Oat glucan-phenolic acid graft copolymer, preparation method thereof and application of oat glucan-phenolic acid graft copolymer as antioxidant antibacterial liquid

Abstract

The invention provides an oat dextran-phenolic acid grafted copolymer, a preparation method thereof and application of the oat dextran-phenolic acid grafted copolymer as an antioxidant antibacterial liquid, and belongs to the technical field of food preservation, phenolic acid and oat dextran are mainly used as reaction substrates, the oat dextran-phenolic acid grafted copolymer is prepared through an N, N '-carbonyldiimidazole method under the assistance of vacuum ultrasound, and the oat dextran-phenolic acid grafted copolymer is used as an antioxidant antibacterial liquid. The synthesis process is simple, the synthesis time can be effectively shortened through vacuum ultrasound, the synthesis efficiency is improved, meanwhile, the oat glucan-phenolic acid grafted copolymer prepared through the N, N '-carbonyldiimidazole method has good antioxidant and antibacterial activity, the shelf life of chilled fresh meat can be effectively prolonged when the oat glucan-phenolic acid grafted copolymer is used for preserving the chilled fresh meat, and the service life of the chilled fresh meat is prolonged. The nutritional ingredients are reserved.

Description

Technical Field

[0001] The invention relates to an oat glucan-phenolic acid graft copolymer for preserving cold fresh meat and a preparation method thereof, and application thereof as an antioxidant and antibacterial liquid, and belongs to the technical field of food preservation. Background Art

[0002] Chilled meat, also known as chilled meat, refers to meat that has its core temperature lowered to (0℃~4℃) in an environment below 0℃ without producing ice crystals. It is popular because of its affordable price and rich nutrition. However, it is easily contaminated by microorganisms during slaughtering, processing, and sales, and its quality such as color and smell are easily changed, resulting in a short shelf life, which restricts the further development of the chilled meat industry. Among them, chilled rabbit meat has a surge in market demand due to its "three highs and three lows" advantages of high protein, high lysine, high digestibility, and low fat, low cholesterol, and low calories. In order to meet consumers' high requirements for freshness, safety, and nutrition, preservation technology has become a key challenge.

[0003] Phenolic acid is a natural antioxidant with abundant sources and is often used to preserve cold fresh meat. However, its application is often limited by its poor water solubility, rapid metabolism, low bioavailability and poor stability. In order to better exert its physiological effects, transport it to the target site, and improve its stability and bioavailability in food processing and storage, phenolic acid can be grafted onto biocompatible and biodegradable carbohydrate molecules through graft copolymerization. For example, CN117567664A discloses a chitosan oligosaccharide phenolic acid derivative and its preparation method and application, wherein phenolic acid and chitosan oligosaccharide are subjected to graft copolymerization reaction, wherein the phenolic acid is gallic acid or p-coumaric acid, the phenolic acid activation time is 12h, chitosan oligosaccharide is added for grafting reaction for 12h, and chitosan oligosaccharide phenolic acid derivatives are obtained after the reaction, and chitosan oligosaccharide phenolic acid derivatives that can inhibit fungi can be obtained, but the grafting reaction time of this technology is long and the production efficiency is low.

[0004] Oat glucan is a compound with excellent properties such as rheological properties and gelling properties, stability, processing properties, safety, and biocompatibility. It has strong biological activity and is also used as an antioxidant component in the preservation of meat products. For example, CN112006085A discloses a composite color-protecting antioxidant coating liquid for meat products, a preparation method, and an application thereof. The raw materials of the coating liquid include gallic acid catechins, gallic acid esters, yeast β-glucan, ascorbic acid, chitosan, and water; the preparation method is as follows: dissolve yeast β-glucan in water, add gallic acid catechins, gallic acid esters, and ascorbic acid to the yeast β-glucan solution, and then add chitosan. Soak the cut meat in the composite color-protecting antioxidant coating liquid or spray the composite color-protecting antioxidant coating liquid on the surface of the meat, then drain, and then package and store in sequence. This technology improves the color-protecting and antioxidant effect of meat products and plays a role in extending the shelf life of the product. Although this composite color-protecting antioxidant coating liquid can play a good role in preserving meat products, it must be compounded with more effective ingredients. It is difficult to achieve a good preservation effect by using yeast β-glucan or gallic acid ester alone, which limits the application of glucan bioactive substances in the preservation of cold fresh meat. At the same time, the commercially available oat glucan also has its inherent high viscosity and poor water solubility, which greatly limits its application in the field of meat product preservation. Summary of the invention

[0005] In view of the shortcomings of the existing chilled meat preservation technology, such as low production efficiency of graft copolymers and poor preservation effect of single ingredients, the present invention provides a preparation method based on oat glucan-phenolic acid graft copolymers and their application as antioxidant and antibacterial liquid, providing a new technical solution for the preservation of chilled meat products.

[0006] A method for preparing an oat glucan-phenolic acid graft copolymer comprises the following steps:

[0007] (1) Under vacuum conditions, phenolic acid and an equal molar amount of N,N'-carbonyldiimidazole (CDI) are dissolved in anhydrous dimethyl sulfoxide (DMSO) at room temperature, and stirred under heating conditions and intermittently ultrasonicated until the phenolic acid and CDI are completely dissolved in DMSO;

[0008] (2) maintaining vacuum conditions, adding oat glucan powder to the solution obtained in step (1), heating and intermittently sonicating to react and synthesize an oat glucan-phenolic acid graft copolymer solution;

[0009] (3) adding at least two volumes of isopropanol to the solution obtained in step (2) to mix the mixture so that the oat glucan-phenolic acid graft copolymer formed by the reaction forms a precipitate, and recovering the precipitate by centrifugation; the precipitate is in the form of particles;

[0010] (4) washing the precipitate obtained in step (3) with isopropanol to remove unreacted phenolic acid and CDI;

[0011] (5) dissolving the precipitate obtained in step (4) in distilled water, adding anhydrous ethanol, centrifuging after alcohol precipitation, and then freeze-drying to obtain the oat glucan-phenolic acid graft copolymer.

[0012] Optionally, in step (1), the heating temperature is 55-65°C, the reaction time is 3.5-4.5h, and intermittent ultrasonic conditions are used, with ultrasound for 1h and intervals for 1h, and the ultrasonic power is 400-500W. Preferably, the heating temperature is 55-65°C, the reaction time is 4h, and intermittent ultrasonic conditions are used, with ultrasound for 1h and intervals for 1h, and the ultrasonic power is 450W. The vacuum conditions in steps (1) and (2) refer to a vacuum degree less than or equal to -0.095MPa. Optionally, the vacuum degree is -0.150MPa to -0.095MPa.

[0013] The present invention has no strict requirements on the amount of DMSO used in step (1). It only requires that phenolic acid and an equimolar amount of N,N'-carbonyldiimidazole (CDI) and the oat glucan powder subsequently added to the reaction liquid can be completely dissolved in DMSO. It is recommended to use 18-22 mL of DMSO for every 1 g of phenolic acid.

[0014] In the present invention, room temperature refers to 20-35°C unless the actual temperature is particularly stated.

[0015] In step (2), the heating temperature is 85-95° C., the reaction time is 3.5-4.5 hours, and intermittent ultrasound is performed during the reaction. Intermittent ultrasound means that ultrasound is stopped for 1 hour after each ultrasound for 1 hour at an ultrasound power of 400-500 W, and this process is repeated multiple times. Preferably, in step (2), the reaction temperature is 90° C., the reaction time is 4 hours, and intermittent ultrasound is performed during the reaction, that is, ultrasound is stopped for 1 hour after each ultrasound for 1 hour at an ultrasound power of 450 W.

[0016] The mass ratio of the phenolic acid used in step (1) to the oat glucan powder added in step (2) is 20:8-12, preferably 20:10.

[0017] Optionally, the centrifugation condition in step (3) is 4500-5500 r / min, and the centrifugation time is 10-20 min. Preferably, the centrifugation condition in step (3) is 5000 r / min, and the centrifugation time is 15 min.

[0018] Preferably, anhydrous ethanol is added in step (5) for alcohol precipitation, and the concentration of ethanol in the solution must be not less than 70% (v / v), and the alcohol precipitation time is 18-22h. Preferably, the concentration of ethanol in the solution is 70% (v / v), and the alcohol precipitation time is 20h. Optionally, the centrifugation conditions in step (5) are 8000-12000r / min, the centrifugation time is 10-20min, and preferably centrifugation at 10000r / min for 15min. The freeze-drying time is at least 24h to remove moisture.

[0019] The antioxidant and antibacterial liquid prepared with the oat glucan-phenolic acid graft copolymer as an effective ingredient can preserve cold fresh meat such as rabbit meat, beef, chicken, mutton, duck meat, pork and the like.

[0020] Preferably, the oat glucan powder is modified oat glucan powder. The modified oat glucan powder is a water-soluble oat glucan powder formed by modifying commercially available oat glucan powder as a raw material, i.e., the modified oat glucan powder. The β-glucan content of the oat glucan powder raw material is 70wt%-80wt%, and it is a white to light yellow odorless powder. More than 90wt% of the powder can pass through an 80-mesh sieve, and the moisture content is less than 5wt%.

[0021] The preparation method of the modified oat glucan powder comprises the following steps:

[0022] A. Add oat glucan to 90℃ deionized water and stir until dissolved;

[0023] B. Add hydrochloric acid to step A, stir and react at 90°C to hydrolyze oat glucan under acidic conditions, and cool to room temperature after the reaction is completed;

[0024] C. adding sodium hydroxide solution to the solution in step B, and adjusting the pH value of the solution to make the pH value of the solution neutral;

[0025] D. adding anhydrous ethanol to the solution in step C to precipitate the modified oat glucan, centrifuging after alcohol precipitation, and then freeze-drying to obtain modified oat glucan powder.

[0026] Preferably, the concentration of hydrochloric acid in step B is 3 mol / L, the concentration of hydrochloric acid in the reaction system obtained after adding hydrochloric acid is 0.5 mol / L, and the reaction time is at least 5 h.

[0027] Preferably, the concentration of the sodium hydroxide solution in step C is 1.0 mol / L, and making the pH of the solution neutral means that the pH value of the solution is 7.0.

[0028] Preferably, in step D, anhydrous ethanol is added to make the concentration of ethanol in the solution not less than 70% (v / v), the alcohol precipitation time is 20 hours, the centrifugal conditions are 10000r / min, the centrifugal time is 15min, and the freeze-drying time is 24 hours.

[0029] Oat glucan has abundant active hydroxyl groups, which make it easy to modify under specific conditions, such as degradation, carboxylmethylation, phosphation, etc., so as to enhance solubility, viscosity, antioxidant and antibacterial ability. The present invention uses oat glucan as raw material, firstly prepares modified oat glucan with higher water solubility by acid degradation method, then grafts phenolic acid onto modified oat glucan by N, N'-carbonyldiimidazole mediation method, synthesizes modified oat glucan-phenolic acid graft copolymer, and the obtained graft copolymer has significantly enhanced antioxidant activity and antibacterial activity. The present invention adopts vacuum ultrasonic assisted technology to greatly shorten the activation time of phenolic acid and the time of chemical reaction. The obtained modified oat glucan-gallic acid graft copolymer is made into rabbit meat antioxidant and antibacterial liquid, which will help to better solve the problem of corruption and deterioration of rabbit meat products during storage and circulation, thereby improving the level of food safety. At the same time, it will also effectively deal with the problem of food waste caused by the short shelf life of rabbit meat products, and promote the rational use and conservation of resources.

[0030] The present invention also provides an application of oat glucan-phenolic acid graft copolymer, which can be used as an effective ingredient or one of the effective ingredients in an antioxidant antibacterial liquid for preserving cold fresh meat, and the antioxidant antibacterial liquid is used for preserving cold fresh meat such as rabbit meat; the oat glucan-phenolic acid graft copolymer is prepared into an antioxidant antibacterial liquid of 1‰ to 5‰, and the solvent is deionized water. Preferably, the antibacterial liquid formula is: calculated by mass, comprising 2 parts of oat glucan-phenolic acid graft copolymer and 998 parts of deionized water, that is, the oat glucan-phenolic acid graft copolymer is prepared into an antioxidant antibacterial liquid of 2‰.

[0031] Preferably, the antioxidant and antibacterial liquid is used for preserving rabbit meat and other meats by dipping, spreading and spraying.

[0032] The immersion method comprises: removing impurities from the surface of the meat product, then immersing the meat in an antioxidant and antibacterial liquid, and taking it out and drying it after 2 minutes;

[0033] The smearing method is: smear the antioxidant and antibacterial liquid evenly on the surface of the fresh meat, so that the fresh meat is covered with a very thin layer of film liquid;

[0034] The spraying method comprises the following steps: loading the antioxidant and antibacterial liquid into a sprayer and spraying the liquid evenly on the surface of the fresh cold meat.

[0035] Compared with the prior art, the present invention has at least the following beneficial effects:

[0036] The present invention uses acid degradation to convert oat glucan raw materials into modified oat glucan with better water solubility. This transformation can significantly improve the solubility and viscosity characteristics of oat glucan molecules, and in the grafting reaction process of oat glucan and phenolic acid, can greatly improve the grafting efficiency between glucan and phenolic acid.

[0037] In order to accelerate and optimize the hydrolysis reaction of oat glucan and the graft copolymerization process of oat glucan and phenolic acid, the present invention adopts vacuum ultrasonic assisted technology, which can significantly shorten the reaction time, reduce the phenolic acid activation reaction time to 4h, and reduce the combination reaction time to 4h.

[0038] The antioxidant and antibacterial liquid prepared by the present invention only uses oat glucan-phenolic acid graft copolymer as an effective ingredient. When the content of the effective ingredient is low, a protective film can be quickly formed on the surface of the cold fresh meat, effectively isolating the external environment, reducing the natural evaporation of water, and at the same time constructing a strong microbial barrier to reduce the invasion of harmful microorganisms such as bacteria and molds, inhibit the growth of microorganisms, and significantly extend the shelf life of the cold fresh meat. The modified oat glucan-gallic acid graft copolymer prepared by the present invention has a high scavenging activity for DPPH free radicals, with a scavenging rate of 65.1%.

[0039] The present invention expands the application of oat glucan and phenolic acid in meat preservation. It can achieve a good preservation effect with only a single effective ingredient and can be produced efficiently. It is expected to provide more options for the subsequent use of compounding technology to improve the quality of meat preservation. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is the H NMR spectrum of oat glucan-phenolic acid.

[0041] Figure 2 The effect of ultrasonic power on grafting rate.

[0042] Figure 3 The sensory index scoring results of rabbit meat.

[0043] Figure 4 The effect of different conditions on the juice loss rate of rabbit meat.

[0044] Figure 5 The effect of TVB-N on rabbit meat under different conditions.

[0045] Figure 6 The effect of pH on rabbit meat under different conditions.

[0046] Figure 7 The effect of different conditions on the total colony count of rabbit meat. DETAILED DESCRIPTION

[0047] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0048] Example 1

[0049] Structure and antioxidant activity of oat glucan-phenolic acid graft copolymers:

[0050] (1)Use 1 The structural properties were analyzed by H NMR. Caffeic acid (CA), gallic acid (GA), oat glucan (OG), modified oat glucan (OGH), oat glucan-caffeic acid graft copolymer (CDI-CAOH), modified oat glucan-caffeic acid graft copolymer (CDI-CAOGH), oat glucan-gallic acid graft copolymer (CDI-GAOH), and modified oat glucan-gallic acid graft copolymer (CDI-GAOGH) were dissolved in 0.5 mL D2O and 0.1 mL DMSO, and their H NMR spectra were measured using a Bruker spectrometer at an operating frequency of 500 MHz. The results are shown in Figure 2. Figure 1 shown.

[0051] from Figure 1 It can be seen that OG and OGH show multiple peaks at δ3.2-3.9ppm, representing hydrogen protons on C-2, C-3 to C-6. Caffeic acid shows proton signals at δ7.38ppm (Hd), δ7.05ppm (Ha), δ6.99ppm (Hb), δ6.80ppm (Hc) and δ6.20ppm (He). A new peak appeared at 6.21-7.32ppm for the caffeic acid graft copolymer, which is the methyl proton of caffeic acid. Compared with the signal peak of the control group, the hydroxyl peak between 3.2-3.9ppm of the caffeic acid graft copolymer was significantly enhanced, indicating that CA may interact with OG / OGH molecules by forming hydrogen bonds, confirming that GA was successfully grafted onto OG / OGH. In addition, the combination of phenol and glucan is formed by the weak CH-π bond between the aromatic residue and the glucan pyran ring. GA has only one peak at 6.99ppm (Ha of the benzene ring). The spectrum of the gallic acid grafted copolymer contains all the peaks of oat glucan, however, a new peak appears at around 7.1 ppm, which is related to the H of the aromatic ring on the glucan chain, again confirming the successful grafting of GA onto OG / OGH.

[0052] (2) The scavenging activity of oat glucan-phenolic acid graft copolymers on DPPH free radicals was determined as follows: CDI-CAOH / CDI-CAOGH / CDI-GAOH / CDI-GAOGH were dissolved in ultrapure water to prepare concentrations of 0.2, 0.4, 0.6, 0.8 and 1.0 mg / ml. CA / GA were dissolved in methanol to prepare the same concentration gradient. Then 100 μL of the test sample was mixed with 100 μL of 0.1 mmol / L DPPH methanol and the solution was placed in a 96-well plate and kept in the dark at room temperature for 30 min. The absorbance of the resulting solution was measured at 517 nm using a Synergy H1 microplate reader. Where A0 is the absorbance value of the blank control (ultrapure water), A1 is the absorbance value of the DPPH solution sample, and A2 is the absorbance value of the ultrapure water sample. Vc was used as a positive antioxidant reference in the DPPH free radical scavenging test.

[0053]

[0054] Results of DPPH free radical scavenging activity of oat glucan-phenolic acid graft copolymers: The DPPH free radical scavenging activities of oat glucan-caffeic acid graft copolymer (CDI-CAOH), modified oat glucan-caffeic acid graft copolymer (CDI-CAOGH), oat glucan-gallic acid graft copolymer (CDI-GAOH), and modified oat glucan-gallic acid graft copolymer (CDI-GAOGH) were 31.09%, 46.38%, 25.75%, and 65.1%, respectively. The results showed that the modified oat glucan-gallic acid graft copolymer synthesized by the reaction had the best antioxidant activity, reaching 65.1%.

[0055] Example 2

[0056] Effect of Vacuum Ultrasonic Assistance on the Synthesis of Oat Glucan-Phenolic Acid Graft Copolymers

[0057] In the process of grafting reaction between oat glucan and phenolic acid, intermittent ultrasound is used to assist the grafting reaction process. Under ultrasound conditions, there is a cavitation effect. Ultrasonic waves produce local negative pressure areas in the liquid, forming tiny bubbles or cavitations. The bubble nuclei vibrate under the action of ultrasound and quickly close to produce strong shock waves and microjets, which increase the movement frequency and speed of liquid molecules, making it easier for phenolic acid molecules to penetrate into the oat glucan and promote the grafting reaction.

[0058] (1) Effect of ultrasonic power on grafting:

[0059] Under vacuum conditions (vacuum degree -0.095MPa), gallic acid and an equimolar amount of CDI were dissolved in DMSO at room temperature and stirred under heating conditions until gallic acid and CDI were completely dissolved in DMSO; the vacuum degree was maintained at -0.095MPa, and modified oat glucan was added to the obtained solution. The effect of different ultrasonic powers on the grafting degree of modified oat glucan-gallic acid graft copolymers was investigated under the conditions of modified oat glucan concentration of 5mg / mL, modified oat glucan and gallic acid mass ratio of 2:1, reaction time of 4h (ultrasound for 1h, intermittent for 1h), and ultrasonic temperature of 90℃. The power used was as follows: Figure 2 shown.

[0060] from Figure 2 It can be seen that the grafting degree increases with the increase of ultrasonic power; when it reaches 450W, the grafting degree is the largest, which is 22.3%; when the power continues to increase, the grafting degree shows a downward trend. This shows that within a certain reaction time, ultrasonic power can accelerate the grafting reaction of oat glucan and phenolic acid.

[0061] (2) Effects of intermittent ultrasound and continuous ultrasound on grafting

[0062] The present invention adopts intermittent ultrasound to assist the grafting reaction, with ultrasound for 1 hour and interval for 1 hour, alternating the ultrasonic working time and the interval time. Compared with continuous ultrasound, this method reduces the temperature rise of the reaction system. This method saves energy, and the ultrasonic interval time can promote the homogenization between material molecules, strengthen the reaction between media, and improve the reaction efficiency.

[0063] Under vacuum conditions (vacuum degree -0.095MPa), gallic acid and equimolar CDI were dissolved in DMSO at room temperature, and stirred under heating conditions until gallic acid and CDI were completely dissolved in DMSO; the vacuum degree was maintained at -0.095MPa, and modified oat glucan was added to the obtained solution. Under the conditions of modified oat glucan concentration of 5mg / mL, modified oat glucan and gallic acid mass ratio of 2:1, reaction time of 4h, ultrasonic temperature of 90℃, and ultrasonic power of 450W, the solution was divided into two groups, one of which was intermittently ultrasonic-assisted, ultrasonic for 1h, intermittent for 1h, and ended after 4 hours, and the other group was continuously ultrasonic for 4h to investigate the effect of different ultrasonic methods on the grafting degree of modified oat glucan-gallic acid graft copolymer. After the reaction was completed for 4h, the grafting rate of the intermittent ultrasonic group was 23.75%, and the grafting rate of the continuous ultrasonic group was 14.7%, and the grafting rate of the intermittent ultrasonic group was significantly better than that of the continuous ultrasonic group.

[0064] From the verification test of the effect of ultrasonic power on grafting and the verification test of the effect of intermittent ultrasound and continuous ultrasound on grafting, it can be seen from the comparison of the grafting rate of the intermittent ultrasound group that the grafting rate reached more than 23%, obtaining a relatively high grafting rate.

[0065] The "oat glucan" described in the following examples refers to commercially available oat glucan, which has a β-glucan content of 70wt%-80wt%, a white to light yellow odorless powder, more than 90wt% of the powder can pass through an 80-mesh sieve, and a moisture content of less than 5wt%; the "modified oat glucan" described in the following examples refers to an oat glucan with better water solubility obtained by modifying "oat glucan" as a raw material.

[0066] Example 3 Antioxidant and antibacterial liquid of modified oat glucan-gallic acid graft copolymer

[0067] This embodiment provides a modified oat glucan-gallic acid graft copolymer antioxidant and antibacterial liquid, which is composed of the following raw materials: 2 parts of modified oat glucan-gallic acid graft copolymer and 998 parts of deionized water.

[0068] In this embodiment, impurities on the surface of the rabbit meat sample were removed, and then the rabbit meat was immersed in an antioxidant and antibacterial liquid, and then taken out and dried after 2 minutes.

[0069] The preparation method of the modified oat glucan-gallic acid antioxidant and antibacterial liquid in this embodiment is as follows: dissolving the modified oat glucan-gallic acid graft copolymer in deionized water.

[0070] The preparation method of the modified oat glucan-gallic acid graft copolymer is as follows:

[0071] (1) 25 g of oat glucan was added to 500 mL of deionized water at 90°C and stirred for 2 h, then 100 mL of 3 mol / L HCl was added to make the concentration of the reaction system 0.5 mol / L, the reaction was continued to be stirred at 90°C for 5 h, then cooled to room temperature, the pH value of the solution was adjusted to 7.0 with 1.0 mol / L NaOH, anhydrous ethanol was added to make the final concentration 70% (v / v), after alcohol precipitation for 20 h, centrifuged at 10000 r / min for 15 min, and finally the precipitate was freeze-dried for 24 h to obtain modified oat glucan. The modified oat glucan has better water solubility than the raw oat glucan.

[0072] (2) Under vacuum conditions (vacuum degree -0.095MPa), 6g of gallic acid and an equal molar amount of CDI were dissolved in anhydrous DMSO (120mL) at room temperature, placed in a reactor, and the mixture was maintained at 60°C, assisted by intermittent ultrasound (ultrasound 1h, intermittent 1h, power 450W), and continuously stirred (300r / min) for 4h to complete the activation of gallic acid. Secondly, 3g of modified oat glucan powder was added to the activated gallic acid solution, and treated at 90°C, vacuum degree -0.095MPa, assisted by intermittent ultrasound (ultrasound 1h, intermittent 1h, power 450W) for 4h to synthesize copolymers. After the reaction was completed, the reaction solution was mixed with twice the volume of isopropanol, and the precipitate was recovered by centrifugation at 5000r / min for 15min. The resulting precipitate was washed twice with isopropanol to remove unreacted gallic acid and CDI. The precipitate was dissolved in 50 mL of distilled water, and anhydrous ethanol was added to make the final ethanol concentration 70% (v / v). After 20 hours of alcohol precipitation, the mixture was centrifuged at 10,000 r / min for 15 minutes. Finally, the precipitate was freeze-dried for 24 hours to obtain the final modified product - modified oat glucan-gallic acid graft copolymer.

[0073] Example 4 Oat glucan-gallic acid graft copolymer antioxidant and antibacterial liquid

[0074] This embodiment provides an oat glucan-gallic acid graft copolymer antioxidant and antibacterial liquid. The oat glucan is commercially available and has not been modified. The oat glucan-gallic acid antioxidant and antibacterial liquid is composed of the following raw materials: 2 parts of oat glucan-gallic acid graft copolymer and 998 parts of deionized water.

[0075] In this embodiment, impurities on the surface of the rabbit meat sample were removed, and then the rabbit meat was immersed in an antioxidant and antibacterial liquid, and then taken out and dried after 2 minutes.

[0076] The preparation method of the oat glucan-gallic acid antioxidant and antibacterial liquid in this embodiment is as follows: dissolving the oat glucan-gallic acid graft copolymer in deionized water.

[0077] The preparation method of oat glucan-gallic acid is:

[0078] Under vacuum conditions (vacuum degree -0.095MPa), 6g of gallic acid and an equal molar amount of CDI were dissolved in anhydrous DMSO (120mL) at room temperature, placed in a reactor, and the mixture was maintained at 60°C, assisted by intermittent ultrasound (ultrasound 1h, intermittent 1h, power 450W), and continuously stirred (300r / min) for 4h to complete the activation of gallic acid. Secondly, 3g of oat glucan powder was added to the activated gallic acid solution, and treated at 90°C, vacuum degree -0.095Mpa, assisted by intermittent ultrasound (ultrasound 1h, intermittent 1h, power 450W) for 4h to synthesize copolymers. After the reaction, the reaction solution was mixed with twice the volume of isopropanol, and the precipitate was recovered by centrifugation at 5000r / min for 15min. The resulting precipitate was washed twice with isopropanol to remove unreacted gallic acid and CDI. The precipitate was dissolved in 50 mL of distilled water, and anhydrous ethanol was added to make the final ethanol concentration 70% (v / v). After 20 hours of alcohol precipitation, the mixture was centrifuged at 10,000 r / min for 15 minutes. Finally, the precipitate was freeze-dried for 24 hours to obtain the final modified product - oat glucan-gallic acid graft copolymer.

[0079] Example 5: Antioxidant and antibacterial liquid of modified oat glucan-caffeic acid graft copolymer

[0080] This embodiment provides a modified oat glucan-caffeic acid graft copolymer antioxidant and antibacterial liquid, which is composed of the following raw materials: 2 parts of modified oat glucan-caffeic acid graft copolymer and 998 parts of deionized water.

[0081] The preparation method of the modified oat glucan-caffeic acid antioxidant and antibacterial liquid in this embodiment is as follows: dissolving the modified oat glucan-caffeic acid graft copolymer in deionized water.

[0082] In this embodiment, impurities on the surface of the rabbit meat sample were removed, and then the rabbit meat was immersed in an antioxidant and antibacterial liquid, and then taken out and dried after 2 minutes.

[0083] The preparation method of the modified oat glucan-caffeic acid is:

[0084] (1) 25 g of oat glucan was added to 500 mL of deionized water at 90° C. and stirred for 2 h. Then, 100 mL of 3 mol / L HCl was added to make the concentration of the reaction system 0.5 mol / L. The reaction was continued to be stirred at 90° C. for 5 h. Then, the solution was cooled to room temperature. The pH value of the solution was adjusted to 7.0 with 1.0 mol / L NaOH. Anhydrous ethanol was added to make the final concentration 70% (v / v). After alcohol precipitation for 20 h, the solution was centrifuged at 10,000 r / min for 15 min. Finally, the precipitate was freeze-dried for 24 h to obtain modified oat glucan.

[0085] (2) Under vacuum conditions (vacuum degree -0.095MPa), 6g of caffeic acid and an equal molar amount of CDI were dissolved in anhydrous DMSO (120mL) at room temperature, placed in a reactor, and the mixture was maintained at 60°C, assisted by intermittent ultrasound (ultrasound 1h, intermittent 1h, power 450W), and continuously stirred (300r / min) for 4h to complete the activation of caffeic acid. Secondly, 3g of modified oat glucan powder was added to the activated caffeic acid solution, and treated at 90°C, vacuum degree -0.095MPa, assisted by intermittent ultrasound (ultrasound 1h, intermittent 1h, power 450W) for 4h to synthesize copolymers. After the reaction was completed, the reaction solution was mixed with twice the volume of isopropanol, and the precipitate was recovered by centrifugation at 5000r / min for 15min. The obtained precipitate was washed twice with isopropanol to remove unreacted caffeic acid and CDI. The precipitate was dissolved in 50 mL of distilled water, and anhydrous ethanol was added to make the final ethanol concentration 70% (v / v). After 20 hours of alcohol precipitation, the mixture was centrifuged at 10,000 r / min for 15 minutes. Finally, the precipitate was freeze-dried for 24 hours to obtain the final modified product - modified oat glucan-caffeic acid grafted copolymer.

[0086] Example 6 Oat glucan-caffeic acid graft copolymer antioxidant and antibacterial liquid

[0087] This embodiment provides an oat glucan-caffeic acid graft copolymer antioxidant and antibacterial liquid, which is composed of the following raw materials: 2 parts of oat glucan-caffeic acid graft copolymer and 998 parts of deionized water.

[0088] The preparation method of the oat glucan-caffeic acid antioxidant and antibacterial liquid in this embodiment is as follows: dissolving the oat glucan-caffeic acid graft copolymer in deionized water.

[0089] In this embodiment, impurities on the surface of the rabbit meat sample were removed, and then the rabbit meat was immersed in an antioxidant and antibacterial liquid, and then taken out and dried after 2 minutes.

[0090] The preparation method of the oat glucan-caffeic acid is as follows:

[0091] Under vacuum conditions (vacuum degree -0.095MPa), 6g of caffeic acid was dissolved and an equal mole of CDI was dissolved in anhydrous DMSO (120mL) at room temperature, placed in a reactor, and the mixture was maintained at 60°C, assisted by intermittent ultrasound (ultrasound 1h, intermittent 1h, power 450W), and continuously stirred (300r / min) for 4h to complete the activation of caffeic acid. Secondly, 3g of oat glucan powder was added to the activated caffeic acid solution, and treated for 4h at 90°C, vacuum degree -0.095Mpa, assisted by intermittent ultrasound (ultrasound 1h, intermittent 1h, power 450W) to synthesize copolymers. After the reaction, the reaction solution was mixed with twice the volume of isopropanol, and the precipitate was recovered by centrifugation at 5000r / min for 15min. The resulting precipitate was washed twice with isopropanol to remove unreacted caffeic acid and CDI. The precipitate was dissolved in 50 mL of distilled water, and anhydrous ethanol was added to make the final ethanol concentration 70% (v / v). After 20 hours of alcohol precipitation, the mixture was centrifuged at 10,000 r / min for 15 minutes. Finally, the precipitate was freeze-dried for 24 hours to obtain the final modified product - oat glucan-caffeic acid grafted copolymer.

[0092] Comparative Example 1

[0093] The difference between Comparative Example 1 and Example 3 is that Example 3 uses a vacuum, ultrasound-assisted method to carry out the grafting reaction, while Comparative Example 1 uses a non-vacuum, ultrasound-assisted method to carry out the grafting reaction, and the other conditions are the same.

[0094] Comparative Example 2

[0095] The difference between Comparative Example 2 and Example 3 is that Example 3 uses a vacuum and ultrasound-assisted method to carry out the grafting reaction, while Comparative Example 2 uses a vacuum and non-ultrasound-assisted method to carry out the grafting reaction, and the other conditions are the same.

[0096] Comparative Example 3

[0097] The difference between Comparative Example 3 and Example 3 is that Example 3 uses a vacuum, ultrasound-assisted method to carry out the grafting reaction, while Comparative Example 3 uses a non-vacuum, non-ultrasound-assisted method to carry out the grafting reaction, and the rest are the same.

[0098] The grafting rates of the products obtained in Comparative Examples 1 to 3 and Example 3 were experimentally determined. The results showed that Example 3 had the highest grafting rate, reaching 23.52%. The grafting rates of Comparative Examples 1 to 3 were 19.23%, 15.36%, and 13.75%, respectively. It can be seen that the reaction grafting rate can be effectively improved under vacuum ultrasonic assisted conditions.

[0099] In addition, from the comparison of grafting rates in Example 3, the verification test of the effect of ultrasonic power on grafting, and the verification test of the effect of intermittent ultrasound and continuous ultrasound on grafting, it can be seen that the grafting rate reached more than 23%. It can be seen that the preparation method of the present invention has good repeatability and the grafting rates obtained in multiple tests are not much different.

[0100] Study on the performance of oat glucan-phenolic acid graft copolymer antioxidant and antibacterial liquid for rabbit meat preservation:

[0101] The oat glucan-phenolic acid graft copolymer antioxidant and antibacterial liquid prepared in Examples 3 to 6 was applied to the preservation of rabbit meat. The test steps were as follows:

[0102] Select fresh rabbit meat and place it in a 4℃ refrigerator to keep the core temperature below 10℃; sterilize the knives and cutting boards in a high-pressure steam sterilizer and irradiate them with ultraviolet light for 15 minutes in advance, and cut the rabbit meat into 200g portions on a sterile operating table for later use. Randomly divide the processed rabbit meat into 4 portions, for a total of two groups:

[0103] Blank group: rabbit meat without any treatment;

[0104] Coating group: The treated rabbit meat samples were immersed in the antioxidant and antibacterial solution, taken out after 2 minutes, and dried naturally at room temperature;

[0105] The rabbit meat of the blank group and the coated group was then wrapped with PE plastic wrap and stored in a 4°C refrigerator for 6 days. The sensory scores, juice loss rate, pH value, volatile basic nitrogen index, and total colony count of the samples were measured on the 0th, 1st, 2nd, 3rd, 4th, 5th, and 6th days.

[0106] Sensory evaluation

[0107] Sensory evaluation is the most intuitive way to evaluate meat. 20 food professionals from the laboratory were selected to score the fresh rabbit meat using a 100-point system, and the meat samples were sensory evaluated in terms of color, smell, and tissue state, with color, tissue state, smell, and viscosity each accounting for 25 points. The evaluation criteria are based on GB / T17239-2022 "Fresh and Frozen Rabbit Meat and By-products", as shown in Table 1, and the scoring criteria are shown in Table 2.

[0108] Table 1 Sensory evaluation standards for fresh rabbit meat

[0109]

[0110] Table 2 Sensory scoring table for fresh rabbit meat

[0111]

[0112]

[0113] Figure 3 The results show that under laboratory conditions, at the end of the experiment, the blank group had reddish brown samples, a strong pungent smell, and no elasticity, indicating spoiled meat; while the samples treated by the coating group were dark red in color and had a slight ammonia smell. The sensory index scoring results of rabbit meat showed that the sensory evaluation index of Example 3 group was significantly better.

[0114] Determination of juice loss rate

[0115] The amount of juice loss is calculated by measuring the difference between the mass of the meat blocks sampled each time and the mass of the meat blocks before storage, and is expressed as a mass fraction.

[0116] Figure 4 It was shown that under laboratory conditions, the juice loss rates of the samples in the coating group and the blank group showed a gradually increasing trend with the extension of time, but the juice loss rate of the blank group was significantly higher than that of the coating group, and the juice loss rate of Example 3 in the coating group was the lowest, indicating that the modified oat glucan-gallic acid graft copolymer in Example 3 had a good effect on the juice loss rate of rabbit meat.

[0117] Determination of Volatile Basic Nitrogen (TVB-N)

[0118] The volatile basic nitrogen value is determined by the automatic Kjeldahl nitrogen analyzer method in accordance with GB 5009.228-2016 "Determination of volatile basic nitrogen in foods".

[0119] Add 10mL of boric acid solution and 5 drops of mixed indicator liquid to the receiving bottle, and insert the lower end of the condenser tube below the liquid surface, accurately draw 10.0mL of filtrate, inject it into the reaction chamber from the small glass cup, wash the small glass cup with 10mL of water and let it flow into the reaction chamber, and then plug the rod-shaped glass stopper. Then inject 5mL of magnesium oxide suspension into the reaction chamber, immediately cover the glass stopper, and add water to the small glass cup to prevent air leakage. Tighten the spiral clamp and start distillation. After distillation for 5 minutes, move the distillate receiving bottle, the liquid surface leaves the lower end of the condenser, and distill for another 1 minute. Then rinse the outside of the lower end of the condenser tube with a small amount of water and remove the distillate receiving bottle. Titrate to the endpoint with hydrochloric acid or sulfuric acid standard titration solution (0.0100mol / L). Use 1 part of methyl red ethanol solution and 5 parts of bromocresol green ethanol solution to mix the indicator solution, and the endpoint color is purple-red. Use 2 parts of methyl red ethanol solution and 1 part of methylene blue ethanol solution to mix the indicator solution, and the endpoint color is blue-purple. At the same time, make a reagent blank.

[0120] According to GB / T5009.44-2003 "Analytical Methods for Hygienic Standards of Meat and Meat Products", meat and meat products are considered to be of primary freshness when the TVB-N value is less than or equal to 15 mg / 100g, of secondary freshness when it is greater than 15 mg / 100g but not exceeding 25 mg / 100g, and are considered to be spoiled meat when the TVB-N value is greater than 25 mg / 100g.

[0121] Figure 5 The results show that under laboratory conditions, the initial content of TVB-N in the sample was 10.15 mg / 100 g. During the refrigeration period, the TVB-N in each group gradually increased, and the final content of TVB-N in the blank group reached 27.50 mg / 100 g, indicating spoiled meat; the final content of TVB-N in the coating group was 19.3-23.4 mg / 100 g, both of which were secondary freshness. Among them, the TVB-N content in the coating group containing the modified oat glucan-gallic acid graft copolymer (Example 3) was the lowest, indicating that the modified oat glucan-gallic acid graft copolymer had the best effect in inhibiting the spoilage of rabbit meat.

[0122] Determination of pH

[0123] After homogenizing the rabbit meat, take 10 g into a beaker, add 90 mL of neutral distilled water, shake for 30 minutes, centrifuge at 4000 r / min for 20 minutes, take the supernatant and measure it with a pH meter. After each measurement, the pH meter measuring head must be rinsed before the next measurement, and the average is taken and recorded.

[0124] According to the provisions of GB / T9695.5-2008 "Determination of pH Value of Meat and Meat Products", meat with a pH between 5.8-6.2 is fresh meat; meat with a pH between 6.3-6.6 is sub-fresh meat; and meat with a pH above 6.7 is spoiled meat.

[0125] Figure 6 The results show that under laboratory conditions, during the experiment, the pH value of each group of fresh rabbit meat increased from 5.91 to between 6.55-7.02. The pH value of the blank group was as high as 7.02, which was spoiled meat; the pH value of the experimental group was between 6.55-6.68, which was sub-fresh meat; it can be seen that the pH of the treated fresh rabbit meat increased more slowly and more stably than that of the untreated one.

[0126] Determination of total colony count

[0127] Take about 25g of sample from different meat samples, cut into pieces, and place in different small beakers. After adding 225mL of sterile water to each beaker, use a homogenizer to homogenize the sample solution. Then, according to the "GB 4789.2-2022 National Food Safety Standard Food Microbiology Examination Colony Count Determination", count the homogenized sample solution according to the conventional method and record the data.

[0128] Figure 7 It shows that under laboratory conditions, the total number of colonies in the blank group exceeded the standard on the 6th day, reaching 6.56log (CFU*g -1 ), the rest of the groups did not exceed 6log(CFU*g -1), the total number of colonies in the blank group was higher than that in other coating groups at the same time, indicating that oat glucan-phenolic acid graft copolymer has a good inhibitory effect on microorganisms on the surface of meat products. At the same time, the total number of colonies in the coating group using modified oat glucan-gallic acid graft copolymer was the smallest on the 6th day, indicating that its antioxidant and antibacterial liquid has the best effect.

[0129] In conclusion, the antioxidant and antibacterial solution containing oat glucan-phenolic acid graft copolymer has a positive effect in extending the shelf life of rabbit meat.

Claims

1. A method for preparing an oat glucan-phenolic acid graft copolymer, characterized in that: The following steps are involved: (1) Under vacuum conditions, phenolic acid and an equal molar amount of CDI are dissolved in DMSO at room temperature, and stirred under heating conditions and sonicated intermittently until the phenolic acid and CDI are completely dissolved in DMSO; (2) maintaining vacuum conditions, adding oat glucan powder to the solution obtained in step (1), heating and intermittently sonicating to react and synthesize an oat glucan-phenolic acid graft copolymer solution; (3) adding isopropanol to the solution obtained in step (2) and mixing to form a precipitate of the oat glucan-phenolic acid graft copolymer formed by the reaction, and recovering the precipitate by centrifugation; (4) washing the precipitate obtained in step (3) with isopropanol; (5) dissolving the precipitate obtained in step (4) in distilled water, adding anhydrous ethanol, centrifuging after alcohol precipitation, and then freeze-drying to obtain the oat glucan-phenolic acid graft copolymer.

2. The method for preparing the oat glucan-phenolic acid graft copolymer according to claim 1, characterized in that: In step (1), the heating temperature is 55-65° C., the reaction time is 3.5-4.5 h, intermittent ultrasound means that the ultrasound is interrupted for 1 h after every 1 h, the ultrasound power is 400-500 W, and the vacuum degree is -0.150 MPa to -0.095 MPa; in step (2), the reaction temperature is 85-95° C., the reaction time is 3.5-4.5 h, intermittent ultrasound means that the ultrasound is interrupted for 1 h after every 1 h, the ultrasound power is 400-500 W, and the vacuum degree is -0.150 MPa to -0.095 MPa.

3. The method for preparing the oat glucan-phenolic acid graft copolymer according to claim 1, characterized in that: The mass ratio of the phenolic acid used in step (1) to the oat glucan powder added in step (2) is 20:8-12.

4. The method for preparing the oat glucan-phenolic acid graft copolymer according to claim 1, characterized in that: The centrifugation conditions of step (3) are 4500-5500 r / min, the centrifugation time is 10-20 min, and the amount of isopropanol used is at least twice the volume of the solution obtained in step (2).

5. The method for preparing the oat glucan-phenolic acid graft copolymer according to claim 1, characterized in that: In step (5), anhydrous ethanol is added for alcohol precipitation so that the concentration of ethanol in the solution is not less than 70% (v / v), and the alcohol precipitation time is 18-22 hours; in step (5), the centrifugal condition is 8000-12000r / min, and the centrifugal time is 10-20min.

6. The method for preparing the oat glucan-phenolic acid graft copolymer according to claim 1, characterized in that: The oat glucan powder is a modified oat glucan powder, and the preparation method of the modified oat glucan powder comprises the following steps: A. Add oat glucan to 90℃ deionized water and stir until dissolved; B. Add hydrochloric acid to step A, stir and react at 90°C to hydrolyze oat glucan under acidic conditions, and cool to room temperature after the reaction is completed; C. adding sodium hydroxide solution to the solution in step B, and adjusting the pH value of the solution to make the pH value of the solution neutral; D. adding anhydrous ethanol to the solution in step C to precipitate the modified oat glucan, centrifuging after alcohol precipitation, and then freeze-drying to obtain the modified oat glucan powder.

7. The method for preparing the oat glucan-phenolic acid graft copolymer according to claim 6, characterized in that: In step B, the concentration of hydrochloric acid is 3 mol / L, the concentration of hydrochloric acid in the reaction system obtained after adding hydrochloric acid is 0.5 mol / L, and the reaction time is at least 5 hours; in step C, the concentration of sodium hydroxide solution is 1.0 mol / L; in step D, anhydrous ethanol is added so that the concentration of ethanol in the solution is not less than 70% (v / v), and the alcohol precipitation time is 20 hours.

8. Oat glucan-phenolic acid graft copolymer obtained by the preparation method according to any one of claims 1 to 7.

9. The use of the oat glucan-phenolic acid graft copolymer according to claim 8, characterized in that: The oat glucan-phenolic acid graft copolymer is prepared into a 1‰ to 5‰ antioxidant and antibacterial liquid, and the solvent is deionized water.

10. The use of the oat glucan-phenolic acid graft copolymer according to claim 9, characterized in that: The oat glucan-phenolic acid graft copolymer was prepared into a 2‰ antioxidant and antibacterial liquid, and the solvent was deionized water.

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