embodiments. In principle, in the present application, as long as there is no technical contradiction or conflict, the various technical features mentioned in the embodiments can be combined in any way to form a corresponding implementable technical solution.

[0059] Unless otherwise defined, the technical terms used in this document have the same meanings as those generally understood by those skilled in the art to which this application belongs; the use of relevant terms in this document is only for describing specific embodiments and is not intended to limit this application.

[0060] In the description of this application, the term "and / or" is an expression used to describe the logical relationship between objects, indicating that three relationships may exist, for example, A and / or B, which means: A exists, B exists, and A and B exist at the same time. In addition, the character " / " in this article generally indicates that the objects before and after are in an "or" logical relationship.

[0061] In the present application, terms such as “first” and “second” are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship of quantity, priority or sequence between these entities or operations.

[0062] Without further limitations, in this application, the words "include", "comprises", "has" or other similar expressions used in the sentences are intended to cover non-exclusive inclusion. These expressions do not exclude the presence of additional elements in the process, method or product including the elements, so that the process, method or product including a series of elements may include not only those limited elements, but also other elements not explicitly listed, or also include elements inherent to such process, method or product.

[0063] Similar to the understanding in the Examination Guidelines, in this application, expressions such as "greater than", "less than", "exceed" and the like are understood to exclude the number itself; expressions such as "above", "below", "within" and the like are understood to include the number itself. In addition, in the description of the embodiments of this application, "multiple" means more than two (including two), and similar expressions related to "multiple" are also understood in this way, such as "multiple groups", "multiple times", etc., unless otherwise clearly and specifically limited.

[0064] In the description of the embodiments of the present application, space-related expressions used, such as "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "vertical", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicate the orientation or position relationship based on the orientation or position relationship shown in the specific embodiments or drawings, and are only for the convenience of describing the specific embodiments of the present application or facilitating the reader's understanding, and do not indicate or imply that the referred device or component must have a specific position, a specific orientation, or be constructed or operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0065] Unless otherwise expressly specified or limited, in the description of the embodiments of the present application, the terms such as "install", "connect", "connect", "fix", "set", etc. used should be understood in a broad sense. For example, the "connection" can be a fixed connection, a detachable connection, or an integrated setting; it can be a mechanical connection, an electrical connection, or a communication connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium; it can be the internal connection of two elements or the interaction relationship between two elements. For technicians in the technical field to which the present application belongs, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0066] Slightly acidic electrolyzed water (SAEW) is a new type of aqueous solution with unique physicochemical properties. It is produced by electrolyzing sodium chloride (NaCl) in an electrolytic cell. Studies have confirmed that SAEW has a strong bactericidal ability and can effectively eliminate pathogens such as Listeria monocytogenes, Escherichia coli, Staphylococcus aureus and Salmonella on the surface of food. In addition to its bactericidal effect, SAEW has been shown to maintain the physical properties, nutritional value and sensory quality of food, thereby extending its shelf life. The application of SAEW in the fruit and vegetable processing industry has attracted widespread attention. Studies have shown that it performs well in the sterilization treatment of a variety of fresh-cut fruits and vegetables, including lettuce, kale, cabbage, bell peppers and lotus roots. Therefore, SAEW is increasingly regarded as a safe, efficient and environmentally friendly disinfectant. When the concentration of slightly acidic electrolyzed water is 50 mg / L, it refers to the mass concentration of effective bactericidal components (including hypochlorous acid, other active chlorine components and related active substances) in the solution. Specifically, 50 mg / L means that in each liter of slightly acidic electrolyzed water, the total mass of these effective bactericidal components reaches 50 mg. This is an important indicator to measure the bactericidal ability and activity of slightly acidic electrolyzed water. Generally, the higher the concentration, the stronger the bactericidal effect may be.

[0067] Natural preservatives are gradually showing a trend of replacing chemical preservatives due to their strong antibacterial activity, safety and non-toxicity, strong thermal stability, biodegradability, wide range of effects, and health benefits for the human body. Antibacterial peptides, also known as antimicrobial peptides or peptide antibiotics, are a class of small peptides produced by a variety of biological cells through induction, which can have broad-spectrum antibacterial, fungal, viral, protozoan, and even tumor cell inhibition effects. They are rich in sources and widely exist in plants, insects, amphibians, aquatic organisms, microorganisms, etc. Most antimicrobial peptides are cationic peptides, which have the advantages of amphiphilicity, good water solubility, thermal stability, low resistance to drug resistance, safety and no toxic side effects, so they have potential application value in the food industry, agriculture, animal husbandry, medicine, aquaculture, and health products and cosmetics processing industries. At present, nisin, the first and only antimicrobial peptide approved for food preservation and freshness preservation, has been used in more than 50 countries and regions. There have been many reports on the research of antimicrobial peptides in the preservation of processed foods, including canned foods, plant protein foods, dairy products, meat products and ethanol beverages, but there are fewer studies on their application in the preservation of fruits and vegetables.

[0068] Zinc and iron, as trace elements, also play an important role in vegetable preservation. Zinc can delay the corruption of vegetables by enhancing plant stress resistance, promoting cell stability, and reducing microbial invasion. Zinc can also regulate the activity of antioxidant enzymes in vegetables, slow down the browning process, and maintain color and nutrients. Iron delays browning by promoting antioxidant enzyme activity, protecting cell membranes, and delaying chlorophyll degradation, thereby maintaining the color and texture of fresh-cut vegetables. Iron, in synergistic effect with zinc and nisin, can significantly enhance the preservation effect and extend the shelf life. .

[0069] Micro-nano ultrasonic technology significantly improves the sterilization effect of slightly acidic electrolyzed water through cavitation effect, mechanical effect and thermal effect. The frequency and power density of ultrasound can be adjusted according to specific needs to optimize the sterilization effect while maintaining the quality of vegetables. Studies have shown that micro-nano ultrasound can not only effectively inactivate bacteria and fungi on the surface of fresh-cut vegetables, but also promote the exchange and metabolism of substances in vegetable cells, further slowing down the process of corruption. In addition, the cavitation effect caused by ultrasound will produce tiny bubbles, which will quickly burst under strong impact, releasing powerful energy, enhancing the effect of solute components on the surface of vegetables, while destroying the cell walls of microorganisms, further improving the sterilization effect. Therefore, micro-nano ultrasonic technology shows great potential in improving the preservation effect and extending the shelf life. .

[0070] At present, most of the research on vegetable salad preservation by domestic and foreign researchers is conducted at 4℃. There are few studies on the preservation of pre-packaged vegetable salads treated with green cold sterilization at 10℃. However, 10℃ is close to the actual shelf storage temperature of fresh-cut vegetables. Studying the preservation effect at this temperature is more in line with the actual conditions in the circulation and sales process. Therefore, combining slightly acidic electrolyzed water, nisin, C 12 H 22 O 14 Zn / C 12 H 22 FeO 14 The solution and micro-nano ultrasound technology can not only improve the preservation effect of fresh-cut vegetables, but also maintain their quality at the actual storage temperature (10°C). At higher temperatures, slightly acidic electrolyzed water and nisin can inhibit the growth of microorganisms, zinc can enhance the stability of cells, and micro-nano ultrasound can effectively delay browning and other quality changes by sterilizing and improving the internal structure of vegetables.

[0071] The fresh lettuce, carrot, chicory, purple cabbage and corn used in the specific embodiments of the present invention are all provided by Fuzhou Youyu Food Technology Co., Ltd.

[0072] The slightly acidic electrolyzed water (SAEW) in the specific embodiment of the present invention is prepared by a DCW hypochlorous acid generator (DCW T10-03, Beijing Wanyu Kaisheng Technology Development Co., Ltd.).

[0073] The nisin used in the specific embodiment of the present invention is provided by Shanghai Youle Food Ingredients Co., Ltd.

[0074] The present invention determines the total colony count in fresh-cut vegetables according to the method of "GB4789.2-2022 National Food Safety Standard Food Microbiology Inspection Colony Count Determination".

[0075] The method for determining the browning degree of the present invention is as follows: accurately weigh 2 g of a sample ground with liquid nitrogen, add 5 mL of 95% ethanol and mix well, centrifuge at 4°C and 10,000×g for 5 min, take the supernatant and determine the absorbance at a wavelength of 410 nm, and the browning degree of the sample is expressed as ΔOD410nm / g.

[0076] The color difference determination method of the present invention is as follows: the color characteristics of fresh-cut lettuce samples are evaluated using a TS70 colorimeter (Sentime Technology Co., Ltd., Shenzhen), and each sample is measured at 10 different points, and the L*, a*, and b* values ​​are recorded.

[0077] The texture of fresh-cut vegetables of the present invention is determined by using a TA-XT expressC texture analyzer, using an A / MORS probe, with a speed of 10 mm / s before the test, a test speed of 2 mm / s, a speed of 10 mm / s after the test, a puncture distance of 5 mm, and a uniform test position each time.

[0078] The total phenol content determination method of the present invention is as follows: accurately weigh 2 g of the liquid nitrogen ground sample, add 5 mL of pre-cooled 1% hydrochloric acid-methanol solution, shake thoroughly to dissolve, place at 4° C. for 10 min, centrifuge at 10000×g for 15 min, collect the supernatant, and determine the absorbance at a wavelength of 280 nm.

[0079] Determination of vitamin C content in fresh-cut vegetables of the present invention: pulverize the sample freeze-dried with liquid nitrogen with a grinder, weigh 2 g of the sample, add 5 ml of pre-cooled 5% TCA solution, centrifuge at 4°C and 12000×g for 20 min, take the supernatant, and dissolve it to 10 ml with 5% TCA solution. Take 3 ml of the extract, add 3 ml of 5% TCA and 3 ml of anhydrous ethanol, shake well, then add 1.5 ml of 0.4% H3PO4-ethanol, 3 ml of 0.5% red phenanthroline-ethanol and 1.5 ml of 0.03% FeCl3-ethanol in sequence, mix well, react at 30°C for 90 min, and then measure the OD value at 534 nm. The results are expressed in g·kg -1 express.

[0080] The method for determining the chlorophyll content of the present invention is as follows: accurately weigh 5 g of a liquid nitrogen-ground sample, add 15 mL of an acetone solution, fully extract, centrifuge at 10,000×g and 4°C for 10 min, take the supernatant and make the volume to 50 mL, determine its absorbance at wavelengths of 663 nm and 645 nm, and use acetone as a blank control test.

[0081] The weight loss rate was determined by weighing and observing 3 boxes of samples, and the calculation formula is as follows:

[0082]

[0083] The sensory evaluation method of the present invention is as follows: 10 professional sensory evaluators are selected to comprehensively score the samples every day, using a nine-point system, with nine points as the full score, five points as average, and one point as inedible, and finally taking the average value. The specific evaluation criteria are shown in Table 1. The full score is 9 points, and the final overall score is calculated by weighted method, that is, the overall sensory score of each treatment group = color change × 30% + texture × 20% + appearance × 30% + smell × 20%. When the score is less than 5 points, it is considered to be unacceptable to customers, that is, the commercial sales limit.

[0084] Table 1 Sensory evaluation standards

[0085] Score (Grading) Color change texture odor shape 9(Ι) none Crisp and tender Strong fresh taste full 7(Ⅱ) Slight color change Relatively crisp and tender Fresh taste is light Slightly wilted 5(Ⅲ) Color change Local softening Slight odor Wilting 3(Ⅳ) Severe color change Softer Strong odor Severe wilting 1(Ⅴ) Severe color change rot Produces odor Severe wilting

[0086] The method for determining the malondialdehyde (MDA) content and enzyme activity of the present invention is: determining the malondialdehyde MDA content, peroxidase (POD), superoxide dismutase (SOD), polyphenol oxidase (PPO) and phenylalanine ammonia lyase (PAL) activities according to the kit method provided by Beijing Solebow Technology Co., Ltd.

[0087] Sequencing analysis of the microbial community amplicon of the present invention: After extracting genomic DNA from the sample, the conserved region of rDNA is amplified using specific primers with barcodes (primer sequence information is shown in Table 2).

[0088] Table 2 Microbial community amplification primer sequence information

[0089]

[0090] Then the PCR amplification products were cut and recovered, and quantified using QuantiFluorTM fluorometer. The purified amplification products were mixed in equal amounts, connected to sequencing adapters, and sequencing libraries were constructed and sequenced on Illumina PE250.

[0091] Microbial diversity research is mainly divided into six parts: alpha and beta diversity research, species analysis, functional research, and environmental relationship research. After sequencing to obtain raw reads, we first filter low-quality reads, then assemble, splice double-end reads into tags, and then filter the tags. The data obtained is called Clean tag. Next, clustering is performed based on Clean tags to remove chimera tags detected during cluster alignment. The final data obtained is Effective tag. After obtaining OTU, OTU abundance statistics are performed based on Effective tag. According to the analysis process, species annotation, alpha diversity analysis, beta diversity analysis, community function prediction, etc. are performed in turn. If there is a valid grouping, inter-group difference comparison and statistical test are performed. Finally, combined with other factors (such as environmental factors), specific advanced analysis such as CCA is performed to answer the relationship between microorganisms and the environment.

[0092] Example 1

[0093] Method for improving shelf life quality of fresh-cut lettuce based on green cold sterilization

[0094] Lettuce (Lactuca sativa L. var. ramosa Hort.) is one of the most consumed fresh vegetables in the world, especially in Europe and North America. As the main producer of lettuce in the world, China plays a pivotal role in the supply of lettuce. Lettuce is mainly used to make salads and is often processed into ready-to-eat products, which require washing and cutting. However, these processing steps make lettuce susceptible to browning at the cut, which is a major challenge that seriously affects the freshness of the product and consumer preference. The browning of fruits and vegetables is a key factor affecting their visual quality and market value, which may further affect consumer choices. This enzymatic browning is mainly driven by the oxidation of PPO and POD, while the synthesis of phenolic substrates is catalyzed by PAL. Traditionally, the fresh-cut food industry uses chemical reagents such as acidifiers, chelating agents and reducing agents to slow down the browning process. However, consumer concerns about the safety of such chemical additives have prompted the development of safer and more natural preservation technologies to extend the shelf life of fresh-cut lettuce.

[0095] The purchased fresh lettuce was first placed in the refrigerator for precooling for 12 hours. At the beginning of the experiment, the mud and damaged parts were washed off, and the parts with bright color and uniform size were selected. The lettuce was cut with a sterilized kitchen knife and cut into uniform strips of fresh-cut lettuce samples with a width of about 1 cm for subsequent use. All fresh-cut lettuce samples were divided into 12 groups and soaked in slightly acidic electrolyzed water with concentrations of 10, 30, 50, and 70 mg L-1 for 5 minutes. The redox potential of the slightly acidic electrolyzed water was about 850-1000 mv and the pH value was 5-6.5; the samples were soaked in nisin with mass concentrations of 100, 300, and 500 mg L-1 for 5 minutes; and 0-2.4 mg L-1 C 12 H 22 O 14 Zn and 0~15mg L-1C 12 H 22 FeO 14 Soak in the solution for 5 minutes; use a micro-nano ultrasonic device at an ultrasonic treatment frequency of 20, 30, and 40kHz, a power density of 100-300W / L, and a treatment time of 5 minutes, and then use a vegetable dryer to spin dry the fresh-cut lettuce for 30-60 seconds. The treated lettuce is packed into a packaging bag, about 70g / bag, to obtain a bagged fresh-cut lettuce product, 40 bags per group for subsequent index testing. All bagged fresh-cut lettuce products are placed in a constant temperature storage box at (10±1)℃, the treatment day is set as day 0, and data are collected once on days 0, 1, 2, 3, 4, and 5.

[0096] Example 2

[0097] Method for improving shelf life quality of fresh-cut lettuce based on green cold sterilization

[0098] The difference from the treatment method in Example 1 is that the samples were immersed in slightly acidic electrolyzed water with a concentration of 10, 30, 50, and 70 mg L-1 for 10 min, and then treated with a micro-nano ultrasonic device at an ultrasonic treatment frequency of 20, 30, and 40 kHz and a power density of 100 to 300 W / L for 5 min, and then 100, 300, and 500 mg L-1 of nisin and 0 to 2.4 mg L-1 of C were used. 12 H 22 O 14 Zn and 0~15mg L-1C 12 H 22 FeO 14 Soak in the solution for 5 minutes, then use a vegetable spin dryer to spin dry the fresh-cut lettuce for 30 to 60 seconds.

[0099] Example 3

[0100] Method for improving shelf life quality of fresh-cut lettuce based on green cold sterilization

[0101] The difference from the treatment method in Example 1 is that the samples were immersed in slightly acidic electrolyzed water with a concentration of 10, 30, 50, and 70 mg L-1 for 5 min, and then treated with a micro-nano ultrasonic device at an ultrasonic treatment frequency of 20, 30, and 40 kHz and a power density of 100 to 300 W / L for 5 min, and then 100, 300, and 500 mg L-1 of nisin and 0 to 2.4 mg L-1 of C- 12 H 22 O 14 Zn and 0~15mg L-1C 12 H 22 FeO 14 Soak in the solution for 10 minutes, then use a vegetable dryer to spin dry the fresh-cut lettuce for 30 to 60 seconds.

[0102] Example 4

[0103] Method for improving shelf life quality of fresh-cut lettuce based on green cold sterilization

[0104] The difference from the treatment method of Example 1 is that after soaking in slightly acidic electrolyzed water with a concentration of 10, 30, 50, and 70 mg L-1 for 5 minutes, a micro-nano ultrasonic device is used at an ultrasonic treatment frequency of 20, 30, and 40 kHz and a power density of 100 to 300 W / L, and the treatment is performed intermittently, that is, each treatment is 2 minutes, with an interval of 1 minute, and a total treatment of 5 minutes, and then 100, 300, and 500 mg L-1 of nisin and 0 to 2.4 mg L-1 of C are used respectively. 12 H 22O 14 Zn and 0~15mg L-1C 12 H 22 FeO 14 Soak in the solution for 5 minutes, then use a vegetable spin dryer to spin dry the fresh-cut lettuce for 30 to 60 seconds.

[0105] Example 5 (S+N group)

[0106] Method for improving shelf life quality of fresh-cut lettuce based on green cold sterilization

[0107] Different from Example 1, the uniform strips of fresh-cut lettuce were placed in 50 mg / L slightly acidic electrolyzed water for 5 min, 300 mg / L nisin and 2 mg L-1C 12 H 22 O 14 The Zn solution was placed in a micro-nano ultrasonic device (ultrasonic treatment frequency of 20kHz, power density of 100W / L) for treatment, and the treatment was carried out for 5 minutes in total with an interval of 1 minute for each treatment for 2 minutes. After that, the fresh-cut lettuce was soaked in the composite solution for 5 minutes, and then directly dried with a vegetable dryer and bagged to obtain a bagged fresh-cut lettuce product.

[0108] Example 6

[0109] Method for improving shelf life quality of fresh-cut carrots based on green cold sterilization

[0110] The difference from Example 1 is that the processing object is fresh carrots, which are cut into uniform filaments of about 2 mm wide and 10 mm long, or carrot slices commonly seen in vegetable salads.

[0111] Example 7

[0112] Method for improving shelf life quality of fresh-cut chicory based on green cold sterilization

[0113] The difference from Example 1 is that the processed object is fresh chicory, which is cut or torn into uniform fresh-cut chicory samples of about 5 cm in length.

[0114] In other implementation cases, the processing objects can also be seasonal vegetables such as broccoli, purple cabbage, corn kernels, or fruits such as cherry tomatoes, dragon fruit, mangoes, strawberries, etc., which involve fresh-cut ingredients that need to be packaged and put on shelves or stored in warehouses waiting to be purchased by consumers.

[0115] Comparative Example 1 (Control Group)

[0116] Different from Example 5, the uniform strips of fresh-cut lettuce samples were directly soaked in reverse osmosis (RO) water for 15 min, instead of using slightly acidic electrolyzed water, nisin, C 12 H 22O 14 The product is treated with Zn solution and micro-nano ultrasonic device, and then directly dried by vegetable drying machine and packed in bags to obtain bagged fresh-cut lettuce product.

[0117] Comparative Example 2 (NaClO group)

[0118] Different from Example 5, the uniform strips of fresh-cut lettuce samples were directly placed in 150 mg L -1 Soak in sodium hypochlorite (NaClO) for 10 min, then add 50 mg L -1 Soak in NaClO for 5 minutes, rinse with RO water, and then directly spin dry with a vegetable spin dryer and bag to obtain a bagged fresh-cut lettuce product.

[0119] Comparative Example 3 (S Group)

[0120] Different from Example 5, the uniform strips of fresh-cut lettuce samples were directly immersed in 50 mg L-1 slightly acidic electrolyzed water SAEW for 15 min, but no micro-nano ultrasonic device, nisin and C were used. 12 H 22 O 14 The Zn solution is further treated, and then the vegetable is directly dried by a vegetable drying machine and bagged to obtain a bagged fresh-cut lettuce product.

[0121] The fresh-cut lettuce samples obtained by processing in Example 5 and Comparative Examples 1-3 were stored at 10±1° C. for 8 days, and the indicators were evaluated every two days.

[0122] See also Figure 1 The changes in browning index over storage time are shown in Figure 2 The browning degree changes with storage time. Figure 1 and Figure 2 It can be seen that the browning index continued to rise during the entire storage period. Compared with the Control group (Control Example 1), by the 8th day, the browning index of the NaClO group (Control Example 2), S group (Control Example 3) and S+N treatment group (Example 5) decreased by 45.9%, 58.2% and 78.0%, respectively. The trend of the change in browning degree is closely related to the browning index. Compared with the Control group (Control Example 1), all three treatment groups had a lower degree of browning during the entire storage period. For example, by the 8th day, the browning degrees of the NaClO (Control Example 2), S (Control Example 3) and S+N treatment groups (Example 5) were 16.8%, 20.1% and 29.9% lower than those of the Control group (Control Example 1), respectively. This shows that the S+N treatment group (Example 5) can most effectively reduce the occurrence of browning in fresh-cut lettuce.

[0123] See also Figure 3As shown in the figure, the chlorophyll content of each fresh-cut lettuce sample changes with the storage time. It can be seen from the figure that the chlorophyll content of the Control group (Comparative Example 1) and the NaClO treatment group (Comparative Example 2) gradually decreases. However, during the period from day 0 to day 6, the chlorophyll content of the S+N treatment group (Example 5) did not change significantly. In addition, compared with the NaClO treatment group (Comparative Example 2) and the S treatment group (Comparative Example 3), the S+N treatment group (Example 5) had a higher chlorophyll content during storage.

[0124] See also Figure 4 As shown in the figure, the total phenol content of each fresh-cut lettuce sample changes with the storage time. It can be seen from the figure that the total phenol content of the Control group (Control Example 1) continues to increase during the entire storage period. The total phenol content of the NaClO treatment group (Control Example 2) fluctuated in the first four days and then increased rapidly. On the other hand, the total phenol content of the S (Control Example 3) and S+N treatment groups (Example 5) increased more slowly during storage. During all storage days, the total phenol content of the treatment groups was always lower than that of the Control group (Control Example 1). By the 8th day, the total phenol content of the S+N treatment group (Example 5) was 23.8% lower than that of the Control group (Control Example 1).

[0125] See also Figure 5 As shown in the figure, the changes in the vitamin C content of each fresh-cut lettuce sample over the storage time, it can be seen from the figure that the vitamin C content is on a downward trend, especially in the Control group (Comparative Example 1), the decline is most obvious. The NaClO group (Comparative Example 2) and the S group (Comparative Example 3) delayed the decline of vitamin C to a certain extent, but the effect was limited. The S+N treatment group (Example 5) performed best and could significantly maintain a higher vitamin C content, especially at 4 days and 8 days, there was a significant difference with the Control group (Comparative Example 1), indicating that the S+N treatment group (Example 5) helps to maintain the nutritional quality of fresh-cut lettuce.

[0126] See also Figure 6 As shown in the figure, the weight loss rate of each fresh-cut lettuce sample changes with the storage time. It can be seen from the figure that the weight loss rate of each group gradually increases, and the weight loss rate of the Control group (Comparative Example 1) is the highest, especially reaching about 8.5% on the 8th day, which is significantly higher than the other treatment groups. The NaClO group (Comparative Example 2) and the S group (Comparative Example 3) can reduce the weight loss rate to a certain extent, but the effect is similar. The S+N treatment group (Example 5) shows the lowest weight loss rate at each time point, indicating that the S+N treatment group (Example 5) can effectively delay the weight loss process and has the best preservation effect.

[0127] See also Figure 7As shown in the figure, the L* value content changes of each fresh-cut lettuce sample over the storage time. It can be seen from the figure that during the 8-day storage period, the L* value representing brightness in all samples decreased. The L* value of the control group (comparative example 1) dropped sharply from 50.87 to 34.41 on the 8th day, while the L* values ​​of the three treatment groups decreased more slowly. From the 4th day, the L* value of the S+N treatment group (example 5) was significantly higher than that of the other two treatment groups.

[0128] See also Figure 8 As shown in the figure, the a* value content changes of each fresh-cut lettuce sample with the passage of storage time, from which it can be seen that the a* value shows an upward trend during storage. In contrast, the a* value of the treatment group increases slowly, and the a* value of the S+N treatment group (Example 5) increases from -5.58 to -4.48.

[0129] See also Fig. 9 As shown in the figure, the changes in the b* value content of each fresh-cut lettuce sample with the passage of storage time, it can be seen from the figure that the change pattern of the b* value is similar to that of the a* value. The b* value of the Control group (Comparative Example 1) continued to decrease during the entire storage process, while the b* value of the NaClO group (Comparative Example 2), S group (Comparative Example 3) and S+N treatment group (Example 5) increased rapidly from the 0th day to the 2nd day, and tended to be stable after the 2nd day.

[0130] See also Fig.10 As shown in the figure, the hardness of each fresh-cut lettuce sample changes with the storage time. It can be seen from the figure that the hardness of each group shows a downward trend, among which the Control group (Comparative Example 1) has the largest decline, especially on the 6th and 8th days, the hardness is significantly reduced. The NaClO group (Comparative Example 2) and the S group (Comparative Example 3) treatments slowed down the hardness decline to a certain extent. The S+N treatment group (Example 5) showed the best hardness retention effect during the entire storage period. Compared with other groups, the difference was particularly significant on the 8th day, indicating that the S+N treatment group (Example 5) can effectively delay the decline in the hardness of fresh-cut lettuce and maintain its texture characteristics.

[0131] See also Fig.11 As shown in the figure, the chewiness of each fresh-cut lettuce sample changes with the storage time. It can be seen from the figure that in the early stage of storage, the chewiness of each group is close, but as the storage time increases, the chewiness of the Control group (Comparative Example 1) decreases significantly, especially on the 6th and 8th days. The NaClO group (Comparative Example 2) and the S group (Comparative Example 3) both show a certain maintenance effect, and the S+N treatment group (Example 5) has the best effect. This shows that the S+N treatment group (Example 5) can effectively delay the decrease in chewiness and maintain the good edible quality of fresh-cut lettuce.

[0132] See also Fig.12 As shown in the figure, the brittleness of each fresh-cut lettuce sample changes with the storage time. It can be seen from the figure that the brittleness of each group shows a downward trend, among which the Control group (Comparative Example 1) has the largest decline, especially on the 6th and 8th days, the brittleness is significantly reduced. The NaClO (Comparative Example 2) and S (Comparative Example 3) treatments slowed down the decline in brittleness to a certain extent. The S+N treatment group (Example 5) showed the best brittleness retention effect during the entire storage period. Compared with other groups, the difference was particularly significant on the 8th day, indicating that the S+N treatment group (Example 5) can effectively delay the decline in the brittleness of fresh-cut lettuce and maintain its texture characteristics.

[0133] See also Fig.13 As shown in the figure, the total colony count of each fresh-cut lettuce sample changes with the storage time. It can be seen from the figure that the total colony count of each group gradually increases, and the total colony count of the Control group (Comparative Example 1) is the highest, especially reaching about 10 on the 8th day. 8 CFU / g, which is significantly higher than that of other treatment groups. The NaClO (Comparative Example 2) and S (Comparative Example 3) treatment groups can reduce the total colony count to a certain extent, while the S+N treatment group (Example 5) shows the lowest total colony count at each time point, indicating that the S+N treatment group (Example 5) can effectively inhibit the reproduction of microorganisms and has a good preservation effect.

[0134] See also Fig.14 As shown in the figure, the sensory evaluation of each fresh-cut lettuce sample with the passage of storage time shows that the sensory evaluation of each group shows a downward trend, among which the Control group (Comparative Example 1) has the largest decline, especially on the 6th and 8th days, the sensory evaluation is significantly reduced. NaClO (Comparative Example 2) and S (Comparative Example 3) treatments slowed down the decline in sensory evaluation to a certain extent. The S+N treatment group (Example 5) showed the best sensory evaluation effect during the entire storage period. Compared with other groups, the difference was particularly significant on the 8th day, indicating that the S+N treatment group (Example 5) can effectively delay the decline in the quality of fresh-cut lettuce and maintain a good sensory evaluation.

[0135] See also Fig.15As shown in the figure, the changes in the malondialdehyde (MDA) content of each fresh-cut lettuce sample over the storage time, it can be seen from the figure that in the Control group (Control Example 1), the MDA content increased sharply from the 0th day to the 6th day, and decreased after the 6th day. The MDA content of the NaClO treatment group (Control Example 2) increased rapidly from the 0th day to the 4th day, and then stabilized. In contrast, the total phenol content of the S (Control Example 3) and S+N treatment groups (Example 5) increased in a fluctuating manner during storage. In addition, throughout the storage period, the MDA content of the three treatment groups was lower than that of the Control group (Control Example 1). On the 6th day, compared with the Control group (Control Example 1), the MDA content of the NaClO group (Control Example 2), the S group (Control Example 3) and the S+N treatment group (Example 5) decreased by 17.3%, 35.6% and 43.1%, respectively. In addition, throughout the 8-day storage period, the MDA content of the S+N treatment group (Example 5) was always lower than that of the other two treatment groups.

[0136] See also Fig.16 As shown in the figure, the changes in the superoxide dismutase (SOD) content of each fresh-cut lettuce sample over the storage time, it can be seen from the figure that the SOD activity increases with the extension of the storage period. The SOD content of the Control group (Comparative Example 1) rises rapidly, reaching 2.2 times the initial value on the 8th day. In contrast, the SOD activity of the three treatment groups increased more slowly during the entire storage period. In comparison, the SOD level of the treatment group was always lower than that of the Control group (Comparative Example 1). At the end of storage, compared with the Control group (Comparative Example 1), the SOD activity of the NaClO (Comparative Example 2), S (Comparative Example 3) and S+N treatment groups (Example 5) decreased by 10.7%, 25.5% and 26.1%, respectively.

[0137] See also Fig.17 The changes in the polyphenol oxidase (PPO) content of each fresh-cut lettuce sample over the storage time are shown in the figure. It can be seen from the figure that the PPO activity initially increases, reaches a peak on the second day, and then decreases. On the second day, the PPO levels of the Control group (Control Example 1), NaClO (Control Example 2), S (Control Example 3) and S+N treatment group (Example 5) were 187, 177, 164 and 154 U g, respectively. -1 During the entire storage process, the PPO activity of each treatment group was lower than that of the Control group (Comparative Example 1).

[0138] See also Fig.18The change of peroxidase (POD) content of each fresh-cut lettuce sample over the storage time is shown in the figure. It can be seen from the figure that the change trends of PPO and POD activities are similar, both of which increase first and then decrease, but the time to reach the peak is different. The PPO activity of the Control group (Comparative Example 1) increased from 5.9 U g on the 0th day to 1.5 U g on the 1st day. -1 Significantly increased to 14 U g on day 6 -1 Statistical analysis showed that between the 2nd and 8th day, the PPO activities of the NaClO (Control Example 2), S (Control Example 3) and S+N treatment groups (Example 5) were lower than those of the Control group (Control Example 1). In addition, during the 6th to 8th day, the PPO level of the S+N treatment group (Example 5) was lower than that of the NaClO group (Control Example 2) and the S group (Control Example 3).

[0139] See also Fig.19 As shown in the figure, the changes in the phenylalanine ammonia lyase (PAL) content of each fresh-cut lettuce sample over the storage time, it can be seen from the figure that the PAL activity decreases with the passage of time. The PAL activity of the S (Comparative Example 3) and S+N treatment groups (Example 5) is lower than that of the Control group (Comparative Example 1). In addition, during the entire storage process, the PAL activity of the S+N treatment group (Example 5) is lower than that of the S treatment group (Comparative Example 3).

[0140] See also Fig. 20 As shown, in the distribution of bacterial communities, unclassified bacteria (Unclassified) dominated, especially in the CK-6d and SN-6d groups. Among them, the abundance of Acidovorax and Pectobacterium increased at 4d and 6d, while in the SN group (Example 5), especially at SN-4d and SN-6d, the abundance of these two types of bacteria decreased significantly, indicating that the treatment measures had an inhibitory effect on their growth, resulting in significant differences in the bacterial community structure between the treatment group and the Control group (Comparative Example 1).

[0141] See also Fig.21As shown, in the distribution of fungal communities, unclassified fungi (Unclassified) have a significant advantage, especially in the SN-6d group, reaching the highest proportion. In addition, the changes in Plectosphaerella are more significant. In the CK group (Control Example 1), the abundance of Plectosphaerella reached a peak at CK-4d and decreased at CK-6d; in contrast, in the S+N treatment group (Example 5), the relative abundance of Plectosphaerella was always low, especially at SN-6d, it was almost suppressed. This shows that the treatment measures have a significant inhibitory effect on the growth of Plectosphaerella, which may help slow down the infection and spread of fungi.

[0142] Studies have shown that the use of SAEW, nisin, C 12 H 22 O 14 Fresh-cut lettuce treated with a combination of Zn and micro-nanoultrasound had good sensory quality when stored for 8 days. The combination significantly reduced the browning index, browning degree, a* and b* values, total bacterial count, weight loss rate, and the activity of browning-related enzymes (SOD, PPO, POD, and PAL), while maintaining a high L* value, vitamin C and chlorophyll content, and texture (hardness, chewiness, and crispness). It also effectively reduced the total phenolic and MDA content in fresh-cut lettuce during storage. In addition, the combined treatment had an inhibitory effect on Flavobacterium, Acidovorax, and Plectosphaerella, and had a regulatory effect on the microbial community. SAEW, nisin, C 12 H 22 O 14 The possible mechanism of Zn and micro-nano-ultrasound combined treatment in inhibiting browning of fresh-cut lettuce and microorganisms Fig. 22 shown.

[0143] In summary, the present invention provides an effective green cold sterilization treatment method, which can significantly improve the shelf life and quality of fresh-cut lettuce, meets consumers' demand for safe and natural food, and has broad market application prospects.

[0144] Finally, it should be noted that although the above embodiments have been described in the specification and drawings of this application, this does not limit the scope of patent protection of this application. All technical solutions generated by replacing or modifying equivalent structures or equivalent processes based on the essential concept of this application using the contents recorded in the specification and drawings of this application, as well as directly or indirectly implementing the technical solutions of the above embodiments in other related technical fields, are included in the scope of patent protection of this application.

Claims

1. A method for improving the shelf life quality of fresh-cut vegetables based on green cold sterilization, characterized in that: The following steps are involved: Precooling: Put the freshly picked vegetables in the refrigerator for precooling; Cutting: taking the washed vegetables and cutting them to obtain fresh-cut vegetables; Soaking: placing the fresh-cut vegetables in a composite treatment system comprising slightly acidic electrolyzed water, nisin, zinc gluconate and / or ferrous gluconate solution and a micro-nano ultrasonic device for treatment; Dehydration: using a vegetable drying machine to dry the fresh-cut vegetables to obtain fresh-cut vegetables to be packaged; Packaging: Packing the fresh-cut vegetables to be packaged, sealing, and obtaining fresh-cut vegetable products; Storage: The fresh-cut vegetable products are stored at 4-10°C. The effective chlorine content ACC of the slightly acidic electrolyzed water is 10-70 mg L-1, the mass concentration of the nisin is 100-500 mg L-1, the concentration of the zinc gluconate solution is 0-2.4 mg L-1, and the concentration of the ferrous gluconate solution is 0-15 mg L-1.

2. The method according to claim 1, characterized in that The temperature of the composite treatment system is 4-10° C., the oxidation-reduction potential (ORP) of the slightly acidic electrolyzed water is greater than or equal to 850 mV, and the pH value is 5-6.

5.

3. The method according to claim 1, characterized in that The micro-nano ultrasonic device is an ultrasonic rod or an ultrasonic preparation device. Optionally, the length and diameter of the ultrasonic rod are 42 cm and 4 cm respectively, the water level is 5 to 10 cm, the treatment frequency is 20 to 40 kHz, the power density is 100 to 300 W / L, the treatment time is 2 to 10 min, and during the treatment process, the zinc gluconate and / or ferrous gluconate solution is used together with nisin.

4. The method according to claim 3, characterized in that The effective chlorine content ACC of the slightly acidic electrolyzed water is not less than 50 mg L-1, and the mass concentration of the nisin is 300 mg L-1.

5. The method according to claim 1, characterized in that The "immersion" step includes the following operations: The fresh-cut vegetables are first soaked in slightly acidic electrolyzed water for 5 to 20 minutes to obtain pretreated fresh-cut vegetables; The pretreated fresh-cut vegetables are transferred into a composite solution containing nisin and zinc gluconate and / or ferrous gluconate solution and soaked for 5 to 20 minutes; Wherein, the slightly acidic electrolyzed water and the composite solution containing nisin and zinc gluconate and / or ferrous gluconate solution are both treated with a micro-nano ultrasonic device for 2 to 10 minutes before being used for soaking the fresh-cut vegetables and pre-treating the fresh-cut vegetables respectively.

6. A fresh-cut vegetable, characterized in that: The method is obtained by the method according to any one of claims 1 to 5.

7. The fresh-cut vegetables according to claim 6, characterized in that: When the shelf life of the fresh-cut vegetables is less than or equal to 5 days, the browning degree is less than or equal to 1.53ΔOD410 nm / g, and the total number of colonies is less than or equal to 1.2×10 5 CFU / g.

8. The fresh-cut vegetables according to claim 7, characterized in that: When the shelf life of the fresh-cut vegetables is less than or equal to 3 days, both Acidovorax and Plectosphaerella are effectively inhibited.

9. Use of the method according to any one of claims 1 to 5 in improving the shelf life quality of fresh-cut vegetables.

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