Antibacterial aerogel water-absorbing liner, preparation method, fresh-keeping method and application

Abstract

The invention belongs to the technical field of food preservation, and relates to an antibacterial aerogel water-absorbing liner as well as a preparation method, a preservation method and application thereof, the aerogel water-absorbing liner comprises a matrix material and an antibacterial agent, the matrix material is a mixture of polyvinyl alcohol and hydroxymethyl cellulose or a mixture of polyvinyl alcohol and sodium alginate, and the antibacterial agent is a mixture of polyvinyl alcohol and hydroxymethyl cellulose. The polyvinyl alcohol accounts for 15-25% of the total mass of the matrix material, and the hydroxymethyl cellulose or sodium alginate accounts for 75-85% of the total mass of the matrix material; the antibacterial agent is selected from one or more of plant essential oil or chitosan, the addition amount of the chitosan is 10-15% of the total mass of the matrix material, the matrix material and the antibacterial agent are blended and then poured into a mold for freeze drying, and the aerogel water absorption liner is obtained. The water-absorbing liner can reduce available water required by microorganism reproduction, and can be combined with antibacterial substances to inhibit the growth of microorganisms in chicken and prolong the refreshing time of chicken.

Description

Technical Field

[0001] The invention belongs to the technical field of food preservation, and relates to an antibacterial aerogel water-absorbing pad and a preparation, preservation method and application thereof. Background Art

[0002] Poultry meat is the second largest meat consumed in my country. Chicken accounts for a large proportion in the dietary structure of Chinese residents. It has the advantages of three highs and one low, namely, high edible part, high content of essential amino acids for the human body, high content of vitamins and beneficial to lowering cholesterol. However, food safety is always a topic that people are concerned about. The more confident people are in the quality and safety of chicken, the more likely they are to buy it frequently. Food quality and safety are also an indispensable guarantee for the life and health of the people and the security and stability of society. The direct means to improve the safety of chicken is the use of chicken preservation technology, so the research on chicken preservation technology is of great significance.

[0003] Factors that affect the rate of meat spoilage mainly include storage temperature, moisture content, water activity, initial microbial count, environmental cleanliness, etc. With the continuous advancement of the broiler industry's "centralized slaughter and cold fresh sales", low-temperature preservation of chicken has received continuous attention. Existing preservation technologies all start with controlling the temperature of processing, logistics, and exhibition sales. In addition to temperature control, chicken preservation is usually combined with other methods, such as gas conditioning, vacuum packaging, preservatives, irradiation, antifreeze preservatives, antibacterial packaging, low-temperature plasma sterilization technology, nanotechnology, etc., to form multiple barrier factors that work with low temperature to jointly inhibit the growth of microorganisms and delay spoilage.

[0004] Aerogel is a new type of material with nanopore size, high conductivity, large porosity, low density, good thermal insulation and other characteristics. It has good application prospects in many fields. Aerogel used as food contact packaging material can isolate food from the external environment, thereby reducing contact with external microorganisms. At the same time, by utilizing the high porosity of aerogel, it can absorb part of the exudate of food well, alleviating the problem of excessive microbial reproduction caused by excessive water activity, thereby accelerating food deterioration. If antibacterial substances such as chitosan, lysozyme, essential oils, etc. are added to the aerogel absorbent pad, it can achieve better food preservation effect. For the packaging space of water-rich food, many packaging material studies focus on the water permeability and oxygen permeability of packaging materials (headspace boxes, atmosphere boxes, skin packaging), but there are not many studies and products on absorbent pads, and related products are not rich and complete enough. At present, the absorbent pads on the market are mainly made of spun yarn and multi-layer plastic film, and the water absorption effect is not very good. Aerogel replaces the water phase originally existing in hydrogel with gas phase. It has nanopore size and good water absorption, so it can become an ideal water-absorbing pad. It absorbs the water seeping from food, slows down the softening and decay of fruits and vegetables, and absorbs the water in meat, reducing the water available to microorganisms in meat, reducing humidity, slowing the growth rate of microorganisms, delaying the deterioration of meat, and increasing the storage and freshness period of fruits, vegetables and meat. Adding antibacterial substances to aerogel can inhibit the growth of microorganisms on aerogel and in food. Aerogel water-absorbing pads have good application prospects in the field of food preservation.

[0005] At present, there is a blank in the market for aerogel type meat absorbent pads. The type of aerogel finally used is a product that caters to market needs in all aspects. Rich experimental data support is conducive to finding and determining the best formula solution. Therefore, the present invention helps to provide a reference type in the process of optimizing the best product, and contributes to the early application of aerogel type chicken absorbent pads in the market. Summary of the invention

[0006] Sodium alginate is a natural polysaccharide with the stability, solubility, viscosity and safety required for pharmaceutical excipients. Chitosan, also known as deacetylated chitosan, is a safe and reliable natural bioactive polysaccharide that is widely found in the shells of crustaceans such as shrimp and crabs. This substance can enhance insulin activity, reduce postprandial hyperglycemia and regulate insulin secretion. Carboxymethyl cellulose (CMC for short) is a commonly used food additive, and its sodium salt (sodium carboxymethyl cellulose) is often used as a thickener and paste. Polyvinyl alcohol is a degradable high molecular organic compound with a white flake, flocculent or powdery solid appearance. It is odorless, relatively stable, non-toxic, and non-irritating to human skin. It is widely used in textiles, paper products, ceramic molding, coatings, etc., and is an important chemical raw material.

[0007] In view of the shortcomings of the prior art, the present invention provides an antibacterial aerogel absorbent pad and its preparation, preservation method and application. The absorbent pad can reduce the portion of physiological saline required for microbial reproduction and work in conjunction with antibacterial substances to inhibit the growth of microorganisms in chicken and extend the shelf life of chicken.

[0008] The technical solution provided by the present invention is as follows:

[0009] The invention provides an antibacterial aerogel water-absorbing pad. The aerogel water-absorbing pad comprises a matrix material and an antibacterial agent. The matrix material is a mixture of polyvinyl alcohol and hydroxymethyl cellulose or a mixture of polyvinyl alcohol and sodium alginate, the polyvinyl alcohol accounts for 15-25% of the total mass of the matrix material, and the hydroxymethyl cellulose or the sodium alginate accounts for 75-85% of the total mass of the matrix material; the antibacterial agent is selected from one or more of plant essential oils or chitosan, and the added amount of the chitosan is 10-15% of the total mass of the matrix material. The matrix material and the antibacterial agent are blended and then poured into a mold for freeze drying to obtain the aerogel water-absorbing pad.

[0010] Furthermore, the plant essential oil is oregano essential oil, and the mass volume ratio of the matrix material to the emulsion loaded with oregano essential oil is 2-5 g / mL.

[0011] The present invention also provides a method for preparing the above-mentioned antibacterial aerogel water-absorbing pad, comprising the following steps: The oregano essential oil emulsion is prepared by mixing ovalbumin and inulin, dissolving them in a phosphate solution, stirring and then ultrasonically treating them, adding oregano essential oil and sucrose fatty acid ester, and performing intermittent shearing using a high-speed shear homogenizer to obtain an emulsion loaded with oregano essential oil; Dissolve carboxymethyl cellulose in deionized water to form a clear solution, dissolve polyvinyl alcohol in deionized water, stir at a water bath temperature and then cool, mix the two solutions to obtain a first mixed solution, and stir with an oregano essential oil emulsion to obtain a second mixed solution, or dissolve sodium alginate and polyvinyl alcohol in deionized water to obtain a first mixed solution, dissolve chitosan in deionized water and drip it into the first mixed solution drop by drop, and then add the oregano essential oil emulsion and stir to obtain a second mixed solution; The second mixed solution is injected into a mold and then freeze-dried to obtain the aerogel water-absorbent pad.

[0012] Furthermore, in the process of preparing the oregano essential oil emulsion, the stirring speed is 450-600 rpm / min, the stirring time is 2-3 h, the ultrasonic treatment time is 10-15 min, and the ultrasonic frequency is 50-100 Hz.

[0013] Furthermore, in the process of preparing the oregano essential oil emulsion, the shear speed of the high-speed shear homogenizer is 8000-10,000 rpm / min, and the intermittent shearing time is 2-3 min.

[0014] Furthermore, the amount of ovalbumin used is 0.32 g, the amount of inulin used is 0.30 g, the amount of phosphate solution used is 120 mL, the amount of oregano essential oil used is 24.71 g, and the amount of sucrose fatty acid ester used is 0.60 g.

[0015] The present invention also provides an antibacterial aerogel water-absorbing pad, which is prepared by the above-mentioned preparation method.

[0016] The present invention also provides a method for preserving fresh cold chicken using the antibacterial aerogel absorbent pad, comprising the following steps: Choose fresh and quarantined chilled chicken and cut it into pieces according to product requirements; Placing the cut chilled fresh chicken and the antibacterial aerogel absorbent pad in a packaging material so that the chilled fresh chicken is in contact with the absorbent pad during storage; The sealed packaging material is placed in a refrigerator for refrigerated storage at a temperature of 0-4°C.

[0017] The present invention also provides the use of the above-mentioned antibacterial aerogel water-absorbing pad in the preservation of chilled fresh chicken.

[0018] Furthermore, the antibacterial aerogel absorbent pad has any of the following functions: (1) Absorb the exudate from cold fresh chicken during storage; (3) Reduce the pH change of fresh chicken during storage; (4) Protect the color of fresh chicken during storage; (5) Inhibit the growth and reproduction of microorganisms in fresh chicken; (6) Prolong the shelf life of fresh chicken.

[0019] Beneficial Effects

[0020] The present invention intends to use two types of cellulose materials, sodium alginate and carboxymethyl cellulose, which have certain antibacterial properties, to react with polyvinyl alcohol respectively, and use essential oil emulsion or essential oil emulsion and chitosan as antibacterial substances to add them thereto, so as to produce two absorbent pads for refrigerated preservation of chicken, which absorb blood or exudate of chicken, reduce the part of physiological saline required for the reproduction of microorganisms, and work in combination with antibacterial substances to inhibit the growth of microorganisms in chicken and extend the shelf life of chicken.

[0021] In this study, two antibacterial aerogel absorbent pads were prepared, namely carboxymethyl cellulose / polyvinyl alcohol / oregano essential oil aerogel absorbent pad (group C) and chitosan / sodium alginate / polyvinyl alcohol / oregano essential oil aerogel absorbent pad (group S), and the physical and chemical properties of the two aerogels and the preservation effect on fresh chicken were evaluated. The prepared aerogels had good water absorption capacity, and group C had greater stress. Under 4 ℃ storage conditions, the preservation effect of fresh chicken showed that the total number of bacteria in group S at 3 days was lower than that in group C and the blank control group, showing a certain antibacterial ability. The aerogels prepared in this study initially showed good liquid absorption capacity and certain antibacterial ability, and after optimization, they can be used for the preservation of fresh chicken.

[0022] The water-absorbent pad of the present invention can be used in the cold chain transportation process of chilled chicken, as well as for home preparation, and can be used in combination with plastic wrap. The aerogel can be used to refrigerate the chicken, avoiding the use of frozen storage, which causes the chicken to be repeatedly thawed and causes the microorganisms to reproduce rapidly. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is the stress-strain curve of the two aerogels;

[0024] Figure 2 This is a diagram of the water absorption effect of two types of aerogels;

[0025] Figure 3 It is the Fourier infrared absorption curve of two aerogels;

[0026] Figure 4 Schematic diagram of the change of total bacteria count in chilled fresh chicken during storage (Note: Different lowercase letters indicate significant differences between different treatment groups at the same storage time (P<0.05); different uppercase letters indicate significant differences between different storage times at the same treatment (P<0.05));

[0027] Figure 5 This is a schematic diagram of the pH changes of fresh chicken during storage;

[0028] Figure 6 This is a schematic diagram of the changes in the mass loss rate of fresh chicken during storage (Note: Different lowercase letters indicate significant differences among different treatment groups (P<0.05)). DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with specific embodiments and accompanying drawings.

[0030] An embodiment of the present invention provides an antibacterial aerogel absorbent pad, the aerogel absorbent pad comprising a matrix material and an antibacterial agent, the matrix material being a mixture of polyvinyl alcohol and hydroxymethyl cellulose or a mixture of polyvinyl alcohol and sodium alginate, the polyvinyl alcohol accounting for 15-25% of the total mass of the matrix material, and the hydroxymethyl cellulose or sodium alginate accounting for 75-85% of the total mass of the matrix material; the antibacterial agent is selected from one or more of plant essential oils or chitosan, the added amount of the chitosan is 10-15% of the total mass of the matrix material, the matrix material and the antibacterial agent are blended and then poured into a mold for freeze drying to obtain an aerogel absorbent pad.

[0031] In this embodiment, the plant essential oil is oregano essential oil, and the mass volume ratio of the matrix material to the emulsion loaded with oregano essential oil is 2-5 g / mL.

[0032] The embodiment of the present invention also provides a method for preparing the above-mentioned antibacterial aerogel water-absorbing pad, comprising the following steps: The oregano essential oil emulsion is prepared by mixing ovalbumin and inulin, dissolving them in a phosphate solution, stirring and then ultrasonically treating them, adding oregano essential oil and sucrose fatty acid ester, and performing intermittent shearing using a high-speed shear homogenizer to obtain an emulsion loaded with oregano essential oil; Dissolve carboxymethyl cellulose in deionized water to form a clear solution, dissolve polyvinyl alcohol in deionized water, stir at a water bath temperature and then cool, mix the two solutions to obtain a first mixed solution, and stir with an oregano essential oil emulsion to obtain a second mixed solution, or dissolve sodium alginate and polyvinyl alcohol in deionized water to obtain a first mixed solution, dissolve chitosan in deionized water and drip it into the first mixed solution drop by drop, and then add the oregano essential oil emulsion and stir to obtain a second mixed solution; The second mixed solution is injected into a mold and then freeze-dried to obtain the aerogel water-absorbent pad.

[0033] In this embodiment, during the preparation of the oregano essential oil emulsion, the stirring speed is 450-600 rpm / min, the stirring time is 2-3 h, the ultrasonic treatment time is 10-15 min, and the ultrasonic frequency is 50-100 Hz.

[0034] In this embodiment, during the preparation of the oregano essential oil emulsion, the shear rate of the high-speed shear homogenizer is 8000-10,000 rpm / min, and the intermittent shearing time is 2-3 min.

[0035] Example 1

[0036] 1. Materials and Methods

[0037] 1.1 Materials and reagents

[0038] 1.1.1 Experimental Materials

[0039] Fresh chicken breast (purchased from Hema Fresh Nanjing Zijin Plaza Store), foam boxes, gun tips, pipettes, plastic round boxes, metal scissors, tweezers, 3M Petrifilm total bacterial count test pieces (Nantong Yuncheng Experimental Equipment Co., Ltd.).

[0040] 1.1.2 Experimental reagents

[0041] Table 1 Experimental reagents

[0042]

[0043] 1.2 Experimental equipment

[0044] The main experimental equipment is as follows:

[0045] Table 2 Experimental equipment

[0046]

[0047] 1.3 Preparation of aerogel absorbent pad

[0048] The present invention intends to construct two types of polysaccharide aerogel absorbent pads. Sodium alginate and polyvinyl alcohol, carboxymethyl cellulose and polyvinyl alcohol are stirred to make two kinds of hydrogels respectively, and then oregano essential oil emulsion obtained by shearing is added, and the mixture is stirred evenly. The mixture is poured into a mold, frozen at -35°C and then freeze-dried to obtain an aerogel absorbent pad.

[0049] 1.3.1 Preparation of oregano essential oil emulsion

[0050] 0.32 g ovalbumin (OVA) and 0.30 g inulin (IN) were mixed and dissolved in a beaker containing 120 mL phosphate solution, stirred at 450 rpm / min for 2 h, and treated with ultrasound for 10 min (ultrasonic frequency was 50 Hz). 24.71 g oregano essential oil (OEO) and 0.60 g sucrose fatty acid ester were added to the above solution, and intermittent shearing was performed at a speed of 10,000 rpm / min for 3 min using a high-speed shear homogenizer. After shearing, an emulsion loaded with oregano essential oil was obtained, which was added to the two prepared hydrogels.

[0051] 1.3.2 Preparation of two types of aerogel absorbent pads

[0052] Preparation of carboxymethyl cellulose / polyvinyl alcohol / oregano essential oil composite aerogel: 200 mL of water was measured with a measuring cylinder, 12.00 g of carboxymethyl cellulose CMC was weighed, and mixed and stirred in a beaker (450 rpm / min) until a clear solution was formed. Then 100 mL of deionized water with 3.0 g of polyvinyl alcohol PVA was added and stirred at a water bath temperature of 80 °C for 2 h, and continued to cool to ambient temperature. The above two solutions were mixed and stirred with 50 mL of oregano essential oil emulsion to obtain a uniform mixed solution. 20 mL of hydrogel was injected into a small plastic box with a syringe and frozen in a refrigerator for 6 h. Finally, the hydrogel injected into the mold was dried in a vacuum freeze dryer for 48 h. The aerogel obtained was named group C aerogel water-absorbing pad.

[0053] Preparation of chitosan / sodium alginate / polyvinyl alcohol / oregano essential oil composite aerogel: Add 200 mL of deionized water to a beaker containing 11.97 g of sodium alginate SA and 2.99 g of polyvinyl alcohol PVA, stir evenly and set aside. Dissolve 2.02 g of water-soluble chitosan in 100 mL of deionized water, stir with a magnetic stirrer for 2 h, then drip the chitosan solution drop by drop into the SA / PVA mixed solution, stir manually for 0.5 h, mix evenly, add 50 mL of oregano essential oil emulsion and stir, and inject 20 mL of hydrogel into a small plastic box with a syringe. After the hydrogel is frozen, vacuum freeze-dried for 48 h to obtain a composite aerogel sample. Finally, dry the hydrogel injected into the mold in a freeze dryer for 48 h. The obtained aerogel is named S group aerogel water-absorbing pad.

[0054] Example 2 Determination of physical properties of aerogel absorbent pad

[0055] The physical properties of the two aerogel water-absorbing pads prepared in Example 1 were tested by water absorption experiment, mechanical strength measurement and Fourier infrared measurement.

[0056] 1. Mechanical strength determination

[0057] The mechanical strength of the aerogel absorbent pads in groups C and S was tested using a physical property tester, and the strain was controlled at 10%-50% using EXPOENT software, and the stress value was recorded in real time. Each group of aerogel absorbent pads was tested 3 times, and the pressure-strain curve drawn by the software was obtained.

[0058] 2. Water absorption observation

[0059] Three portions of each of the S group and C group aerogel absorbent pads were cut into 1 × 1 cm sizes on a cutting board and placed in a plastic box. Deionized water 2000 times the weight of the aerogel was added and placed at room temperature for 24 h to observe the water absorption and expansion state of the aerogel.

[0060] 3. Fourier transform infrared absorption spectroscopy

[0061] The principle of Fourier infrared spectrometer testing is to determine the specific conditions of functional groups and chemical bonds in a substance based on the absorption of different infrared lights by functional groups and chemical bonds in the substance. The C group and S group aerogel absorbent pads were measured using a Fourier infrared spectrometer to obtain the infrared absorption curves of the two groups of aerogel absorbent pads. The two infrared absorption curves were compared and analyzed to determine the differences in the molecules and chemical bonds that constitute the aerogel material.

[0062] 4. Experimental results

[0063] 4.1 Mechanical strength

[0064] Excellent mechanical strength helps the aerogel absorbent pad maintain its complete structure during meat storage, so that it will not be damaged by food squeezing. Figure 1 The results showed that with the increase of strain, group C had higher stress than group S, that is, carboxymethyl cellulose aerogel had higher strength than sodium alginate aerogel, was less likely to be damaged during storage, and reduced the deformation and bending of the aerogel absorbent pad caused by water penetration.

[0065] 4.2 Water absorption observation

[0066] Aerogel absorbent pads with high water absorption capacity can absorb some food exudates, thereby alleviating the excessive growth of microorganisms caused by excessive water activity and slowing down the process of food spoilage. Figure 2 As shown, it can be observed that both groups of aerogels float in deionized water. After 24 hours of water absorption, the two samples fully absorb water and swell. This may be because the aerogels prepared by the vacuum freeze-drying method have a high porosity, which provides more adsorption space for water molecules and gives them a higher water absorption capacity.

[0067] 4.3 Fourier transform infrared absorption spectroscopy

[0068] Depend on Figure 3 It can be seen that the aerogel has a wavelength of 1170 cm -1 , 1200 cm -1 About 1500 cm -1 About 3300 cm -1 There are obvious absorption peaks on the left and right: 1170 cm -1The bending vibration of CO bond is at 1200 cm -1 The stretching vibration of CH and CC is at 1500 cm -1 The double bond stretching vibration region, 3300 cm -1 The peak at 750 cm is caused by the vibration of OH. The curves of the two are basically overlapped in the Fourier infrared spectrum, and the more obvious difference in absorption rate appears at 750 cm -1 , which is the out-of-plane bending vibration of CH of benzene ring substitution and olefins and aromatics, reflects the different vibration intensities of CH, which may also be the microscopic molecular structure root of the mechanical differences between the two aerogel macro materials. -1 There are certain differences in the overlapping peaks of the OH and NH stretching vibration peaks on the left and right, indicating that there are intramolecular and intermolecular hydrogen bonds of different strengths between the hydroxyl and amino groups, and these different hydrogen bonding effects may affect the water absorption capacity of the aerogel.

[0069] The present invention prepares two antibacterial aerogel absorbent pads by reacting sodium alginate and carboxymethyl cellulose with polyvinyl alcohol to load oregano essential oil. The absorbent pads are used to preserve fresh chicken. The water absorption of the two aerogels was observed, and the Fourier infrared absorption rate and pressure-strain curve were measured. The water absorption observation results showed that after 24 hours of water absorption, the two samples fully absorbed water and expanded, and both groups of aerogels floated in deionized water, which shows that both have high water absorption capacity; the curves of the two groups of aerogels in the Fourier infrared spectrum basically overlap, and the more obvious difference in absorption rate appears at 750 cm -1 , here is the out-of-plane bending vibration of CH of benzene ring substitution and olefins and aromatics, reflecting the different vibration intensities of CH. In addition, the two have different vibrations at 3300cm -1 There are certain differences in the overlapping peaks of the OH and NH stretching vibration peaks on the left and right, indicating that there are intramolecular and intermolecular hydrogen bonds of different strengths between the hydroxyl and amino groups; the results of the pressure-strain curves show that group C has higher stress than group S.

[0070] Example 3: Fresh-keeping of Chilled Chicken Breast and Determination of Related Indicators

[0071] The specific experimental plan is as follows:

[0072] The aerogel absorbent pads in group C and group S were named C and S, respectively. N was the blank control. Before each measurement of the total number of bacteria, the physiological saline, pipette tips, test tubes, scissors and other reagents and items were sterilized in an autoclave.

[0073] On day 0, prepare 9 plastic round boxes and mark them as C1, C2, C3, S1, S2, S3, N1, N2, and N3 with a marker.

[0074] 1. Determination of total bacterial count

[0075] Use scissors to cut about 10 g of chicken breast, put it into a sample homogenizer bag, add 90 mL of normal saline (the preparation method of normal saline is: take sodium chloride and add 99.1 mL of distilled water, shake well to make 100 mL of normal saline with a concentration of 0.9%), homogenize with a slapping homogenizer for 2 min, use a pipette to draw 1 mL of sample solution into 9 mL of normal saline, repeat the operation to get 10 -1 , 10 -2 , 10 -3 For the gradient dilution sample solution, use a pipette to draw 1 mL of sample solution and drop it vertically in the center of the test piece (from high dilution concentration to low dilution concentration), cover it with the upper film, and slowly flatten it to allow the sample solution to spread on the test piece to the maximum extent but not leak from the edge. Repeat each gradient twice, put it in a plastic bag, mark it and put it in a 37 ℃ constant temperature box for 72 hours, count and record the number of colonies formed, and take the average of the two repeated treatments. The results are displayed as logarithmic CFU / g meat.

[0076] Six pieces of chicken breast meat, about 10 g each, were cut into pieces and placed on plastic boxes C1, C2, S1, S2, N1, and N2, which were then placed in foam boxes and stored in cold storage. C1, S1, N1 and C2, S2, N2 were taken out at 3d and 7d, respectively, and the aerogel samples adsorbed in the refrigerated meat were picked out with tweezers. 90 mL of deionized water was added to the sample meat and homogenized in a sterile homogenizer for 2 min to prepare a series of dilution solutions. 10 mL of the sample solution was taken out with a pipette, respectively. -3 , 10 -4 , 10 -5 and 10 -6 , 10 -7 , 10 -8 1 mL of the sample solution of different dilutions (from high dilution concentration to low dilution concentration) is dripped vertically on the center of the rapid test paper, covered with the upper film, and slowly flattened to allow the sample solution to spread on the test piece to the maximum extent but not leak from the edge. Each gradient is repeated twice, put into a plastic bag, mark it and put it into a 37 ℃ constant temperature box for 72 hours, count and record the number of colonies formed, and take the average of the two repeated treatments. The results are displayed as logarithmic CFU / g meat.

[0077] 2. pH and colorimetry

[0078] Three pieces of chicken breast, each about 10 g, were cut into pieces and placed in C3, D3, and N3 respectively, and the weights were recorded. A pH meter was used to measure the pH, and the results were repeated three times to take the average value. A colorimeter was used to measure L* (brightness value), a* (redness value), and b* (yellowness value), and the results were repeated three times to take the average value. The measurement time points were 1 d, 3 d, 5 d, and 7 d.

[0079] 3. Determination of weight loss rate

[0080] The weight loss rate was calculated as the percentage of the weight difference before and after 7 days of cold storage to the initial weight.

[0081] 4. Data processing

[0082] The experimental data were processed using Excel software, and Origin software was used for drawing. The pressure-strain curves of the two aerogel water-absorbing pads, Fourier infrared absorption spectra, point-line graphs of total bacterial counts, point-line graphs of pH changes, and data tables of chromaticity and acidity were obtained. The water loss during storage was calculated by the percentage of the weight difference before and after a group of chicken breasts stored for 7 days to the initial weight. SPSS software was used for significance analysis, and the data were expressed as mean ± standard deviation. P < 0.05 indicated that there was a significant difference between the data.

[0083] 5. Experimental results

[0084] 5.1 Total bacterial count

[0085] The total number of bacteria can reflect the degree of microbial contamination of food, and thus judge the freshness of the food. Sothem et al. (Comparative Study on the Quality of Fresh Chicken Meat of Different Varieties and Storage Methods [D]. Yangzhou: Yangzhou University, 2021.) proposed a recommended standard for evaluating the total number of colonies in the hygienic indicators of meat quality: 10 for fresh meat 4 CFU / g or less, and 10 for second-fresh meat 4 -10 6 CFU / g, 10 6 CFU / g or above indicates spoiled meat.

[0086] Depend on Figure 4 It can be seen that at 0 days, because the same sample was tested, the colony formation numbers of the three groups were all 1.31×10 4 CFU / g, belonging to sub-fresh meat, the total number of bacteria in the S group was significantly lower than that in the C and N groups on day 3 ( P <0.05), which is three orders of magnitude less. Among them, group S is still sub-fresh meat, while groups N and C are already spoiled meat, which shows that group S has an antibacterial effect within 3 days. However, when stored for 7 days, the number of colonies in group S was not significantly different from that in the other two groups ( P >0.05), indicating that the antibacterial capacity of the active substances in this experiment had been exhausted after 3 days.

[0087] 5.2 pH changes

[0088] Normal meat pH range is generally between 5.6-6.2. Meat pH affects meat quality, including color, tenderness, flavor, water retention, etc. In this experiment, the pH changes of the three groups of chicken breast meat showed an overall upward trend. This is because as the storage time increases, microorganisms multiply in large numbers, and the protein in the chicken breast meat is decomposed into nitrogen-containing compounds, producing ammonia and amine volatile compounds, which leads to an increase in pH. Figure 5 It can be seen that although the pH value of chicken breast meat in group S was lower than that of the other two groups on day 1, it rose rapidly compared with the other two groups afterwards. When stored for 3 days, the pH value of group S was higher than the limit of 6.2, while that of groups C and N was lower than 6.2. In addition, the pH value of the three groups exceeded 7.0 on day 7, indicating that obvious quality deterioration had occurred.

[0089] 5.3 Color difference

[0090] Meat color is an important indicator of meat appearance quality, which directly determines consumers' preference and acceptance of chicken and can also reflect its freshness. * It is related to the degree of protein denaturation and pH value. Meat with low pH value and high degree of protein denaturation tends to have higher L* value. This experiment measured the color difference of chicken breast meat in three groups at 0 d, 1 d, and 5 d, including L * 、a * , b * Value, where L * The values ​​of the three groups are all in a downward trend, b * The values ​​of the three groups all increase first and then decrease. * The values ​​are decreasing all the time. The values ​​of a in groups S and N are * The values ​​decrease first and then increase.

[0091] Table 3 Changes in L* value of fresh chicken during storage

[0092]

[0093] 5.4 Weight loss rate

[0094] The mass loss rate of the samples stored in the refrigerator for 7 days was measured. Figure 6It can be seen that the S group had the highest mass loss rate during storage, followed by the C group, which were much higher than the N group. The storage loss value of the S group was 77%. More than half of the weight loss may be because the samples in this experiment were cut meat rather than whole chickens, and water was easily lost from the cut surface. The aerogel absorbent pad had a strong water absorption capacity, and excessive water loss under capillary action led to excessive mass loss. In addition, due to the decomposition of microorganisms, the original structure of the chicken breast was destroyed, reducing the water holding capacity of the chicken breast and increasing its mass loss. The difference in water absorption capacity between the aerogel absorbent pads of the S group and the C group led to the difference in water absorption capacity between the two, which was manifested as the difference in the mass loss of the chicken breast. However, the storage loss of the N group was the smallest, which may be due to the absence of the absorbent pad. The lost water was still adsorbed on the surface of the chicken breast, resulting in a lower mass loss rate. The water adsorbed on the surface of the chicken breast provided a medium for the reproduction of microorganisms, resulting in more serious corruption and deterioration of the chicken breast, which was consistent with the results of the changes in the total number of bacteria in 5.1.

[0095] During the processing, transportation and storage of fresh chicken, it is difficult to avoid the influence of external factors such as juice loss and microbial contamination. The lost juice contains a large amount of small molecular nutrients, in which microorganisms can continue to grow and multiply and accelerate the spoilage of fresh chicken, resulting in the occurrence of corruption phenomena such as stickiness, odor, and discoloration of meat, affecting the sensory quality and edible value of fresh chicken. Aerogel can be used to prepare water-absorbing pads due to its high porosity and nanopore size, effectively embedding active substances into nanopores, absorbing the exuded juice during the storage of fresh chicken, and releasing antibacterial substances to achieve the effect of preserving fresh chicken. Essential oil is a volatile plant extract, which is generally considered to be an active substance acceptable to consumers and has excellent antibacterial properties.

[0096] The present invention uses highly absorbent polymer materials loaded with oregano essential oil to prepare two antibacterial aerogel absorbent pads for fresh-keeping of chilled chicken. The microbial indexes and physical and chemical indexes of 0-7 d fresh-keeping chicken were analyzed. Spoilage bacteria colonize on the surface of fresh-keeping meat during slaughter and transportation. The number of spoilage bacteria increases rapidly during storage, resulting in a sharp decline in meat quality. The total colony count is an important indicator for measuring the freshness of fresh-keeping meat. With the extension of storage time, the total number of bacteria in each group shows an upward trend. The C and N groups exceed the national standard of 6 log CFU / g at 3 d, while the S group exceeds the national standard at 7 d. Antibacterial oregano essential oil and chitosan are added to the S group, which effectively inhibits the growth of microorganisms. Among them, chitosan has multiple amino and hydroxyl functional groups, which makes it have a positive charge. It can combine with the cell membrane with negative charge on the surface of bacteria, thereby destroying the integrity of the bacterial cell membrane. This action process may cause the leakage of substances inside the bacterial cells, thereby interfering with the normal function of the cells. As the storage process is prolonged, the water-absorbent aerogel pad absorbs water while releasing active ingredients (oregano essential oil), which migrate from the pad to the surface of the chicken breast and exert its antibacterial and antioxidant effects. Oregano essential oil has a significant inhibitory effect on microorganisms in chilled chicken breast, pork, and ground beef. This is because oregano essential oil contains a large amount of phenols and terpenes. These compounds can increase the permeability of cell membranes by destroying cell membrane structures, and can inhibit cell growth and conidia germination by damaging various enzyme systems, thereby inhibiting the growth of microorganisms in meat, slowing down the spoilage process, and maintaining its quality.

[0097] As the storage time increased, the pH of each group showed a trend of first decreasing and then increasing. The pH of group S exceeded the pH limit of 6.2 for fresh meat at 3 days, and that of groups C and N exceeded the limit at 4 days. The freshness of fresh chicken meat is closely related to its pH value. The pH value of fresh chicken meat should be between 5.9 and 6.2. In the initial stage of storage, the cells of slaughtered chicken meat will undergo the process of oxidative decomposition of organic matter to produce energy (such as glycogen consumption), and a certain amount of organic acids (lactic acid and pyruvic acid, etc.) will accumulate in the cells, resulting in a gradual decrease in the pH value of fresh chicken meat at the initial stage of storage. However, as the storage time goes by, nitrogen-containing substances such as proteins and amino acids in fresh chicken meat are gradually hydrolyzed into weakly alkaline amine metabolites under the action of endogenous proteases. This process can neutralize the organic acids accumulated at the initial stage of storage and continuously increase the pH of fresh chicken meat. At the same time, the microbial colony continues to grow in this process, and some microorganisms will produce alkaline metabolic wastes during their life activities, thereby further increasing the pH value of fresh chicken meat. By using antibacterial aerogel absorbent pads during the storage of chicken breast, the pH change of chicken breast during storage can be effectively reduced. On the one hand, the absorbent aerogel absorbent pads absorb excess water, reduce the medium required for microbial reproduction, and slow down the growth of microorganisms. On the other hand, the antibacterial function of chitosan and oregano essential oil inhibits the growth of microorganisms, reduces the decomposition process of molecules such as proteins, maintains the stability of the chicken breast tissue system, and thus better maintains the pH level of the chicken breast.

[0098] Chroma is an important indicator for measuring the freshness of chilled meat. With the increase of storage time, chilled meat deteriorates, its hemoglobin and myoglobin are oxidized, and the redness value of the surface of chilled meat decreases and the yellowness value increases. In the results of the present invention, as the storage time increases, the L* value of each group shows a decreasing trend, and the glossiness of the surface of chilled chicken decreases. The degree of reduction in group C is more significant than that in group S and group N. At 5 days, the a* value of group C is significantly lower than that of group S and group N, and the b* value of group C and group N is significantly higher than that of group S. This is attributed to the inhibitory effect of chitosan and oregano essential oil on microorganisms in group S, which slows down the microbial reproduction process, reduces the utilization of chilled chicken protein by microorganisms, and reduces protein oxidation. Therefore, the yellowness value at 5 days is lower than that of group C and group N, indicating that the aerogel antibacterial water-absorbing pad prepared in this study has an inhibitory effect on microorganisms and plays a certain protective role on meat color.

[0099] The quality loss of chicken breast during storage may be related to water loss and decomposition of organic matter such as protein. By using antibacterial aerogel absorbent pads to preserve chicken breast, excess water can be effectively absorbed. At the same time, the absorbed water causes the aerogel to swell and release antibacterial substances (oregano essential oil), thereby exerting its antibacterial function, which is more conducive to the preservation of chicken breast.

[0100] The microbial and physicochemical indicators of fresh chicken meat from 0 to 7 days were analyzed. Groups C and N exceeded the national standard of 6 log CFU / g on the 3rd day, while Group S exceeded the national standard on the 7th day. Antibacterial oregano essential oil and chitosan were added to Group S, which effectively inhibited the growth of microorganisms in the early stage of storage. Group S exceeded the pH limit of 6.2 for fresh meat on the 3rd day, while Groups C and N exceeded the limit on the 4th day. On the 5th day, the pH of Group C exceeded the limit of 6.2 for fresh meat. * The values ​​were significantly lower than those of the S and N groups. * Values, b of Group C and Group N * The value was significantly higher than that of group S, which was attributed to the inhibitory effect of chitosan and oregano essential oil on microorganisms in group S, which slowed down the process of microbial reproduction. The aerogel antibacterial water-absorbent pad prepared in this study has an inhibitory effect on bacteria and plays a certain protective role on meat color.

[0101] Example 4

[0102] The present invention also provides a method for preserving fresh chicken using the antibacterial aerogel water-absorbing pad in Example 1, comprising the following steps: Choose fresh and quarantined chilled chicken and cut it into pieces according to product requirements; Placing the cut chilled fresh chicken and the antibacterial aerogel absorbent pad in a packaging material so that the chilled fresh chicken is in contact with the absorbent pad during storage; The sealed packaging material is placed in a refrigerator for refrigerated storage at a temperature of 0-4°C.

[0103] The water-absorbent pad of the present invention can be used in the cold chain transportation process of chilled chicken, as well as for home preparation, and can be used in combination with plastic wrap. The aerogel can be used to refrigerate the chicken, avoiding the use of frozen storage, which causes the chicken to be repeatedly thawed and causes the microorganisms to reproduce rapidly.

[0104] Although the present invention has been described in detail above with general descriptions and specific embodiments, those skilled in the art may make some modifications or improvements based on the present invention. However, these modifications or improvements made on the basis of not departing from the connotation of the present invention all belong to the scope of protection claimed by the present invention.

Claims

1. An antibacterial aerogel absorbent pad, characterized in that: The aerogel water-absorbing pad comprises a matrix material and an antibacterial agent, wherein the matrix material is a mixture of polyvinyl alcohol and hydroxymethyl cellulose or a mixture of polyvinyl alcohol and sodium alginate, wherein the polyvinyl alcohol accounts for 15-25% of the total mass of the matrix material, and the hydroxymethyl cellulose or the sodium alginate accounts for 75-85% of the total mass of the matrix material; the antibacterial agent is selected from one or more of plant essential oils or chitosan, and the added amount of the chitosan is 10-15% of the total mass of the matrix material; the matrix material and the antibacterial agent are blended and then poured into a mold for freeze drying to obtain the aerogel water-absorbing pad.

2. The antibacterial aerogel absorbent pad according to claim 1, characterized in that: The plant essential oil is oregano essential oil, and the mass volume ratio of the matrix material to the emulsion loaded with oregano essential oil is 2-5 g / mL.

3. The method for preparing the antibacterial aerogel water-absorbing pad according to any one of claims 1 to 2, characterized in that: The following steps are involved: The oregano essential oil emulsion is prepared by mixing ovalbumin and inulin, dissolving them in a phosphate solution, stirring and then ultrasonically treating them, adding oregano essential oil and sucrose fatty acid ester, and performing intermittent shearing using a high-speed shear homogenizer to obtain an emulsion loaded with oregano essential oil; Dissolve carboxymethyl cellulose in deionized water to form a clear solution, dissolve polyvinyl alcohol in deionized water, stir at a water bath temperature and then cool, mix the two solutions to obtain a first mixed solution, and stir with an oregano essential oil emulsion to obtain a second mixed solution, or dissolve sodium alginate and polyvinyl alcohol in deionized water to obtain a first mixed solution, dissolve chitosan in deionized water and drip it into the first mixed solution drop by drop, and then add the oregano essential oil emulsion and stir to obtain a second mixed solution; The second mixed solution is injected into a mold and then freeze-dried to obtain the aerogel water-absorbent pad.

4. The method for preparing the antibacterial aerogel water-absorbing pad according to claim 3, characterized in that: In the process of preparing the oregano essential oil emulsion, the stirring speed is 450-600 rpm / min, the stirring time is 2-3 h, the ultrasonic treatment time is 10-15 min, and the ultrasonic frequency is 50-100 Hz.

5. The method for preparing the antibacterial aerogel water-absorbing pad according to claim 3, characterized in that: In the process of preparing the oregano essential oil emulsion, the shear speed of the high-speed shear homogenizer is 8000~10,000rpm / min, and the intermittent shear time is 2~3min.

6. The method for preparing the antibacterial aerogel water-absorbing pad according to claim 3, characterized in that: The amount of ovalbumin used is 0.32 g, the amount of inulin used is 0.30 g, the amount of phosphate solution used is 120 mL, the amount of oregano essential oil used is 24.71 g, and the amount of sucrose fatty acid ester used is 0.60 g.

7. An antibacterial aerogel water-absorbing pad, characterized in that: Prepared by the preparation method according to any one of claims 3 to 6.

8. The method for preserving chilled fresh chicken by using the antibacterial aerogel absorbent pad according to any one of claims 1 to 2 and 7, characterized in that: The following steps are involved: Choose fresh and quarantined chilled chicken and cut it into pieces according to product requirements; Placing the cut chilled fresh chicken and the antibacterial aerogel absorbent pad in a packaging material so that the chilled fresh chicken is in contact with the absorbent pad during storage; The sealed packaging material is placed in a refrigerator for refrigerated storage at a temperature of 0-4°C.

9. Use of the antibacterial aerogel absorbent pad according to any one of claims 1 to 2 and 7 in preserving chilled chicken.

10. The use according to claim 9, characterized in that: The antibacterial aerogel water-absorbing pad has any of the following functions: (1) Absorb the exudate from cold fresh chicken during storage; (3) Reduce the pH change of fresh chicken during storage; (4) Protect the color of fresh chicken during storage; (5) Inhibit the growth and reproduction of microorganisms in fresh chicken; (6) Prolong the shelf life of fresh chicken.

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