A non-contact pork preservation method combining a composite essential oil emulsion, an electrostatic field and modified atmosphere

Abstract

This invention discloses a non-contact method for preserving pork using a composite essential oil emulsion combined with an electrostatic field and modified atmosphere packaging. The prepared composite essential oil nanoemulsion is packaged in polyethylene packaging, and the chilled pork is preserved using an electrostatic field synergistic with modified atmosphere packaging. A simple ultrasonic method is used to prepare a composite essential oil nanoemulsion composed of composite essential oils and Tween 80. This prepared emulsion and cooled, acid-removed pork are then placed in an O2 atmosphere. 2 CO 2 N 2 The product is stored in modified atmosphere packaging bags of polyethylene at 4±1℃. This invention can effectively control the increase in total bacterial count, volatile basic nitrogen, and pH of chilled pork during storage, better maintain the product's textural properties, color, and sensory quality, and extend the shelf life of chilled pork by 4-6 days.

Description

A non-contact method for pork preservation using a compound essential oil emulsion combined with electrostatic field and modified atmosphere. Technical Field

[0001] This invention belongs to the field of preservation technology, specifically relating to a non-contact method for preserving chilled pork by combining a natural composite essential oil nanoemulsion with a high-voltage electrostatic field and modified atmosphere packaging. Background Technology

[0002] Pork, a common food ingredient, is widely popular due to its rich nutrition and good taste. However, its abundant nutrients also provide a better environment for the growth and reproduction of microorganisms, thus reducing the quality of the pork. Refrigeration and freezing are the most common methods for preserving pork, but frozen pork is more suitable for long-distance transportation because the ice crystals formed during freezing can damage the pork's structure, leading to increased juice loss. Fresh pork is more susceptible to microbial invasion at various stages of the supply chain, resulting in a certain degree of drip loss, which not only affects the appearance of the pork but also its flavor and nutritional value. Therefore, more and more pork is being sold as chilled meat. Of course, chilled pork also has a series of problems, such as spoilage caused by microorganisms, the production of foul odors, and a deterioration in taste. Currently, modified atmosphere packaging, irradiation, preservatives, and active packaging are used for chilled pork to slow down spoilage, extend shelf life, and ensure safety.

[0003] Wang Dan et al. (2019) disclosed "A xanthan gum-emulsified essential oil nanoemulsion and its preparation method and application" (Publication No.: CN 110178892A). This method prepares a xanthan gum-emulsified essential oil nanoemulsion through high-speed dispersion and applies it to fresh-cut fruits and vegetables. The main components and proportions of the emulsion are: a composite oil phase with clove essential oil as the main component, 1-20%; xanthan gum solution, 60-78%; and octenyl succinate starch ester solution, 15-23%. This emulsion preparation method requires a relatively high rotation speed and a long dispersion time, and the octenyl succinate starch ester used is expensive, resulting in a large particle size in the formed emulsion, which is not conducive to production applications.

[0004] In 2016, Yin Hao disclosed a natural preservative for chilled pork and its preparation method (Publication No.: CN106212634A). The natural preservative contains 4.4-5.2% antibacterial agent, 11-15% synergist, 30-35% traditional Chinese medicine extract, and water. Some materials in the natural preservative are extracted using supercritical CO2 extraction methods, which results in high costs. Furthermore, the traditional Chinese medicine extract contains a significant amount of volatile antibacterial agents, making it impossible to guarantee antibacterial stability during the application of chilled pork.

[0005] Wang Fei et al. (2018) disclosed a method for preparing a natural preservative coating for chilled meat (Publication No.: CN109090208A). This method involves fusing a concentrated flavonoid extract from sunflower flowers with yeast cells to obtain the natural preservative coating. While this method is effective in preserving chilled meat, its preparation process is overly complex and cumbersome, and the consistency of the prepared results cannot be guaranteed, making large-scale application difficult.

[0006] He Xiangwei et al. (2023) disclosed a natural food preservative composition and its application (Publication No.: CN116965448A). The main components of the composition are kojic acid, cinnamaldehyde, eugenol and ε-polylysine. Among them, the main antibacterial agents cinnamaldehyde and eugenol are volatile substances. Although the composition has a synergistic effect to improve the preservative performance, the stability of the composition needs to be studied. Moreover, the method of application described in the method is spraying, which may affect the final quality of the composition due to volatilization during the process.

[0007] Liu Yixiang et al. (Application Publication No.: CN 106387017B) disclosed a nano-preservative for chilled pork, its preparation method, and preservation method. This method uses fucoidan extracted from natural seaweed, which is then subjected to high-pressure degradation and spray drying to obtain the nano-preservative, which is then applied to chilled pork. While this method is green and safe and can extend the shelf life of chilled pork, the lack of a good color preservation method during refrigeration leads to a rapid loss of the pork's red color, potentially causing a decrease in consumer purchasing desire.

[0008] In 2018, Cui Fei et al. disclosed a modified atmosphere packaging technology for chilled pork (application publication number: CN109006969A). This method involves cutting the pork, filling it with 78-80% oxygen and 20-22% carbon dioxide, packaging it, and then placing it in a cold storage. While this method effectively preserves the color and flavor of the pork and avoids secondary contamination, the gaseous environment provides a better environment for aerobic microorganisms, potentially accelerating protein degradation.

[0009] Zeng Shaofu et al.'s study on the preservation effect of fresh pork ("Release of cinnamaldehyde in chitosan composite active packaging film and its application in the cold storage of fresh pork") demonstrated that the composite film formed by chitosan encapsulating cinnamaldehyde can achieve antibacterial effects and slow down the deterioration of pork quality through the slow release of cinnamaldehyde, extending the shelf life of chilled pork to 7 days. The concentration of cinnamaldehyde used in this study ranged from a minimum of 0.5% to a maximum of 2.0%, and there was a possibility that the residual amount of cinnamaldehyde exceeded the national standard throughout the preservation process.

[0010] Zhou Qiang et al. studied the effects of cinnamon oil-modified atmosphere packaging (MAP) on chilled meat ("The Effect of Cinnamon Oil-Chitosan Coating-Modified Atmosphere Packaging on the Quality of Chitosan Meat"), demonstrating that cinnamon oil-chitosan coating combined with MAP can inhibit bacterial growth while protecting the color of pork during refrigeration. However, even with this method, it is still difficult to reduce the initial total bacterial count in the pork, leading to a rapid increase in the total bacterial count later and accelerating the reduction of shelf life. Summary of the Invention

[0011] The purpose of this invention is to provide a non-contact method for preserving pork using a composite essential oil emulsion combined with electrostatic field and modified atmosphere packaging. This invention utilizes a nanoemulsion containing different concentrations and proportions of cinnamon oil, oregano oil, lemon oil, and clove oil, pretreated with a high-voltage electrostatic field, and then combined with modified atmosphere packaging to inhibit the deterioration of pork color and the increase in total bacterial count during refrigeration. This combined technology can slow down the quality deterioration of pork during refrigeration, especially in terms of color, total bacterial count, pH, and volatile basic nitrogen. It inhibits the deterioration process of pork better than single treatments, maintains the nutritional and sensory quality of chilled pork for a longer period, and extends shelf life.

[0012] The technical solution of this invention:

[0013] A non-contact method for preserving pork using a compound essential oil emulsion combined with an electrostatic field and modified atmosphere packaging includes the following steps:

[0014] (1) Pork selection: Select pork that has been pre-cooled and aged after slaughter;

[0015] (2) Preparation of composite essential oil nanoemulsion: Cinnamon essential oil, oregano essential oil, lemon essential oil, clove essential oil, Tween 80 and water were mixed in proportion and then a natural composite essential oil nanoemulsion was prepared by ultrasonic method and put into a breathable bottle.

[0016] (3) Film packaging: The pork in step (1) and the breathable bottle containing the composite essential oil nanoemulsion in step (2) are placed in a polyethylene film packaging bag for film packaging;

[0017] (4) High voltage electrostatic field treatment: The pork packaged in the film in step (3) is treated in a high voltage electrostatic field.

[0018] (5) Modified atmosphere packaging: After the pork in the film package treated by the high voltage electrostatic field in step (4) is filled with gas by the modified atmosphere packaging machine, it is sealed by the heat sealing machine.

[0019] (6) Refrigeration and preservation: Place the pork in the modified atmosphere package (5) in a refrigerated environment.

[0020] Furthermore, the pork parts mentioned in step (1) are pork hind leg muscle, pork tenderloin, pork belly and pork hock.

[0021] Furthermore, in step (2), the mass concentrations of cinnamon oil, oregano oil, lemon oil, and clove oil in the natural compound essential oil nanoemulsion are all 0.05-0.2%, and the mass concentration of Tween 80 is 0.5-1%.

[0022] Furthermore, in step (2), the ultrasound duration is 5-10 min and the amplitude is 25-60 kHz.

[0023] Furthermore, in step (2), the breathable bottle is a glass bottle, and the breathable material of the breathable cap of the breathable bottle is polyvinylidene fluoride, which can realize the slow release of essential oils in the composite essential oil nanoemulsion.

[0024] Furthermore, in step (3), the size of the polyethylene film packaging bag is 400-700mm × 300-500mm, and the thickness is 10-25μm. The permeability of the polyethylene film of the packaging bag to oxygen, carbon dioxide, and water vapor is 0.010-0.020mL / m² at 22±1℃ and 90±4% relative humidity. -2 d -1 atm -1 0.070-0.080 mL m -2 d -1 atm -1 and 5.40-5.50g mm m -2 d -1 atm -1 The density of the packaging bag is 0.85 g / cm³. 3 ~0.95g / cm 3 .

[0025] Furthermore, in step (3), the pork body does not come into contact with the composite essential oil nanoemulsion in the breathable bottle, but only shares the same space.

[0026] Furthermore, in step (4), the high-voltage electrostatic field parameters are 10-50kV / m, and the processing time is 0.5-6h.

[0027] Furthermore, in step (5), during the bagging process of the modified atmosphere packaging machine, a vacuum is first drawn, and then a mixed gas is introduced. When the types of introduced gases are N2, O2, and CO2, the volume ratio of the introduced gases is N2: 10%–40%, O2: 50%–80%, and CO2: 10%–20%. When the types of introduced gases are N2 and O2, the volume ratio of N2 and O2 is N2: 10%–50% and O2: 50%–90%. When the types of introduced gases are O2 and CO2, the volume ratio of O2 and CO2 is O2: 50%–90% and CO2: 10%–50%.

[0028] Furthermore, in step (6), the storage environment temperature during the refrigeration process is 4±1℃ and the relative humidity is 90±4%RH.

[0029] The beneficial effects of this invention are:

[0030] (1) The natural compound essential oil nanoemulsion was prepared by emulsification using a simple ultrasonic method. The emulsification method encapsulates cinnamon essential oil, oregano essential oil, lemon essential oil, and clove essential oil in Tween 80, which reduces the volatility of the natural compound essential oils during preparation and reduces the release of the initial special flavor.

[0031] (2) The high voltage electrostatic field can effectively kill the microorganisms that are initially present in pork and reduce the total number of initial colonies in pork. At the same time, the energy of the high voltage electrostatic field can puncture the emulsion, thereby allowing the essential oil to be released better.

[0032] (3) The red color of pork needs to be maintained by oxygen. Modified atmosphere packaging can maintain the red color of pork during refrigeration by improving the concentration of gas under refrigeration conditions, thereby increasing consumers' desire to buy.

[0033] (4) Combining essential oil emulsions with electric fields and modified atmosphere packaging are three separate methods. The difficulty in combining them lies in the fact that essential oil emulsions are rich in essential oil substances, which can lead to direct contact with food and cause some concentrations to exceed the standard. This invention combines the three methods through a non-contact approach, which extends the shelf life of pork while protecting the safety of pork as a food product.

[0034] The inventors of this invention, by encapsulating natural compound essential oils within a Tween 80 atmosphere, fully utilized the properties of nanoemulsions to maintain the antibacterial properties while reducing the volatility of the natural compound essential oils. High-voltage electrostatic field treatment effectively reduced the initial total bacterial count in pork and punctured the natural compound essential oil nanoemulsion, making the antibacterial effect more pronounced during refrigeration. Modified atmosphere packaging effectively maintained the blood-red color of the pork during refrigeration. These three methods exhibit strong correlation throughout the entire pork preservation process and are indispensable. Specifically, the application of electric field technology reduced the initial total bacterial count in the pork sample, but it could not slow down the rapid deterioration of pork during refrigeration. Typically, modified atmosphere packaging for pork uses nitrogen to control microbial growth; oxygen-enriched modified atmosphere packaging slows the fading of the pork's blood-red color, but it also provides sufficient oxygen concentration to aerobic microorganisms, leading to a rapid increase in the total bacterial count during refrigeration. The compound essential oils dispersed in the packaging environment have an inhibitory effect on various bacteria, demonstrating a good effect on pork quality control during refrigeration. However, the lack of packaging leads to the rapid evaporation of the compound essential oils, and the lack of an electric field prevents the compound essential oil nanoemulsion from being quickly punctured, slowing down the release of the compound essential oils and causing a rapid decline in pork quality during refrigeration. Therefore, the combination of these three technologies has a significant synergistic effect. Simultaneously, the breathable bottle containing the natural compound essential oil nanoemulsion effectively isolates the essential oils from the pork through a breathable membrane, ensuring the release of the essential oils while achieving an ideal non-contact preservation effect. Therefore, this invention emphasizes the ratio and concentration of natural essential oils in the nanoemulsion, the non-contact method, the intensity of the high-voltage electrostatic field, and the gas ratio of the modified atmosphere packaging. Detailed Implementation

[0035] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and implementations of the present invention. The technical solutions of the present invention will be further described below in conjunction with specific embodiments.

[0036] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0037] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0038] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0039] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0040] The breathable bottles used in the embodiments and comparative examples of this invention are: BKMAM transparent glass sample bottles with a specification of 10 mL; the breathable caps are Yichen 10 mL bottle caps with an inner polyvinylidene fluoride membrane.

[0041] Example 1

[0042] A non-contact method for preserving chilled pork hind leg muscle using a natural compound essential oil nanoemulsion combined with a high-voltage electrostatic field and modified atmosphere packaging includes the following steps:

[0043] (1) Select pig hind leg muscles that have been pre-cooled for 1 hour after slaughter and aged for 24 hours and divided into 100g portions;

[0044] (2) Mix 0.5g cinnamon essential oil, 0.5g oregano essential oil, 0.5g lemon essential oil, 0.5g clove essential oil with 10g Tween 80, add 988.0g deionized sterile water, and sonicate for 10min under an ultrasonic amplitude of 50kHz to obtain a nanoemulsion containing 0.05% natural compound essential oil (each essential oil component in cinnamon essential oil, oregano essential oil, lemon essential oil, and clove essential oil accounts for 0.05% of the total mass), and put it into a breathable bottle with a breathable cap made of polyvinylidene fluoride.

[0045] (3) Polyethylene film packaging: The pork from step (1) and the breathable bottle from step (2) are placed in a polyethylene film packaging bag for film packaging; the polyethylene film is 400mm × 300mm in size and 25μm in thickness. The polyethylene film of the packaging bag has a permeability of 0.015mL / m² to oxygen, carbon dioxide, and water vapor at 22±1℃ and 90±4% relative humidity.-2 d -1 atm -1 0.075 mL m -2 d -1 atm -1 and 5.45g mm m -2 d -1 atm -1 The density of the packaging bag is 0.90 g / cm³. 3 .

[0046] (4) High voltage electrostatic field treatment: The pork packaged in the film in step (3) is treated in a 35kV / m high voltage electrostatic field for 2 hours.

[0047] (5) Modified atmosphere packaging: After the pork in the film package treated by the high voltage electrostatic field in step (4) is filled with gas (80% oxygen + 20% nitrogen) by a modified atmosphere packaging machine, it is sealed by a heat sealing machine;

[0048] (6) Cold storage preservation: The pork in (5) modified atmosphere packaging is placed in a cold storage environment with a storage temperature of 4±1℃ and a relative humidity of 90±4%RH.

[0049] Storage results showed that, compared with the untreated group (control example 1), treatment with a gas ratio of 80% oxygen + 20% nitrogen, a high-voltage electrostatic field of 35kV / m, and 0.05% natural compound essential oil nanoemulsion significantly slowed down the rate of increase in total bacterial count, volatile basic nitrogen, and pH at the end of storage (16 days). The redness of the pork was well maintained, the rate of deterioration in pork quality was slowed down, and the sensory evaluation was better than that of control example 1. Although there was cinnamaldehyde residue, the value was lower than the national standard.

[0050] Example 2

[0051] A non-contact method for preserving chilled pork tenderloin using a natural compound essential oil nanoemulsion combined with a high-voltage electrostatic field and modified atmosphere packaging includes the following steps:

[0052] (1) Select pork tenderloin that has been pre-cooled for 1 hour after slaughter and aged for 24 hours and divided into 20g portions;

[0053] (2) Mix 2.0g cinnamon essential oil, 2.0g oregano essential oil, 2.0g lemon essential oil, 2.0g clove essential oil with 10g Tween 80, add 982.0g deionized sterile water, and sonicate for 8 minutes under an ultrasonic amplitude of 45kHz to obtain a nanoemulsion containing 0.2% natural compound essential oil (each essential oil component in cinnamon essential oil, oregano essential oil, lemon essential oil, and clove essential oil accounts for 0.2% of the total mass), and put it into a breathable bottle with a breathable cap made of polyvinylidene fluoride;

[0054] (3) Polyethylene film packaging: The pork from step (1) and the breathable bottle from step (2) are placed in a polyethylene film packaging bag for film packaging; the polyethylene film is 500mm × 350mm in size and 15μm in thickness. The polyethylene film of the packaging bag has a permeability of 0.010mL / m² to oxygen, carbon dioxide, and water vapor at 22±1℃ and 90±4% relative humidity. -2 d -1 atm -1 0.070 mL m -2 d -1 atm -1 and 5.40g mm m -2 d -1 atm -1 The density of the packaging bag is 0.85 g / cm³. 3 .

[0055] (4) High voltage electrostatic field treatment: The pork packaged in the film in step (3) is treated in a 20kV / m high voltage electrostatic field for 2 hours.

[0056] (5) Modified atmosphere packaging: After the pork in the film package treated by the high voltage electrostatic field in step (4) is filled with gas (60% oxygen + 20% nitrogen + 20% carbon dioxide) by a modified atmosphere packaging machine, it is sealed with a heat sealer.

[0057] (6) Cold storage preservation: The pork in (5) modified atmosphere packaging is placed in a cold storage environment with a storage temperature of 4±1℃ and a relative humidity of 90±4%RH.

[0058] Storage results showed that treatment with a gas ratio of 60% oxygen + 20% nitrogen + 20% carbon dioxide, combined with a high-voltage electrostatic field of 20kV / m and 0.2% natural compound essential oil nanoemulsion, significantly slowed down the rate of change of various indicators (calculated with the value at day 0) at the end of storage compared with the untreated group (control example 1). The rate of increase of total bacterial count, volatile basic nitrogen and pH was slowed down. The redness of the pork was well maintained, the rate of poor pork quality was slowed down, and the sensory evaluation was better than control example 1. Although there was cinnamaldehyde residue, the value was lower than the national standard.

[0059] Example 3

[0060] A non-contact method for preserving chilled pork belly using a natural compound essential oil nanoemulsion combined with a high-voltage electrostatic field and modified atmosphere packaging includes the following steps:

[0061] (1) Select pork belly that has been pre-cooled for 1 hour after slaughter and aged for 24 hours and divided into 500g portions;

[0062] (2) Mix 1.0g of cinnamon essential oil, 1.0g of oregano essential oil, 1.0g of lemon essential oil, 1.0g of clove essential oil with 10g of Tween 80, add 986.0g of deionized sterile water, and sonicate for 5min under an ultrasonic amplitude of 60kHz to obtain a nanoemulsion containing 0.1% of natural compound essential oils (each essential oil component in cinnamon essential oil, oregano essential oil, lemon essential oil, and clove essential oil accounts for 0.1% of the total mass), and put it into a breathable bottle with a breathable cap made of polyvinylidene fluoride;

[0063] (3) Polyethylene film packaging: The pork from step (1) and the breathable bottle from step (2) are placed in a polyethylene film packaging bag for film packaging; the polyethylene film is 700mm × 400mm in size and 20μm in thickness. The polyethylene film of the packaging bag has a permeability of 0.015mL / m² to oxygen, carbon dioxide, and water vapor at 22±1℃ and 90±4% relative humidity. -2 d -1 atm -1 0.075 mL m -2 d -1 atm -1 and 5.50g mm m -2 d -1 atm -1 The density of the packaging bag is 0.90 g / cm³. 3 .

[0064] (4) High voltage electrostatic field treatment: The pork packaged in the film in step (3) was treated in a 45kV / m high voltage electrostatic field for 5 hours.

[0065] (5) Modified atmosphere packaging: After the pork in the film package treated by the high voltage electrostatic field in step (4) is filled with gas (80% oxygen + 10% nitrogen + 10% carbon dioxide) by a modified atmosphere packaging machine, it is sealed by a heat sealer.

[0066] (6) Cold storage preservation: The pork in (5) modified atmosphere packaging is placed in a cold storage environment with a storage temperature of 4±1℃ and a relative humidity of 90±4%RH.

[0067] Storage results showed that, compared with the untreated group (control example 1), treatment with a gas ratio of 80% oxygen + 10% nitrogen + 10% carbon dioxide, a high-voltage electrostatic field of 45kV / m, and 0.1% natural compound essential oil nanoemulsion significantly slowed down the rate of increase in total bacterial count, volatile basic nitrogen, and pH at the end of storage compared with the untreated group (control example 1). The redness of the pork was well maintained, the rate of deterioration in pork quality was slowed down, and the sensory evaluation was better than control example 1. Although there was cinnamaldehyde residue, the value was lower than the national standard.

[0068] Example 4

[0069] A non-contact method for preserving chilled pork hock using a natural compound essential oil nanoemulsion combined with a high-voltage electrostatic field and modified atmosphere packaging includes the following steps:

[0070] (1) Select pork hock meat that has been pre-cooled for 1 hour after slaughter and aged for 24 hours and divided into 150g portions;

[0071] (2) Mix 1.5g of cinnamon essential oil, 1.5g of oregano essential oil, 1.5g of lemon essential oil, 1.5g of clove essential oil with 10g of Tween 80, add 984.0g of deionized sterile water, and sonicate for 6 minutes under an ultrasonic amplitude of 40kHz to obtain a nanoemulsion containing 0.15% natural compound essential oil (each essential oil component in cinnamon essential oil, oregano essential oil, lemon essential oil, and clove essential oil accounts for 0.15% of the total mass), and put it into a breathable bottle with a breathable cap made of polyvinylidene fluoride;

[0072] (3) Polyethylene film packaging: The pork from step (1) and the breathable bottle from step (2) are placed in a polyethylene film packaging bag for film packaging; the polyethylene film is 450mm×450mm in size and 25μm in thickness. The polyethylene film of the packaging bag has a permeability of 0.020mL / m² to oxygen, carbon dioxide, and water vapor at 22±1℃ and 90±4% relative humidity. -2 d -1 atm -1 0.080 mL m -2 d -1 atm -1 and 5.40g mm m -2 d -1 atm -1 The density of the packaging bag is 0.85 g / cm³. 3 .

[0073] (4) High voltage electrostatic field treatment: The pork packaged in the film in step (3) is treated in a 30kV / m high voltage electrostatic field for 3 hours.

[0074] (5) Modified atmosphere packaging: After the pork in the film package treated by the high voltage electrostatic field in step (4) is filled with gas (80% oxygen + 20% carbon dioxide) by a modified atmosphere packaging machine, it is sealed by a heat sealer.

[0075] (6) Cold storage preservation: The pork in (5) modified atmosphere packaging is placed in a cold storage environment with a storage temperature of 4±1℃ and a relative humidity of 90±4%RH.

[0076] Storage results showed that, compared with the untreated group (control example 1), treatment with a gas ratio of 90% oxygen + 10% carbon dioxide, a high-voltage electrostatic field of 30kV / m, and 0.15% natural compound essential oil nanoemulsion significantly slowed down the rate of change of various indicators (calculated with the value of day 0) at the end of storage. This was due to the treatment of the gas ratio of 90% oxygen + 10% carbon dioxide, a high-voltage electrostatic field of 30kV / m, and a high-voltage electrostatic field of 0.15% natural compound essential oil nanoemulsion. The redness of the pork was well maintained, the rate of deterioration of pork quality was slowed down, and the sensory evaluation was better than that of control example 1. Although there was cinnamaldehyde residue, the value was lower than the national standard.

[0077] Experimental methods:

[0078] 1. Total bacterial count

[0079] Mix 5g of pork sample with 45mL of 0.90% sodium chloride solution, shake thoroughly, and then dilute with sterile physiological saline to an appropriate concentration. Place 1mL of the diluted solution in a sterile agar plate and add an appropriate amount of agar for counting. Incubate at 37±0.5℃ for 48h, then count viable cells. The results are expressed as 1g CFU / g. Measure the values ​​from three pieces of pork and take the average.

[0080] 2. Volatile basic nitrogen

[0081] The nitrogen was determined using the fully automated Kjeldahl method. 10g of pork was mixed with 75mL of boiled distilled water, homogenized, and allowed to stand for 30min. The sample was then distilled for 5min using a fully automated Kjeldahl nitrogen analyzer. The volatiles produced during distillation were absorbed by 30mL of 20g / L boric acid. Titration was performed with 0.01mol / L hydrochloric acid solution. Three pieces of pork were measured, and the average value was taken.

[0082] 3. pH

[0083] Homogenize 5g of pork with 45mL of boiled distilled water for 1 minute, then measure the pH value. Repeat three times for each group.

[0084] 4. Color difference

[0085] The color characteristics of pork were measured using a colorimeter. Color was measured at three different locations on each piece of pork, with a bloom time of 1 second. Triple measurements were taken for each group of three samples, and the average value of the results was calculated.

[0086] 5. Texture properties

[0087] The texture analyzer is equipped with a TA / 0.5 cylindrical probe for testing the firmness of pork.

[0088] 6. Sensory evaluation

[0089] Sensory evaluation was conducted by a 12-member trained panel (male-to-female ratio) assessing changes in pork quality during refrigeration. Overall acceptability was evaluated using a seven-point hedonic scale, ranging from 3 (very much liked) to -3 (very little liked). The 12 panel members (consistently assigned) evaluated pork samples every two days, for a total of six sensory evaluations over the course of the experiment. Each evaluation involved one panel member evaluating three different samples from each group. Since the panel members were between 25 and 30 years old, the evaluation results are expressed as the average score.

[0090] 7. Cinnamaldehyde residue

[0091] The content of cinnamaldehyde in pork was determined according to the national standard method GB 5009.281-2020.

[0092] Note: The above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention. Therefore, although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention. All technical solutions and improvements that do not depart from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

[0093] Compare with Examples 1-9

[0094] Comparative Example 1 underwent no treatment and only participated in steps (3) and (6). Comparative Example 2 used the same preparation process as Example 4, except that in Comparative Example 2, the breathable bottle in step (2) contained sterile water, and the remaining steps were the same as in Example 4. Comparative Example 3 used the same preparation process as Example 4, except that step (2) in Comparative Example 3 did not include a breathable bottle, i.e., the reaction up to step (3) was a contact reaction between pork and the composite essential oil nanoemulsion. Comparative Example 4 used the same preparation process as Example 4, except that Comparative Example 4 only performed steps (1), (2), (3), (5), and (6), and did not perform step (4). Comparative Example 5 used the same preparation process as Example 4, except that Comparative Example 5 only performed steps (1), (2), (3), (4), and (6), and did not perform step (5). Comparative Example 6 used the same preparation process as Example 4, except that in Comparative Example 6, step (2) contained sterile water in the breathable bottle, and step (4) was not performed. Comparative Example 7 used the same preparation process as Example 4, except that the breathable bottle in step (2) of Comparative Example 7 contained sterile water, and step (5) was not performed. Comparative Example 8 used the same preparation process as Example 4, except that step (2) of Comparative Example 8 did not include a breathable bottle, that is, the reaction up to step (3) was a contact reaction between pork and the composite essential oil nanoemulsion, and step (4) was not performed. Comparative Example 9 used the same preparation process as Example 4, except that step (2) of Comparative Example 9 did not include a breathable bottle, that is, the reaction up to step (3) was a contact reaction between pork and the composite essential oil nanoemulsion, and step (5) was not performed. The storage time was 16 days, and performance tests were conducted every two days during this period, as detailed in Table 1:

[0095] Table 1 Comparison of test indicators during storage period between different embodiments and control examples.

[0096]

[0097]

[0098]

[0099]

[0100]

[0101]

[0102] As shown in Table 1 above, the combination of natural compound essential oil nanoemulsion and high-voltage electrostatic field with modified atmosphere packaging significantly inhibits bacterial growth in pork and effectively controls the increase in pH and volatile basic nitrogen. After 4 days of refrigeration, the indicators of all examples were better than those of the control examples, indicating that the pork still had good texture, redness, and sensory evaluation after 4 days of storage. The samples treated with modified atmosphere packaging alone performed better in maintaining redness, because oxygen provides an environment for the survival of myoglobin. The treatment with natural compound essential oil emulsion effectively inhibited microorganisms in pork, resulting in a slower increase in the total bacterial count. The high-voltage electrostatic field effectively killed the original bacterial colonies in pork and broke the outer wall of the emulsion, allowing the natural compound essential oil to be released better, resulting in a better antibacterial effect. Meanwhile, the pork quality-related results of Control Examples 3, 8, and 9 were similar to those of the examples, but the cinnamaldehyde residue was greater than the national standard of 0.02 mg / kg. This indicates that the non-contact treatment method effectively ensured antibacterial properties while reducing essential oil residue, allowing the pork to meet the national standard level. Overall, the synergy of these three technologies is more advantageous in pork preservation than either one or two of them combined, while the use of non-contact methods further ensures the safety of the pork.

Claims

1. A non-contact method for preserving pork using a composite essential oil emulsion combined with an electrostatic field and modified atmosphere, characterized in that, Includes the following steps: (1) Pork selection: Select pork that has been pre-cooled and deacidified after slaughter; (2) Preparation of composite essential oil nanoemulsion: Mix cinnamon essential oil, oregano essential oil, lemon essential oil, clove essential oil, Tween 80 and water in proportion and prepare a natural composite essential oil nanoemulsion by ultrasonic method, and put it into a breathable bottle; (3) Film packaging: Put the pork in step (1) and the breathable bottle containing the composite essential oil nanoemulsion in step (2) into a polyethylene film packaging bag for film packaging; (4) High voltage electrostatic field treatment: Treat the film-packaged pork in step (3) in a high voltage electrostatic field; (5) Modified atmosphere packaging: Treat the pork in step (4) in a high voltage electrostatic field. (6) Cold storage: The pork packaged in the film after high voltage electrostatic field treatment is filled with gas by a modified atmosphere packaging machine and then sealed with a heat sealer; (7) Cold storage: The pork packaged in (5) is placed in a cold storage environment; In step (3), the pork body and the composite essential oil nanoemulsion in the breathable bottle do not come into contact, but only share the same space; In step (2), the mass concentration of cinnamon essential oil, oregano essential oil, lemon essential oil and clove essential oil in the natural composite essential oil nanoemulsion is 0.05-0.2%, and the mass concentration of Tween 80 is 0.5-1%; In step (4), the high voltage electrostatic field parameters are 10-50kV / m, and the treatment time is 0.5-6h.

2. The non-contact pork preservation method according to claim 1, which combines a composite essential oil emulsion with an electrostatic field and modified atmosphere, is characterized in that... The pork cuts mentioned in step (1) are pork hind leg muscle, pork tenderloin, pork belly and pork hock.

3. The non-contact pork preservation method according to claim 1, which combines a composite essential oil emulsion with an electrostatic field and modified atmosphere, is characterized in that... In step (2), the ultrasound duration is 5-10 min and the amplitude is 25-60 kHz.

4. The non-contact pork preservation method according to claim 1, which combines a composite essential oil emulsion with an electrostatic field and modified atmosphere, is characterized in that... In step (2), the breathable bottle is a glass bottle, and the breathable material of the breathable cap of the breathable bottle is polyvinylidene fluoride, which can realize the slow release of essential oils in the composite essential oil nanoemulsion.

5. The non-contact pork preservation method according to claim 1, which combines a composite essential oil emulsion with an electrostatic field and modified atmosphere, is characterized in that... In step (3), the polyethylene film packaging bag has a size of 400-700mm × 300-500mm and a thickness of 10-25μm. The polyethylene film of the packaging bag has a permeability of 0.010-0.020mLm to oxygen, carbon dioxide, and water vapor at 22±1℃ and 90±4% relative humidity. -2 d -1 atm -1 0.070-0.080 mLm -2 d -1 atm -1 and 5.40-5.50 gmm -2 d -1 atm -1 The density of the packaging bag is 0.85 g / cm³. 3 ~0.95g / cm 3 .

6. The non-contact pork preservation method according to claim 1, which combines a composite essential oil emulsion with an electrostatic field and modified atmosphere, is characterized in that... In step (5), during the bagging process of the modified atmosphere packaging machine, a vacuum is first drawn, and then a mixed gas is filled in. When the types of gas filled in are N2, O2 and CO2, the volume ratio of the filled gas is N2: 10%~40%, O2: 50%~80%, and CO2: 10%~20%. When the types of gas filled in are N2 and O2, the volume ratio of N2 and O2 is N2: 10%~50% and O2: 50%~90%. When the types of gas filled in are O2 and CO2, the volume ratio of O2 and CO2 is O2: 50%~90% and CO2: 10%~50%.

7. The non-contact pork preservation method according to claim 1, which combines a composite essential oil emulsion with an electrostatic field and modified atmosphere, is characterized in that... In step (6), the storage environment temperature during the refrigeration process is 4±1℃ and the relative humidity is 90±4%RH.

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