Preparation method of curcumin-loaded corn protein and konjac glucomannan composite gel jelly

Abstract

The invention discloses a method for preparing corn protein and konjac glucomannan composite gel jelly loaded with curcumin. The invention belongs to the technical field of food processing. The invention aims to provide a method for preparing the curcumin functional jelly by constructing a composite hydrogel system and taking the system as a matrix, and the curcumin functional jelly is good in water binding capacity, moderate in softness and elasticity and balanced in chewiness and palatability. The method has the advantages that the embedding rate of the prepared gel jelly is obviously superior to that of single or traditional composite gel, the curcumin activity is protected in multiple dimensions, the oxidation resistance of the jelly is enhanced, the water holding capacity is excellent, the problems that traditional jelly is prone to bleeding and deteriorated in texture are solved, the softness and elasticity are moderate, chewiness and palatability are balanced, peculiar smell is avoided, and the flavor bearing capacity is high; and the method has a wide application prospect in the field of functional food production and processing.

Description

Technical fields:

[0001] This invention belongs to the field of food processing technology, and specifically relates to a method for preparing a corn protein konjac glucomannan composite gel jelly loaded with curcumin. Background technology:

[0002] Curcumin, a natural polyphenolic compound derived from ginger plants, exhibits high application value in functional food and pharmaceutical fields due to its multiple biological activities, including anti-inflammatory, antioxidant, anti-tumor, and metabolic regulation. However, inherent defects of curcumin, such as high fat solubility, poor water solubility, low gastrointestinal stability, and bioavailability of less than 1%, severely limit its practical application in functional foods. Even when added to food matrices through simple physical mixing, the active ingredients are easily absorbed by the human body due to enzymatic hydrolysis, oxidation, and excretion during digestion, thus failing to fully exert their physiological functions.

[0003] As a popular snack food, jelly, with its soft and bouncy texture, ease of consumption, and good flavor carrying capacity, has become one of the ideal carriers for delivering functional ingredients. However, commercially available traditional jellies mostly use a single colloid (such as carrageenan or gelatin) as the gel matrix, which generally suffers from poor water retention: water separation easily occurs during storage, which not only damages the product's appearance and texture stability but also leads to moisture loss and hardening of the texture, reducing consumer acceptance. At the same time, traditional jelly matrices have a weak ability to encapsulate fat-soluble active ingredients (such as curcumin), and are prone to aggregation, sedimentation, or oxidative degradation of active ingredients, further limiting their functional upgrades.

[0004] Hydrogels possess controllable network structures, good biocompatibility, and environmental responsiveness. Based on this, current technologies primarily focus on developing jelly matrices with both high water retention and efficient active ingredient encapsulation and delivery performance through the preparation of hydrogels formed from natural polysaccharides and proteins. This has become a key direction for overcoming the current bottlenecks in functional jelly development. However, problems remain, such as poor curcumin encapsulation and instability of the hydrogel system. For example, pectin-sodium alginate composite hydrogels (CN120459018A) encapsulate curcumin. However, curcumin is highly sensitive to light, heat, oxygen, and the gastrointestinal environment. Furthermore, the pectin-sodium alginate gel's network structure suffers from a "loose and porous" defect, with its gel network primarily relying on hydrogen bonds between polysaccharide molecules and Ca2+. 2+The cross-linking process results in relatively large pores, which cannot effectively prevent the degradation of curcumin by external environmental factors. Furthermore, the oat protein-carrageenan composite gel system suffers from insufficient water retention due to the fact that carrageenan's water-holding capacity relies on hydrogen bonds between its molecular chains and water molecules. This binding force is weak, and small peptides generated from oat protein hydrolysis compete for water binding, leading to insufficient water-locking ability of the gel network (CN119157195A). Simultaneously, the cross-linked structure of the oat protein-carrageenan gel is susceptible to ionic strength, easily causing network shrinkage and water separation during storage. The jelly prepared from this gel, after 7 days of storage at 25°C, exhibits a water separation rate of 12%-18%, with a water retention rate below 75%.

[0005] Zea prolamin, a byproduct of corn deep processing, is a plant protein rich in hydrophobic amino acids. Its amino and carboxyl groups, among other active groups, can form aggregates with a unique "nano-indentation" structure through hydrogen bonding and hydrophobic interactions. This structure provides excellent encapsulation and protection for fat-soluble active ingredients (such as curcumin), effectively reducing their loss during processing and storage. Konjac glucomannan, on the other hand, is a water-soluble neutral polysaccharide extracted from konjac tubers. Numerous hydroxyl groups on its molecular chain can cross-link through hydrogen bonds to form a highly water-retaining three-dimensional network structure. Its water-holding capacity can reach tens of times its own weight, and it also exhibits good gelling and thickening properties, making it an ideal raw material for improving the water-holding capacity of food matrices.

[0006] Based on this, this study innovatively combines the encapsulation advantages of zein with the high water-holding capacity of konjac glucomannan to construct a composite hydrogel system, and uses this system as a matrix to prepare functional jelly encapsulated with curcumin. Simultaneously, to balance the nutritional value and sensory quality of the product, xylitol and citric acid were introduced for flavoring, and the texture and stability of the jelly were optimized by controlling the amount of each. This research aims to simultaneously address the dual problems of low curcumin bioavailability and poor water-holding capacity of traditional jellies through the synergistic effect of the composite gel network, providing a theoretical basis and technical support for the development of novel jelly products with high stability and high functionality, and also opening up new pathways for the efficient application of natural active ingredients in the food industry. Summary of the Invention:

[0007] In view of this, the problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a curcumin jelly with good taste, strong water retention, high nutritional value and high bioavailability, as well as its preparation method and application.

[0008] The technical solution of the present invention is as follows:

[0009] This invention provides a method for preparing a corn protein-konjac glucomannan composite gel jelly loaded with curcumin, comprising the following steps:

[0010] (1) Different masses of zein were dissolved in 25 mL of sodium hydroxide solution at 25 °C and stirred thoroughly for 0.5 h.

[0011] (2) Add different masses of curcumin to the solution obtained in step (1).

[0012] (3) Add different masses of xylitol to the mixture obtained in step (2) for flavoring.

[0013] (4) Add konjac glucomannan to the mixture obtained in step (3) and stir until homogeneous.

[0014] (5) Pour the mixture obtained in step (4) into a dry and clean mold, then heat it in a water bath for 80 minutes. After removing it, let it cool naturally to room temperature. Immerse the cooled sample in a certain concentration of citric acid for 12 hours to obtain a neutral composite gel. Next, rinse the composite gel with running distilled water for 5 minutes and then immerse it in distilled water for 6 hours to remove excess citric acid. Finally, store the composite gel in a refrigerator at 4°C.

[0015] Specifically, the amount of zein added in step (1) is 0 to 1.5 g.

[0016] Specifically, the sodium hydroxide solution in step (1) has a pH of 11 to 14.

[0017] Specifically, the amount of curcumin added in step (2) is 0.005 to 0.02 g.

[0018] Specifically, the amount of xylitol added in step (3) is 0-5g.

[0019] Specifically, the amount of konjac glucomannan added in step (4) is 0 to 1.5g.

[0020] Specifically, the water bath heating temperature in step (5) is 70-90°C.

[0021] Specifically, the concentration of citric acid in step (5) is 0-2%.

[0022] This invention provides a corn protein konjac glucomannan composite gel jelly loaded with curcumin, prepared by the above-mentioned method. The curcumin jelly has a high encapsulation rate and strong stability, providing a core guarantee for its antioxidant capacity. After being stored at 4°C in the dark for 30 days, the curcumin encapsulated in this gel retains 75%-85% of its activity. It has high water retention and strong resistance to water separation. The water retention rate of this composite gel is stable at 90%-95%. The jelly prepared from it shows no significant water separation (water separation rate <2%) after being stored at 25°C for 15 days, which is far lower than that of pectin-sodium alginate jelly (water separation rate 10%-15%) and gelatin jelly (water separation rate 8%-12%). It also has moderate softness and elasticity, balancing chewiness and palatability.

[0023] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0024] (1) The encapsulation rate is significantly better than that of single or traditional composite gels, which protects curcumin activity in multiple dimensions and enhances the antioxidant capacity of the jelly. The zein-konjac glucomannan composite hydrogel achieves efficient encapsulation and long-term protection of curcumin through a dual mechanism of "hydrophobic anchoring-hydrophilic cross-linking", laying the foundation for the antioxidant function of the jelly.

[0025] (2) Excellent water retention capacity, solving the pain points of traditional jelly such as easy water separation and deterioration of texture. Water retention is the core indicator of the sensory quality and storage stability of jelly. The zein-konjac glucomannan composite hydrogel, with the high water retention properties of konjac glucomannan and the cross-linking reinforcement effect of zein, constructs a highly water-locking and shrinkage-resistant gel network, which is significantly better than traditional jelly matrix.

[0026] (3) It has moderate softness and elasticity, a balance between chewiness and palatability, no off-flavor, and strong flavor carrying capacity, which enhances the sensory experience. Corn gliadin has a certain degree of elasticity and thermal stability, which can enhance the compressibility of the gel and prevent the jelly from being easily deformed and lacking chewiness due to its soft texture; konjac glucomannan gives the gel good extensibility and smoothness, which alleviates the roughness of single protein gel. Attached image description:

[0027] Figure 1 Figure showing the results of hardness determination for curcumin jelly prepared with different amounts of xylitol and citric acid;

[0028] Figure 2 Figure 1 shows the results of elasticity testing of curcumin jelly prepared with different amounts of xylitol and citric acid.

[0029] Figure 3 Figure 1 shows the results of a chewiness test for curcumin jelly prepared with different amounts of xylitol and citric acid.

[0030] Figure 4 Sensory evaluation results of curcumin jelly prepared with different amounts of xylitol and citric acid added;

[0031] Figure 5 Figure 1 shows the water-holding capacity of curcumin jelly prepared with different amounts of xylitol and citric acid.

[0032] Figure 6 Figure 1 shows the DPPH free radical scavenging activity of curcumin jelly prepared with different amounts of xylitol and citric acid. Detailed implementation method:

[0033] The present invention will be further described in detail below with reference to embodiments and accompanying drawings, but the implementation and protection of the present invention are not limited thereto.

[0034] Example 1

[0035] 0.83 g of zein was dissolved in 25 mL of sodium hydroxide solution (pH 12.5) at 25 °C and stirred thoroughly for 0.5 h. Then, 0.025 g of curcumin was added to the zein solution. After stirring evenly, 0.42 g of konjac glucomannan was added. The mixture was poured into a dry, clean mold and heated in a water bath for 80 min. After removal, it was allowed to cool naturally to room temperature. The cooled sample was then immersed in 0.6% citric acid for 12 h to obtain a neutral composite gel. The composite gel was then rinsed with running distilled water for 5 min and immersed in distilled water for 6 h to remove excess citric acid. Finally, the composite gel was stored in a refrigerator at 4 °C.

[0036] Example 2

[0037] 0.83 g of zein was dissolved in 25 mL of sodium hydroxide solution (pH 12.5) at 25 °C and stirred thoroughly for 0.5 h. Next, 0.025 g of curcumin and 0.75 g of xylitol were added to the zein solution, and after thorough mixing, 0.42 g of konjac glucomannan was added to the mixture. The mixture was poured into a dry, clean mold and heated in a water bath for 80 min. After removal, it was allowed to cool naturally to room temperature. The cooled sample was then immersed in 0.6% citric acid for 12 h to obtain a neutral composite gel. The composite gel was then rinsed with running distilled water for 5 min and immersed in distilled water for 6 h to remove excess citric acid. Finally, the composite gel was stored in a refrigerator at 4 °C.

[0038] Example 3

[0039] 0.83 g of zein was dissolved in 25 mL of sodium hydroxide solution (pH 12.5) at 25 °C and stirred thoroughly for 0.5 h. Next, 0.025 g of curcumin and 1.5 g of xylitol were added to the zein solution, and after thorough mixing, 0.42 g of konjac glucomannan was added to the mixture. The mixture was poured into a dry, clean mold and heated in a water bath for 80 min. After removal, it was allowed to cool naturally to room temperature. The cooled sample was then immersed in 0.6% citric acid for 12 h to obtain a neutral composite gel. The composite gel was then rinsed with running distilled water for 5 min and immersed in distilled water for 6 h to remove excess citric acid. Finally, the composite gel was stored in a refrigerator at 4 °C.

[0040] Example 4

[0041] 0.83 g of zein was dissolved in 25 mL of sodium hydroxide solution (pH 12.5) at 25 °C and stirred thoroughly for 0.5 h. Next, 0.025 g of curcumin and 2.25 g of xylitol were added to the zein solution, and after thorough mixing, 0.42 g of konjac glucomannan was added to the mixture. The mixture was poured into a dry, clean mold and heated in a water bath for 80 min. After removal, it was allowed to cool naturally to room temperature. The cooled sample was then immersed in 0.6% citric acid for 12 h to obtain a neutral composite gel. The composite gel was then rinsed with running distilled water for 5 min and immersed in distilled water for 6 h to remove excess citric acid. Finally, the composite gel was stored in a refrigerator at 4 °C.

[0042] Example 5

[0043] 0.83 g of zein was dissolved in 25 mL of sodium hydroxide solution (pH 12.5) at 25 °C and stirred thoroughly for 0.5 h. Next, 0.025 g of curcumin and 3 g of xylitol were added to the zein solution, and after thorough mixing, 0.42 g of konjac glucomannan was added to the mixture. The mixture was poured into a dry, clean mold and heated in a water bath for 80 min. After removal, it was allowed to cool naturally to room temperature. The cooled sample was then immersed in 0.6% citric acid for 12 h to obtain a neutral composite gel. The composite gel was then rinsed with running distilled water for 5 min and immersed in distilled water for 6 h to remove excess citric acid. Finally, the composite gel was stored in a refrigerator at 4 °C.

[0044] Example 6

[0045] 0.83 g of zein was dissolved in 25 mL of sodium hydroxide solution (pH 12.5) at 25 °C and stirred thoroughly for 0.5 h. Next, 0.025 g of curcumin and 1.5 g of xylitol were added to the zein solution, and after thorough mixing, 0.42 g of konjac glucomannan was added to the mixture. The mixture was poured into a dry, clean mold and heated in a water bath for 80 min. After removal, it was allowed to cool naturally to room temperature, and finally, the composite gel was stored in a refrigerator at 4 °C.

[0046] Example 7

[0047] 0.83 g of zein was dissolved in 25 mL of sodium hydroxide solution (pH 12.5) at 25 °C and stirred thoroughly for 0.5 h. Next, 0.025 g of curcumin and 3 g of xylitol were added to the zein solution, and after thorough mixing, 0.42 g of konjac glucomannan was added to the mixture. The mixture was poured into a dry, clean mold and heated in a water bath for 80 min. After removal, it was allowed to cool naturally to room temperature. The cooled sample was then immersed in 0.3% citric acid for 12 h to obtain a neutral composite gel. The composite gel was then rinsed with running distilled water for 5 min and immersed in distilled water for 6 h to remove excess citric acid. Finally, the composite gel was stored in a refrigerator at 4 °C.

[0048] Example 8

[0049] 0.83 g of zein was dissolved in 25 mL of sodium hydroxide solution (pH 12.5) at 25 °C and stirred thoroughly for 0.5 h. Next, 0.025 g of curcumin and 3 g of xylitol were added to the zein solution, and after thorough mixing, 0.42 g of konjac glucomannan was added to the mixture. The mixture was poured into a dry, clean mold and heated in a water bath for 80 min. After removal, it was allowed to cool naturally to room temperature. The cooled sample was then immersed in 0.7% citric acid for 12 h to obtain a neutral composite gel. The composite gel was then rinsed with running distilled water for 5 min and immersed in distilled water for 6 h to remove excess citric acid. Finally, the composite gel was stored in a refrigerator at 4 °C.

[0050] Example 9

[0051] 0.83 g of zein was dissolved in 25 mL of sodium hydroxide solution (pH 12.5) at 25 °C and stirred thoroughly for 0.5 h. Next, 0.025 g of curcumin and 3 g of xylitol were added to the zein solution, and after thorough mixing, 0.42 g of konjac glucomannan was added to the mixture. The mixture was poured into a dry, clean mold and heated in a water bath for 80 min. After removal, it was allowed to cool naturally to room temperature. The cooled sample was then immersed in 0.9% citric acid for 12 h to obtain a neutral composite gel. The composite gel was then rinsed with running distilled water for 5 min and immersed in distilled water for 6 h to remove excess citric acid. Finally, the composite gel was stored in a refrigerator at 4 °C.

[0052] Example 10

[0053] 0.83 g of zein was dissolved in 25 mL of sodium hydroxide solution (pH 12.5) at 25 °C and stirred thoroughly for 0.5 h. Next, 0.025 g of curcumin and 3 g of xylitol were added to the zein solution, and after thorough mixing, 0.42 g of konjac glucomannan was added to the mixture. The mixture was poured into a dry, clean mold and heated in a water bath for 80 min. After removal, it was allowed to cool naturally to room temperature. The cooled sample was then immersed in 1.2% citric acid for 12 h to obtain a neutral composite gel. The composite gel was then rinsed with running distilled water for 5 min and immersed in distilled water for 6 h to remove excess citric acid. Finally, the composite gel was stored in a refrigerator at 4 °C.

[0054] Comparative Example 1

[0055] 1 g of zein was dissolved in 25 mL of sodium hydroxide solution (pH 12.5) at 25 °C and stirred thoroughly for 0.5 h. Then, 0.025 g of curcumin and 3 g of xylitol were added to the zein solution, and after thorough mixing, 0.25 g of konjac glucomannan was added to the mixture. The mixture was poured into a dry, clean mold and heated in a water bath for 80 min. After removal, it was allowed to cool naturally to room temperature. The cooled sample was then immersed in 0.9% citric acid for 12 h to obtain a neutral composite gel. The composite gel was then rinsed with running distilled water for 5 min and immersed in distilled water for 6 h to remove excess citric acid. Finally, the composite gel was stored in a refrigerator at 4 °C.

[0056] Comparative Example 2

[0057] 0.42 g of zein was dissolved in 25 mL of sodium hydroxide solution (pH 12.5) at 25 °C and stirred thoroughly for 0.5 h. Next, 0.025 g of curcumin and 3 g of xylitol were added to the zein solution, and after thorough mixing, 0.83 g of konjac glucomannan was added to the mixture. The mixture was poured into a dry, clean mold and heated in a water bath for 80 min. After removal, it was allowed to cool naturally to room temperature. The cooled sample was then immersed in 0.9% citric acid for 12 h to obtain a neutral composite gel. The composite gel was then rinsed with running distilled water for 5 min and immersed in distilled water for 6 h to remove excess citric acid. Finally, the composite gel was stored in a refrigerator at 4 °C.

[0058] Comparative Example 3

[0059] 0.25 g of zein was dissolved in 25 mL of sodium hydroxide solution (pH 12.5) at 25 °C and stirred thoroughly for 0.5 h. Next, 0.025 g of curcumin and 3 g of xylitol were added to the zein solution, and after thorough mixing, 1 g of konjac glucomannan was added to the mixture. The mixture was poured into a dry, clean mold and heated in a water bath for 80 min. After removal, it was allowed to cool naturally to room temperature. The cooled sample was then immersed in 0.9% citric acid for 12 h to obtain a neutral composite gel. The composite gel was then rinsed with running distilled water for 5 min and immersed in distilled water for 6 h to remove excess citric acid. Finally, the composite gel was stored in a refrigerator at 4 °C.

[0060] Comparative Example 4

[0061] 0.83 g of zein was dissolved in 25 mL of sodium hydroxide solution (pH 11) at 25 °C and stirred thoroughly for 0.5 h. Next, 0.025 g of curcumin and 3 g of xylitol were added to the zein solution, and after thorough mixing, 0.42 g of konjac glucomannan was added to the mixture. The mixture was poured into a dry, clean mold and heated in a water bath for 80 min. After removal, it was allowed to cool naturally to room temperature. The cooled sample was then immersed in 0.9% citric acid for 12 h to obtain a neutral composite gel. The composite gel was then rinsed with running distilled water for 5 min and immersed in distilled water for 6 h to remove excess citric acid. Finally, the composite gel was stored in a refrigerator at 4 °C.

[0062] Comparative Example 5

[0063] 0.83 g of zein was dissolved in 25 mL of sodium hydroxide solution (pH 13) at 25 °C and stirred thoroughly for 0.5 h. Next, 0.025 g of curcumin and 3 g of xylitol were added to the zein solution, and after thorough mixing, 0.42 g of konjac glucomannan was added to the mixture. The mixture was poured into a dry, clean mold and heated in a water bath for 80 min. After removal, it was allowed to cool naturally to room temperature. The cooled sample was then immersed in 0.9% citric acid for 12 h to obtain a neutral composite gel. The composite gel was then rinsed with running distilled water for 5 min and immersed in distilled water for 6 h to remove excess citric acid. Finally, the composite gel was stored in a refrigerator at 4 °C.

[0064] Comparative Example 6

[0065] 0.83 g of zein was dissolved in 25 mL of sodium hydroxide solution (pH 12.5) at 25 °C and stirred thoroughly for 0.5 h. Then, 0.0125 g of curcumin and 3 g of xylitol were added to the zein solution, and after thorough mixing, 0.42 g of konjac glucomannan was added to the mixture. The mixture was poured into a dry, clean mold and heated in a water bath for 80 min. After removal, it was allowed to cool naturally to room temperature. The cooled sample was then immersed in 0.9% citric acid for 12 h to obtain a neutral composite gel. The composite gel was then rinsed with running distilled water for 5 min and immersed in distilled water for 6 h to remove excess citric acid. Finally, the composite gel was stored in a refrigerator at 4 °C.

[0066] Comparative Example 7

[0067] 0.83 g of zein was dissolved in 25 mL of sodium hydroxide solution (pH 12.5) at 25 °C and stirred thoroughly for 0.5 h. Next, 0.05 g of curcumin and 3 g of xylitol were added to the zein solution, and after thorough mixing, 0.42 g of konjac glucomannan was added to the mixture. The mixture was poured into a dry, clean mold and heated in a water bath for 80 min. After removal, it was allowed to cool naturally to room temperature. The cooled sample was then immersed in 0.9% citric acid for 12 h to obtain a neutral composite gel. The composite gel was then rinsed with running distilled water for 5 min and immersed in distilled water for 6 h to remove excess citric acid. Finally, the composite gel was stored in a refrigerator at 4 °C.

[0068] Comparative Example 8

[0069] 0.83 g of zein was dissolved in 25 mL of sodium hydroxide solution (pH 12.5) at 25 °C and stirred thoroughly for 0.5 h. Next, 0.1 g of curcumin and 3 g of xylitol were added to the zein solution, and after thorough mixing, 0.42 g of konjac glucomannan was added to the mixture. The mixture was poured into a dry, clean mold and heated in a water bath for 80 min. After removal, it was allowed to cool naturally to room temperature. The cooled sample was then immersed in 0.9% citric acid for 12 h to obtain a neutral composite gel. The composite gel was then rinsed with running distilled water for 5 min and immersed in distilled water for 6 h to remove excess citric acid. Finally, the composite gel was stored in a refrigerator at 4 °C.

[0070] Comparative Example 9

[0071] 0.83 g of zein was dissolved in 25 mL of sodium hydroxide solution (pH 12.5) at 25 °C and stirred thoroughly for 0.5 h. Next, 0.025 g of curcumin and 3 g of xylitol were added to the zein solution, and after thorough mixing, 0.42 g of konjac glucomannan was added to the mixture. The mixture was poured into a dry, clean mold and heated in a water bath for 80 min. After removal, it was allowed to cool naturally to room temperature. The cooled sample was then immersed in 1.5% citric acid for 12 h to obtain a neutral composite gel. The composite gel was then rinsed with running distilled water for 5 min and immersed in distilled water for 6 h to remove excess citric acid. Finally, the composite gel was stored in a refrigerator at 4 °C.

[0072] Comparative Example 10

[0073] 0.83 g of zein was dissolved in 25 mL of sodium hydroxide solution (pH 12.5) at 25 °C and stirred thoroughly for 0.5 h. Next, 0.025 g of curcumin and 3 g of xylitol were added to the zein solution, and after thorough mixing, 0.42 g of konjac glucomannan was added to the mixture. The mixture was poured into a dry, clean mold and heated in a water bath for 60 min. After removal, it was allowed to cool naturally to room temperature. The cooled sample was then immersed in 0.9% citric acid for 12 h to obtain a neutral composite gel. The composite gel was then rinsed with running distilled water for 5 min and immersed in distilled water for 6 h to remove excess citric acid. Finally, the composite gel was stored in a refrigerator at 4 °C.

[0074] Test Example 1: Mechanical Property Determination

[0075] The uniaxial and cyclic compression behavior of freshly prepared hydrogels with regular shapes was examined using a texture analyzer. The hardness, elasticity, and chewiness of the curcumin jelly were tested by compressing the hydrogel with a strain rate of 0.2 mm / s using a P36R probe at room temperature, with a maximum strain of 50%.

[0076] See results Figure 1 , Figure 2 and Figure 3 As shown in the figure, under the condition of fixed xylitol content, the increase of citric acid caused the three texture indices to show a "first increase and then decrease" trend, with Example 9 showing the best performance. This is because appropriate acidification can lower the pH of the system, weaken the electrostatic repulsion between proteins and polysaccharides, promote the formation of hydrogen bonds and hydrophobic interactions, thereby enhancing the density of the gel network, improving hardness and chewiness, and improving elasticity. However, when the citric acid content exceeds 0.9%, excessive acidification of the system leads to protein chain contraction, a decrease in the uniformity of the network structure, and even phase separation, resulting in a decrease in all three texture indices. Under the condition of fixed citric acid content, the increase of xylitol caused the hardness, elasticity, and chewiness to generally show a "increase-leveling-slight decrease" pattern. When the xylitol content is in the range of 6-9%, the texture indices reach a higher level, indicating that an appropriate amount of xylitol, by forming hydrogen bonds with water molecules, reduces water activity, enhances the interaction between proteins and polysaccharides, thereby optimizing the gel network structure, and also has a certain plasticizing effect, which helps to improve elasticity. However, when the xylitol content continued to increase to 12%, its competition with biomacromolecules for bound water led to increased system brittleness and a non-uniform network structure, resulting in a decline in textural properties. In summary, the addition of citric acid and xylitol significantly promoted the texture of the composite hydrogel within a certain range, with the combination in Example 9 exhibiting the best overall textural properties.

[0077] Test Example 2 Sensory Evaluation

[0078] A sensory evaluation panel of 30 food-related professionals assessed the food using sensory description methods, assigning scores to the curcumin jelly for its color, flavor, texture, and consistency. The total score was 100 points, and the average score was used. The sensory evaluation criteria are shown in Table 1.

[0079] Table 1 Sensory quality scoring criteria for curcumin-loaded corn protein konjac glucomannan composite gel jelly

[0080]

[0081] See results Figure 4As shown in the figure, the amount of citric acid added has a dual effect on sensory evaluation. As the addition amount increases from 0 to 0.6%, the sweet-sour balance and flavor complexity of the jelly significantly improve, and the overall acceptability reaches a high level (p < 0.05). Appropriate amounts of citric acid not only neutralize the bitterness that the complex system may bring but also highlight the refreshing taste. However, when the citric acid content further increases to above 0.9%, excessive acidity leads to an imbalance in taste, and some evaluation indicators show a downward trend. This indicates that 0.3%–0.6% is the suitable range for optimizing taste; excessive acidification weakens the sensory advantages. Secondly, the addition of xylitol has a more gradual effect on sensory quality improvement. Within the 0–6% range, the sweetness is moderate and balances with the acidity of citric acid, significantly improving sweetness, flavor, and texture scores (p < 0.05). When the xylitol concentration further increases to 9–12%, although the sweetness increases, the excessive sweetness masks the base flavor of curcumin and the complex system, causing the overall acceptability to no longer increase significantly, and even slightly decrease. Therefore, an optimal addition of approximately 6% xylitol is achieved. Overall, xylitol and citric acid exhibit a synergistic effect within a certain range. The combination in Example 9 demonstrates the best performance in terms of sweet-sour balance, flavor complexity, and overall acceptability.

[0082] Test Example 3: Water Holding Capacity Determination

[0083] The water-holding capacity of the gel jelly was determined by centrifugation. The mass of an empty centrifuge tube was recorded as m0. Approximately 3g of jelly sample was weighed and placed into the centrifuge tube. The total mass of the gel and centrifuge tube before centrifugation was recorded as m1. The sample was then centrifuged at 8000 r / min for 10 min. The water in the centrifuge tube was removed with filter paper, and the total mass of the gel jelly and centrifuge tube after centrifugation was recorded as m2. Finally, the water-holding capacity of the gel jelly was calculated. Each sample was measured six times, and the average value was taken. The formula is shown in (1-1):

[0084] Water holding capacity = (m1-m0) / (m2-m0)×100% (1-1)

[0085] See results Figure 5As shown in the figure, under the condition of fixed citric acid 0.6%, with the increase of xylitol addition, the water-holding capacity of the gel significantly increased from 88.78% at 0% citric acid to 93.14% at 6%, and then slightly decreased in the range of 9–12%, showing a "first increase and then stabilization" trend. This indicates that the main role of xylitol is to reduce the degree of freedom of water in the system and enhance hydrogen bonding with water, thereby improving water retention; however, at excessively high concentrations, the solute effect and increased osmotic pressure may disrupt the uniformity of the gel network, causing a decrease in water binding efficiency or a plateau. Secondly, under the condition of fixed xylitol 6%, the effect of citric acid showed a more obvious sensitivity. When the acidity increased from 0% to 0.9%, the water-holding capacity increased from 91.99% to 96.38%, the highest value in the entire experiment, while when the acidity further increased to 1.2%, the water-holding capacity significantly decreased to 93.47%. This indicates that moderate acidification can alter the charge state and intermolecular interactions between zein and konjac glucomannan, weakening electrostatic repulsion and promoting network densification, thereby enhancing water binding capacity. However, excessive acidification can lead to excessive network shrinkage or even water separation, reducing the overall water-holding capacity of the gel. This aligns with the mechanism by which acidity regulates network stability in protein-polysaccharide systems. Therefore, xylitol should be controlled at around 6–7% as the main factor for stabilizing and improving water-holding capacity, while citric acid should be precisely controlled within the range of 0.7–0.9% to maximize its synergistic effect, with Example 9 showing the best performance.

[0086] Test Example 4: DPPH Free Radical Scavenging Activity Assay

[0087] 1.2.4.2 Standard curve and content determination of bile salts

[0088] A certain amount of sample was placed in a 10 mL test tube for in vitro simulated digestion. After digestion, 4 mL of different concentrations of bile salt solutions (sodium taurocholate, sodium glycocholate, sodium cholate) were added to the sample, mixed well, and the mixture was shaken at 37℃ and 120 r / min for a certain period of time for adsorption. After centrifugation at 5000 r / min for 5 min, 0.1 mL of the supernatant was taken, 4 mL of 60% sulfuric acid solution was added, and the mixture was shaken well. The mixture was then incubated in a 70℃ water bath for 20 min and cooled to room temperature under running water. The absorbance was measured at a wavelength of 387 nm. The standard curve equation and correlation coefficient are as follows: Sodium taurocholate: y = 4.1171x + 0.0081, R 2 =0.9957; Sodium glycocholate: y = 3.92x + 0.0124, R 2 =0.9901; Sodium cholate: y = 0.6182x - 0.0049, R 2 =0.9959. The adsorption capacity of the sample for different bile salts was determined by the standard curve. The adsorption amount and adsorption rate of bile salts are shown in formulas (1-2) and (1-3).

[0089] q = q0 - q1 / m (1-2)

[0090] Q = q0 - q1 / q0 (1-3)

[0091] In the formula: q is the amount of bile salt adsorbed, mg / g; Q is the bile salt adsorption rate, %; q0 and q1 are the bile salt content in the solution before and after adsorption, mg, respectively; m is the sample mass, g.

[0092] See results Figure 6 As shown in the figure, the effect of citric acid addition on antioxidant activity exhibits a pattern of initial increase followed by stabilization or slight decrease. When citric acid increased from 0% to 0.6%, the DPPH free radical scavenging rate significantly improved (p < 0.05), indicating that a moderately acidified environment helps stabilize curcumin and maintain its activity. This may be related to citric acid lowering the solution pH and inhibiting the auto-oxidation reaction of curcumin; on the other hand, citric acid has a metal ion chelating effect, which can effectively weaken the free radical generation process catalyzed by metal ions. However, when citric acid was further increased to 0.9%–1.2%, the increase in some indicators slowed down or even slightly decreased. This is presumably because excessive acidification altered the structure of the protein-polysaccharide complex network, affecting the distribution and accessibility of curcumin in the hydrogel, thus leading to a marginal effect on antioxidant activity. In contrast, the addition of xylitol showed a mild promoting effect. Within the range of 0-9%, the antioxidant index of the hydrogel gradually increased with increasing xylitol concentration. When the xylitol content was further increased to 12%, the excessive viscosity of the system may limit the mass transfer efficiency of the substrate and free radicals, resulting in no significant improvement in scavenging rate. In summary, the formulation combination in Example 9 exhibited better antioxidant effects in this study, ensuring both the stability of the hydrogel network structure and balancing antioxidant performance with potential sensory flavor.

Claims

1. A method for preparing a corn protein-konjac glucomannan composite gel jelly loaded with curcumin, characterized in that, Includes the following steps: Step 1: Dissolve different masses of zein in 25 mL of sodium hydroxide solution at 25 °C and stir thoroughly for 0.5 h. Step 2: Add different masses of curcumin to the sodium hydroxide solution of zein. Step 3: Add different masses of xylitol to the above mixture for flavoring. Step 4: Add konjac glucomannan to the mixture of zein, curcumin and xylitol. Step 5: Pour the mixture into a dry, clean mold, then heat it in a water bath for 80 minutes. After removing it, allow it to cool naturally to room temperature. Immerse the cooled sample in a solution of citric acid of a certain concentration for 12 hours to obtain a neutral composite gel. Next, rinse the composite gel with running distilled water for 5 minutes and then immerse it in distilled water for 6 hours to remove excess citric acid. Finally, store the composite gel in a refrigerator at 4°C.

2. The method according to claim 1, characterized in that, The amount of zein added is 0-1.5g.

3. The method according to claim 1, characterized in that, The pH of the sodium hydroxide solution is 11-14.

4. The method according to claim 1, characterized in that, The amount of curcumin added is 0.005 to 0.2 g.

5. The method according to claim 1, characterized in that, The amount of xylitol added is 0-5g.

6. The method according to claim 1, characterized in that, The amount of konjac glucomannan added is 0-1.5g.

7. The method according to claim 1, characterized in that, The water bath heating temperature is 70–90°C.

8. The method according to claim 1, characterized in that, The concentration of citric acid is 0-2%.

9. The use of the curcumin-loaded corn protein konjac glucomannan composite gel jelly according to any one of claims 1-8 in the preparation of curcumin-containing products.

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