A squid fresh-keeping composite film and a preparation method thereof

Abstract

The application discloses a kind of squid fresh-keeping composite film, which is made of the following raw materials by mass percentage: 10-12% polyvinyl alcohol, 5-6% beeswax, 0.1-0.2% modified nano-TiO2, 5-6% lysozyme nanocellulose, 1-2% glycerol, 1-2% sucrose ester, 2-3% sodium dodecyl sulfonate, 0.3-0.5% glutathione, and the balance is water, the sum of the mass percentage of each component is 100%. The squid fresh-keeping composite film of the application has satisfactory appearance performance, mechanical properties, hydrophobic properties, antibacterial properties, barrier properties and transparency, and can effectively prolong the shelf life of squid ice storage as a fresh squid packaging material. The application also discloses a method for preparing the squid fresh-keeping composite film, which has simple preparation steps, low equipment requirements and strong operability. The film solution obtained has good film-forming properties, component uniformity and appearance performance, ensuring the comprehensive performance of the composite film prepared therefrom.

Description

TECHNICAL FIELD

[0001] The present application relates to squid preservation technology field, especially to a kind of squid preservation composite film and preparation method thereof. BACKGROUND

[0002] Squid is a very important marine economic product in China, with the characteristics of short breeding cycle, large breeding quantity, rich nutrition and delicious taste, which is deeply loved by consumers. Due to the factors such as perishable squid, difficult to control transportation conditions, environmental pollution, the development of its preservation technology has become an objective demand of the industry.

[0003] Currently, fresh squid on shore is usually preserved by ice storage, i.e. a preservation method using ice to cool the squid. However, the ice storage preservation time is still short, generally only about 7 days.

[0004] A squid preservation method is disclosed in Chinese patent with application publication number CN104886225A and application publication date September 9, 2015. In the method, polyaspartic acid is dissolved in water, then sodium alginate is added and stirred uniformly, and finally phytic acid is added and stirred uniformly to prepare a squid preservative. Fresh squid is washed, cut into capsules, then cut into pieces, and then placed in the squid preservative at a temperature of 4℃ for uniform soaking. The squid pieces are taken out, drained, and placed in a 4℃ environment for natural air drying. A layer of preservation film is formed on the surface of the air-dried squid pieces. The preservation method is a coating preservation method, which has the following defects: (1) the squid surface is smooth, and the coating liquid is difficult to uniformly adhere to the squid surface, resulting in uneven coating and film formation, and poor actual preservation effect; (2) the operation is complicated and inefficient, as it requires soaking, draining and air drying; and (4) soaking can cause the squid meat to swell, resulting in the loss of nutrients and flavor substances. SUMMARY

[0005] The present application provides a squid preservation composite film as a packaging material for fresh squid, which can prolong the preservation period of squid ice storage preservation, to solve the above-mentioned problems of the existing squid coating preservation method.

[0006] The present application also provides a squid preservation film preparation method, which has simple preparation steps, low equipment requirements and strong operability.

[0007] In order to achieve the above object, the application adopts the following technical scheme: a squid fresh-keeping composite film is made of the following raw materials in percentage by mass: 10-12% of polyvinyl alcohol, 5-6% of beeswax, 0.1-0.2% of modified nano-TiO2, 5-6% of lysozyme nanocellulose, 1-2% of glycerol, 1-2% of sucrose ester, 2-3% of sodium dodecyl sulfonate, 0.3-0.5% of glutathione, and the balance is water, the sum of the percentage by mass of each component is 100%. Different film-forming materials have different film-forming characteristics, and different film-forming materials all have their own problems, therefore, in actual application, in order to achieve good use and fresh-keeping effect, the selection of specific film-forming material is very important; polyvinyl alcohol is easy to form a film, pure polyvinyl alcohol film has strong gas barrier property, but has poor moisture resistance, is easy to absorb moisture and swell, and after absorbing moisture, is easy to produce the phenomenon of adhesion, and under low temperature and low humidity conditions, the film will appear hard and brittle, etc., at the same time, the film formed by polyvinyl alcohol is easy to oxidize and turn yellow, lacks antibacterial property, which hinders its application as a packaging and fresh-keeping film; in order to expand the application of polyvinyl alcohol in fresh-keeping packaging, in the application, beeswax is added for blending, beeswax has antioxidant property and antibacterial property, by adding beeswax, the problems of easy oxidation and turning yellow of the film formed by polyvinyl alcohol and lack of antibacterial property can be solved, at the same time, beeswax can also improve the hydrophobicity, ductility and gloss of the film, but the film formed by beeswax is not transparent, adding beeswax will affect the transparency and color of the film (make the film color yellow), therefore, in the application, modified nano-TiO2 is added to improve the transparency of the film, at the same time, can offset the yellow phase in the film to make it white, in addition, the modified nano-TiO2 can also improve the strength, toughness, waterproof property and antibacterial property of the film; the modified nano-TiO2 has good dispersibility in water, can avoid the problem of pores on the surface of the film caused by the difficulty of uniform dispersion of nano-TiO2 in water; the lysozyme nanocellulose is nanocellulose (NCC) loaded with lysozyme, the nanocellulose can form a network structure with polyvinyl alcohol and beeswax, as a dispersed phase to enhance the performance of the film, the lysozyme can endow the film with antibacterial property, the lysozyme is loaded on the nanocellulose, is uniformly dispersed, and has a slow-release effect; the sodium dodecyl sulfonate as a surfactant and dispersant can make each component uniformly dispersed and enhance the stability; the sucrose ester plays a role of defoaming; the glutathione as an antioxidant can further inhibit the oxidation and turning yellow of the film formed by polyvinyl alcohol.

[0008] Preferably, the modified nano-TiO2 is prepared by the following method: nano-TiO2 is added into ethanol, silane coupling agent (APS) is added into water, the two are mixed by ultrasonic mixing, filtration, and the filtrate is vacuum dried to obtain the modified nano-TiO2.

[0009] Preferably, 0.1-0.12 g of nano-TiO2 is added into 10 mL of ethanol; 1.0-1.1 mL of silane coupling agent (APS) is added into 10 mL of water.

[0010] Preferably, the lysozyme nanocellulose is prepared by adding nanocellulose into water to form a stable suspension, then adding lysozyme, shaking thoroughly, and placing in a 30-40°C water bath for 20-30 minutes, and then centrifuging and drying the obtained gel to obtain the lysozyme nanocellulose.

[0011] Preferably, 10-15g of nanocellulose is added into 150mL of water, and the amount of lysozyme added is 0.04-0.06% of the mass of the water.

[0012] A method for preparing a squid fresh-keeping composite film comprises the following steps:

[0013] (1) After weighing the raw materials according to the above mass percentages, the beeswax, polyvinyl alcohol and sucrose ester are added into water, heated until the beeswax and polyvinyl alcohol are completely dissolved, and then constant-temperature stirring is performed. In the present application, the beeswax, polyvinyl alcohol and sucrose ester are compounded and heated to form a stable emulsion to ensure uniformity.

[0014] (2) After cooling to 50-60°C, sodium dodecyl sulfonate and modified nano-TiO2 are added and ultrasonically mixed. The modified nano-TiO2 is still difficult to achieve an ideal dispersion state in water, so in the present application, sodium dodecyl sulfonate is added and ultrasonic mixing is performed to assist dispersion, and the ultrasonic mixing can also defoam, so that the modified nano-TiO2 can achieve an ideal dispersion state.

[0015] (3) Lysozyme nanocellulose and glutathione are added and stirred until uniform, and then vacuum defoaming is performed to obtain a film solution. The order and conditions of adding the raw materials are very critical and can directly affect the form, color and uniformity of the film solution, thereby affecting the color and performance of the film. In the present application, by controlling the order and conditions of adding the raw materials, the film solution obtained is slightly yellow, viscous and transparent, and has good film-forming properties, component uniformity and appearance performance.

[0016] (4) The film solution is cast or blade-coated onto a flat plate, dried, and then the film is peeled off to obtain a film.

[0017] (5) After the film is balanced, a squid fresh-keeping composite film is obtained.

[0018] Preferably, in step (1), heating is performed to 90-95°C, and constant-temperature stirring is performed for at least 2h.

[0019] Preferably, in step (2), the ultrasonic power is 240-300W, and the ultrasonic time is 40-60min.

[0020] Preferably, in step (4), the drying temperature is 50-70°C, and the thickness of the film is 0.5-0.8mm.

[0021] As preferred, in step (5), the specific step of balancing is: placing the film in a constant temperature and humidity chamber at 25 DEG C and 55% relative humidity for 48 hours.

[0022] Therefore, the present application has the following beneficial effects:

[0023] (1) Polyvinyl alcohol and beeswax are selected as film-forming materials, and nano-TiO2, glycerol and other components are added to prepare a composite film which has satisfactory appearance, mechanical properties, hydrophobic properties, antibacterial properties, barrier properties and transparency. The composite film can effectively prolong the shelf life of fresh squid during ice storage, and expand the application of polyvinyl alcohol in fresh-keeping packaging.

[0024] (2) The present application provides a preparation method of the squid fresh-keeping composite film, which has simple preparation steps, low equipment requirements and strong operability. The film liquid obtained has good film-forming properties, component uniformity and appearance, and the comprehensive properties of the composite film prepared therefrom are ensured. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is the actual photograph of the film liquid in Example 1.

[0026] Figure 2 is the actual photograph of the film liquid in Comparative Example 1.

[0027] Figure 3 is the actual photograph of the film liquid in Comparative Example 2.

[0028] Figure 4 is the actual photograph of the film liquid in Comparative Example 3.

[0029] Figure 5 is the actual photograph of the film liquid in Comparative Example 4.

[0030] Figure 6 is the K value change graph of squid during cold storage.

[0031] Figure 7 is the TVB-N value change graph of squid during cold storage.

[0032] Figure 8 is the total number of bacterial colonies of squid during cold storage. DETAILED DESCRIPTION

[0033] The present application will be further described below in combination with the drawings and specific embodiments.

[0034] Example 1

[0035] (1) Weigh each raw material according to the mass percentage of 10% polyvinyl alcohol, 5% beeswax, 0.1% modified nano-TiO2, 5% lysozyme nanocellulose, 2% glycerol, 2% sucrose ester, 3% sodium dodecyl sulfate, 0.5% glutathione, and the balance being water. Add beeswax, polyvinyl alcohol and sucrose ester to water, heat to 90°C to completely dissolve beeswax and polyvinyl alcohol, and stir at a constant temperature for 2 hours. Modified nano-TiO2 is prepared by the following method: add 0.1g nano-TiO2 to 10mL ethanol, add 1.0mL silane coupling agent to 10mL water, mix the two by ultrasonic mixing, filter, and vacuum dry the filter to obtain modified nano-TiO2.

[0036] Lysozyme nanocellulose was prepared by the following method: 10g of nanocellulose was added to 150mL of water and stirred evenly to form a stable suspension. Lysozyme was then added at a concentration of 0.04% of the water mass. After thorough shaking, the mixture was placed in a 30℃ water bath for 20min, centrifuged, and the resulting gel was dried to obtain lysozyme nanocellulose.

[0037] (2) After cooling to 50-60℃, add sodium dodecyl sulfonate and modified nano TiO2, mix by ultrasonication with an ultrasonic power of 240W and an ultrasonic time of 40min.

[0038] (3) Add lysozyme, nanocellulose and glutathione, stir evenly to obtain membrane solution;

[0039] (4) The film solution is cast onto a glass plate, dried at 60°C, and then peeled off to obtain a thin film with a thickness of 0.8 mm;

[0040] (5) After balancing the film, cut it to obtain the squid preservation composite film (e.g. Figure 1 As shown in the figure, the specific steps for equilibration are as follows: place the film in a constant temperature and humidity chamber at 25°C and 55% relative humidity for 48 hours to equilibrate.

[0041] from Figure 1 It can be seen that the obtained film is slightly yellow, viscous and transparent, with a glossy appearance and good composition uniformity.

[0042] Comparative Example 1

[0043] The difference between Comparative Example 1 and Example 1 is that no modified nano-TiO2 was added; the modified nano-TiO2 was replaced with water. The rest is the same as in Example 1, wherein the film obtained in step (3) is as follows: Figure 2 As shown.

[0044] from Figure 2 It can be seen that the film obtained in Comparative Example 1 has a better color than... Figure 1 The film is more yellow, indicating that the modified TiO2 can counteract the yellowing caused by the addition of beeswax.

[0045] Comparative Example 2

[0046] The difference between Comparative Example 2 and Example 1 is that propolis is not added, propolis is replaced by tapioca starch, and the rest is the same as Example 1, wherein the film obtained in step (3) is as shown in Figure 3 .

[0047] It can be seen from Figure 3 that the film obtained in Comparative Example 2 is lighter in color than the film in Example 1, and there is no obvious difference in other aspects, and the reason is that propolis will affect the color of the film, and the color of tapioca starch is transparent and will not affect the color of the film. Figure 1

[0048] Comparative Example 3

[0049] The difference between Comparative Example 3 and Example 1 is that lysozyme nanocellulose is not added, and lysozyme nanocellulose is replaced by water, and the rest is the same as Example 1, wherein the film obtained in step (3) is as shown in Figure 4 .

[0050] It can be seen from Figure 4 that the film obtained in Comparative Example 3 has no obvious difference in appearance with the film in Example 1. Figure 1

[0051] Comparative Example 4

[0052] The difference between Comparative Example 4 and Example 1 is that all the raw materials are mixed at one time, heated to 90°C, ultrasonically mixed, the ultrasonic power is 240W, the ultrasonic time is 40min, and the film solution is obtained; The film solution is cast onto a glass flat plate, dried at 60°C, and the film is peeled off to obtain a squid fresh-keeping composite film with a thickness of 0.8mm (as shown in Figure 5 ).The specific steps of the film are as follows: the film is placed in a constant temperature and humidity box at 25°C and 55% relative humidity for 48h.

[0053] It can be seen from Figure 5 that the film obtained in Comparative Example 4 has similar color to the film in Example 1, but the color is obviously uneven (the color of the edge is lighter than the color of the middle), and the surface is not flat, which shows that the mixing uniformity and film-forming property of the film solution in Comparative Example 4 are poor, which affects the appearance performance of the film. Figure 1 (1) The mechanical properties, water vapor permeability, swelling degree, contact angle and antibacterial properties of the composite films obtained in Example 1 and Comparative Examples 1-4 were determined, and the specific determination methods were as follows:

[0054]

[0055] ​​(1) Mechanical property measurement: The flat and even film without damage was cut into a strip of 15 mm x 100 mm, and fixed on the tensile probe of a texture analyzer (TA.XT Plus texture analyzer). The probe was stretched at a constant speed of 0.8 mm / s for 100 mm until the film was pulled apart. The tensile strength and elongation at break were recorded, and each group was repeated 5 times to take the average value.

[0056] Tensile strength calculation formula: TS = Fm / (L x W), wherein TS is the tensile strength (MPa); Fm is the maximum tension (N) when the film is broken; L is the film thickness (mm); and W is the film width (mm).

[0057] Elongation at break calculation formula: EB = (Lmax - L0) / L0 x 100%, wherein EB is the elongation at break, Lmax is the maximum length (m) when the film is broken, and L0 is the initial film length (m).

[0058] (2) Water vapor permeability: 11 mL of deionized water was added to a plastic moisture permeation cup (7 cm in diameter and 200 mL in capacity), and an 80 mm x 80 mm film was used to seal the mouth of the moisture permeation cup. After weighing, it was placed in a constant temperature and humidity chamber (25°C, 50% relative humidity), and weighed every 1 h. Each test was repeated 3 times to take the average value.

[0059] Water vapor permeability calculation formula: WVP = (m x L) / (A x t x AP), wherein WVP is the water vapor permeability, m is the mass of water permeated through the film (g); L is the thickness of the film (m); A is the water permeation area (m 2 ); t is the permeation time (s); and AP is the water vapor pressure difference (Pa).

[0060] (3) Swelling degree: The film was cut into a 10 mm x 20 mm strip, dried at 45°C for 24 h, and weighed to record W1. Then the strip was immersed in deionized water at room temperature, and after 24 h, the surface liquid was absorbed with filter paper and weighed to record W2.

[0061] The swelling degree of the film was calculated according to the following formula: Swelling degree (%) = (W 2- W2) / W1 x 100%.

[0062] (4) Contact angle: The surface contact angle of the film was measured using a contact angle measuring device (OCA50, Germany). The film was cut into a long strip and pasted on the sample table, and then 4 μL of water droplets were dropped on the surface of the film using a microsyringe, and the contact angle was measured.

[0063] The specific measurement results of the mechanical properties, water vapor permeability, swelling degree, contact angle and antibacterial properties of the composite film are shown in Table 1.

[0064] Table 1 Mechanical properties, water vapor permeability, swelling degree, contact angle and antibacterial property of the composite film

[0065] As can be seen from Table 1, the composite film obtained in Example 1 has the best comprehensive performance, and the composite films obtained in Comparative Examples 1-3 have poor comprehensive performance, which are all inferior to the composite film obtained in Example 1.

[0066] (II) Squid freshness index determination: After the squid was removed from the inside and washed and drained, it was placed in a disposable packaging tray, packaged with the film in Example 1 and Comparative Examples 1-4, and then placed in a 4°C refrigerator for cold storage. After 14 days of cold storage, samples were taken every 2 days, and K value, total volatile base nitrogen (TVB-N) value and total bacterial count were determined, with ordinary PE preservative film as a control group. Among them, the TVB-N value refers to GB 5009.228-2016 "National Food Safety Standard Determination of Volatile Base Nitrogen in Food"; the total bacterial count refers to GB 4789.2-2016 "Food Microbiological Examination Determination of Total Bacterial Count"; and the K value refers to SC / T 3048-2014 "Determination of Freshness Index K Value of Fish".

[0067] The change of the K value determined is shown in Figure 6 The K value is the ratio of the total amount of ATP decomposition products hypoxanthine riboside (HxR) and hypoxanthine (Hx) to the total amount of all related ATP, and is one of the important indicators representing the freshness of aquatic products. With the extension of storage time, ATP in the muscle tissue of aquatic products is rapidly decomposed, the contents of HxR and Hx gradually increase, the K value increases, and the freshness of aquatic products decreases. When the K value is ≤20%, the freshness is high. As can be seen from Figure 6 , the K value of the squid packaged with the film obtained in Example 1 is 18.6% on the 12th day, and exceeds 20% (23.2%) on the 14th day, indicating that the composite film of the application effectively delays the decomposition of ATP in squid during cold storage.

[0068] The change of the TVB-N value determined is shown in Figure 7 According to GB 5009.228-2016 "National Food Safety Standard Determination of Volatile Base Nitrogen in Food", the TVB-N content in meat and meat products ≤15 mg / 100 g is fresh meat, and the TVB-N content >20 mg / 100 g is deteriorated meat; the TVB-N value of fresh marine products is generally ≤30 mg / 100 g, and from Figure 7It can be seen that the TVB-N value of the squid packaged with the film obtained in Example 1 was 28.78 mg / 100g on the 12th day, which was still less than 30 mg / 100g. It only exceeded 30 mg / 100g on the 14th day (33.18 mg / 100g). This shows that the composite film of the present invention can effectively inhibit the generation of TVB-N in squid during refrigeration and delay spoilage.

[0069] The total number of bacterial colonies obtained by measurement is as follows: Figure 8 As shown. From Figure 8 It can be seen that the total bacterial count of all squid samples increased with the extension of storage time. However, the squid packaged with the film obtained in Example 1 had a total bacterial count of 8.681g (CFU / g) on ​​the 14th day, which was significantly lower than that of squid packaged with other films, indicating that the composite film of this application has excellent antibacterial properties.

[0070] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Other variations and modifications are possible without departing from the technical solutions described in the claims.

Claims

1. A squid fresh-keeping composite film, characterized in that, The raw materials are prepared by the following mass percentages: 10-12% polyvinyl alcohol, 5-6% beeswax, 0.1-0.2% modified nano-TiO2, 5-6% lysozyme nanocellulose, 1-2% glycerol, 1-2% sucrose ester, 2-3% sodium dodecyl sulfonate, 0.3-0.5% glutathione, and the balance is water, the sum of the mass percentages of each component is 100%; the modified nano-TiO2 is prepared by the following method: 0.1-0.12g nano-TiO2 is added to 10mL ethanol, 1.0-1.1mL silane coupling agent is added to 10mL water, both are mixed by ultrasonic mixing, filtration, and the filtrate is vacuum dried to obtain the modified nano-TiO2; the lysozyme nanocellulose is prepared by the following method: 10-15g nanocellulose is added to 150mL water and stirred uniformly to form a stable suspension, then lysozyme is added, and after sufficient shaking, it is placed in a 30-40℃ water bath for 20-30min, centrifugal separation, and the obtained gelatinous material is dried to obtain the lysozyme nanocellulose; The squid fresh-keeping composite film is prepared by the following method: (1) After weighing each raw material according to the above mass percentages, the beeswax, polyvinyl alcohol and sucrose ester are added to water, heated to completely dissolve the beeswax and polyvinyl alcohol, and then constant temperature stirring is carried out; (2) After cooling to 50-60℃, sodium dodecyl sulfonate and modified nano-TiO2 are added and ultrasonic mixing is carried out; (3) Lysozyme nanocellulose and glutathione are added, and after uniform stirring, vacuum degassing is carried out to obtain a film solution; (4) The film solution is cast or blade coated onto a flat plate, dried, and then the film is peeled off to obtain a film; (5) After the film is balanced, a squid fresh-keeping composite film is obtained.

2. The squid fresh-keeping composite film according to claim 1, characterized in that, The lysozyme addition amount is 0.04-0.06% of the mass of water.

3. The squid fresh-keeping composite film according to claim 1, characterized in that, In step (1), heating is carried out to 90-95℃, and constant temperature stirring is carried out for at least 2h.

4. The squid fresh-keeping composite film according to claim 1, characterized in that, In step (2), the ultrasonic power is 240-300W, and the ultrasonic time is 40-60min.

5. The squid fresh-keeping composite film according to claim 1, characterized in that, In step (4), the drying temperature is 50-70℃, and the film thickness is 0.5-0.8mm.

6. The squid fresh-keeping composite film according to claim 1, characterized in that, In step (5), the specific steps for balancing are as follows: the film is placed in a constant temperature and humidity chamber at 25℃ and a relative humidity of 55% for 48h.

Images