Food 3D printing ink and preparation method thereof

Abstract

The invention relates to the field of food 3D printing, and discloses food 3D printing ink and a preparation method thereof.The preparation method comprises the following steps that fish skin is soaked with a citric acid solution, then washed with water, stirred, filtered and dried, and fish gelatin is obtained; adjusting the pH value of the obtained fish gelatin to 7.5-8.5, mixing with alkaline enzyme, dividing into two parts, carrying out microwave treatment on one part for 10-15 minutes, carrying out microwave treatment on the other part for 20-25 minutes, respectively carrying out enzyme inactivation after microwave treatment, centrifuging, taking supernate, and freeze-drying to obtain a fish gelatin hydrolysate; the preparation method comprises the following steps: dissolving fish gelatin hydrolysate and starch in water, and standing at room temperature to form gel; according to the invention, fish skin is taken as a raw material, the fish gelatin hydrolysate is prepared by microwave processing, and the food 3D printing ink with relatively high printing precision can be obtained after interaction with starch, so that utilization of fish processing byproducts is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of 3D food printing, and in particular to a food 3D printing ink and a preparation method thereof. Background Art

[0002] Fish processing by-products are fish materials left over from primary processing during fish production. By weight, these by-products represent approximately 50% of the raw material. Due to their high organic matter content, fish processing by-products are classified as certified waste and are more expensive to dispose of. This increases waste disposal costs without providing value-added solutions.

[0003] 3D printing of food-grade materials offers novel, customized culinary products. A variety of edible materials can be used in 3D printing to create complex food structures. Carbohydrate-based materials are popular for this purpose. However, carbohydrate 3D printing presents several challenges, such as limited structural integrity, susceptibility to water absorption, and lack of nutritional value. Some researchers have suggested that mixing carbohydrates with proteins may be a solution. Since approximately 50% (w / w) of the dry weight of seafood waste is protein, applying fish processing byproducts to 3D food printing could benefit the seafood industry.

[0004] Prior research has explored the use of surimi as a 3D printing material. For example, patent publication number CN109077256A discloses a method for preparing and applying surimi for 3D printing. This method uses fish as the primary raw material and proceeds through five steps: pretreatment, mincing, rinsing, dehydration, and surimi preparation to produce surimi suitable for 3D printing. However, research has yet to explore how to utilize fish processing byproducts to create ink suitable for 3D printing. Summary of the Invention

[0005] The present invention aims to overcome the above-mentioned problems existing in the prior art and provides a food 3D printing ink and a preparation method thereof. Fish skin is used as raw material, fish gelatin hydrolysate is prepared by microwave processing, and after interaction with starch, a food 3D printing ink with high printing accuracy can be obtained, realizing the utilization of fish processing by-products.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: A method for preparing food 3D printing ink comprises the following steps: (1) soaking the fish skin in a citric acid solution, washing it with water, stirring it, filtering it, and drying it to obtain fish glue; (2) The pH value of the obtained fish gelatin was adjusted to 7.5-8.5, mixed with alkaline enzyme, and then divided into two parts, one part was microwave-treated for 10-15 minutes, and the other part was microwave-treated for 20-25 minutes. The microwave power during the treatment was 50-100W; after microwave treatment, the enzymes were inactivated respectively, and then the supernatant was collected after centrifugation and freeze-dried to obtain fish gelatin hydrolyzate; (3) Dissolving fish gelatin hydrolysate and starch in water at a mass ratio of 40:60 to 60:40, and allowing to stand at room temperature to form a gel to obtain the food 3D printing ink; in the fish gelatin hydrolysate, the mass ratio of the fish gelatin hydrolysate obtained by microwave treatment for 10 to 15 minutes to the fish gelatin hydrolysate obtained by microwave treatment for 20 to 25 minutes is 1:5 to 10.

[0007] Utilizing fish protein as a byproduct of fish processing is crucial. Among various types of fish protein, fish gelatin extracted from fish skin has attracted widespread attention and is considered a significant source of gelatin, alongside mammalian gelatin. Fish gelatin hydrolysates facilitate the absorption and digestion of amino acids, and their texture and improved water solubility make them easier to incorporate into daily diets. This invention uses fish skin as a raw material to prepare fish gelatin, which is then processed using microwaves to produce fish gelatin hydrolysate. This processed fish gelatin hydrolysate, combined with starch in varying proportions, can be used as a 3D printing ink. This approach significantly increases the value of fish processing byproducts, enhances their economic value, is environmentally friendly, alleviates the increased processing costs associated with fish processing byproducts, and provides a new food-grade material for 3D printing.

[0008] Gels made of starch alone have poor stability. The present invention combines fish gelatin hydrolysate with starch as a 3D printing ink. Fish gelatin hydrolysate exhibits strong water-holding capacity. This enhanced water-retention capacity inhibits water movement and provides a better solid gel structure with reduced viscosity. The interaction between carbohydrates and proteins can address the shortcomings of carbohydrates in 3D printing, such as limited structural integrity, sensitivity to moisture, and lack of nutritional value.

[0009] Furthermore, the present invention utilizes microwave processing to prepare fish gelatin hydrolyzate, which is more efficient than traditional hydrolysis methods. Fish gelatin hydrolyzates of varying degrees of hydrolysis form different gel networks with starch, which in turn influence the printing precision of 3D printing inks. Ideal 3D printing inks should possess a balance between high elastic storage capacity and moderate viscosity (high elastic storage capacity not only helps prevent excessive deformation or sagging of the printed structure during printing but also enables faster printing speeds because the material can quickly recover its shape after extraction; 3D printing inks have a certain viscosity, which helps achieve better layer adhesion and smooth ink deposition, improving overall print quality. However, excessively high viscosity makes extrusion through the 3D printer nozzle difficult), facilitating layer-by-layer printing. Therefore, in order to ensure that the 3D printing ink has good printing performance, the present invention controls the microwave treatment time and the degree of hydrolysis of fish gelatin, mixes two fish gelatin hydrolysates with different hydrolysis degrees, and reacts them with starch. The resulting gel structure can have both a high storage modulus (reflecting the material's ability to store elastic energy) and a medium loss modulus (related to the material's viscosity), thereby obtaining a food 3D printing ink with high printing precision.

[0010] Preferably, the fish skin in step (1) comes from lungfish.

[0011] Preferably, the mass concentration of the citric acid solution in step (1) is 0.2-0.3%, the mass volume ratio of fish skin to citric acid solution is 1 g:3-5 mL, and the immersion time of fish skin in the citric acid solution is 12-24 h.

[0012] Preferably, the stirring temperature in step (1) is 60-70° C., and the stirring time is 6-8 h.

[0013] Preferably, the drying temperature in step (1) is 55-65° C., and the drying time is 40-60 min.

[0014] Preferably, the alkaline enzyme in step (2) is alkaline protease; the volume fraction of the added alkaline enzyme is 1-3%.

[0015] Preferably, the temperature during the microwave treatment in step (2) is 50-60°C.

[0016] Preferably, the temperature for enzyme inactivation in step (2) is -20 to -25°C, and the time for enzyme inactivation is 5 to 10 minutes.

[0017] Preferably, the temperature during centrifugation in step (2) is 0-4°C, the centrifugal force is 9000-11000×g, and the time is 10-20 min.

[0018] Preferably, in step (3), the volume ratio of the total mass of fish gelatin hydrolyzate and starch to water is 7-8 g:50 mL.

[0019] The present invention also provides a food 3D printing ink prepared using the above preparation method.

[0020] Therefore, the present invention has the following beneficial effects: (1) Using fish skin as raw material, we deeply explore the added value of fish processing by-products, increase the economic value of fish processing by-products, are environmentally friendly, and alleviate the problem of increased costs in processing fish processing by-products; (2) Combining fish gelatin hydrolysate with starch as 3D printing ink, the interaction between carbohydrates and proteins can solve the shortcomings of carbohydrates in 3D printing, such as limited structural integrity, sensitivity to moisture, and lack of nutritional value; (3) Microwave processing was used to prepare fish gelatin hydrolysate. Compared with traditional hydrolysis, microwave processing improved the efficiency of enzyme hydrolysis of fish skin gelatin while ensuring nutrition. (4) Two fish gelatin hydrolysates with different hydrolysis degrees are mixed and reacted with starch, so that the resulting gel structure can have both high elastic storage capacity and appropriate viscosity, thereby obtaining food 3D printing ink with high printing accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 1 is an SEM image of the fish gelatin hydrolyzate in Example 1 of the present invention; wherein a is untreated fish gelatin; b is fish gelatin after microwave treatment for 10 minutes; and c is fish gelatin after microwave treatment for 20 minutes.

[0022] Figure 2 3D printing ink of the present invention; wherein a is comparative example 1, b is comparative example 2, c is embodiment 1, d is embodiment 2, and e is comparative example 3.

[0023] Figure 3 3D printing ink of the present invention; wherein a is comparative example 1, b is comparative example 2, c is embodiment 1, d is embodiment 2, and e is comparative example 3.

[0024] Figure 4 is the viscosity curve of the 3D printing ink of the present invention.

[0025] Figure 5 3D printing inks of Example 1, Comparative Examples 4, and 5 of the present invention are plotted against storage modulus and angular frequency.

[0026] Figure 6 3D printing inks of Example 1, Comparative Examples 4, and 5 of the present invention are plotted against loss modulus and angular frequency.

[0027] Figure 7 This is a picture of a physical product printed by the 3D printing ink in Example 1 of the present invention.

[0028] Figure 8 This is a physical picture of the product printed by the 3D printing ink in Comparative Example 4 of the present invention.

[0029] Figure 9 This is a physical picture of the product printed by the 3D printing ink in Comparative Example 5 of the present invention. DETAILED DESCRIPTION

[0030] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0031] In the present invention, unless otherwise specified, all equipment and raw materials can be purchased from the market or are commonly used in the industry. The methods in the following embodiments, unless otherwise specified, are all conventional methods in the art.

[0032] Overall embodiment: A method for preparing food 3D printing ink comprises the following steps: (1) soaking the fish skin in a citric acid solution, washing it with water, stirring it, filtering it, and drying it to obtain fish glue; (2) The pH value of the obtained fish gelatin was adjusted to 7.5-8.5, mixed with alkaline enzyme, and then divided into two parts, one part was microwave-treated for 10-15 minutes, and the other part was microwave-treated for 20-25 minutes. The microwave power during the treatment was 50-100W; after microwave treatment, the enzymes were inactivated respectively, and then the supernatant was collected after centrifugation and freeze-dried to obtain fish gelatin hydrolyzate; (3) Dissolving fish gelatin hydrolysate and starch in water at a mass ratio of 40:60 to 60:40, and allowing to stand at room temperature to form a gel to obtain the food 3D printing ink; in the fish gelatin hydrolysate, the mass ratio of the fish gelatin hydrolysate obtained by microwave treatment for 10 to 15 minutes to the fish gelatin hydrolysate obtained by microwave treatment for 20 to 25 minutes is 1:5 to 10.

[0033] As a specific embodiment, the fish skin in step (1) comes from lungfish.

[0034] As a specific embodiment, the mass concentration of the citric acid solution in step (1) is 0.2-0.3%, the mass volume ratio of fish skin to citric acid solution is 1 g:3-5 mL, and the immersion time of fish skin in the citric acid solution is 12-24 h.

[0035] As a specific implementation manner, the temperature during stirring in step (1) is 60-70° C., and the stirring time is 6-8 hours.

[0036] As a specific implementation manner, the drying temperature in step (1) is 55-65° C., and the drying time is 40-60 min.

[0037] As a specific embodiment, the alkaline enzyme in step (2) is alkaline protease; the volume fraction of the added alkaline enzyme is 1-3%.

[0038] As a specific embodiment, the temperature during microwave treatment in step (2) is 50-60°C.

[0039] As a specific embodiment, the temperature for enzyme inactivation in step (2) is -20 to -25°C, and the time for enzyme inactivation is 5 to 10 minutes.

[0040] As a specific embodiment, the temperature during centrifugation in step (2) is 0-4°C, the centrifugal force is 9000-11000×g, and the time is 10-20 min.

[0041] As a specific embodiment, in step (3), the volume ratio of the total mass of fish gelatin hydrolyzate and starch to water is 7-8 g:50 mL.

[0042] Example 1: A method for preparing food 3D printing ink comprises the following steps: (1) Fresh Australian lungfish was selected, and the fish skin was taken and soaked in a 0.25 wt% citric acid solution for 12 hours, with the mass volume ratio of fish skin to citric acid solution being 1 g:4 mL; then the fish skin was washed with distilled water, vigorously stirred at 65 ° C for 7 hours with a volume ratio of distilled water to citric acid solution of 1:1, and then filtered with cotton cloth. The filtrate was dried in a vacuum evaporator at 60 ° C for 50 min to obtain fish glue.

[0043] (2) The pH value of the obtained fish gelatin was adjusted to 8.0 with sodium hydroxide solution, and the mixture was mixed with alkaline protease at a volume fraction of 2%. The mixture was then divided into two parts, one part was microwave-treated for 10 min, and the other part was microwave-treated for 20 min. The microwave power was 60 W and the temperature was 55 °C. After microwave treatment, the enzymes were inactivated at -20 °C for 5 min, and then centrifuged at 10,000 × g and 4 °C for 15 min. The supernatant was collected and freeze-dried to obtain fish gelatin hydrolysate.

[0044] The degree of hydrolysis (DH) of the obtained gelatin hydrolysate was determined as follows: 1.5 g of freeze-dried fish gelatin hydrolysate was dissolved in deionized water to a volume of 50 mL; the pH of the solution was adjusted to 7.0 with 0.1 mol / L sodium hydroxide, 10 mL of 38% (v / v) formaldehyde was added, and the solution was stored at room temperature (25°C) for 5 min; standard 0.1 mol / L sodium hydroxide was used for titration at pH 8.5, and the amount of free amino groups (FAGs) was calculated based on the consumed volume; the total nitrogen (TN) in the sample was determined by the Kjeldahl method according to standard procedures. The results showed that the DH of the fish gelatin hydrolysate obtained by microwave treatment for 10 min was 65.37%; the DH of the fish gelatin hydrolysate obtained by microwave treatment for 20 min was 74.53%.

[0045] The microstructure of fish glue before and after microwave treatment was observed by SEM. Figure 1 The surface of untreated fish glue shows an uneven, mountain-like topology ( Figure 1 a in the figure); After 10 min of microwave treatment, the uneven surface became flat with a few indentations and holes ( Figure 1 b in the figure); after 20 min of microwave treatment, the number of such features increased ( Figure 1 c) in the above example.

[0046] (3) Dissolve fish gelatin hydrolyzate and starch in water at a mass ratio of 40:60, and allow to stand at room temperature to form a gel to obtain the food 3D printing ink, as shown in the figure. Figure 2 As shown in c, the SEM image is as Figure 3 As shown in c; in the fish gelatin hydrolysate, the mass ratio of the fish gelatin hydrolysate obtained by microwave treatment for 10 min to the fish gelatin hydrolysate obtained by microwave treatment for 20 min is 1:5; the volume ratio of the total mass of the fish gelatin hydrolysate and starch to water is 7.5 g:50 mL.

[0047] Example 2: A method for preparing food 3D printing ink comprises the following steps: (1) Fresh Australian lungfish was selected, and the fish skin was taken and soaked in a 0.25 wt% citric acid solution for 12 hours, with the mass volume ratio of fish skin to citric acid solution being 1 g:4 mL; then washed with distilled water, vigorously stirred at 65°C with a volume ratio of distilled water to citric acid solution of 1:1 for 7 hours, and then filtered with cotton cloth. The filtrate was dried in a vacuum evaporator at 60°C for 50 minutes to obtain fish glue; (2) The pH value of the obtained fish gelatin was adjusted to 8.0 with sodium hydroxide solution, and the mixture was mixed with alkaline protease at a volume fraction of 2%. The mixture was then divided into two parts, one part was microwave-treated for 10 min, and the other part was microwave-treated for 20 min. The microwave power was 60 W and the temperature was 55 °C. After microwave treatment, the enzyme was inactivated at -20 °C for 5 min, and then centrifuged at 10,000 × g and 4 °C for 15 min. The supernatant was collected and freeze-dried to obtain fish gelatin hydrolyzate. (3) Dissolve fish gelatin hydrolyzate and starch in water at a mass ratio of 60:40 and allow to stand at room temperature to form a gel to obtain the food 3D printing ink, as shown in the figure. Figure 2 As shown in d, the SEM image Figure 3 As shown in d; in the fish gelatin hydrolysate, the mass ratio of the fish gelatin hydrolysate obtained by microwave treatment for 10 min to the fish gelatin hydrolysate obtained by microwave treatment for 20 min is 1:5; the volume ratio of the total mass of fish gelatin hydrolysate and starch to water is 7.5 g:50 mL.

[0048] Example 3: A method for preparing food 3D printing ink comprises the following steps: (1) Fresh Australian lungfish was selected, and the fish skin was taken and soaked in a 0.25 wt% citric acid solution for 12 hours, with the mass volume ratio of fish skin to citric acid solution being 1 g:4 mL; then washed with distilled water, vigorously stirred at 65°C with a volume ratio of distilled water to citric acid solution of 1:1 for 7 hours, and then filtered with cotton cloth. The filtrate was dried in a vacuum evaporator at 60°C for 50 minutes to obtain fish glue; (2) The pH value of the obtained fish gelatin was adjusted to 8.0 with sodium hydroxide solution, and the mixture was mixed with alkaline protease at a volume fraction of 2%. The mixture was then divided into two parts, one part was microwave-treated for 10 min, and the other part was microwave-treated for 20 min. The microwave power was 60 W and the temperature was 55 °C. After microwave treatment, the enzyme was inactivated at -20 °C for 5 min, and then centrifuged at 10,000 × g and 4 °C for 15 min. The supernatant was collected and freeze-dried to obtain fish gelatin hydrolyzate. (3) Dissolving fish gelatin hydrolysate and starch in water at a mass ratio of 40:60 and allowing to stand at room temperature to form a gel to obtain the food 3D printing ink; in the fish gelatin hydrolysate, the mass ratio of the fish gelatin hydrolysate obtained by microwave treatment for 10 min to the fish gelatin hydrolysate obtained by microwave treatment for 20 min is 1:8; and the volume ratio of the total mass of the fish gelatin hydrolysate and starch to water is 7.5 g:50 mL.

[0049] Example 4: A method for preparing food 3D printing ink comprises the following steps: (1) Fresh Australian lungfish was selected, and the fish skin was taken and soaked in a 0.25 wt% citric acid solution for 12 hours, with the mass volume ratio of fish skin to citric acid solution being 1 g:4 mL; then washed with distilled water, vigorously stirred at 65°C with a volume ratio of distilled water to citric acid solution of 1:1 for 7 hours, and then filtered with cotton cloth. The filtrate was dried in a vacuum evaporator at 60°C for 50 minutes to obtain fish glue; (2) The pH value of the obtained fish gelatin was adjusted to 8.0 with sodium hydroxide solution, and the mixture was mixed with alkaline protease at a volume fraction of 2%. The mixture was then divided into two parts, one part was microwave-treated for 10 min, and the other part was microwave-treated for 20 min. The microwave power was 60 W and the temperature was 55 °C. After microwave treatment, the enzyme was inactivated at -20 °C for 5 min, and then centrifuged at 10,000 × g and 4 °C for 15 min. The supernatant was collected and freeze-dried to obtain fish gelatin hydrolyzate. (3) Dissolving fish gelatin hydrolysate and starch in water at a mass ratio of 40:60 and allowing to stand at room temperature to form a gel to obtain the food 3D printing ink; in the fish gelatin hydrolysate, the mass ratio of the fish gelatin hydrolysate obtained by microwave treatment for 10 min to the fish gelatin hydrolysate obtained by microwave treatment for 20 min is 1:10; and the volume ratio of the total mass of the fish gelatin hydrolysate and starch to water is 7.5 g:50 mL.

[0050] Example 5: A method for preparing food 3D printing ink comprises the following steps: (1) Fresh Australian lungfish was selected, and the fish skin was taken and soaked in a 0.25 wt% citric acid solution for 12 hours, with the mass volume ratio of fish skin to citric acid solution being 1 g:4 mL; then washed with distilled water, vigorously stirred at 65°C with a volume ratio of distilled water to citric acid solution of 1:1 for 7 hours, and then filtered with cotton cloth. The filtrate was dried in a vacuum evaporator at 60°C for 50 minutes to obtain fish glue; (2) The pH value of the obtained fish gelatin was adjusted to 8.0 with sodium hydroxide solution, and the mixture was mixed with alkaline protease at a volume fraction of 2%. The mixture was then divided into two parts, one part was microwave-treated for 15 min, and the other part was microwave-treated for 20 min. The microwave power was 50 W and the temperature was 55 °C. After microwave treatment, the enzyme was inactivated at -20 °C for 5 min, and then centrifuged at 10,000 × g and 4 °C for 15 min. The supernatant was collected and freeze-dried to obtain fish gelatin hydrolyzate. (3) Dissolving fish gelatin hydrolysate and starch in water at a mass ratio of 40:60 and allowing to stand at room temperature to form a gel to obtain the food 3D printing ink; in the fish gelatin hydrolysate, the mass ratio of the fish gelatin hydrolysate obtained by microwave treatment for 15 minutes to the fish gelatin hydrolysate obtained by microwave treatment for 20 minutes is 1:5; and the volume ratio of the total mass of the fish gelatin hydrolysate and starch to water is 7.5 g:50 mL.

[0051] Example 6: A method for preparing food 3D printing ink comprises the following steps: (1) Fresh Australian lungfish was selected, and the fish skin was taken and soaked in a 0.25 wt% citric acid solution for 12 hours, with the mass volume ratio of fish skin to citric acid solution being 1 g:4 mL; then washed with distilled water, vigorously stirred at 65°C with a volume ratio of distilled water to citric acid solution of 1:1 for 7 hours, and then filtered with cotton cloth. The filtrate was dried in a vacuum evaporator at 60°C for 50 minutes to obtain fish glue; (2) The pH value of the obtained fish gelatin was adjusted to 8.0 with sodium hydroxide solution, and the mixture was mixed with alkaline protease at a volume fraction of 2%. The mixture was then divided into two parts, one part was microwave-treated for 10 min, and the other part was microwave-treated for 25 min. The microwave power was 100 W and the temperature was 55 °C. After microwave treatment, the enzyme was inactivated at -20 °C for 5 min, and then centrifuged at 10,000 × g and 4 °C for 15 min. The supernatant was collected and freeze-dried to obtain fish gelatin hydrolyzate. (3) Dissolving fish gelatin hydrolysate and starch in water at a mass ratio of 40:60 and allowing to stand at room temperature to form a gel to obtain the food 3D printing ink; in the fish gelatin hydrolysate, the mass ratio of the fish gelatin hydrolysate obtained by microwave treatment for 10 min to the fish gelatin hydrolysate obtained by microwave treatment for 25 min is 1:5; and the volume ratio of the total mass of the fish gelatin hydrolysate and starch to water is 7.5 g:50 mL.

[0052] Comparative Example 1: A method for preparing food 3D printing ink comprises the following steps: The starch is dissolved in water and placed at room temperature to form a gel to obtain the food 3D printing ink; the physical picture is as follows Figure 2 As shown in a, the SEM image is as Figure 3 As shown in a; the volume ratio of starch mass to water is 7.5g:50mL.

[0053] Comparative Example 2: A method for preparing food 3D printing ink comprises the following steps: (1) Fresh Australian lungfish was selected, and the fish skin was taken and soaked in a 0.25 wt% citric acid solution for 12 hours, with the mass volume ratio of fish skin to citric acid solution being 1 g:4 mL; then washed with distilled water, vigorously stirred at 65°C with a volume ratio of distilled water to citric acid solution of 1:1 for 7 hours, and then filtered with cotton cloth. The filtrate was dried in a vacuum evaporator at 60°C for 50 minutes to obtain fish glue; (2) The pH value of the obtained fish gelatin was adjusted to 8.0 with sodium hydroxide solution, and the mixture was mixed with alkaline protease at a volume fraction of 2%. The mixture was then divided into two parts, one part was microwave-treated for 10 min, and the other part was microwave-treated for 20 min. The microwave power was 60 W and the temperature was 55 °C. After microwave treatment, the enzyme was inactivated at -20 °C for 5 min, and then centrifuged at 10,000 × g and 4 °C for 15 min. The supernatant was collected and freeze-dried to obtain fish gelatin hydrolyzate. (3) Dissolve fish gelatin hydrolyzate and starch in water at a mass ratio of 20:80, and allow to stand at room temperature to form a gel to obtain the food 3D printing ink, as shown in the figure. Figure 2 As shown in b, the SEM image is as Figure 3 As shown in b; in the fish gelatin hydrolysate, the mass ratio of the fish gelatin hydrolysate obtained by microwave treatment for 10 min to the fish gelatin hydrolysate obtained by microwave treatment for 20 min is 1:5; the volume ratio of the total mass of the fish gelatin hydrolysate and starch to water is 7.5 g:50 mL.

[0054] Comparative Example 3: A method for preparing food 3D printing ink comprises the following steps: (1) Fresh Australian lungfish was selected, and the fish skin was taken and soaked in a 0.25 wt% citric acid solution for 12 hours, with the mass volume ratio of fish skin to citric acid solution being 1 g:4 mL; then washed with distilled water, vigorously stirred at 65°C with a volume ratio of distilled water to citric acid solution of 1:1 for 7 hours, and then filtered with cotton cloth. The filtrate was dried in a vacuum evaporator at 60°C for 50 minutes to obtain fish glue; (2) The pH value of the obtained fish gelatin was adjusted to 8.0 with sodium hydroxide solution, and the mixture was mixed with alkaline protease at a volume fraction of 2%. The mixture was then divided into two parts, one part was microwave-treated for 10 min, and the other part was microwave-treated for 20 min. The microwave power was 60 W and the temperature was 55 °C. After microwave treatment, the enzyme was inactivated at -20 °C for 5 min, and then centrifuged at 10,000 × g and 4 °C for 15 min. The supernatant was collected and freeze-dried to obtain fish gelatin hydrolyzate. (3) Dissolve fish gelatin hydrolyzate and starch in water at a mass ratio of 80:20 and allow to stand at room temperature to form a gel to obtain the food 3D printing ink, as shown in the figure. Figure 2 As shown in e, the SEM image is as Figure 3 As shown in e; in the fish gelatin hydrolysate, the mass ratio of the fish gelatin hydrolysate obtained by microwave treatment for 10 min to the fish gelatin hydrolysate obtained by microwave treatment for 20 min is 1:5; the volume ratio of the total mass of fish gelatin hydrolysate and starch to water is 7.5g:50mL.

[0055] Comparative Example 4: A method for preparing food 3D printing ink comprises the following steps: (1) Fresh Australian lungfish was selected, and the fish skin was taken and soaked in a 0.25 wt% citric acid solution for 12 hours, with the mass volume ratio of fish skin to citric acid solution being 1 g:4 mL; then washed with distilled water, vigorously stirred at 65°C with a volume ratio of distilled water to citric acid solution of 1:1 for 7 hours, and then filtered with cotton cloth. The filtrate was dried in a vacuum evaporator at 60°C for 50 minutes to obtain fish glue; (2) The pH value of the obtained fish gelatin was adjusted to 8.0 with sodium hydroxide solution, and the mixture was mixed with alkaline protease at a volume fraction of 2%. The mixture was microwave-treated for 10 min at a microwave power of 60 W and a temperature of 55°C. After microwave treatment, the enzyme was inactivated at -20°C for 5 min, and then centrifuged at 10,000 × g and 4°C for 15 min. The supernatant was collected and freeze-dried to obtain fish gelatin hydrolyzate. (3) Dissolving fish gelatin hydrolysate and starch in water at a mass ratio of 40:60 and leaving the mixture at room temperature to form a gel to obtain the food 3D printing ink; the volume ratio of the total mass of the fish gelatin hydrolysate and starch to water is 7.5 g:50 mL.

[0056] Comparative Example 5: A method for preparing food 3D printing ink comprises the following steps: (1) Fresh Australian lungfish was selected, and the fish skin was taken and soaked in a 0.25 wt% citric acid solution for 12 hours, with the mass volume ratio of fish skin to citric acid solution being 1 g:4 mL; then washed with distilled water, vigorously stirred at 65°C with a volume ratio of distilled water to citric acid solution of 1:1 for 7 hours, and then filtered with cotton cloth. The filtrate was dried in a vacuum evaporator at 60°C for 50 minutes to obtain fish glue; (2) The pH value of the obtained fish gelatin was adjusted to 8.0 with sodium hydroxide solution, and the mixture was mixed with alkaline protease at a volume fraction of 2%. The mixture was microwave-treated for 20 min at a microwave power of 60 W and a temperature of 55°C. After microwave treatment, the enzyme was inactivated at -20°C for 5 min, and then centrifuged at 10,000 × g and 4°C for 15 min. The supernatant was collected and freeze-dried to obtain fish gelatin hydrolyzate. (3) Dissolving fish gelatin hydrolysate and starch in water at a mass ratio of 40:60 and leaving the mixture at room temperature to form a gel to obtain the food 3D printing ink; the volume ratio of the total mass of the fish gelatin hydrolysate and starch to water is 7.5 g:50 mL.

[0057] from Figure 3 As can be seen from the figure, in the 3D printing ink made of pure starch in Comparative Example 1, the gel forms an irregular network containing large and uneven gaps ( Figure 3 In contrast, the addition of 20% fish gelatin hydrolysate in Comparative Example 2 formed a tighter and more regular network ( Figure 3 (b), the density of the network increases with the increase of the percentage of fish gelatin hydrolysate added ( Figure 3 In the SEM image of the gel made from 80% fish gelatin hydrolysate in Comparative Example 3, no gaps in the network could be detected ( Figure 3 e in the above example).

[0058] The viscosity of the 3D printing ink obtained in the above examples and comparative examples was tested, and the results were as follows: Figure 4 As shown in . Figure 4 It can be seen that when too much (Comparative Example 3) or too little (Comparative Examples 1 and 2) fish gelatin hydrolysate is added, the viscosity of the 3D printing ink will decrease.

[0059] The relationship between the storage modulus and loss modulus of the 3D printing inks obtained in Example 1 and Comparative Examples 4 and 5 and the angular frequency was tested, and the results are as follows: Figure 5 and Figure 6 As shown in . The storage modulus is related to the elastic behavior of the material. It measures the ability of the material to store elastic energy and return it when the applied stress is removed; a higher storage modulus indicates that the material can withstand deformation and stress without significant permanent deformation; this is beneficial for maintaining the shape fidelity of the printed layer; a high storage modulus not only helps prevent excessive deformation or sagging of the printed structure during printing, but also allows for faster printing speeds because the material can quickly recover its shape after extraction. 3D printing materials with low storage modulus will result in poor layer adhesion. The loss modulus is related to the viscous behavior of the material. For 3D printing inks, a moderate loss modulus is ideal. It provides a certain degree of viscosity during printing, which helps achieve better layer adhesion and smooth deposition of the ink, helping to improve overall printing quality; but 3D printing inks with too high a loss modulus are too viscous, making them difficult to extrude through the 3D printer nozzle. The ideal 3D printing ink should have a balanced combination of high storage modulus and moderate loss modulus to facilitate layer-by-layer printing. From Figure 5 and Figure 6It can be seen that the amount of fish gelatin hydrolyzate with different hydrolysis degrees in Example 1 is within the scope of the present invention, and the prepared 3D printing ink has the best balance of these parameters; while in Comparative Example 4, the fish gelatin hydrolyzate treated with microwaves for only 10 minutes has a small storage modulus and loss modulus; in Comparative Example 5, the fish gelatin hydrolyzate treated with microwaves for only 20 minutes has a small storage modulus, which is not conducive to improving the 3D printing accuracy.

[0060] In order to verify the above conclusions, the present invention uses the 3D printing ink prepared in the above comparative examples and embodiments to print 2D and 3D shapes, such as Figures 7 to 9 As shown in . It can be seen that the 3D printing ink with a balance of high storage modulus and medium loss modulus in Example 1 shows good printing accuracy, while the 3D printing inks in Comparative Examples 4 and 5 cannot obtain printed images with good accuracy.

[0061] The texture analysis of the printed 3D product is shown in Table 1.

[0062] Table 1: Texture analysis results

[0063] As can be seen from Table 1, the food printed with the 3D printing ink prepared by the method of the present invention in the examples has better texture characteristics than the food printed with the 3D printing ink in the comparative examples.

Claims

1. A method for preparing food 3D printing ink, characterized in that: The steps include: (1) soaking fish skin in a citric acid solution, washing it with water, stirring it, filtering it, and drying it to obtain fish glue; (2) adjusting the pH value of the obtained fish gelatin to 7.5-8.5, mixing with alkaline enzyme, and then dividing into two parts, one part is microwave-treated for 10-15 min, and the other part is microwave-treated for 20-25 min, and the microwave power during the treatment is 50-100 W; after microwave treatment, the enzymes are inactivated respectively, and then the supernatant is taken after centrifugation, and freeze-dried to obtain fish gelatin hydrolyzate; (3) Dissolving fish gelatin hydrolysate and starch in water at a mass ratio of 40:60 to 60:40, and leaving at room temperature to form a gel to obtain the food 3D printing ink; in the fish gelatin hydrolysate, the mass ratio of the fish gelatin hydrolysate obtained by microwave treatment for 10 to 15 minutes to the fish gelatin hydrolysate obtained by microwave treatment for 20 to 25 minutes is 1:5 to 10.

2. The method for preparing the food 3D printing ink according to claim 1, characterized in that: The fish skin described in step (1) comes from lungfish.

3. The method for preparing food 3D printing ink according to claim 1, characterized in that: The mass concentration of the citric acid solution in step (1) is 0.2-0.3%, the mass volume ratio of fish skin to citric acid solution is 1 g:3-5 mL, and the immersion time of fish skin in the citric acid solution is 12-24 h.

4. The method for preparing the food 3D printing ink according to claim 1 or 3, characterized in that: The stirring temperature in step (1) is 60-70° C., and the stirring time is 6-8 h.

5. The method for preparing food 3D printing ink according to claim 1, characterized in that: The drying temperature in step (1) is 55-65°C and the drying time is 40-60 minutes.

6. The method for preparing food 3D printing ink according to claim 1, characterized in that: The alkaline enzyme described in step (2) is alkaline protease; the volume fraction of the added alkaline enzyme is 1-3%.

7. The method for preparing food 3D printing ink according to claim 1, characterized in that: The temperature during the microwave treatment in step (2) is 50-60°C.

8. The method for preparing the food 3D printing ink according to claim 1 or 6, characterized in that: In step (2), the temperature for enzyme inactivation is -20 to -25°C, and the time for enzyme inactivation is 5 to 10 min; the temperature during centrifugation is 0 to 4°C, the centrifugal force is 9000 to 11000×g, and the time is 10 to 20 min.

9. The method for preparing food 3D printing ink according to claim 1, characterized in that: In step (3), the volume ratio of the total mass of fish gelatin hydrolysate and starch to water is 7-8 g:50 mL.

10. A food 3D printing ink, characterized in that: It is prepared using the preparation method described in any one of claims 1 to 9.

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