Edible film for preserving dairy products, preparation method and application thereof

Abstract

The present invention relates to the technical field of food preservative materials, and specifically to an edible film for preserving dairy products, and a preparation method and application thereof. The preparation method of the edible film for preserving dairy products provided by the present invention realizes the cross-linking of guar gum and casein by citric acid, and uses glycerol to fill the network structure, thereby forming an edible film in the form of a macromolecular film. The edible film obtained by the present invention has good mechanical tensile properties and strong physical barrier properties, and can effectively delay the oxidation and corruption process of dairy products and inhibit the growth of microorganisms in food. In addition, the above-mentioned preparation method provided by the present invention completely adopts non-toxic and harmless raw materials to prepare the edible film, has a simple process, relatively mild reaction conditions, and low requirements on equipment, and can realize large-scale industrial production. It has high economic, social and ecological value and is suitable for use in food preservation industries such as dairy products.

Description

Technical Field

[0001] The invention relates to the technical field of food preservation materials, and in particular to an edible film for preserving dairy products, and a preparation method and application thereof. Background Art

[0002] With the development of science and technology and the improvement of living standards, people are paying more and more attention to food health, and the waste caused by food spoilage is becoming more and more serious. At the same time, the widespread use of plastic packaging is causing serious damage to the environment and posing potential risks to human health. Therefore, it is urgent to develop environmentally friendly food preservation technology to adapt to the development needs of the times and meet the increasingly stringent food preservation requirements.

[0003] By preparing biodegradable functional packaging materials, the shelf life of food can be extended, and it has the characteristics of biosafety, which has become the focus of more and more researchers. Among them, biopolymer materials such as proteins, polysaccharides, and lipids have the advantages of being non-toxic, harmless, renewable, and biodegradable, and have been widely used in the field of food packaging. Among them, edible film is a kind of edible film with a network structure with barrier properties and selective air permeability formed by the interaction of biomacromolecules (such as polysaccharides, proteins, lipids, etc.) through intermolecular hydrogen bonds and electrostatic attraction. In the application process, edible film not only provides a solution to the pollution problem caused by plastic packaging, but also the biomacromolecules that constitute the edible film themselves have certain nutritional value, which can eliminate the safety hazards caused by packaging rupture due to heating or excessive oil in food. Therefore, edible film has a good development prospect in the field of food packaging.

[0004] In the prior art, in order to improve the mechanical properties of edible films, proteins and polysaccharides are often composited into films to prepare edible films. However, the water-resistant and oxygen-isolating properties of the composite films of proteins and polysaccharides are often poor, and usually cannot meet the higher requirements for the preservation effect of special high-protein foods such as solid dairy products (such as cheese). Therefore, technicians will inevitably introduce some toxic inorganic chemical reagents to enhance the membrane structure and improve the water-resistant and oxygen-isolating properties of the composite film. However, the introduced inorganic chemical reagents are difficult to completely remove by dialysis alone in the later stage, and there are still certain potential hazards.

[0005] Based on this, how to develop a composite edible film that is completely made of non-toxic and harmless materials and has good mechanical properties and water-resistant and oxygen-insulating properties to meet the higher and more stringent preservation requirements of foods such as dairy products has become a technical problem to be solved by the present invention. Summary of the invention

[0006] In order to solve the above problems, the purpose of the present invention is to provide a method for preparing an edible film for preserving dairy products, which completely adopts non-toxic and harmless raw materials to prepare the edible film, has a simple process, relatively mild reaction conditions, and low requirements on equipment, and can realize large-scale industrial production. The prepared edible film has excellent mechanical properties, water resistance and oxygen isolation properties, and biological safety, and is suitable for use in the food preservation industry.

[0007] In addition, the present invention also aims to provide an edible film for preserving dairy products prepared by the above preparation method. Further, the present invention also aims to provide the application of the above edible film for preserving dairy products.

[0008] To achieve the above object, the technical solution adopted by the present invention is:

[0009] A method for preparing an edible film for preserving dairy products comprises the following steps:

[0010] (1) mixing guar gum, citric acid, sodium hypophosphite and water, heating and stirring at 70-90° C., then cooling, adjusting the pH, and obtaining a gum solution; the mass ratio of the guar gum, citric acid and sodium hypophosphite is 1:(0.7-0.8):(0.3-0.4);

[0011] (2) mixing the glue solution with glycerol and casein solution, heating and stirring at 30-50° C. to obtain a film-forming solution;

[0012] (3) The film-forming liquid is cast into a film, and then dried to obtain an edible film for preserving dairy products.

[0013] As a preferred solution, in step (1), the amount of water used is 80 to 120 mL per gram of guar gum.

[0014] As a preferred solution, in step (1), the heating and stirring time at 70-90° C. is 20-60 min; and the pH is adjusted to 4.0-6.0.

[0015] As a preferred solution, in step (2), the concentration of the casein solution is 2% to 5% m / V; the volume ratio of the glue solution to glycerol and casein solution is 4:(0.3 to 0.5):(20 to 30).

[0016] As a preferred solution, in step (2), the heating and stirring time at 30-50° C. is 1-10 min.

[0017] As a preferred solution, in step (3), the drying temperature is 40 to 80° C., and the drying time is 1 to 8 hours.

[0018] As a preferred solution, the thickness of the edible film for preserving dairy products obtained in step (3) is 0.04 to 0.1 mm, more preferably 0.06 mm.

[0019] An edible film for preserving dairy products prepared by the preparation method.

[0020] The application of the edible film for preserving dairy products is the application of the edible film in preserving dairy products; the application method is to coat the edible film on the surface of the dairy product to be preserved to achieve the preservation of the dairy product.

[0021] As a preferred solution, the dairy product is a solid dairy product with a water content of 10% to 15%. Further, the present invention does not specifically limit the type of dairy product, and it can meet the preservation requirements of common solid dairy products in the field. Preferably, the dairy product is one of yak cheese, cheese blocks, milk lumps, dry cheese strips, and toffee.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] The preparation method of the edible film for preserving dairy products provided by the present invention realizes the cross-linking of guar gum and casein by food-grade biological organic acid (citric acid), and utilizes glycerol to fill the network structure, thereby forming an edible film in the form of a macromolecular film. The mechanical tensile property of the edible film obtained by the present invention is good, and the physical barrier property is strong, and it can effectively delay the oxidation and corruption process of dairy products, and inhibit the growth of microorganisms in food. Experiments have confirmed that the edible film is applied to the preservation of dairy products, which can improve the storage period of food and maximize its original quality and commodity value, and is safe and environmentally friendly. In addition, the above-mentioned preparation method provided by the present invention is completely prepared by non-toxic and harmless raw materials for edible film preparation, and the process is simple, the reaction conditions are relatively mild, and the equipment requirements are not high, and large-scale industrial production can be realized, and it has high economic, social and ecological value, and is suitable for use in the food preservation industry.

[0024] The edible film for preserving dairy products provided by the present invention has better mechanical tensile properties than a single casein edible film, can withstand a large tensile force and remain intact without breaking, and improves the problem that conventional single polysaccharide films have more pores. In addition, the edible film provided by the present invention has better transparency, can effectively block moisture and oxygen, and reduce the corruption and deterioration of foods such as cheese due to water loss or oil oxidation. At the same time, the edible film has good product adhesion, can be easily covered on the surface of food, and is not easy to fall off. In addition, the edible film of the present invention has better ductility and mechanical tensile properties, and has lower solubility and stronger tolerance to water. In addition, the edible film of the present invention has no peculiar smell, no special flavor, will not confuse the original flavor texture of the product, and has a certain soil degradability, and has a wide range of application prospects in the field of high-protein dairy product preservation. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is an appearance diagram of the edible film for preserving dairy products prepared in Example 1 of the present invention;

[0026] Figure 2 The mechanical tensile properties of the edible films prepared in Comparative Examples 1 to 3 are compared;

[0027] Figure 3 The mechanical tensile properties of the edible films prepared in Example 1 of the present invention and Comparative Example 1 and Comparative Examples 4 to 6 are compared;

[0028] Figure 4 Comparative results of water solubility, swelling property and water vapor permeability of edible films prepared in Comparative Examples 1 to 3;

[0029] Figure 5 The comparison results of water solubility, swelling property and water vapor permeability of edible films prepared in Example 1 of the present invention and Comparative Example 1 and Comparative Examples 4 to 6 are shown;

[0030] Figure 6 The opacity comparison results of the edible films prepared in Comparative Examples 1 to 3 are shown;

[0031] Figure 7 The opacity comparison results of the edible films prepared in Example 1 of the present invention and Comparative Example 1 and Comparative Examples 4 to 6 are shown;

[0032] Figure 8 The oxygen transmission rate comparison results of the edible films prepared in Comparative Examples 1 to 3 are shown;

[0033] Fig. 9 The oxygen transmission rate comparison results of the edible films prepared in Example 1 of the present invention and Comparative Example 1 and Comparative Examples 4 to 6 are shown;

[0034] Fig.10 The product appearance pictures of the test group, the blank group and the control group obtained after the edible film prepared in Example 1 of the present invention was used to preserve yak cheese;

[0035] Fig.11 The effects of the edible film prepared in Example 1 of the present invention on the soluble protein content of food in the experimental group, the blank group and the control group after being used to preserve yak cheese;

[0036] Fig.12 The effects of the edible film prepared in Example 1 of the present invention on the acidity of food obtained in the experimental group, the blank group and the control group after being used to preserve yak cheese;

[0037] Fig.13 The effects of the edible film prepared in Example 1 of the present invention on the water activity of food obtained by the experimental group, the blank group and the control group after being used for preserving yak cheese;

[0038] Fig.14 The effects of the edible film prepared in Example 1 of the present invention on food texture in the experimental group, blank group and control group obtained after being used to preserve yak cheese. DETAILED DESCRIPTION

[0039] The technical scheme and technical effects of the present invention will be clearly and completely described below in conjunction with specific embodiments and experimental examples. However, it should be understood by those skilled in the art that the embodiments are only used to illustrate the technical scheme of the present invention and should not be regarded as limiting the scope of protection of the present invention. The experimental methods used in the following examples are conventional methods unless otherwise specified; the raw materials used are all commonly used in the art, available to the public or commercially available, unless otherwise specified.

[0040] In the following examples, guar gum was used from Aladdin Biochemical Technology Co., Ltd., and casein product number M85B was from a food company in Beijing. The casein solution was prepared by dissolving casein in water and stirring in a water bath at 40°C for 4 hours.

[0041] Example 1

[0042] This embodiment provides an edible film for preserving dairy products, which is prepared by a preparation method comprising the following steps:

[0043] (1) Weigh 1 g of guar gum, 0.75 g of citric acid, and 0.375 g of sodium hypophosphite respectively in a container, heat to 85° C. in a water bath, add 100 mL of purified water to the container under rapid stirring to ensure that no residual clots remain after dissolution, cover the container with a lid and continue heating at 85° C. for 30 min, then cool naturally to 50° C., adjust the pH to 5.0, and obtain a glue solution;

[0044] (2) Take 4 mL of glue and 0.4 mL of glycerol and add them to 25 mL of 3% m / V casein solution, heat and stir at 40°C for 2 min to ensure sufficient mixing, and obtain a membrane-forming solution;

[0045] (3) 10 mL of the film-forming solution was poured into a 9 cm diameter circular mold, placed in a 60°C oven for drying for 5 h, and then the film was removed to obtain the edible film of Example 1 with a thickness of 0.06 mm. The appearance of the edible film obtained in Example 1 is shown in FIG. Figure 1 As shown, its surface is regular and flat, without pores, defects and good transparency.

[0046] Comparative Example 1

[0047] This comparative example provides an edible film for preserving dairy products. The preparation method of the film is basically the same as that of Example 1. The difference between the two is that the comparative example uses an equal mass of taro gum instead of guar gum, and the rest is the same as Example 1.

[0048] Comparative Example 2

[0049] This comparative example provides an edible film for preserving dairy products. The preparation method of the film is basically the same as that of Example 1. The difference between the two is that this comparative example uses an equal mass of taro gum instead of guar gum, and an equal mass of malic acid instead of citric acid. The rest is the same as Example 1.

[0050] Comparative Example 3

[0051] This comparative example provides an edible film for preserving dairy products. The preparation method of the film is basically the same as that of Example 1. The difference between the two is that this comparative example uses an equal mass of taro gum instead of guar gum, and an equal mass of tartaric acid instead of citric acid. The rest is the same as Example 1.

[0052] Comparative Example 4

[0053] This comparative example provides an edible film for preserving dairy products. The preparation method of the film is substantially the same as that of Example 1. The difference between the two is that the comparative example uses an equal mass of locust bean gum instead of guar gum, and the rest is the same as Example 1.

[0054] Comparative Example 5

[0055] This comparative example provides an edible film for preserving dairy products. The preparation method of the film is substantially the same as that of Example 1. The difference between the two is that this comparative example uses an equal mass of sesbania gum instead of guar gum, and the rest is the same as Example 1.

[0056] Comparative Example 6

[0057] This comparative example provides an edible film for preserving dairy products. The preparation method of the film is substantially the same as that of Example 1. The difference between the two is that the comparative example uses an equal mass of fenugreek gum instead of guar gum, and the rest is the same as that of Example 1.

[0058] Experimental Example 1: Evaluation of the properties of edible films

[0059] 1.1 Mechanical tensile properties test

[0060] The mechanical tensile properties of the edible films obtained in Example 1 and Comparative Examples 1 to 6 were measured using a TA.XT Plus C texture analyzer. During the experiment, the edible film was cut into a rectangle of 10 mm × 30 mm, and the texture analyzer parameters were set. The test mode was tensile, the pre-test speed was 1.00 mm / s, the test speed was 2.00 mm / s, the post-test speed was 10 mm / s, the trigger force was 5 g, and the rupture sensitivity was 20 g. Then, the mechanical tensile properties were tested, and the tensile strength and elongation at break of the edible film sample were calculated by Formula 1 and Formula 2.

[0061] Wherein, F is the maximum tensile force at the moment of fracture (N); T and W are the thickness (mm) and width (mm) of the edible film strip after cutting, respectively; L0 is the initial length of the edible film strip between the probes; and L is the length of the edible film strip at the moment of fracture.

[0062] The mechanical tensile properties of the edible films prepared in Comparative Examples 1 to 3 are compared as follows: Figure 2 The mechanical tensile properties of the edible films prepared in Example 1, Comparative Example 1, and Comparative Examples 4 to 6 are shown in FIG. Figure 3 shown.

[0063] Depend on Figure 2 It can be seen that when the type of polysaccharide (taro gum) used is the same, the use of different organic acids for cross-linking has different effects on the mechanical properties of the edible film. Among them, the tensile strength and elongation at break of the edible film cross-linked with citric acid are significantly improved compared with the edible film cross-linked with malic acid and tartaric acid (P<0.01), indicating that the mechanical properties of the edible film cross-linked with citric acid are the best.

[0064] Depend on Figure 3 It can be seen that the edible film obtained by cross-linking casein with guar gum in Example 1 has a tensile strength that is significantly better than (P<0.05) that of other experimental groups, and the elongation at break of the guar gum group is significantly higher than (P<0.05) that of the locust bean gum group, the sesbania gum group, and the fenugreek gum group, and is basically equivalent to the taro gum group. These results show that the edible film obtained by cross-linking casein with guar gum in the present invention has the best mechanical properties.

[0065] 1.2 Water solubility, swelling and water vapor transmission rate test

[0066] The edible films obtained in Example 1 and Comparative Examples 1 to 6 were cut into 40 mm × 20 mm sizes and soaked in 15 mL of deionized water for 24 h to evaluate the solubility of the edible films. Furthermore, the samples of different edible films were slowly stirred at 25 ° C for 15 h, and then centrifuged at 8000 r / min for 15 min, the supernatant was removed, and the lower layer of precipitate was taken, and the precipitate was dried at 105 ° C for 24 h. The solubility and swelling degree of the edible film were calculated using Formula 3 and Formula 4, respectively.

[0067] Where M0 represents the initial mass of the sample, M1 represents the mass of the precipitate, and M2 represents the mass of the sample after drying.

[0068] In addition, the water vapor permeability is measured in accordance with the national standard (GB / T1037-88). During the test, the anhydrous CaCl2 is first ground and placed in an oven for drying for 24 hours. Each group uses 5g of ground anhydrous CaCl2 and puts it into a 20mL centrifuge tube. Subsequently, the edible film samples obtained in Example 1 and Comparative Examples 1 to 6 are placed on the surface of the centrifuge tube and sealed with a combination of paraffin and beeswax. The sealed centrifuge tube is then placed in a constant temperature and humidity chamber and maintained at 37°C and 50% relative humidity for 24 hours. The water vapor permeability is calculated according to Formula 5.

[0069] Wherein, Δm represents the weight increase observed after weight stabilization, in g; m0 represents the initial mass of calcium chloride, in g; A represents the penetration area of ​​the edible film sample, in cm 2 ; t represents the duration of the test interval, in h; d represents the thickness of the edible film sample, in cm.

[0070] The comparison results of water solubility, swelling property and water vapor permeability of the edible films prepared in Comparative Examples 1 to 3 are as follows: Figure 4 The comparison results of water solubility, swelling property and water vapor permeability of the edible films prepared in Example 1 and Comparative Example 1 and Comparative Examples 4 to 6 are shown in FIG. Figure 5 shown.

[0071] Depend on Figure 4 It can be seen that when the type of polysaccharides is the same, the solubility of the experimental group cross-linked with citric acid is slightly lower than that of the malic acid group, and significantly lower than (P<0.05) the tartaric acid group. The swelling degree is significantly lower than (P<0.05) the malic acid group and the tartaric acid group. The water vapor permeability is slightly lower than that of the malic acid group and the tartaric acid group, and there is no significant difference among the three (P>0.05). These results indicate that the edible film cross-linked with citric acid has the best water resistance.

[0072] Depend on Figure 5 It can be seen that the solubility and swelling degree of the edible film obtained by cross-linking casein with guar gum in the present invention are significantly lower than those of other experimental groups (P<0.05). In addition, there is no significant difference in the water vapor permeability of the edible film (P<0.05), and the guar gum group is slightly lower than the other groups. These conclusions show that compared with several other galactomannans, the edible film prepared by guar gum in the present invention has the best water resistance.

[0073] 1.3. Opacity test

[0074] The absorbance of the edible film was measured at 600 nm using a visible light spectrophotometer. The edible films of Example 1 and Comparative Examples 1 to 6 were cut into rectangles of 1.0 cm × 3.0 cm and carefully placed in a cuvette with tweezers to test the absorbance at 600 nm. With air as the zero point control, the opacity of the edible film was calculated as shown in Formula 6:

[0075] In the formula, A 600 is the absorbance of the edible film sample at 600 nm, and d is the thickness of the edible film sample.

[0076] The opacity comparison results of the edible films prepared in Comparative Examples 1 to 3 are as follows: Figure 6 The opacity comparison results of the edible films prepared in Example 1 and Comparative Example 1 and Comparative Examples 4 to 6 are shown in FIG. Figure 7 shown.

[0077] Depend on Figure 6 It can be seen that there is no significant difference in the opacity of the edible films cross-linked by the three organic acids.

[0078] Depend on Figure 7 It can be seen that the transparency of the edible film obtained by cross-linking casein with tsara gum is the best, followed by sesbania gum group and fenugreek gum group, and locust bean gum group and guar gum group. However, the transparency results of the above groups can clearly reflect the details of the quality, appearance, color and other details of the coated products, and will not interfere with consumers' judgment of the product itself, meeting the application requirements.

[0079] 1.4. Oxygen Transmission Rate

[0080] The test method is similar to that of water vapor transmission rate. Each group uses 5 mL of vegetable oil and is placed in a 20 mL centrifuge tube. Subsequently, the edible film samples of Example 1 and Comparative Examples 1 to 6 are placed on the surface of the centrifuge tube and sealed with a combination of paraffin and beeswax. The sealed centrifuge tube is then placed in a constant temperature and humidity chamber and maintained at 37°C and 50% relative humidity for 24 hours. The peroxide value of the vegetable oil in the centrifuge tube is then measured using the sodium thiosulfate method, and the oxygen transmission rate of the edible film is expressed by the peroxide value of the vegetable oil.

[0081] The oxygen permeability comparison results of the edible films prepared in Comparative Examples 1 to 3 are as follows: Figure 8 The oxygen permeability comparison results of the edible films prepared in Example 1 and Comparative Example 1 and Comparative Examples 4 to 6 are shown in FIG. Fig. 9 shown.

[0082] like Figure 8 As shown, the peroxide value of vegetable oil in the tube corresponding to the edible film cross-linked with citric acid was significantly lower (P<0.05) than that in the malic acid group and the tartaric acid group, indicating that the edible film cross-linked with citric acid has the best oxygen barrier property.

[0083] Depend on Fig. 9 It can be seen that the oxygen permeability of the edible film obtained by cross-linking casein with guar gum in Example 1 of the present invention is significantly lower (P<0.05) than that of the taro gum group, sesbania gum group, and fenugreek gum group, and slightly lower than that of the locust bean gum group. These results show that the present invention can obtain the best oxygen barrier property by cross-linking casein with guar gum.

[0084] Experimental Example 2: Evaluation of the Storage Performance of Yak Cheese

[0085] The commercial product "High-speed Rail Yak Fruit Grain Cheese" was used as an application object to investigate the effect of the edible film of the present invention on the storage performance of yak cheese.

[0086] Experimental groups: the blank group was a yak cheese sample not coated with an edible film; the control group was a yak cheese sample in original packaging (a plastic shell wrapped in tin foil); the experimental group was a yak cheese sample coated with an edible film obtained by completely coating the surface of the yak cheese with the edible film prepared in Example 1 of the present invention.

[0087] Experimental process: Prepare fresh yak cheese from the same batch with a shelf life, cut the cheese into small square pieces of equal size with a stainless steel blade, and perform corresponding treatments according to the experimental groups to obtain yak cheese samples of the experimental group, blank group, and control group. The appearance is shown in Figure 10, and then record the soluble protein content, acidity, water activity, and texture properties of each group of yak cheese samples after storage for 3d, 6d, 9d, and 12d.

[0088] 2.1. Soluble protein content test

[0089] The soluble protein content test was conducted by mixing yak cheese and deionized water at a ratio of 1:20, centrifuging at 8000 r / min for 5 min, taking the supernatant, and measuring the casein concentration using a BCA kit, which was recorded as the soluble protein content of the yak cheese in this group. Fig.11 shown.

[0090] Depend on Fig.11 It can be seen that as time goes by, the soluble protein content of each group gradually decreases, which is related to the deterioration of protein, and the solubility of protein denaturation decreases. The soluble protein content of the control group is significantly higher than that of the blank group (P<0.05), but there is a statistical difference between the control group and the experimental group, and between the experimental group and the blank group (P>0.05). The experimental group is slightly lower than the control group and higher than the blank group, which reflects the oxygen barrier property of the edible film. The research results show that the edible film of the present invention has a certain preservation effect on the protein in yak cheese.

[0091] 2.2 Acidity test

[0092] The acidity test is to measure the pH value of the supernatant in the previous step with a pH meter, which is recorded as the acidity of the yak cheese in this group. Fig.12 shown.

[0093] Depend on Fig.12 It can be seen that there was no statistical difference in the acidity of yak cheese among the control group, experimental group and blank group (P>0.05). As time went by, the acidity of yak cheese in each group increased. The acidity of the experimental group was similar to that of the control group and slightly greater than that of the blank group. This reflects the oxygen barrier property of the edible film, which inhibits the growth of aerobic bacteria. It also reflects that the edible film has antibacterial potential and reduces the acid production of microorganisms.

[0094] 2.3 Water activity test

[0095] The water activity test was performed by weighing the yak cheese and placing it in a crucible and drying it in an oven at 150°C for 1 hour. The water activity was calculated using Equation 7: In the formula, M1 represents the mass of yak cheese before drying, and M2 represents the mass of yak cheese after drying. The water activity of yak cheese is as follows: Fig.13 shown.

[0096] Depend on Fig.13 It can be seen that there are significant differences in the moisture content of each group (P<0.05), which indicates that water activity is the main factor in the preservation of yak cheese. It can be observed that with the passage of time, the water activity of yak cheese gradually decreases. This is because there is moisture circulation between yak cheese and the air. By comparing the experimental group with the blank group, it can be found that the edible film can effectively reduce the moisture loss of yak cheese, which is related to the water vapor barrier and water absorption capacity of the edible film. In addition, the edible film in this study has a similar water activity to yak cheese, which can achieve the effect of blocking moisture.

[0097] 2.4 Texture test

[0098] The texture of yak cheese was measured using a TA.XT Plus C texture analyzer. The mode was set to TPA mode, the probe used was a P / 36R probe, the pre-test speed was set to 3mm / s, the mid-test speed was set to 1mm / s, the post-test speed was set to 5mm / s, and the deformation distance was set to 5mm. This part mainly measured the hardness, springiness, chewiness, and cohesiveness of yak cheese using the texture analyzer. The measurement results are shown in the figure below. Fig.14 shown.

[0099] Depend on Fig.14 It can be seen that the hardness of the three groups is significantly different. The hardness of the blank group is significantly greater than that of the experimental group and the control group (P<0.05). Except for 3d, the difference between the experimental group and the control group is significant (P<0.05). The elasticity of the blank group, the control group and the experimental group is significant (P<0.05). The blank group has worse elasticity. These conclusions show that the edible film of the present invention effectively controls the hardening of yak cheese in the air, and maintains the elasticity of yak cheese to a certain extent. Further, the chewiness of the blank group and the control group is significantly different (P<0.05), and the experimental group reduces the chewiness of yak cheese to a certain extent, which shows that the coating of the edible film can reduce the work done by the teeth when chewing yak cheese to a certain extent. The cohesion of the blank group is significantly higher than that of the experimental group and the control group (P<0.05), indicating that the edible film can reduce the increase in the cohesion of yak cheese. Comprehensive texture results show that the edible film of the present invention can effectively maintain the texture of yak cheese and extend the shelf life of food.

[0100] From the above results, it can be seen that the edible film provided by the present invention as a bio-based packaging is slightly less effective than the traditional packaging of tinfoil + plastic used in the control group, but the preservation effect of the edible film provided by the present invention is significantly better than that of the blank group (i.e. completely exposed and unpackaged). Therefore, it can completely replace traditional packaging such as tinfoil and plastic to a certain extent, and reduce the pollution and harm of plastic packaging to human health and the social environment.

[0101] In summary, the preparation method of the edible film for the preservation of dairy products provided by the present invention realizes the cross-linking of guar gum and casein by food-grade biological organic acid (citric acid), and utilizes glycerol to fill the network structure, thereby forming an edible film in the form of a macromolecular film. The mechanical tensile property of the edible film obtained by the present invention is good, and the physical barrier property is strong, which can effectively delay the oxidation and corruption process of high-protein dairy foods such as cheese, and inhibit the growth of microorganisms in food. Experiments have confirmed that the edible film is applied to the preservation of dairy products, which can improve the storage period of food and maximize its original quality and commodity value, and is safe and environmentally friendly. In addition, the above-mentioned preparation method provided by the present invention is completely prepared by non-toxic and harmless raw materials for edible film preparation, the process is simple, the reaction conditions are relatively mild, and the equipment requirements are not high, and large-scale industrial production can be achieved, and it has a good application prospect in the field of high-protein food preservation.

[0102] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection of the present invention.

Claims

1. A method for preparing an edible film for preserving dairy products, characterized in that: The following steps are involved: (1) guar gum, citric acid, sodium hypophosphite and water are mixed, heated and stirred at 70-90° C., then cooled, and the pH value is adjusted to obtain a gum solution; the mass ratio of the guar gum, citric acid and sodium hypophosphite is 1:(0.7-0.8):(0.3-0.4); (2) mixing the glue solution with glycerol and casein solution, heating and stirring at 30-50° C. to obtain a film-forming solution; (3) The film-forming liquid is cast into a film, and then dried to obtain an edible film for preserving dairy products.

2. The method for preparing an edible film for preserving dairy products according to claim 1, characterized in that: In step (1), the amount of water used is 80-120 mL per gram of guar gum.

3. The method for preparing an edible film for preserving dairy products according to claim 1, characterized in that: In step (1), the heating and stirring time at 70-90° C. is 20-60 min; and the pH is adjusted to 4.0-6.

0.

4. The method for preparing an edible film for preserving dairy products according to any one of claims 1 to 3, characterized in that: In step (2), the concentration of the casein solution is 2%-5% m / V; the volume ratio of the glue solution to glycerol and casein solution is 4:(0.3-0.5):(20-30).

5. The method for preparing an edible film for preserving dairy products according to any one of claims 1 to 3, characterized in that: In step (2), the heating and stirring time at 30-50° C. is 1-10 min.

6. The method for preparing an edible film for preserving dairy products according to any one of claims 1 to 3, characterized in that: In step (3), the drying temperature is 40-80°C and the drying time is 1-8 hours.

7. The method for preparing an edible film for preserving dairy products according to any one of claims 1 to 3, characterized in that: The thickness of the edible film for preserving dairy products obtained in step (3) is 0.04-0.1 mm.

8. An edible film for preserving dairy products prepared by the preparation method according to any one of claims 1 to 7.

9. An application of the edible film for preserving dairy products as claimed in claim 8, characterized in that: The application is the application of the edible film in the preservation of dairy products; the application method is to coat the edible film on the surface of the dairy product to be preserved to achieve the preservation of the dairy product.

10. The use of the edible film for preserving dairy products according to claim 9, characterized in that: The dairy product is a solid dairy product with a water content of 10% to 15%; the dairy product is one of yak cheese, cheese blocks, milk lumps, dry cheese strips, and toffee.

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