Preparation method of curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel, product and application thereof

Abstract

The application discloses a preparation method of curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel, a product and application thereof. The preparation method comprises the following steps: after carboxymethyl chitosan, dialdehyde starch and curcumin are fully mixed, the mixture is fully placed, and the hydrogel is obtained. The hydrogel provided by the application has excellent self-healing performance, exhibits excellent antibacterial performance under the assistance of photodynamic technology, and exhibits unique advantages in cold-chain food preservation. In addition, the hydrogel ice block of the application cannot melt, and solves the problems that traditional ice is easily melted into water in the transportation process, and cross contamination of microorganisms is caused. The preparation method is simple and easy to implement, the conditions are mild, the cost is low, mass production is facilitated, and the hydrogel has a wide application prospect in food low-temperature preservation.

Description

Technical Field

[0001] This invention relates to the field of food preservation technology, specifically to a method for preparing a curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel, its product, and its application. Background Technology

[0002] Traditional water ice is widely used as a cooling medium in the food supply chain due to its high latent heat of fusion, which is close to 0°C. However, melted ice water is prone to cross-contamination by microorganisms, posing a food safety risk. Currently, various alternatives to traditional water ice have been developed, such as ice packs, ice cubes with added antibacterial agents, silicone, and plastic ice cubes. However, these alternatives have safety issues such as odor, material decomposition, and leakage.

[0003] In recent years, those skilled in the art have developed gelatin-based hydrogels as alternatives to traditional water ice. For example, adding sodium menadione bisulfite to gelatin-based hydrogels imparts photoactivated antibacterial, antifungal, and anti-yeast properties. However, such gelatin-based hydrogels are poorly self-healing and cannot be reused. Therefore, there is an urgent need to develop novel self-healing hydrogels with good antibacterial properties. Summary of the Invention

[0004] To address the aforementioned problems in the prior art, this invention provides a method for preparing a curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel, along with its product and applications.

[0005] The first objective of this invention is to provide a method for preparing a curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel.

[0006] A second objective of this invention is to provide a curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel obtained according to the preparation method described above.

[0007] A third objective of this invention is to provide the application of the curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel in cryopreservation.

[0008] A fourth objective of this invention is to provide the application of the curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel in food preservation.

[0009] The fifth object of the present invention is to provide the application of the curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel in the preparation of photodynamic antibacterial products.

[0010] To achieve the above objectives, the present invention is implemented through the following solution:

[0011] Carboxymethyl chitosan is a water-soluble polysaccharide derivative obtained by carboxymethylation modification of natural chitosan. The introduction of carboxymethyl (-CH2COOH) groups into its molecular chain through carboxymethylation significantly enhances its water solubility and chemical activity, while retaining the natural antibacterial properties, biocompatibility, and biodegradability of chitosan. Compared to unmodified chitosan (which is only soluble in acidic media), carboxymethyl chitosan can be stably dissolved under neutral and weakly alkaline conditions, greatly expanding its application potential in food, medicine, and other fields. The amino (-NH2) and carboxylic acid (-COOH) groups on its molecular chain endow it with zwitterionic properties, allowing it to crosslink with other biomacromolecules through electrostatic interactions, hydrogen bonds, or dynamic covalent bonds (such as Schiff base reactions with aldehyde compounds), forming a multifunctional hydrogel network with self-healing capabilities. Furthermore, carboxymethyl chitosan exhibits broad-spectrum antibacterial activity against Gram-positive bacteria, Gram-negative bacteria, and fungi, and its degradation products are non-toxic and harmless, meeting the safety requirements for food contact materials, making it an ideal choice for developing environmentally friendly antibacterial materials.

[0012] Dialdehyde starch is an important starch derivative, obtained by introducing aldehyde groups onto the hydroxyl groups of starch molecules through an oxidation reaction. This chemical modification significantly enhances the reactivity of starch, giving it unique application potential in multiple fields. Dialdehyde starch not only retains some of the basic properties of starch but also possesses new functional properties due to its modified structure, such as antibacterial properties, biocompatibility, and biodegradability, making it promising for broad applications in biomedicine, packaging materials, and the textile industry.

[0013] Curcumin, a natural polyphenol compound, possesses excellent antioxidant, anti-inflammatory, and antibacterial properties and is widely used in food, pharmaceuticals, and cosmetics. With the support of photodynamic therapy, the antibacterial activity of curcumin is significantly enhanced, demonstrating its enormous application potential in the field of antibacterial preservation.

[0014] This invention addresses the shortcomings of existing cold chain food preservation technologies by using carboxymethyl chitosan, dialdehyde starch, and curcumin to prepare a hydrogel. This hydrogel can be rapidly formed through simple vortex mixing, eliminating the need for a complex rehydration process. Both carboxymethyl chitosan and dialdehyde starch are natural polysaccharides with good biocompatibility and inherent antibacterial properties. The hydrogel formed by their combination exhibits excellent biocompatibility and biodegradability. Furthermore, the amino groups in carboxymethyl chitosan can adsorb and disrupt bacterial structures, while dialdehyde starch can form dynamic imine bonds to enhance bacterial performance. The loaded curcumin exhibits photodynamic antibacterial activity under light irradiation, synergistically inhibiting bacterial growth in conjunction with the hydrogel's properties.

[0015] A method for preparing a curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel involves thoroughly mixing carboxymethyl chitosan, dialdehyde starch, and curcumin, and then allowing the mixture to stand for a sufficient period of time to obtain the hydrogel.

[0016] In the hydrogel, the mass fraction of carboxymethyl chitosan is 2% to 5%, the mass fraction of dialdehyde starch is 1% to 4%, and the concentration of curcumin is 0.25 μM to 25 μM.

[0017] Preferably, the dialdehyde starch is obtained by oxidative modification of starch with sodium periodate; the starch is corn starch, corn starch nanoparticles, or water-soluble starch.

[0018] More preferably, the dialdehyde starch is obtained by oxidative modification of water-soluble starch with sodium periodate.

[0019] Preferably, the aldehyde content of the dialdehyde starch is 1.14 to 1.99 mmol / g.

[0020] Preferably, the method includes the following steps: thoroughly mixing an ethanol solution of curcumin, dialdehyde starch, and water to obtain a curcumin-dialdehyde starch solution; then thoroughly mixing a carboxymethyl chitosan solution with the curcumin-dialdehyde starch solution and allowing it to stand for a while to obtain the hydrogel.

[0021] Preferably, the mass fraction of carboxymethyl chitosan in the hydrogel is 4%.

[0022] Preferably, the mass fraction of the dialdehyde starch in the hydrogel is 2%.

[0023] Preferably, the concentration of the dialdehyde starch in the hydrogel is 2.5 μM to 25 μM.

[0024] More preferably, the concentration of the dialdehyde starch in the hydrogel is 25 μM.

[0025] The curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel obtained by any of the preparation methods described above should also be within the scope of protection of this invention.

[0026] The application of the curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel in cryopreservation should also be within the scope of protection of this invention, wherein the hydrogel replaces ice.

[0027] The application of the curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel in food preservation should also be within the scope of protection of this invention.

[0028] The application of the curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel in the preparation of photodynamic antibacterial products should also be within the scope of protection of this invention.

[0029] Preferably, the photodynamic antibacterial process is performed using a blue LED.

[0030] A method for food preservation, wherein the food is preserved using the curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel.

[0031] Preferably, during storage, the light is irradiated with a blue LED.

[0032] Preferably, the preservation is performed at low temperature.

[0033] More preferably, the low temperature is 0°C to 6°C.

[0034] More preferably, the low temperature is 0°C.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The hydrogel provided by this invention possesses excellent self-healing properties and exhibits superior antibacterial properties with the aid of photodynamic technology, demonstrating unique advantages in cold chain food preservation. Furthermore, the hydrogel ice blocks of this invention do not melt, solving the problem of traditional ice easily melting into water during transportation, leading to cross-contamination of microorganisms. Moreover, the preparation method is simple and easy to implement, with mild conditions and low cost, facilitating large-scale production and showing broad application prospects in low-temperature food preservation. Attached Figure Description

[0037] Figure 1 The colony count results of Staphylococcus aureus in hydrogels of carboxymethyl chitosan-dialdehyde starch loaded with different concentrations of curcumin.

[0038] Figure 2 To preserve the colony counts of salmon at different time points in a hydrogel of carboxymethyl chitosan-dialdehyde starch loaded with 25 μM curcumin.

[0039] Figure 3 Results of pH values ​​for preserving salmon at different times in a hydrogel loaded with 25 μM curcumin and carboxymethyl chitosan-dialdehyde starch.

[0040] Figure 4 TBARS values ​​of salmon were preserved at different time points in a hydrogel of carboxymethyl chitosan-dialdehyde starch loaded with 25 μM curcumin.

[0041] Figure 5 Results of the preservation of the textural properties of salmon in a hydrogel of carboxymethyl chitosan-dialdehyde starch loaded with 25 μM curcumin at different times: a represents hardness, b represents elasticity, c represents chewiness, and d represents resilience. Detailed Implementation

[0042] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods; the materials and reagents used, unless otherwise specified, are commercially available.

[0043] Example 1: A method for preparing a curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel

[0044] 1. Preparation of carboxymethyl chitosan

[0045] 20.0 g of chitosan powder was dispersed in 100 g of a 50 wt% sodium hydroxide aqueous solution and alkalized overnight (12 h) at -20 °C to obtain alkalized chitosan. After thawing, the alkalized chitosan was transferred to a round-bottom flask, and 100 mL of isopropanol was added. The mixture was stirred vigorously at room temperature (25 °C) for 5 min until it was evenly dispersed. Separately, 57.0 g of monochloroacetic acid was dissolved in 100 mL of isopropanol and added dropwise to the round-bottom flask over 30 min, with continuous stirring for 1.5 h. Subsequently, the mixture was refluxed and stirred in a 60 °C water bath for 2 h.

[0046] After the reaction was completed, the residual solvent was discarded, and the product was washed twice with 70% (v / v) aqueous ethanol solution. Then, the solid product was washed once with ethanol and dried at room temperature (25°C) to obtain the solid product.

[0047] 20g of the solid product was dissolved in 600mL of distilled water, placed in a 3.5K dialysis bag, dialyzed with distilled water for 3 days, and then freeze-dried to obtain carboxymethyl chitosan.

[0048] 2. Preparation of dialdehyde starch

[0049] In this embodiment, dialdehyde starch is prepared using natural corn starch.

[0050] Disperse 5g of natural corn starch in 250mL of distilled water and adjust the pH to 3.5 with hydrochloric acid. Add 1.190g of sodium periodate and react in a 30℃ water bath in the dark for 4 hours.

[0051] After the reaction was completed, 1 mL of ethylene glycol was added and stirred for 1 h to quench the unreacted sodium periodate. Then, it was placed in a 3.5 K dialysis bag and dialyzed with distilled water for 3 days before freeze drying to obtain dialdehyde starch with an aldehyde content of 1.78 mmol / g, which was designated as dialdehyde natural corn starch.

[0052] 3. Preparation of hydrogels

[0053] Curcumin stock solution was dissolved in anhydrous ethanol to obtain a 200 μM curcumin ethanol solution. The 200 μM curcumin ethanol solution and dialdehyde natural corn starch were added to 1 mL of distilled water and stirred until homogeneous to obtain a curcumin-dialdehyde natural corn starch solution, wherein the final mass fraction of the dialdehyde natural corn starch was 2%.

[0054] Carboxymethyl chitosan was dissolved in 2 mL of distilled water to obtain a carboxymethyl chitosan solution, wherein the final mass fraction of carboxymethyl chitosan was 4%.

[0055] A curcumin-dialdehyde natural corn starch solution and a carboxymethyl chitosan solution were vortexed at a volume ratio of 1:2 and allowed to stand at room temperature (25℃) for 15 minutes to obtain a hydrogel with a curcumin content of 0.5 μM.

[0056] Example 2: A method for preparing a curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel

[0057] It is basically the same as Example 1, except that the curcumin content in the hydrogel is 2.5 μM.

[0058] Example 3: A method for preparing a curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel

[0059] It is basically the same as Example 1, except that the curcumin content in the hydrogel is 5 μM.

[0060] Example 4: A method for preparing a curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel

[0061] It is basically the same as Example 1, except that the curcumin content in the hydrogel is 10 μM.

[0062] Example 5: A method for preparing a curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel

[0063] It is basically the same as Example 1, except that the curcumin content in the hydrogel is 25 μM.

[0064] Example 6: A method for preparing a curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel

[0065] 1. Preparation of carboxymethyl chitosan

[0066] Same as Example 1.

[0067] 2. Preparation of dialdehyde starch

[0068] This embodiment uses corn starch nanoparticles to prepare dialdehyde starch. The corn starch nanoparticles can be prepared as follows: 5g (dry basis) of natural corn starch is accurately weighed and dispersed in distilled water to prepare a suspension with a concentration of 50mg / mL. The suspension is then continuously stirred in a boiling water bath for 30min to complete the gelatinization process. After the starch paste cools to 60℃, it is ultrasonically broken down using a low-temperature ultrasonic extractor. The frequency is set to 20kHz, the power to 900W, and the working mode is alternating between a 5s pulse period and a 2s interval, for 10min to ensure effective temperature control. The resulting homogenized starch solution is then diluted to a concentration of 10mg / mL and rapidly mixed with an equal volume of anhydrous ethanol at 8000r / min using a high-speed homogenizer at room temperature, and homogenized for 5min. The resulting mixture is then centrifuged at 4500×g for 20min to separate the nanoparticles. The supernatant is then discarded, and the precipitate is collected. Finally, the centrifuged product was dried in a forced-air drying oven at 45°C and then ground and granulated through a 120-mesh standard sieve to obtain corn starch nanoparticle powder with uniform particle size.

[0069] Disperse 5g of corn starch nanoparticle powder in 250mL of distilled water and adjust the pH to 3.5 with hydrochloric acid. Add 1.190g of sodium periodate and react in a 30℃ water bath in the dark for 4 hours.

[0070] After the reaction was completed, 1 mL of ethylene glycol was added and stirred for 1 h to quench the unreacted sodium periodate. Then, the mixture was placed in a 3.5 K dialysis bag and dialyzed with distilled water for 3 days before being freeze-dried to obtain dialdehyde starch with an aldehyde content of 1.99 mmol / g, which was designated as dialdehyde corn starch nanoparticles.

[0071] 3. Preparation of hydrogels

[0072] Curcumin stock solution was dissolved in anhydrous ethanol to obtain a 200 μM curcumin ethanol solution. The 200 μM curcumin ethanol solution and dialdehyde corn starch nanoparticles were added to 1 mL of distilled water and stirred until homogeneous to obtain a curcumin-dialdehyde corn starch nanoparticle solution, wherein the final mass fraction of dialdehyde starch nanoparticles was 2%.

[0073] Carboxymethyl chitosan was dissolved in 2 mL of distilled water to obtain a carboxymethyl chitosan solution, wherein the final mass fraction of carboxymethyl chitosan was 4%.

[0074] A curcumin-dialdehyde corn starch nanoparticle solution and a carboxymethyl chitosan solution were vortexed at a volume ratio of 1:2 and allowed to stand at room temperature (25℃) for 1 min to obtain a hydrogel-like ice block with a curcumin content of 0.5 μM.

[0075] Example 7: A method for preparing a curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel

[0076] It is basically the same as Example 6, except that the curcumin content in the hydrogel is 2.5 μM.

[0077] Example 8: A method for preparing a curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel

[0078] It is basically the same as Example 6, except that the curcumin content in the hydrogel is 5 μM.

[0079] Example 9: A method for preparing a curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel

[0080] It is basically the same as Example 6, except that the curcumin content in the hydrogel is 10 μM.

[0081] Example 10: A method for preparing a curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel

[0082] It is basically the same as Example 6, except that the curcumin content in the hydrogel is 25 μM.

[0083] Example 11: A method for preparing a curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel

[0084] 1. Preparation of carboxymethyl chitosan

[0085] Same as Example 1.

[0086] 2. Preparation of dialdehyde starch

[0087] In this embodiment, dialdehyde starch was prepared using water-soluble starch (CAS No.: 9005-84-9).

[0088] Disperse 5g of water-soluble starch in 250mL of distilled water and adjust the pH to 3.5 with hydrochloric acid. Add 1.190g of sodium periodate and react in a 30℃ water bath in the dark for 4 hours.

[0089] After the reaction was completed, 1 mL of ethylene glycol was added and stirred for 1 h to quench the unreacted sodium periodate. Then, the mixture was placed in a 3.5 K dialysis bag and dialyzed with distilled water for 3 days. After freeze drying, a dialdehyde starch with an aldehyde content of 1.14 mmol / g was obtained, which was designated as dialdehyde water-soluble starch.

[0090] 3. Preparation of hydrogels

[0091] The curcumin stock solution was dissolved in anhydrous ethanol to obtain a 200 μM curcumin ethanol solution. The 200 μM curcumin ethanol solution and dialdehyde water-soluble starch were added to 1 mL of distilled water and stirred until homogeneous to obtain a curcumin-dialdehyde water-soluble starch solution, wherein the final mass fraction of the dialdehyde water-soluble starch was 2%.

[0092] Carboxymethyl chitosan was dissolved in 2 mL of distilled water to obtain a carboxymethyl chitosan solution, wherein the final mass fraction of carboxymethyl chitosan was 4%.

[0093] A curcumin-dialdehyde water-soluble starch solution and a carboxymethyl chitosan solution were vortexed at a volume ratio of 1:2 and allowed to stand at room temperature (25℃) for 5 minutes to obtain a hydrogel-like ice block with a curcumin content of 0.5 μM.

[0094] Example 12: A method for preparing a curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel

[0095] It is basically the same as Example 11, except that the curcumin content in the hydrogel is 2.5 μM.

[0096] Example 13: A method for preparing a curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel

[0097] It is basically the same as Example 11, except that the curcumin content in the hydrogel is 5 μM.

[0098] Example 14: A method for preparing a curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel

[0099] It is basically the same as Example 11, except that the curcumin content in the hydrogel is 10 μM.

[0100] Example 15: A method for preparing a curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel

[0101] This example is essentially the same as Example 11, except that the curcumin content in the hydrogel is 25 μM. Comparative Example 1: A method for preparing a carboxymethyl chitosan-dialdehyde starch hydrogel.

[0102] The process is basically the same as in Example 1, except that in step "3, preparation of hydrogel", the dialdehyde natural corn starch is added to 1 mL of distilled water and stirred evenly to obtain a dialdehyde natural corn starch solution, wherein the final mass fraction of the dialdehyde natural corn starch is 2%.

[0103] Carboxymethyl chitosan was dissolved in 2 mL of distilled water to obtain a carboxymethyl chitosan solution, wherein the final mass fraction of carboxymethyl chitosan was 4%.

[0104] A hydrogel was obtained by vortexing a solution of dialdehyde natural corn starch and a solution of carboxymethyl chitosan at a volume ratio of 1:2 and allowing it to stand at room temperature (25°C) for 10 minutes.

[0105] Comparative Example 2: A method for preparing a carboxymethyl chitosan-dialdehyde starch hydrogel

[0106] The process is basically the same as in Example 6, except that in step "3, preparation of hydrogel", the dialdehyde corn starch nanoparticles are added to 1 mL of distilled water and stirred evenly to obtain a dialdehyde corn starch nanoparticle solution, wherein the final mass fraction of the dialdehyde corn starch nanoparticles is 2%.

[0107] Carboxymethyl chitosan was dissolved in 2 mL of distilled water to obtain a carboxymethyl chitosan solution, wherein the final mass fraction of carboxymethyl chitosan was 4%.

[0108] A hydrogel was obtained by vortexing a solution of dialdehyde corn starch nanoparticles and a solution of carboxymethyl chitosan at a volume ratio of 1:2 and allowing it to stand at room temperature (25°C) for 1 min.

[0109] Comparative Example 3: A method for preparing a carboxymethyl chitosan-dialdehyde starch hydrogel

[0110] The process is basically the same as in Example 11, except that in step "3, preparation of hydrogel", the dialdehyde dialdehyde water-soluble starch is added to 1 mL of distilled water and stirred evenly to obtain a dialdehyde dialdehyde water-soluble starch solution, wherein the final mass fraction of the dialdehyde dialdehyde water-soluble starch is 2%.

[0111] Carboxymethyl chitosan was dissolved in 2 mL of distilled water to obtain a carboxymethyl chitosan solution, wherein the final mass fraction of carboxymethyl chitosan was 4%.

[0112] A hydrogel was obtained by vortexing a dialdehyde water-soluble starch solution and a carboxymethyl chitosan solution at a volume ratio of 1:2 and allowing it to stand at room temperature (25°C) for 5 minutes.

[0113] Application Example 1: Evaluation of Self-Healing Performance

[0114] After the hydrogels of Examples 1-15 and Comparative Examples 1-3 were frozen and solidified, they were cut in half, reassembled, and their self-healing properties were observed. Furthermore, each hydrogel was subjected to repeated freeze-thaw cycles to observe its self-healing behavior.

[0115] The results showed that the self-healing properties of the hydrogels in Comparative Examples 1 and 2 deteriorated significantly after three freeze-thaw cycles, and the self-healing time was significantly prolonged. In contrast, the self-healing properties of the hydrogels in Examples 1 to 10 remained basically unchanged after three freeze-thaw cycles. The self-healing properties of the hydrogel in Comparative Example 3 remained basically unchanged after three freeze-thaw cycles, but the self-healing ability decreased and the self-healing time was significantly prolonged after five freeze-thaw cycles. In contrast, the self-healing properties of the hydrogels in Examples 11 to 15 remained basically unchanged after five freeze-thaw cycles.

[0116] This indicates that the curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel provided by the present invention has excellent self-healing properties, is resistant to repeated freeze-thaw cycles, and can be reused.

[0117] Application Example 2: Evaluation of Antibacterial Performance

[0118] 100 μL of a concentration of 10 8 A CFU / mL suspension of Staphylococcus aureus (strain number: ATCC29213) was inoculated onto hydrogels of Examples 1-15 and Comparative Examples 1-3, respectively. Each hydrogel was then irradiated under a blue LED (20W, wavelength 455-460nm) for 30 min for photodynamic antimicrobial (PDI) treatment. After treatment, physiological saline was added at a ratio of 1:9 (w / v), and homogenized in a homogenizer at a frequency of 8 times / second for 10 min. Subsequently, 100 μL of the diluted solution was spread onto soybean casein agar medium and incubated overnight (12 h) at 37°C before colony counting.

[0119] like Figure 1 As shown, compared with the hydrogel of Comparative Example 1, the colony count of the hydrogels of Examples 1-5 was significantly reduced, and the colony count was negatively correlated with the curcumin concentration; the higher the curcumin concentration, the fewer the colony count. Compared with the hydrogel of Comparative Example 2, the colony count of the hydrogel of Example 6 was reduced, and the colony count of the hydrogels of Examples 7-10 was significantly reduced, and the colony count was also negatively correlated with the curcumin concentration. Compared with the hydrogel of Comparative Example 3, the colony count of the hydrogel of Example 11 was reduced, and the colony count of the hydrogels of Examples 12-15 was significantly reduced, and the colony count was also negatively correlated with the curcumin concentration.

[0120] The above results indicate that the curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel provided by the present invention has a significant antibacterial effect against Staphylococcus aureus and exhibits excellent long-lasting antibacterial properties.

[0121] Application Example 3: Evaluation of the Preservation Performance of Ice Cubes

[0122] 1. Low-temperature preservation of fish samples

[0123] Frozen salmon meat samples were thawed and cut into 11mm×11mm×8mm blocks, which were then divided into 4 groups and randomly stacked in beakers to create an irregular surface for the food. These groups were designated as the control group, hydrogel ice block sample 1, hydrogel ice block sample 2, and hydrogel ice block sample 3.

[0124] At room temperature, the hydrogels from Examples 5, 10, and 15 were sequentially placed into beakers containing hydrogel-like ice cube samples 1, 2, and 3, respectively. Under gravity, each hydrogel flowed downwards, gradually filling the gaps between the fish meat and forming a tight physical barrier. The samples were stored at 0°C for 5 days. During this period, the fish meat samples from hydrogel-like ice cube samples 1, 2, and 3 were exposed to a blue LED light daily for 30 minutes for PDI photodynamic inactivation treatment. The control group was stored directly at 0°C for 5 days without any treatment.

[0125] 2. Microbial index testing of salmon

[0126] The total bacterial count of each group was determined at 0, 1, 3, and 5 days after storage. The fish meat samples were crushed and added to a sterile sampling bag along with 9 times the volume of physiological saline. The mixture was homogenized in a homogenizer at a frequency of 8 times / second for 10 minutes to form a homogeneous mixture. Subsequently, 100 μL of the 2- to 6-fold dilution was spread on soybean casein agar medium and incubated overnight (12 h) at 37°C before colony counting.

[0127] like Figure 2 As shown, after 5 days of storage, the total bacterial count of fish samples 1-3 (hydrogel ice cube samples) was significantly lower than that of the control group.

[0128] The above results indicate that the curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel provided by the present invention has good antibacterial properties, can significantly inhibit the growth of microorganisms under low temperature storage, has good preservation effect, and is conducive to extending the shelf life of fresh food. It can be used as an antibacterial and preservation-like ice cube.

[0129] 3. Testing of chemical indicators in salmon

[0130] (1) pH measurement

[0131] Take salmon samples and place them in a sterile homogenization bag. Add physiological saline at a ratio of 1:9 (w / v) and mix. Homogenize in a beater homogenizer at a frequency of 8 times / second for 10 minutes. After homogenization, measure the pH using a pH meter.

[0132] like Figure 3As shown, the initial pH of salmon samples 1–3 treated with hydrogel ice was 6.13–6.23, which is within the normal range for fresh salmon. The pH of all salmon samples gradually increased during storage. The main reason for the pH increase was that the fish entered the autolysis stage, where endogenous enzymes and exogenous enzymes produced by microorganisms decomposed proteins, producing alkaline amines, including ammonia, trimethylamine, and histamine. However, compared to the control group, the pH increase of salmon treated with PDI-mediated hydrogel ice was slower.

[0133] The above results indicate that the curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel provided by this invention can effectively inhibit the growth of microorganisms and their enzyme activity under PDI-mediated storage, reduce the degree of protein degradation, and avoid the large accumulation of ammonia and amine compounds, thereby maintaining the pH value of raw salmon within a reasonable range.

[0134] (2) Determination of thiobarbituric acid value (TBARS)

[0135] The oxidation of unsaturated fatty acids in fish fat produces MDA, which can react with thiobarbituric acid to form a colorimetric compound called thiobarbituric acid reactants (TBARS). By measuring the content of this colorimetric compound, the degree of fat oxidation in salmon meat can be reflected.

[0136] Add 1g of homogenized salmon meat to 5mL of 7.5% trichloroacetic acid solution. Place the mixture on a shaker and shake at 150rpm for 30min, then filter through filter paper to obtain the supernatant. Transfer 5mL of the supernatant and add 5mL of 0.02mol / L thiobarbituric acid solution, reacting in a boiling water bath for 40min. After cooling to room temperature, add 5mL of chloroform, shake well, and let stand. Take an appropriate amount of the upper layer solution and measure the absorbance at wavelengths of 532nm and 600nm, according to the formula: Calculate the TBARS value of salmon.

[0137] Changes in TBARS in salmon during 0℃ storage are as follows: Figure 4As shown, the initial TBARS value of salmon in each group was 2.6 mg MDA / 100g. The TBARS value of the control group samples showed a significant upward trend, reaching 13.86 mg MDA / 100g by the end of the 5th day of storage. Compared with the untreated control group, the TBARS growth rate of salmon treated with PDI-mediated hydrogel ice (hydrogel ice sample 1, hydrogel ice sample 2, and hydrogel ice sample 3) was slower during storage, much lower than that of the control group. Specifically, on the fifth day, the TBARS value of salmon treated with hydrogel ice sample 1 was only 7.71 mg MDA / 100g, that of salmon treated with hydrogel ice sample 2 was 7.81 mg MDA / 100g, and that of salmon treated with hydrogel ice sample 3 was 8.01 mg MDA / 100g.

[0138] The above results indicate that the curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel provided by the present invention significantly inhibits the increase in TBARS value of salmon mediated by PDI when used for salmon storage, and significantly inhibits the oxidation of fat in salmon flesh.

[0139] 4. Salmon textural properties testing

[0140] Salmon samples were divided into 11mm × 11mm × 8mm rectangular standard specimens. The hardness, elasticity, chewiness, and resilience of the salmon were determined using a texture analyzer in TPA mode. The TPA mode parameters were set as follows: probe type P36R (cylindrical flat-bottom probe, 36mm diameter), pre-test speed 1.0mm / s, mid-test speed 1mm / s, post-test speed 1mm / s, and trigger force 5g.

[0141] Hardness refers to the maximum peak value during the first compression, such as... Figure 5 As shown in Figure a, the salmon in each group showed an initial increase in hardness during storage at 0℃. The increased hardness may be due to protein denaturation and changes in enzyme activity when thawed and then stored at 0℃, leading to protein aggregation and cross-linking, thus increasing the meat's hardness. Subsequently, due to the action of microorganisms and biological enzymes, muscle fibers gradually broke down, and the disulfide bonds of proteins were destroyed, resulting in muscle softening and deterioration, ultimately leading to a decrease in hardness. Compared to the control group, the salmon treated with PDI-mediated hydrogel ice samples 1-3 showed a more slow decrease in hardness.

[0142] Elasticity refers to the ratio of the height of the second compression to the height of the first compression, and is used to assess the speed and extent to which a sample recovers its deformation after being compressed. For example... Figure 5As shown in b, with the extension of storage time, the elasticity of salmon flesh in the control group gradually decreased. This is due to the decrease in intercellular cohesion and protein degradation, resulting in a decrease in elasticity and toughness, and thus a poorer recovery ability after compression. However, the salmon treated with PDI-mediated hydrogel ice samples 1-3 showed a slower rate of decrease on days 1 and 3, indicating that it has a certain inhibitory effect on the growth of microorganisms and the activity of autolysins. In addition, on day 5, the elasticity of salmon treated with hydrogel ice samples 1-3 actually increased. This may be due to the moist surface characteristics of hydrogel ice samples 1-3 and the synergistic enhancement of antibacterial properties by PDI treatment, thereby effectively inhibiting the loss of fish flesh moisture and the process of protein hydrolysis during storage, and ultimately maintaining the elastic properties of muscle tissue.

[0143] Chewing capacity refers to the energy required for food to be chewed in the mouth and reach a stable state before swallowing. It is an important indicator for evaluating food texture and is a comprehensive result of reduced muscle hardness, decreased intercellular cohesion, and reduced muscle elasticity. For example... Figure 5 As shown in c, the chewiness of the control group gradually decreased during storage, while the chewiness of salmon treated with PDI-mediated hydrogel ice samples 1-3 decreased more slowly.

[0144] Resilience refers to the ability of food to return to its original shape or state after being compressed. For example... Figure 5 As shown in d, the resilience of salmon flesh in each group gradually decreased with the extension of storage time. Compared with the control group, the resilience of salmon treated with PDI-mediated hydrogel ice samples 1-3 decreased more gradually.

[0145] In summary, the curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel provided by this invention has a significant preservation effect on salmon storage. Through PDI-mediated synthesis, it can inhibit microbial growth, maintain pH value, reduce lipid oxidation, and maintain good textural properties.

[0146] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description and ideas, and it is neither necessary nor possible to exhaustively describe all implementation methods here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel, characterized in that, The process includes the following steps: thoroughly mixing carboxymethyl chitosan, dialdehyde starch, and curcumin, and then allowing the mixture to stand for a while to obtain the hydrogel. In the hydrogel, the mass fraction of carboxymethyl chitosan is 2% to 5%, the mass fraction of dialdehyde starch is 1% to 4%, and the concentration of curcumin is 0.25 μM to 25 μM.

2. The preparation method according to claim 1, characterized in that, The dialdehyde starch is obtained by oxidative modification of starch with sodium periodate; the starch is corn starch, corn starch nanoparticles, or water-soluble starch.

3. The preparation method according to claim 2, characterized in that, The dialdehyde starch is obtained by oxidative modification of water-soluble starch with sodium periodate.

4. The preparation method according to claim 1, characterized in that, The aldehyde content of the dialdehyde starch is 1.14–1.99 mmol / g.

5. The preparation method according to claim 1, characterized in that, Includes the following steps: A curcumin-dialdehyde starch solution was obtained by thoroughly mixing an ethanol solution of curcumin, dialdehyde starch, and water. After thoroughly mixing the carboxymethyl chitosan solution and the curcumin-dialdehyde starch solution, and allowing them to stand for a while, the hydrogel is obtained.

6. The preparation method according to claim 1, characterized in that, In the hydrogel, the concentration of curcumin is 2.5 μM to 25 μM.

7. The curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel obtained by the preparation method according to any one of claims 1 to 6.

8. The application of the curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel of claim 7 in cryopreservation, characterized in that, The hydrogel replaces ice.

9. The application of the curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel of claim 7 in food preservation.

10. The application of the curcumin-loaded carboxymethyl chitosan-dialdehyde starch hydrogel of claim 7 in the preparation of photodynamic antibacterial products.

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