CN114847333A - A kind of electrostatic spray coating method for meat preservation - Google Patents

Abstract

The invention belongs to the technical field of meat product preservation and antibacterial packaging, in particular to an electrostatic spray coating method for meat preservation. First, a coating liquid is prepared, and chitosan is dissolved in an aqueous glacial acetic acid solution to obtain a chitosan solution, which is mixed with a gelatin solution to obtain a chitosan-gelatin blend solution, and then glycerol is added and filtered to obtain a coating liquid. Then select meat products, wash them with sodium hypochlorite solution and distilled water in turn, and cut them according to the needs after washing to obtain meat samples; arrange them on a metal rack, and use an electrostatic spraying system to spray the coating liquid onto the meat samples. Surface; after coating, drain the excess film liquid, and use the automatic air drying system to air dry the film to complete the film. The invention has the advantages of improving the appearance quality of the coating film, improving the operating environment of the coating film, reducing the working intensity and improving the working efficiency of the coating film, etc. When applied to the preservation of meat, the loss of film materials can be reduced, the performance of the coating film can be improved, the fresh-keeping ability can be enhanced, and the meat preservation can be prolonged. Class preservation time.

Description

A kind of electrostatic spray coating method for meat preservation

technical field

The invention belongs to the technical field of meat product preservation and antibacterial packaging, in particular to an electrostatic spray coating method for meat preservation.

Background technique

At present, the existing coating film preservation technology realizes the high-quality preservation of meat by forming a film layer with physical barrier and physiological inhibition functions on the surface of the meat. The quality of the film layer determines the preservation effect of the meat, and the whole coating film In the process, the coating method is a direct factor affecting the quality of the film. At present, although the common film coating method is simple to operate and does not require additional expensive equipment, it has problems such as poor film coating and waste of film liquid. Therefore, developing a suitable coating method has practical significance for improving the quality of film formation and reducing the production cost.

Electrostatic spraying (ES) is a highly potential spraying technology. This method uses the action of high-voltage electrostatic field to move material particles to the surface of the target along the electric field lines, and then deposit a new technology into a uniform film. ES technology can improve the transfer efficiency of traditional spraying methods. Compared with traditional spraying, it can save raw materials (10-45%), reduce pollution (15-20%), and have better coating performance. When the spray material is ejected from the ES nozzle, it is fully charged and decomposed into smaller and relatively dispersed particles or droplets, which are deposited on the track due to electrostatic attraction. During the ES process, the target to be coated acts as an electrostatic system The anode and material. ES has attracted a lot of attention in the food industry due to its advantages of material saving, high efficiency and continuous industrial operation.

SUMMARY OF THE INVENTION

The invention aims to solve the problems of poor film coating and waste of film liquid in the existing fresh-keeping coating methods. The invention provides an electrostatic spray coating method for meat fresh-keeping. Compared with the traditional spray method, The use of electrostatic spraying has a series of advantages such as improving the appearance quality of the coating film, improving the operating environment of the coating film, reducing the working intensity and improving the working efficiency of the coating film. Applied in the field of meat preservation, it can reduce the loss of film material, improve the performance of the coating film, enhance the preservation ability of the coating film, and prolong the preservation time of meat.

The present invention realizes the above-mentioned technical purpose through the following technical means, and specifically comprises the following steps:

(1) Preparation of coating liquid;

S1. Weigh chitosan (CS) and dissolve it in an aqueous glacial acetic acid solution, and react under certain temperature conditions to obtain a chitosan solution;

S2. take a certain amount of gelatin and dissolve it in water, and obtain a gelatin solution after reacting under a certain temperature condition;

S3. Mix the chitosan solution and the gelatin solution by volume, stir and react at a certain temperature to obtain a chitosan-gelatin blend solution, add glycerol as a plasticizer, and then filter to remove impurities to obtain a coating liquid .

(2) Pretreatment of meat products;

Select meat products, and sequentially wash them with sodium hypochlorite solution and distilled water, which is conducive to the adhesion of the electrostatic spray coating film; after cleaning, cut into pieces according to requirements to obtain meat samples;

(3) Coating the meat;

Arrange the meat samples on a metal rack, and use an electrostatic spraying system to spray the coating liquid prepared in step (1) on the surface of the meat samples; the coated meat is placed on a stainless steel screen to drain excess film. liquid, and then use the automatic air-drying system to air-dry the film at a certain temperature to complete the coating film.

Further, in S1 of step (1), the volume concentration of the glacial acetic acid aqueous solution is 2% to 5%; the mass concentration of the chitosan solution is 1% to 3%; the adjustment to a certain temperature is 40 to 5%. 65°C; the reaction time is 2-5h.

Further, the mass concentration of the gelatin solution in S2 of step (1) is 1%-3%; the certain temperature condition is 30-80°C, and the reaction time is 1-5h.

Further, in S3 of step (1), the volume ratio of the chitosan solution and the gelatin solution when mixed is 1:1; the volume concentration of the glycerol is 3% to 5%; the certain temperature condition is 50 to 80 ℃, the stirring reaction time is 2-5h; the volume ratio of the glycerol and the chitosan-gelatin blend solution is 0.5-0.8:1.

Further, the residual chlorine value of the sodium hypochlorite solution in step (2) is 500-1000ppm.

Further, during the spraying described in step (3), the distance between the surface of the meat sample and the nozzle is 250-350mm, the applied voltage is 15kV-40kV, and the spraying pressure is ≥ 0.2MPa and the material of 50μL/min～200μL/min is used. spray at the flow rate.

Further, the certain temperature condition in step (3) is 30-80°C.

Beneficial effects of the present invention:

(1) The present invention can charge the meat with electrostatic attraction to the target, thereby reducing material loss and improving efficiency.

(2) The present invention can also make the material more fine and uniform, improve the coating performance, enhance the fresh-keeping ability of the coating film, and prolong the fresh-keeping time of meat.

(3) The present invention has simple process, high production efficiency, complete and smooth appearance of the coating film, consistent thickness and stable performance.

Description of drawings

Figure 1 is a schematic diagram of the principle of electrostatic spraying.

FIG. 2 is the SEM images of the film layers formed by the dip coating method (A), the brush coating method (B), the spraying method (C) and the electrostatic spraying method (D).

Figure 3 is an AFM image of the film layers formed by dip coating (A), brush coating (B), spray coating (C) and electrostatic spray coating (D).

Figure 4 is a graph of the film liquid transfer efficiency of dip coating method (A), brush coating method (B), spray method (C) and electrostatic spray method (D); different lowercase letters in the figure indicate significant differences (P<0.05 ).

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the specific embodiments and the accompanying drawings.

Example 1:

(1) Weigh chitosan and dissolve it in an aqueous acetic acid solution with a mass concentration of 2%, and react at 60° C. for 2 hours to obtain a chitosan solution; wherein the mass concentration of the chitosan solution is 2%;

Weigh the gelatin and dissolve it in water, react at 60°C for 2 hours, and obtain a gelatin solution after the reaction; the mass concentration of the gelatin solution is 2%;

Mix the chitosan solution and the gelatin solution in a ratio of 1:1, react at 60 °C for 2 hours, and continuously stir during the period to fully mix the two to obtain a chitosan-gelatin blend solution, which is added with a volume concentration of 5%. The volume ratio of glycerol and chitosan-gelatin blend solution is 0.5:1 as plasticizer; then filter to remove impurities to obtain coating liquid.

(2) pretreating the meat product, wash it successively with 800ppm sodium hypochlorite solution and distilled water for 3min, remove the impurities and microorganisms on the meat surface; then cut into five groups of 2cm square pieces as meat samples;

(3) Coating the meat samples by dip coating method. Immerse the meat sample in the film coating solution obtained in step (1) for 3 minutes; place the coated meat sample on a stainless steel mesh to drain excess film liquid, and then use an automatic air-drying system to air-dry at 60° C. to form a film. After coating, put the meat in the refrigerator at 4°C for future use.

Example 2:

(1) Weigh chitosan and dissolve it in an aqueous acetic acid solution with a mass concentration of 2%, and react at 60° C. for 2 hours to obtain a chitosan solution; wherein the mass concentration of the chitosan solution is 2%;

Weigh the gelatin and dissolve it in water, react at 60°C for 2 hours, and obtain a gelatin solution after the reaction; the mass concentration of the gelatin solution is 2%;

Mix the chitosan solution and the gelatin solution in a ratio of 1:1, react at 60 °C for 2 hours, and continuously stir during the period to fully mix the two to obtain a chitosan-gelatin blend solution, which is added with a volume concentration of 5%. The volume ratio of glycerol and chitosan-gelatin blend solution is 0.5:1 as plasticizer; then filter to remove impurities to obtain coating liquid.

(2) Pretreating the meat product, washing it with 800ppm sodium hypochlorite solution and distilled water for 3 minutes to remove impurities and microorganisms on the meat surface. Cut into five groups of 2cm square pieces to obtain meat samples.

(3) Use the brush coating method to coat the meat pieces. Soak the paint with 1/2 of the soft bristles, and brush it on the surface of the meat block in a certain direction to ensure that the surface of the meat block is completely covered by the paint; the coated meat block is placed on a stainless steel screen to drain the excess film liquid, and then Use an automatic air-drying system to air-dry at 60°C to form a film. After coating, the meat pieces are stored in a refrigerator at 4°C for later use.

Example 3:

(1) Weigh chitosan and dissolve it in an aqueous acetic acid solution with a mass concentration of 2%, and react at 60°C for 2 hours to obtain a chitosan solution; wherein the mass concentration of chitosan is 2%;

Weigh the gelatin and dissolve it in water, react at 60°C for 2 hours, and obtain a gelatin solution after the reaction; the mass concentration of the gelatin solution is 2%;

Mix the chitosan solution and the gelatin solution in a ratio of 1:1, react at 60 °C for 2 hours, and continuously stir during the period to fully mix the two to obtain a chitosan-gelatin blend solution, which is added with a volume concentration of 5%. The volume ratio of glycerol and chitosan-gelatin blend solution is 0.5:1 as plasticizer; then filter to remove impurities to obtain coating liquid.

(2) Pretreating the meat product, washing it with 800ppm sodium hypochlorite solution and distilled water for 3 minutes to remove impurities and microorganisms on the meat surface. Cut into five groups of 2cm square pieces to obtain meat samples.

(3) The meat block is coated with a spray method. Place the meat samples on a metal rack in a square arrangement, and use an electrostatic spraying system to spray the coating liquid prepared in step (1) on the surface of the meat samples; wherein, the diameter of the nozzle is 3 mm, and the distance between the surface of the meat samples and the nozzle is is 300mm, the spraying speed and feeding pressure are set to 100μL/min and 0.25MPa respectively; the coated meat is placed on a stainless steel screen to drain excess film liquid, and then the automatic air-drying system is used to air-dry at 60 °C to form a film. After coating, put the meat in the refrigerator at 4°C for future use.

Example 4:

(1) Weigh chitosan and dissolve it in an aqueous acetic acid solution with a mass concentration of 2%, and react at 60°C for 2 hours to obtain a chitosan solution; wherein the mass concentration of chitosan is 2%;

The gelatin was weighed and dissolved in water, and reacted at 60° C. for 2 h to obtain a gelatin solution after the reaction. The mass concentration of the gelatin solution is 2%;

Mix the chitosan solution and the gelatin solution in a ratio of 1:1, react at 60 °C for 2 hours, and continuously stir during the period to fully mix the two to obtain a chitosan-gelatin blend solution, which is added with a volume concentration of 5%. The volume ratio of glycerol and chitosan-gelatin blend solution is 0.5:1 as plasticizer; then filter to remove impurities to obtain coating liquid.

(2) Pretreating the meat product, washing it with 800 ppm sodium hypochlorite solution and distilled water for 3 min to remove impurities and microorganisms on the meat surface; cutting into five groups of 2 cm square pieces to obtain meat samples.

(3) Coating the meat samples by electrostatic spraying. Arrange the meat pieces on a metal rack, and use an electrostatic spraying system to spray the coating liquid prepared in step (1) on the surface of the meat piece sample; set the diameter of the nozzle to be 3 mm, and the distance from the surface of the meat piece sample to the nozzle to be 300 mm. The voltage is 25kV, the spraying speed and feeding pressure are set to 100μL/min and 0.25MPa respectively; the coated meat pieces are placed on a stainless steel screen to drain excess film liquid, and then an automatic air-drying system is used to air-dry at 60 °C to form a film , After coating, put the meat in the refrigerator at 4°C for future use.

Electron microscopy was performed on the active composite films coated in different ways, as follows:

Using scanning electron microscopy, we can deeply understand the morphology and structure of the film, and analyze the quality of the film formed by different coating methods from the microscopic level. The surface SEM images of the films formed by the four coating methods are shown in Figure 2.

The results show that the surface uniformity of the film formed by the dip coating method is good, and there are hardly any heterostructures and cracks and holes. The brush coating method shows uneven surface morphology, high roughness, and traces of brushing can be clearly observed, which are prone to problems such as brush marks, sagging and uneven brushing. The film layers formed by the spraying method and the electrostatic spraying method have relatively flat surface morphology, but some traces of spraying appear on the surfaces of both. In contrast, electrostatic spraying has far fewer traces, probably due to the orderly deposition of negatively charged droplets on the positively charged sample surface along the electric field lines. In addition, it can be seen from the figure that the surface of the film formed by the electrostatic spraying method has almost no impurities and is the smoothest, while the surface of the film formed by the dip coating method has the most impurities.

The atomic force microscope analysis and test of the film layer of the active composite film coated by different methods are as follows:

AFM can be used to analyze the surface morphology of the film formed on the meat surface by different coating methods; Figure 3 shows the dip coating method (A), brush coating method (B), spray method (C) and electrostatic spray method (D). ) AFM images of the formed film layers; the small figures below the (A), (B), (C) and (D) figures are the microstructure figures of the corresponding films.

Figure 3 presents the 2D surface and 3D topography images of the film layers within a scan area of 10 × 10 μm, where Rq and Ra are the surface roughness indices.

The results showed that the dip coating method had the lowest Rq and Ra values, which were 9.61 and 7.58 nm, respectively, which indicated that the film formed by dip coating had the lowest surface roughness and the best uniformity. The roughness of the film formed by brushing is the highest, with Rq and Ra values reaching 33.9 and 26.9 nm, which may be related to the easy generation of brush marks and uneven coating, which is also proved by the microstructure of the film. Compared with the film formed by spraying, the roughness index of electrostatic spraying is significantly reduced (Rq is reduced from 25.4 to 14.8 nm, Ra is reduced from 20.6 to 12.2 nm), which can also be visually observed from the 3D topography image. The latter has less ups and downs. This shows that the film formed by the electrostatic spraying method has a lower roughness and a smoother surface. This may be because the film liquid uses the property of attracting opposite charges after being negatively charged to form a layer-by-layer deposition effect on the surface of the meat, thereby ensuring the uniformity of the film layer.

The transfer efficiency of the membrane liquid was analyzed and tested for the active composite membranes coated by different methods. The details are as follows: The transfer efficiency of the membrane liquid is an important indicator for evaluating the coating method. Choosing a high-efficiency coating method can avoid the waste of membrane liquid. ,reduce manufacturing cost. The results are shown in Fig. 4. The transfer efficiency of dip coating is the lowest, and the transfer efficiency of electrostatic spraying is the highest, which is 56.2%, which is 1.6 times that of spraying. This is because electrostatic spraying can make the sprayed droplets negatively charged, and the electrostatic attraction between the charged droplets and the positively charged substrate can realize the targeted adsorption of the film liquid, which increases the deposition amount of the film liquid on the interface. In addition, due to the same-charge repulsion between the charged droplets, the droplets will not aggregate before reaching the target, which ensures the minimization of the mass of a single droplet, so that the electrostatic attraction can break through the effect of gravity and change the movement of the droplets trajectory.

To sum up, the electrostatic spraying method of the present invention is a potential coating method, which can charge the sprayed coating medium, and follows the principle of "same-sex repelling, opposite-sex attracting", under the action of high-voltage electric field It forms an encircling effect on the coated object, and finally deposits a uniform and firm film on the target. In addition, the technology also has the advantages of saving paint, safety and high efficiency, and provides a new and efficient coating method for the field of coating film preservation.

Explanation: The above embodiments are only used to illustrate the present invention and not to limit the technical solutions described in the present invention; therefore, although this specification has described the present invention in detail with reference to the above-mentioned various embodiments, those of ordinary skill in the art should It should be understood that the present invention can still be modified or equivalently replaced; and all technical solutions and improvements that do not depart from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims (7)

1. an electrostatic spray coating method for meat preservation, is characterized in that, comprises the following steps: (1) Preparation of coating liquid; S1. Weigh chitosan and dissolve it in an aqueous glacial acetic acid solution, and react under certain temperature conditions to obtain a chitosan solution; S2. take a certain amount of gelatin and dissolve it in water, and obtain a gelatin solution after reacting under a certain temperature condition; S3. Mix the chitosan solution and the gelatin solution by volume, stir and react at a certain temperature to obtain a chitosan-gelatin blend solution, add glycerol as a plasticizer, and then filter to remove impurities to obtain a coating liquid ; (2) choose the meat product, wash it with sodium hypochlorite solution and distilled water successively, it is beneficial to the electrostatic spraying coating film adhesion afterwards; After cleaning, carry out segmentation according to demand, obtain the meat sample; (3) Arrange the meat samples obtained in step (2) on a metal frame, and use an electrostatic spraying system to spray the coating liquid prepared in step (1) on the surface of the meat samples; Drain the excess film liquid on the stainless steel screen, and then use the automatic air drying system to air dry the film at a certain temperature to complete the coating film. 2. a kind of electrostatic spray coating method for meat preservation according to claim 1, is characterized in that, the volume concentration of the glacial acetic acid aqueous solution described in the S1 of step (1) is 2%～5%; The mass concentration of the chitosan solution is 1%-3%; the temperature adjusted to a certain temperature is 40-65°C; the reaction period is 2-5h. 3. a kind of electrostatic spray coating method for meat preservation according to claim 1, is characterized in that, the mass concentration of gelatin solution described in S2 of step (1) is 1%～3%; The certain temperature condition is 30～80℃, and the reaction time is 1～5h. 4. a kind of electrostatic spray coating method for meat preservation according to claim 1, is characterized in that, the volume ratio when mixing chitosan solution and gelatin solution described in the S3 of step (1) is 1 : 1; the volume concentration of the glycerol is 3% to 5%; the certain temperature condition is 50 to 80°C, and the stirring reaction time is 2 to 5 hours; the volume ratio of the glycerol to the chitosan-gelatin blend solution 0.5-0.8:1. 5. a kind of electrostatic spray coating method for meat preservation according to claim 1, is characterized in that, in step (2), the residual chlorine value of sodium hypochlorite solution is 500-1000ppm. 6. a kind of electrostatic spray coating method for meat preservation according to claim 1 is characterized in that, when spraying described in step (3), the distance from the surface of the meat piece sample to the nozzle is 250～350mm, The applied voltage is 15kV～40kV, and the spraying pressure is ≥0.2MPa and the material flow rate is 50μL/min～200μL/min. 7. A kind of electrostatic spray coating method for meat preservation according to claim 1, is characterized in that, the certain temperature condition described in step (3) is 30-80 ℃.

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