Method for improving spontaneous discoloration rate of starch gel 4D printing

Abstract

The invention belongs to the technical field of food 4D printing, and particularly relates to a method for improving the spontaneous discoloration rate of starch gel 4D printing. The method for increasing the starch gel 4D printing spontaneous discoloration rate comprises the following steps that two starch base materials are sufficiently mixed, homogenized, gelatinized, cooled, gelatinized, charged and degassed, a double-layer structure model is drawn, printing parameters are set, double-nozzle 3D printing is conducted, printed cubic starch gel is subjected to microwave-hot air combined thermal induction, and the starch gel 4D printing spontaneous discoloration rate is increased. And the color is rapidly and spontaneously changed and homogenized. The method can improve the spontaneous discoloration rate of the 4D starch gel, improves the color uniformity of the product, and realizes personalized, functional and diversified customization of printed food.

Description

Technical Field

[0001] The invention belongs to the technical field of food 4D printing, and in particular relates to a method for improving the spontaneous color change rate of starch gel 4D printing. Background Art

[0002] 3D printing technology, also known as additive manufacturing technology, is a technology that uses computer slicing and layer-by-layer deposition of printing materials to build a preset three-dimensional entity based on a three-dimensional model. Compared with the traditional "subtractive manufacturing" method of producing three-dimensional products, 3D printing technology can produce more complex and sophisticated products through computer modeling, which can greatly reduce production time and cost. Food 3D printing technology combines 3D printing with food manufacturing to build complex structures, which can promote the sustainable development of food production, simplify the supply chain, and reduce resource waste. As an extension of 3D printing technology, food 4D printing can enable 3D printed products to respond to external stimuli and change their properties or functions over time, making the products diversified. However, the development of food 4D printing technology is still in its early stages, and the materials suitable for food 4D printing are very scarce and cannot meet the needs of consumers.

[0003] Starch is one of the staple foods in people's daily diet. It has the advantages of wide sources, economical and practical, good biocompatibility, etc., and is widely used in the field of food processing. Purple sweet potato (Ipomoea batatas L.Lam) is a starchy fruit and vegetable with rheological and gel properties, rich in anthocyanins, and can change color under different pH conditions. It is one of the key materials for 4D printed food. However, as a ready-to-eat product, the color change time of 4D printed food is relatively long, and the printing accuracy and stability of the entire system are not satisfactory. Therefore, preparing a printing substrate with good printing accuracy and self-supporting ability, and realizing the rapid spontaneous color change of 4D printed food is the focus of the present invention.

[0004] Zhang Min et al. (2020) disclosed a method for 4D printing artistic cold dishes by using microwave-induced spontaneous deformation (CN111543664A), which belongs to the field of new food processing. The invention first mixes fructose syrup, water, potato flour, potato starch, and food colloid evenly, then homogenizes, cooks, cools, and loads, and then performs 3D printing on food-grade PA / PE pad paper according to the selected 3D printing model and parameters, and appropriately cuts to obtain a double-layer structure of mashed potato / paper. Subsequently, the printed sample is subjected to microwave induction, and the sample will spontaneously bend and deform perpendicular to the printing path, and the material can be printed into different two-dimensional shapes into a three-dimensional spatial structure, realizing the diversification, personalization, and automated production of products. The invention mainly involves adjusting the printing material model and microwave parameters to realize the transformation of a two-dimensional shape into a three-dimensional spatial structure, while the present invention mainly involves the spontaneous discoloration of printed food.

[0005] Zhang Min et al. (2021) disclosed a method for realizing 4D printing of colored jelly by spontaneous color change of blueberry anthocyanins (CN110122813A), which involves food processing technology and belongs to the field of food processing technology. The invention first carries out the process of raw material mixing, blending, homogenization, gelation, cooling, loading, and degassing to prepare a gel color-carrying layer containing anthocyanins and a gel color-controlling layer with different pH values, and then uses a dual-nozzle printer to perform layer-by-layer alternating printing of multi-material color-carrying layers and color-controlling layers according to the established 3D printing model. The food printed by the invention has variable color and richer visual effects, and can realize personalized and diversified production of products. The invention mainly involves adjusting the pH value of the color-controlling layer of the printing material to realize the spontaneous color change of 3D printed food, while the present invention mainly involves increasing the spontaneous color change rate of 3D printed food.

[0006] Liu Yang et al. (2021) disclosed a method for preparing anthocyanin spontaneous color-changing coffee latte art and its 4D printing (CN115886109A), in which anthocyanin, flavoring agent, antioxidant, water, emulsifier, thickener, edible acidic and alkaline reagents are mixed, emulsified, thickened, and the pH is adjusted in sequence to obtain a 3D inkjet printing ink with bright and stable color, good taste, suitable viscosity, and good fluidity. Then, it is applied to the 3D self-service printing production of coffee latte art, and the color change reaction of the anthocyanin component and the coffee liquid occurs during the contact period, thereby achieving the 4D printing color-changing coffee latte art effect. The invention can add a unique taste and health benefits to coffee, and can also increase the fun and entertainment of eating. The invention mainly relates to a 3D inkjet printing ink containing anthocyanin, while the present invention mainly relates to an extruded 3D printing starch gel with spontaneous color-changing properties.

[0007] Shi Aimin et al. (2023) disclosed a preparation method and application of an O / W high internal phase Pickering emulsion for 3D / 4D printing (CN117898419A), adding polysaccharides to a plant protein solution to prepare a composite microgel particle dispersion, dissolving curcumin in an oil phase to prepare a dispersion, dissolving sodium bicarbonate in a composite microgel particle dispersion to prepare a continuous phase, and slowly adding the dispersed phase to the continuous phase to obtain an O / W high internal phase Pickering emulsion. The invention adjusts the concentration of the composite microgel particles so that the Pickering emulsion has excellent stability, rheological properties, and 3D printing characteristics, and can realize the preparation of 4D printed food. The invention mainly relates to an O / W high internal phase Pickering emulsion containing curcumin for 3D / 4D printing, while the present invention mainly relates to a starch gel that improves the spontaneous color change rate of 4D printing. Summary of the invention

[0008] In view of this, the present invention aims at the problem that the 4D printing food in the prior art has a slow color change rate and poor color uniformity, resulting in a lack of application scenarios for food 4D printing technology, and provides a method for improving the spontaneous color change rate of starch gel 4D printing. This method not only has the advantages of being natural and environmentally friendly, and can fully broaden the utilization of plant resources, but also has the potential for personalized customized food with nutritional enhancement, health benefits, fun and entertainment. The obtained 4D printed food is rich in nutrition, has a distinctive flavor and dynamic visual effects, promotes the diversified development of the fruit and vegetable processing industry chain, and develops 4D printed food that meets the appearance, taste, and health requirements.

[0009] In order to achieve the above object, the object of the present invention is to provide a method for improving the spontaneous color change rate of starch gel 4D printing, using the following technical scheme:

[0010] A method for improving the spontaneous color change rate of starch gel 4D printing, using purple sweet potato gel containing anthocyanins and starch gels with different pH values ​​as base materials, preparing a three-dimensional double-layer structure through a dual-nozzle printer, and using a microwave-hot air combined thermal induction method to achieve rapid spontaneous color change of 4D printed products.

[0011] Furthermore, the method for improving the spontaneous color change rate of starch gel 4D printing comprises the following steps:

[0012] (1) mixing purple sweet potato powder, hydrophilic colloid, and distilled water in proportion, homogenizing at high speed, sealing with plastic wrap, heating in a water bath for 20-30 min until completely gelatinized, and cooling in an ice bath to room temperature to obtain purple sweet potato gel;

[0013] (2) starch, hydrophilic colloid, xylitol, and buffer solution are fully mixed according to a certain proportion, homogenized at a high speed, sealed with plastic wrap, heated in a water bath for 20-30 min until completely gelatinized, and cooled in an ice bath to room temperature to obtain starch gels of different pH values;

[0014] (3) respectively loading the purple sweet potato gel obtained in step (1) and the starch gels of different pH values ​​obtained in step (2) into a double-nozzle printing cylinder and performing vacuum degassing;

[0015] (4) Using computer software to draw the cylindrical double-layer structure, set parameters, and perform 3D printing;

[0016] (5) The printed cubic starch gel is placed in a microwave-hot air combined dryer, and heat-induced rapid formation of a spontaneously discolored and uniformly colored 4D printed starch gel.

[0017] Furthermore, the hydrophilic colloid in steps (1) and (2) is one or more of guar gum, locust bean gum, xanthan gum, and carrageenan, and the starch is one or more of wheat starch, potato starch, corn starch, and yam starch.

[0018] Furthermore, in the steps (1) and (2), the high-speed homogenization is carried out at 6000-8000 rpm for 3-5 min, and the water bath heating temperature is 85-95° C.

[0019] Furthermore, in terms of mass percentage, in step (1), the purple sweet potato flour is 14-18%, and the hydrophilic colloid is 1.0%-1.6%; in step (2), the starch is 12-16%, the hydrophilic colloid is 1.0%-1.6%, and the xylitol is 4-6%.

[0020] Furthermore, the buffer solution in step (2) is a combination of one or more of citric acid, disodium hydrogen phosphate, sodium carbonate, and sodium bicarbonate, and the pH values ​​are 3, 5, 7, 9, and 11, respectively.

[0021] Furthermore, in step (3), the degassing is performed at a vacuum degree of 0.02-0.05 MPa for 20-30 seconds.

[0022] Furthermore, in the step (4), the double-layer structure is a purple potato gel in the lower layer and a starch gel in the upper layer, and both layers are 20 mm×6 mm (diameter×height) cylinders; the filling density is 100%, the printing speed is 15-20 mm / s, the printing temperature is 25°C, the nozzle diameter is 0.84 mm, and the relative positions of the upper nozzle and the lower nozzle are set to X=67.0 mm, Y=1.0 mm.

[0023] Furthermore, in step (5), the microwave power is 4-6 W / g, the hot air temperature is 45-50° C., and the thermal induction time is 2-3 min.

[0024] Furthermore, the 4D printed starch gel has an accuracy of greater than 95%, and during thermal induction, the printed gel will quickly change from white to red, purple, blue, and green according to different pH values, with a color uniformity of greater than 80%.

[0025] Compared with the prior art, the present invention uses purple sweet potato gel as anthocyanin carrier and starch gel as different pH carriers, and utilizes the principle that the structural change of anthocyanin under different pH conditions leads to different color development, thereby realizing the 4D printing spontaneous color change of starch gel, enriching the visual dynamic effect and entertainment of the product, and improving the fun and intelligence of the product. In addition, the present invention promotes the rapid pH migration and uniform water distribution between starch gel and purple sweet potato gel through the microwave-hot air combined heat induction method, improves the spontaneous color change rate of 4D printed starch gel and the color uniformity of the product, and the physiological function of anthocyanin provides nutritional and health effects for printed products, which greatly meets consumers' personalized, functional and diversified customization needs for food. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0027] Figure 1 This is an example diagram of the product of the present invention, wherein, from left to right, they are after printing, after color change at pH 3, after color change at pH 5, after color change at pH 7, after color change at pH 9, and after color change at pH 11. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] The word "embodiment" used here as an "exemplary" does not necessarily mean that any embodiment described is superior to or better than other embodiments. Unless otherwise specified, the performance index tests in the embodiments of this application are performed using conventional test methods in the art. It should be understood that the terms described in this application are only used to describe specific implementation methods and are not used to limit the content disclosed in this application.

[0030] Unless otherwise specified, the technical and scientific terms used in this document have the same meanings as commonly understood by ordinary technicians in the technical field to which this application belongs; other experimental methods and technical means not specifically specified in this application refer to experimental methods and technical means commonly used by ordinary technicians in this field.

[0031] In order to better illustrate the content of the present application, numerous specific details are provided in the specific examples below. It should be understood by those skilled in the art that the present application can also be implemented without certain specific details. In the embodiments, some methods, means, instruments, equipment, etc. well known to those skilled in the art are not described in detail in order to highlight the main purpose of the present application.

[0032] Under the premise of no conflict, the technical features disclosed in the embodiments of the present application can be combined arbitrarily, and the resulting technical solutions belong to the contents disclosed in the embodiments of the present application.

[0033] The present invention provides a method for improving the spontaneous color change rate of starch gel 4D printing, which belongs to the technical field of food 4D printing. The method for improving the spontaneous color change rate of starch gel 4D printing according to the present invention comprises the following steps: respectively fully mixing, homogenizing, gelatinizing, cooling, gelatinizing, loading, degassing, drawing a double-layer structure model, setting printing parameters, and double-nozzle 3D printing of two starch base materials, and subjecting the printed cubic starch gel to microwave-hot air combined thermal induction to make its color change rapidly and spontaneously and homogenize. The present invention can improve the spontaneous color change rate of 4D starch gel, while improving the color uniformity of the product, and realize the personalization, functionalization and diversified customization of printed food.

[0034] In order to better understand the present invention, the present invention is further specifically described below through the following examples, but it should not be understood as a limitation of the present invention. Some non-essential improvements and adjustments made by technicians in this field based on the above invention content are also considered to fall within the protection scope of the present invention.

[0035] Example 1

[0036] Purple sweet potato powder and guar gum are dispersed in water in proportion, and the purple sweet potato powder is added in an amount of 16% by mass, and the guar gum is added in an amount of 1.2%. The mixture is homogenized at 6000 rpm for 5 minutes to fully mix the mixture to prevent agglomeration, and the mixture is placed in a water bath at 85°C for 30 minutes, sealed with a plastic wrap during the period to prevent water loss, and cooled to room temperature in an ice bath to form a purple sweet potato gel. A buffer solution with pH values ​​of 3 and 5 is prepared using citric acid and sodium dihydrogen phosphate, and wheat starch and xanthan gum are dispersed in the buffer solution in proportion, and the wheat starch is added in an amount of 14% by mass, the guar gum is added in an amount of 1.4%, and the xylitol is added in an amount of 4%. The mixture is homogenized at 8000 rpm for 5 minutes to fully mix the mixture to prevent agglomeration, and the mixture is placed in a water bath at 90°C for 30 minutes, sealed with a plastic wrap during the period to prevent water loss, and cooled to room temperature in an ice bath to form a starch gel with pH values ​​of 3 and 5, respectively. Purple potato gel and acid starch gel were loaded into the upper nozzle and lower nozzle barrel respectively, and the vacuum was 0.02-0.05MPa for degassing for 30s, and the bubbles in the barrel were removed. A cylindrical model of 20mm×6mm (diameter×height) was drawn, and the printing speed was set to 15mm / s, the printing temperature was 25°C, the nozzle diameter was 0.84mm, and the relative positions of the upper nozzle and the lower nozzle were set to X=67.0mm, Y=1.0mm, and the printing accuracy was greater than 95%. After printing, the sample was placed in a microwave-hot air combined dryer, and the microwave power was set to 4W / g, the hot air temperature was 45°C, and the thermal induction time was 2min. The printed starch gel double-layer structure was uniformly red (C*=6.86, h°=343.72) and purple (C*=4.61, h°=322.54), and the color uniformity was greater than 80%.

[0037] Example 2

[0038] Purple sweet potato powder and guar gum are dispersed in water in proportion, and the purple sweet potato powder is added in an amount of 16% by mass, and the guar gum is added in an amount of 1.2%. The mixture is homogenized at 6000 rpm for 5 minutes to fully mix the mixture to prevent agglomeration, and the mixture is placed in a water bath at 85°C for 30 minutes, sealed with a plastic wrap during the period to prevent water loss, and cooled to room temperature in an ice bath to form a purple sweet potato gel. A buffer solution with pH values ​​of 9 and 11 is prepared using sodium carbonate and sodium bicarbonate, and wheat starch and xanthan gum are dispersed in the buffer solution in proportion, and the wheat starch is added in an amount of 14% by mass, the guar gum is added in an amount of 1.4%, and the xylitol is added in an amount of 4%. The mixture is homogenized at 8000 rpm for 5 minutes to fully mix the mixture to prevent agglomeration, and the mixture is placed in a water bath at 90°C for 30 minutes, sealed with a plastic wrap during the period to prevent water loss, and cooled to room temperature in an ice bath to form a starch gel with pH values ​​of 9 and 11, respectively. Purple potato gel and acid starch gel were loaded into the upper nozzle and lower nozzle barrel respectively, and the vacuum was 0.02-0.05MPa for degassing for 30s, and the bubbles in the barrel were removed. A cylindrical model of 20mm×6mm (diameter×height) was drawn, and the printing speed was set to 15mm / s, the printing temperature was 25°C, the nozzle diameter was 0.84mm, and the relative positions of the upper nozzle and the lower nozzle were set to X=67.0mm, Y=1.0mm, and the printing accuracy was greater than 95%. After printing, the sample was placed in a microwave-hot air combined dryer, and the microwave power was set to 4W / g, the hot air temperature was 50°C, and the thermal induction time was 2min. The printed starch gel double-layer structure showed uniform blue (C*=1.74, h°=192.17) and green (C*=2.59, h°=163.72), and the color uniformity was greater than 80%.

[0039] In order to further demonstrate the beneficial effects of the present invention and to better understand the present invention, the properties and application performance of the method for improving the spontaneous color change rate of starch gel 4D printing disclosed in the present invention are further illustrated by the following comparative examples, but it is not to be understood as a limitation of the present invention. The properties of the method obtained by other measurement experiments performed by technicians in this field according to the above-mentioned invention content and the applications based on the above-mentioned properties are also deemed to fall within the scope of protection of the present invention.

[0040] Comparative Example 1

[0041] Purple sweet potato powder and guar gum are dispersed in water in proportion, and the purple sweet potato powder is added in an amount of 16% by mass, and the guar gum is added in an amount of 1.2%. The mixture is homogenized at 6000 rpm for 5 minutes to fully mix the mixture to prevent agglomeration, and the mixture is placed in a water bath at 85°C for 30 minutes, sealed with a plastic wrap during the period to prevent water loss, and cooled to room temperature in an ice bath to form a purple sweet potato gel. A buffer solution with a pH of 7 is prepared using sodium carbonate and sodium bicarbonate, and wheat starch and xanthan gum are dispersed in the buffer solution in proportion, and the wheat starch is added in an amount of 14% by mass, the guar gum is added in an amount of 1.4%, and the xylitol is added in an amount of 4%. The mixture is homogenized at 8000 rpm for 5 minutes to fully mix the mixture to prevent agglomeration, and the mixture is placed in a water bath at 90°C for 30 minutes, sealed with a plastic wrap during the period to prevent water loss, and cooled to room temperature in an ice bath to form starch gels with pH values ​​of 9 and 11, respectively. The purple potato gel and acid starch gel were loaded into the upper nozzle and the lower nozzle barrel respectively, and the vacuum was 0.02-0.05MPa for degassing for 30s to remove the bubbles in the barrel, and a 20mm×6mm (diameter×height) cylindrical model was drawn. The printing speed was set to 15mm / s, the printing temperature was 25°C, the nozzle diameter was 0.84mm, and the relative position of the upper nozzle and the lower nozzle was set to X=67.0mm, Y=1.0mm, and the printing accuracy was greater than 95%. After the printing was completed, after being placed at room temperature for 3h, the printed starch gel double-layer structure showed a more uniform purple-blue color.

[0042] Comparative Example 2

[0043] Purple sweet potato powder and guar gum are dispersed in water in proportion, and the purple sweet potato powder is added in an amount of 16% by mass, and the guar gum is added in an amount of 1.2%. The mixture is homogenized at 6000 rpm for 5 minutes to fully mix the mixture to prevent agglomeration, and the mixture is placed in a water bath at 85°C for 30 minutes, sealed with a plastic wrap during the period to prevent water loss, and cooled to room temperature in an ice bath to form a purple sweet potato gel. A buffer solution with a pH of 7 is prepared using sodium carbonate and sodium bicarbonate, and wheat starch and xanthan gum are dispersed in the buffer solution in proportion, and the wheat starch is added in an amount of 14% by mass, the guar gum is added in an amount of 1.4%, and the xylitol is added in an amount of 4%. The mixture is homogenized at 8000 rpm for 5 minutes to fully mix the mixture to prevent agglomeration, and the mixture is placed in a water bath at 90°C for 30 minutes, sealed with a plastic wrap during the period to prevent water loss, and cooled to room temperature in an ice bath to form starch gels with pH values ​​of 9 and 11, respectively. The purple potato gel and acid starch gel were loaded into the upper nozzle and the lower nozzle barrel respectively, and the vacuum was 0.02-0.05MPa for degassing for 30s, and the bubbles in the barrel were removed. A cylindrical model of 20mm×6mm (diameter×height) was drawn, and the printing speed was set to 15mm / s, the printing temperature was 25°C, the nozzle diameter was 0.84mm, and the relative position of the upper nozzle and the lower nozzle was set to X=67.0mm, Y=1.0mm, and the printing accuracy was greater than 95%. The sample was placed in a hot air oven at 50°C and a thermal induction time of 30min. The printed starch gel double-layer structure showed a uniform purple-blue color (C*=2.76, h°=295.96), and the color uniformity was greater than 80%.

[0044] Therefore, the present invention adopts microwave-hot air combined thermal induction technology, which effectively improves the spontaneous color change rate of 4D printing compared with room temperature placement and hot air induction technology.

[0045] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for improving the spontaneous color change rate of starch gel 4D printing, characterized in that: Using purple sweet potato gel containing anthocyanins and starch gel with different pH values ​​as the base materials, a three-dimensional double-layer structure was prepared by a dual-nozzle printer, and a microwave-hot air combined thermal induction method was used to achieve rapid spontaneous color change of 4D printed products.

2. The method for improving the spontaneous discoloration rate of starch gel 4D printing according to claim 1, characterized in that: The steps include: (1) mixing purple sweet potato powder, hydrophilic colloid, and distilled water in proportion, homogenizing at high speed, sealing with plastic wrap, heating in a water bath for 20-30 min until completely gelatinized, and cooling in an ice bath to room temperature to obtain purple sweet potato gel; (2) starch, hydrophilic colloid, xylitol, and buffer solution are fully mixed according to a certain proportion, homogenized at a high speed, sealed with plastic wrap, heated in a water bath for 20-30 min until completely gelatinized, and cooled in an ice bath to room temperature to obtain starch gels of different pH values; (3) respectively loading the purple sweet potato gel obtained in step (1) and the starch gel of different pH values ​​obtained in step (2) into a double-nozzle printing cylinder and performing vacuum degassing; (4) Using computer software to draw the cylindrical double-layer structure, set parameters, and perform 3D printing; (5) The printed cubic starch gel is placed in a microwave-hot air combined dryer, and heat-induced rapid formation of a spontaneously discolored and uniformly colored 4D printed starch gel.

3. The method for improving the spontaneous discoloration rate of starch gel 4D printing according to claim 2, characterized in that, The hydrophilic colloid in steps (1) and (2) is one or more of guar gum, locust bean gum, xanthan gum, and carrageenan, and the starch is one or more of wheat starch, potato starch, corn starch, and yam starch.

4. The method for improving the spontaneous discoloration rate of starch gel 4D printing according to claim 2, characterized in that, In the steps (1) and (2), the high-speed homogenization is carried out at 6000-8000 rpm for 3-5 minutes, and the water bath heating temperature is 85-95°C.

5. The method for improving the spontaneous discoloration rate of starch gel 4D printing according to claim 2, characterized in that: In terms of mass percentage, in the step (1), the purple sweet potato flour is 14-18%, and the hydrophilic colloid is 1.0%-1.6%; in the step (2), the starch is 12-16%, the hydrophilic colloid is 1.0%-1.6%, and the xylitol is 4-6%.

6. The method for improving the spontaneous discoloration rate of starch gel 4D printing according to claim 2, characterized in that: The buffer solution in step (2) is a combination of one or more of citric acid, disodium hydrogen phosphate, sodium carbonate, and sodium bicarbonate, and the pH values ​​are 3, 5, 7, 9, and 11, respectively.

7. The method for improving the spontaneous discoloration rate of starch gel 4D printing according to claim 2, characterized in that: In the step (3), the vacuum degree is 0.02-0.05 MPa and degassing is performed for 20-30 seconds.

8. The method for improving the spontaneous discoloration rate of starch gel 4D printing according to claim 2, characterized in that: The double-layer structure in step (4) is that the purple sweet potato gel is in the lower layer and the starch gel is in the upper layer, and both layers are 20 mm×6 mm (diameter×height) cylinders; the filling density is 100%, the printing speed is 15-20 mm / s, the printing temperature is 25° C., the nozzle diameter is 0.84 mm, and the relative positions of the upper nozzle and the lower nozzle are set to X=67.0 mm, Y=1.0 mm.

9. The method for improving the spontaneous discoloration rate of starch gel 4D printing according to claim 2, characterized in that: In the step (5), the microwave power is 4-6 W / g, the hot air temperature is 45-50° C., and the thermal induction time is 2-3 min.

10. The method for improving the spontaneous discoloration rate of starch gel 4D printing according to claim 1, characterized in that: The accuracy of 4D printed starch gel is greater than 95%. During thermal induction, the printed gel will quickly change from white to red, purple, blue, and green according to different pH values, and the color uniformity is greater than 80%.

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