Photodynamic antibacterial liquid for fresh keeping of silver carp balls as well as preparation method and application of photodynamic antibacterial liquid

Abstract

The invention discloses photodynamic antibacterial liquid for fresh keeping of silver carp balls as well as a preparation method and application of the photodynamic antibacterial liquid, and belongs to the technical field of food fresh keeping. According to the invention, two coating solutions are prepared to research the influence of the coating solutions on the quality change of the fish balls in the storage period: one is a chitosan coating solution loaded with cinnamyl aldehyde-tannic acid nano-emulsion, cinnamyl aldehyde and tannic acid are natural compounds and are proved to have strong oxidation resistance, chitosan has broad-spectrum antibacterial property, and the coating solution is a chitosan coating solution loaded with cinnamyl aldehyde-tannic acid nano-emulsion; the shelf life of the food can be obviously prolonged; according to the photodynamic mediated gallic acid antibacterial liquid, research shows that a polyphenol aqueous solution can be subjected to photooxidation after being subjected to light irradiation treatment, active oxygen is generated, and the antibacterial liquid has high antibacterial activity. The silver carp balls which are more easily deteriorated are researched and selected, and the fish balls are treated by adding a coating preservation technology, so that the influence of different coating solutions on the quality of the fish balls in the storage period and an antibacterial mechanism are researched, and an instructive effect is provided for later application of the coating technology and preservation of the fish balls.

Description

Technical Field

[0001] This invention relates to the field of food preservation technology, and in particular to a photodynamic antibacterial liquid for preserving silver carp balls, its preparation method, and its application. Background Technology

[0002] Edible coatings (ECs) are thin, edible materials formed on food in liquid form. They are typically made from a variety of edible, biodegradable, non-toxic, and biocompatible components, including polysaccharides, proteins, essential oils, and biocomposite materials. As an emerging food preservation technology, ECs can extend shelf life and improve food quality. Existing research has shown that coating technology can extend the shelf life of surimi products by preventing bacterial growth and fat oxidation during storage. Therefore, developing new edible coatings is crucial for the food preservation field. Summary of the Invention

[0003] The purpose of this invention is to provide a photodynamic antibacterial liquid for preserving silver carp balls, its preparation method and application, so as to solve the problems existing in the prior art.

[0004] To achieve the above objectives, the present invention provides the following solution: One of the technical solutions of the present invention is a method for preparing a photodynamic antibacterial liquid for preserving silver carp balls, comprising the following steps: irradiating a gallic acid solution with a desktop UV-C intermittent light source, filtering the irradiated gallic acid solution, and obtaining the UVC-GA antibacterial liquid.

[0005] The second technical solution of the present invention is the UVC-GA antibacterial liquid prepared by the preparation method.

[0006] The third technical solution of the present invention is the application of the UVC-GA antibacterial liquid in the preservation of silver carp balls.

[0007] The fourth technical solution of the present invention is a method for preserving silver carp balls, wherein the silver carp balls are immersed in the UVC-GA antibacterial solution for 5 minutes, drained, packed into a sterilized food packaging box and sealed, and stored in a refrigerator at 4°C.

[0008] Based on the above technical solution, the present invention has the following technical effects: This invention investigated the effects of two coating solutions on the quality changes of fish balls during storage: First, a chitosan coating solution loaded with cinnamaldehyde-tannic acid nanoemulsion. Cinnamaldehyde and tannic acid are both natural compounds proven to have strong antioxidant properties, while chitosan possesses broad-spectrum antibacterial activity, significantly extending the shelf life of food. Second, a photodynamic-mediated gallic acid antibacterial solution. Studies have shown that aqueous solutions of polyphenols undergo photo-oxidation after light irradiation, generating reactive oxygen species with strong antibacterial activity. This invention focuses on silver carp fish balls, which are more prone to spoilage, and treats them with coating preservation technology. The aim is to study the effects of different coating solutions on the quality of fish balls during storage and their antibacterial mechanisms, providing guidance for future applications of coating technology and fish ball preservation. Attached Figure Description

[0009] Figure 1 The appearance (A) and particle size distribution (B) of the coating solution are shown.

[0010] Figure 2 To enhance the performance of the coating solution in inhibiting Pseudomonas aeruginosa.

[0011] Figure 3 The effect of the coating solution on bacterial cell morphology (5,000×) is shown. A to C represent CK, UVC-GA and CS / CIN-TA, respectively.

[0012] Figure 4 The effect of coating on the total bacterial count of fish balls during refrigeration.

[0013] Figure 5 The effect of coating on the pH value of fish balls during refrigeration.

[0014] Figure 6 The effect of coating on the water retention of fish balls during cold storage.

[0015] Figure 7 The effect of coating on the whiteness of fish balls during refrigeration.

[0016] Figure 8 The effect of coating on the gel strength of fish balls during cold storage.

[0017] Figure 9 The effect of coating on the hardness of fish balls during refrigeration.

[0018] Figure 10 The effect of coating on the moisture state changes of fish balls during cold storage.

[0019] Figure 11 The effect of coating on the change of moisture distribution in fish balls during cold storage.

[0020] Figure 12 The effect of coating on the TVB-N value of fish balls during cold storage.

[0021] Figure 13 The effect of coating on the protein pattern of fish balls during refrigeration. Detailed Implementation

[0022] Unless otherwise specified, the technical solutions described in this invention are all conventional solutions in the field, and the reagents or raw materials used are all purchased from commercial channels or are publicly available unless otherwise specified.

[0023] This invention provides a method for preparing a photodynamic antibacterial liquid for preserving silver carp balls, comprising the following steps: irradiating a gallic acid solution with a desktop UV-C intermittent light source, filtering the irradiated gallic acid solution, and obtaining the UVC-GA antibacterial liquid.

[0024] In some specific implementations, the parameters of the desktop UV-C intermittent light source are a wavelength of 254 nm and an average intensity of 4540 µW / cm². 2 Maximum liquid penetration is 17 cm.

[0025] In some specific implementations, the concentration of the gallic acid solution is 0.15 mol / L.

[0026] In some specific implementations, the irradiation conditions are 4 J / cm². 2 The intensity was continuously irradiated for 12 hours.

[0027] In some specific implementations, the filter uses a pore size of 0.25 µm.

[0028] The present invention also provides a UVC-GA antibacterial solution prepared by the above preparation method.

[0029] This invention also provides the application of the UVC-GA antibacterial liquid in the preservation of silver carp balls.

[0030] This invention also provides a method for preserving silver carp balls, wherein the silver carp balls are immersed in the UVC-GA antibacterial solution for 5 minutes, drained, packed into a sterilized food packaging box and sealed, and stored in a refrigerator at 4°C.

[0031] Example 1 1 Experimental Methods 1.1 Sample Preparation 1.1.1 Preparation of photodynamic antibacterial solution Following the method of Gan Hui et al., a desktop UV-C intermittent light source was used with a wavelength of 254 nm and an average intensity of 4540 µW / cm². 2The maximum liquid penetration is 17 cm. Gallic acid (GA) was prepared to a standard concentration of 0.15 mol / L with deionized water, transferred to sterile crystal culture dishes, and incubated in a UV chamber at 4 J / cm². 2 Irradiation was carried out continuously for 12 hours. The irradiated GA was filtered through a sterile filter with a pore size of 0.25 µm to obtain the UVC-GA antibacterial solution, which was then stored at room temperature in the dark. To ensure the stability of the antibacterial activity of UVC-GA, the solution was not stored for more than 4 weeks.

[0032] 1.1.2 Preparation of chitosan coating solution loaded with cinnamaldehyde-tannic acid nanoemulsion Following and slightly modifying the method of Shao et al., cinnamaldehyde-tannic acid nanoemulsions (CIN-TAs) were prepared using an ultrasonic-assisted method. First, an aqueous solution of tannic acid (1 mg / mL, 20 mL) was added dropwise to 80 μL of anhydrous ethanol under magnetic stirring to obtain a crude emulsion. Then, the emulsion was ultrasonically treated at 300 W for 20 min (2 s sonication, 2 s pause, cycle) to obtain CIN-TA. Next, chitosan was completely dissolved in a 1% (wt%) aqueous solution of acetic acid to obtain a homogeneous and transparent solution. The prepared CIN-TAs were then added to the chitosan solution and magnetically stirred at room temperature for 2 h to obtain a chitosan / cinnamaldehyde-tannic acid nanoemulsion coating CS / CIN-TA (1.5 wt% CS + 0.1% TA + 0.4% CIN).

[0033] 1.1.3 Fish ball processing Fish balls were prepared using conventional methods in the field. The fish balls were then divided into three groups: a control group (CK), a UVC-GA group, and a CS / CIN-TA group. Each fish ball was immersed in one of the two prepared coating solutions for 5 minutes, drained, and treated with distilled water as a control. They were then packaged in sterilized food containers, sealed, and immediately stored at 4°C. The day of treatment was recorded as day 0 of storage. Samples were randomly taken on days 0, 3, 5, 10, and 15 for index determination.

[0034] 1.1.4 Analysis of the antibacterial activity of the coating solution After activating the Pseudomonas aeruginosa strain, it was diluted with LB medium to a bacterial concentration of 1×10⁻⁶. 6 CFU / mL. The antibacterial activity of the coating solutions UVC-GA and CS / CIN-TA was determined by the perforation method. Culture dishes inoculated with 0.1 mL of Pseudomonas were incubated in a constant temperature incubator at 37℃ for 48 h, and the diameter of the inhibition zone was observed and measured.

[0035] 2 Results Analysis 2.1 Appearance and particle size of the coating solution The appearance and particle size distribution of the coating solution are as follows: Figure 1 As shown, the UVC-GA solution is nearly colorless and transparent, and has little impact on the whiteness of the fish balls after coating. The CS / CIN-TA solution, however, is pale purple and has a slight impact on the color of the fish balls after coating. Particle size analysis indicates that the main component of the UVC-GA solution is gallic acid, which exists in molecular form in a completely dissolved state with an average particle size of approximately 1 nm, while the CS / CIN-TA solution has a particle size of approximately 1,000 nm. The particle size of the coating solution is closely related to the preservation effect of the fish balls. Smaller particle sizes in the coating solution make it easier to form a uniform and dense film on the surface of the fish balls, reducing the penetration of oxygen and moisture and delaying the growth of spoilage bacteria.

[0036] 2.2 Antibacterial properties of the coating solution The inhibition zone method was used to characterize the antibacterial properties of the two coating solutions against *Pseudomonas aeruginosa*. Figure 2 As shown, both UVC-GA and CS / CIN-TA exhibit antibacterial activity, with UVC-GA showing an inhibition zone diameter of approximately 4 mm and CS / CIN-TA approximately 8 mm. UVC-GA, due to its lower solution viscosity and stronger diffusion and penetration, caused a color change in the culture medium near the inhibition zone after photo-oxidation. The stronger antibacterial performance of CS / CIN-TA may be attributed to the synergistic antibacterial effect of chitosan with tannic acid and cinnamaldehyde.

[0037] 2.3 Effects of coating solution on bacterial cell morphology Scanning electron microscopy (SEM) was used to observe the effects of coating solutions on the morphology of *Pseudomonas aeruginosa* cells. The results showed that, compared to untreated *P. aeruginosa* cells, bacteria treated with UVC-GA and CS / CIN-TA exhibited significant wrinkling and cell surface damage, with cell contents leaking out. Untreated bacteria, however, maintained a relatively smooth and intact surface without morphological damage. This suggests that UVC-GA and CS / CIN-TA treatments may weaken the stability and integrity of the bacterial cell membrane, altering cell membrane permeability and leading to the leakage of some cellular components such as proteins and reducing sugars, thus producing an antibacterial effect. The more severe cell damage after UVC-GA treatment indicates that photodynamic-mediated gallic acid can produce a significant sterilization effect. Gallic acid can interact with the bacterial cell membrane; after light irradiation, the polyphenolic hydroxyl groups of gallic acid undergo photooxidation, leading to lipid peroxidation in bacterial cells and affecting the structure and function of the bacterial phospholipid membrane.

[0038] 2.4 Effect of coating on total bacterial count of fish balls during cold storage Total bacterial count is a crucial indicator of the freshness of fish ball samples. During refrigeration, the total bacterial count of fish balls in different treatment groups increased to varying degrees with increasing storage time, with the control group showing the fastest increase. The differences between the UVC-GA and CS / CIN-TA treatment groups were relatively small. Throughout the entire storage process, the total bacterial count in the coating treatment group was significantly lower than that in the control group. According to GB10136-2015, "National Food Safety Standard for Aquatic Animal Products," the total microbial count in cooked fish balls should not exceed 5 × 10⁻⁶. 4 CFU / g (lgN value approximately 4.7lg CFU / g). On day 10 of refrigeration, the coating-treated group had 2.8 lg CFU / g and 2.66 lg CFU / g lower CFU / g than the control group, respectively. At this point, the total bacterial count in the treated group was just above the acceptable range. The results indicate that coating treatment at 4°C can effectively inhibit the growth and reproduction of microorganisms in fish ball samples, extending the shelf life of the fish balls by approximately 5 days.

[0039] 2.5 Effect of coating on pH changes during fish ball refrigeration pH affects the tenderness, flavor, and other qualities of fish balls, and is one of the important indicators of their freshness. A stable pH value means that the edible quality of surimi products is more stable. The effects of different coating solutions on the pH value of fish balls during refrigeration are as follows: Figure 5 As shown, with increasing storage time, the pH value of each group showed a trend of first increasing and then decreasing throughout the storage period. In the initial storage stage (day 0), the pH value of all treatment groups was lower than that of the control group. This is likely because gallic acid in UVC-GA, tannic acid in CS / CIN-TA, and the 1% acetic acid solution used to dissolve chitosan are all weakly acidic, causing the pH value of the fish balls to decrease after coating treatment. With prolonged storage, the decomposition of proteins by microorganisms promoted the accumulation of alkaline nitrogenous compounds such as amines and trimethylamine, leading to a slight increase in pH value. Towards the end of storage, the pH value decreased due to the oxidative rancidity of fats and the accumulation of lactic acid produced by bacterial metabolism. The control group showed the most significant pH decrease during this stage, indicating that the coating treatment effectively inhibited the metabolic activity of microorganisms in the fish balls, maintained the relative stability of the sample pH value, and preserved the quality of the fish balls.

[0040] 2.6 Effect of coating on the water-holding capacity of fish balls during cold storage Water-holding capacity is an important indicator of fish ball quality. Actin and myosin in fish meat cross-link to form a three-dimensional network structure, giving surimi products their water-holding capacity. This property reflects the state of the gel network within the sample. During storage, microbial activity and endogenous enzymes lead to the degradation of myofibrillar proteins, reducing the protein's ability to bind water. Therefore, changes in water-holding capacity can serve as an important indicator of fish ball freshness. Figure 6The study demonstrated the effect of coating on the water-holding capacity of fish balls during refrigeration. During refrigeration, the water-holding capacity of all groups of fish balls showed an overall decreasing trend. By day 15 of storage, the water-holding capacity of the control group, UVC-GA group, and CS / CIN-TA group decreased by 19.5%, 14.1%, and 17.6%, respectively. The decreasing trend was slower after coating treatment, which may be because the coating solution has antibacterial activity, inhibiting the decomposition of proteins by microorganisms, slowing down the destruction of the gel network structure, and delaying spoilage. Simultaneously, the coating solution can, to some extent, reduce the evaporation loss of water from the fish balls, maintaining their water-holding capacity.

[0041] 2.7 Effect of coating on whiteness of fish balls during cold storage The color of surimi products is a key factor affecting consumption. Changes in whiteness often occur during the storage of surimi products, which usually means changes in the product's nutritional value and a decrease in overall acceptance. It can most directly reflect the freshness of fish balls. Figure 7 This study demonstrates the effect of different coating solutions on the whiteness of fish balls under refrigeration at 4℃. In the control group, whiteness did not change significantly in the early storage period (0-5 days) (P>0.05). However, with the increased proliferation of microorganisms leading to lipid oxidation and protein degradation, the fish balls began to spoil after 5 days of storage, and their whiteness rapidly decreased. By the end of storage (day 15), yellow spots gradually appeared on the surface of the fish balls in the control group, and the color of the fish balls darkened. In contrast, the whiteness of the coated group decreased slightly after 15 days of refrigeration, indicating that the coating solution can inhibit the growth of microorganisms in the fish balls, delay protein oxidation, and simultaneously block oxygen contact to reduce the rate of lipid oxidation, thus slowing down the spoilage of the fish balls and effectively maintaining their color and stabilizing their overall sensory quality.

[0042] 2.8 Effect of coating on the texture of fish balls during refrigeration Gelatin strength and hardness were used to analyze the texture of samples from different treatment groups. Figure 8 The gel strength results are shown. The control group and CS / CIN-TA group samples showed no significant change in gel strength in the early stages of storage (P>0.05), but the gel strength began to decrease after 10 days of storage. In contrast, the UVC-GA group samples showed no significant change in gel strength throughout the entire storage period (P<0.05), indicating that the UVC-GA coating solution had the most significant effect on maintaining the gel structure of the fish balls. Hardness changes are shown below. Figure 9As shown, the hardness of the samples in each treatment group initially increased and then decreased with prolonged storage time. This may be because the low-temperature environment in the early stage of storage promotes the cross-linking of myosin and actin, forming a denser three-dimensional gel network; simultaneously, the corn starch molecules in the fish balls undergo short-term rearrangement due to aging, resulting in a temporary increase in hardness. As the storage process progresses, microbial metabolic activities and the action of endogenous enzymes lead to the degradation of myofibrillar proteins, disrupting the gel structure and causing a decrease in hardness. Comparative analysis shows that the UVC-GA group has a significant advantage in maintaining texture stability.

[0043] 2.9 Effect of coating on moisture state changes of fish balls during cold storage Relaxation time can reflect the degree of freedom of water. The shorter the relaxation time (T2), the tighter the binding between water and sample components, and vice versa, it indicates that the proportion of free water is increased. Figure 10 The results show the changes in the moisture state of fish balls during storage. All treatment groups showed a trend of decreasing non-flowing water and increasing free water with increasing storage time, but the water migration rate of the coated groups was significantly lower than that of the control group. This indicates that the antibacterial coating effectively delays the breakdown of the gel network structure by inhibiting the hydrolysis of the surimi matrix by microorganisms, thereby maintaining the stability of moisture distribution. Figure 11 The changes in moisture distribution of fish balls in different treatment groups during refrigeration were shown. With increasing storage time, the image brightness of the fish balls in the control group showed a red attenuation trend. The fish balls treated with the CS / CIN-TA coating solution maintained stable moisture distribution in the early stages of storage, but at the end of storage (day 15), the red signal intensity decreased significantly, indicating that the conversion of non-flowing water into free water within the sample was weakened, leading to moisture loss. In contrast, the image brightness of the fish balls in the UVC-GA group remained stable throughout the storage process, indicating that this coating solution can effectively maintain the moisture distribution of the fish balls during the shelf life, reducing moisture loss and preserving the quality of the fish balls.

[0044] 2.10 Effect of coating on TVB-N value of fish balls during cold storage Volatile basic nitrogen (TVB-N) is an important indicator for evaluating the freshness of aquatic products. It reflects the degree to which protein and non-protein nitrogenous substances decompose under the action of microorganisms and endogenous enzymes, producing alkaline compounds such as ammonia and amines. Figure 12It can be seen that the TVB-N value of fish balls in all treatment groups showed an increasing trend with the increase of storage time, but the increase rate of the coating treatment group was significantly lower than that of the control group. In the early stage of storage, the TVB-N value of each group increased slowly, but increased rapidly with the increase of storage time. This may be due to the large-scale proliferation of microorganisms in the later stage of storage, which decomposed protein and non-protein nitrogenous substances to generate a large amount of volatile nitrogenous substances, causing the TVB-N value of each group to rise rapidly. The TVB-N value of the control group reached 21.89 mg / 100g after 15 days of storage, exceeding the national standard limit of 20 mg / 100g, while the TVB-N values ​​of the UVC-GA and CS / CIN-TA groups were still within the acceptable range on day 15. Compared with the CK group, the TVB-N values ​​of the UVC-GA and CS / CIN-TA groups decreased by 46.07% and 48.26% respectively on day 15. The above results demonstrate that the coating solution effectively inhibits the protein degradation process by suppressing microbial proliferation and enzymatic activity, thereby significantly delaying the spoilage rate of fish balls.

[0045] 2.11 Effect of coating on protein composition of fish balls during refrigeration SDS-PAGE gel electrophoresis results of fish balls from different treatment groups during refrigeration are as follows: Figure 13 As shown in the image, the spectrum reveals the presence of actin (48 kDa), tropomyosin (35 kDa), and myosin light chain (14 kDa), proteins that play crucial roles in maintaining the cytoskeleton and myofibril structure. In the early stages of storage, the intensity of protein bands in all samples showed little change. However, with increasing storage time, after day 10, myosin and tropomyosin began to degrade to varying degrees, with the most significant changes observed in the control group (CK). By day 15, actin in the CK group had almost disappeared, indicating possible degradation into peptides or other small molecules. Compared to the CK group, the degree of protein degradation was less in the later stages of storage, demonstrating that the coating treatment effectively inhibited protein degradation and delayed the spoilage of the fish balls.

[0046] This invention focuses on silver carp fish balls and prepared two coating solutions, UVC-GA and CS / CIN-TA. The antibacterial properties of the coating solutions and the physicochemical properties of the fish balls after refrigeration at 4°C for 0, 3, 5, 10, and 15 days, including texture, color, water retention, total bacterial count, pH value, TVB-N value, and moisture distribution, were measured to explore the preservation effects of the two edible coatings.

[0047] The results show that: Edible coating treatments, especially UVC-GA treatment, effectively maintained the textural stability of fish balls and significantly inhibited the growth of microorganisms. Compared with the control group, UVC-GA treatment extended the shelf life of silver carp fish balls by 100% during storage at 4°C. On day 10, compared with the CK group, the TVB-N and total bacterial count (TVC) in the UVC-GA group decreased by 46.07% and 36.85%, respectively.

[0048] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments 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 preserving silver carp fish balls, characterized in that, Immerse the silver carp balls in UVC-GA antibacterial solution for 5 minutes, drain them, pack them into sterilized food packaging boxes and seal them, and store them in a refrigerator at 4°C. The preparation method of the UVC-GA antibacterial solution includes the following steps: irradiating gallic acid solution with a desktop UV-C intermittent light source, filtering the irradiated gallic acid solution, and obtaining the UVC-GA antibacterial solution.

2. The preservation treatment method according to claim 1, characterized in that, The parameters of the tabletop UV-C intermittent light source are: wavelength of 254 nm and average intensity of 4540 µW / cm². 2 Maximum liquid penetration is 17 cm.

3. The preservation treatment method according to claim 1, characterized in that, The concentration of the gallic acid solution is 0.15 mol / L.

4. The preservation treatment method according to claim 1, characterized in that, The irradiation conditions were 4 J / cm². 2 The intensity was continuously irradiated for 12 hours.

5. The preservation treatment method according to claim 1, characterized in that, The filter uses a pore size of 0.25 µm.

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