Real-time visual detection method for freshness of coconut water

Abstract

The invention discloses a real-time visual detection method for freshness of coconut water. The real-time visual detection method comprises the following steps: step 1, preparing colored dried small shrimps by utilizing shrimp shells of black tiger shrimps; and 2, completely soaking the colored dried small shrimps obtained in the step 1 in coconut water, and detecting the freshness of the coconut water in real time. The main component of the colored dried small shrimps prepared by the method is chitosan, and the chitosan is arranged in a chiral nematic helical structure and has color-changing responsiveness to acid and aldehyde substances generated after coconut water is deteriorated, so that the deterioration of the coconut water can be indicated through the color change of the surface of the dried small shrimps when the colored dried small shrimps are put into the coconut water; the real-time and visual detection of the freshness of coconut water is realized, the detection accuracy is high, and the problems of high cost, complicated operation, low accuracy and incapability of real-time detection in the existing determination method are solved.

Description

Technical Field

[0001] This invention belongs to the technical field of food testing methods, and relates to a real-time visual detection method for the freshness of coconut water. Background Technology

[0002] Coconut water, as a natural and nutritious health beverage, has gained widespread popularity worldwide in recent years. Its sweet taste and rich content of electrolytes, vitamins, and minerals are its main selling points. However, coconut water (especially NFC – non-concentrated or freshly squeezed) is essentially a complex, highly perishable, low-acidic liquid. During processing, storage, transportation, and sales, its freshness rapidly declines due to factors such as microbial contamination, enzymatic reactions, oxidation, and temperature fluctuations. This manifests as flavor degradation (sourness, rancidity, alcoholic taste, etc.), color changes, increased turbidity, and nutrient degradation, severely impacting the product's sensory quality, safety, and commercial value. Currently, the industry primarily relies on the following methods to assess coconut water freshness: (a) Sensory evaluation: This method relies on trained personnel to make subjective judgments based on sight (color, turbidity), smell (odor), and taste (texture, flavor). While direct, this approach has significant drawbacks, such as strong subjectivity, difficulty in standardizing evaluation criteria, susceptibility to the evaluator's state, low efficiency, and inability to achieve rapid, large-scale online testing. More importantly, sensory evaluation may not be sensitive enough or accurate enough to detect slight but substantial initial changes in freshness.

[0003] (II) Physicochemical index testing: pH: Fresh coconut water is typically slightly acidic. With microbial fermentation (such as by lactic acid bacteria and yeast), the pH value decreases significantly. Soluble solids / total sugar (TSS / Brix): Microbial consumption of sugars leads to a decrease in TSS. Titrative acidity: Reflects an increase in total acid content. Similar to pH, its changes may be lagging and cannot distinguish between different types of acids (e.g., lactic acid and acetic acid produce different intensities of off-flavors). Conductivity: Related to ion concentration, it may increase with the accumulation of microbial metabolites, but its specificity is poor and it is easily affected by mineral content.

[0004] (iii) Detection of specific metabolites (such as ethanol, ethyl acetate, etc.): Gas chromatography (GC) and other methods are used to detect volatile substances produced by spoilage. This method is relatively accurate, but it usually requires complex sample pretreatment, expensive instruments and equipment, professional operators, and a long analysis time (several hours), making it difficult to meet the needs of rapid screening on production lines or in the distribution process.

[0005] (iv) Microbiological testing: Determining total bacterial count, yeast count, and mold count is one of the gold standards for assessing safety and spoilage levels. However, traditional plate culture methods are time-consuming (typically requiring 48-72 hours or even longer) and cannot provide immediate results to guide rapid decision-making (such as product release and inventory turnover). Rapid microbial detection methods (such as ATP bioluminescence assay) are expensive and may be affected by the complex matrix of coconut water.

[0006] In summary, the main problems and challenges of existing technologies are as follows: (1) Poor timeliness: Microbial culture and some physicochemical / chromatographic analysis are time-consuming, making it impossible to monitor freshness in real time or near real time, which may lead to problematic products entering the market or causing unnecessary inventory losses; (2) Subjectivity and non-objectivity: Sensory evaluation relies on subjective human judgment, lacks objective and quantitative standards, and has poor reproducibility; (3) Complex operation and high cost: Accurate metabolite analysis or rapid microbial detection usually requires expensive equipment, professional personnel and laboratory environment, which is costly and the operation process is complex, making it unsuitable for rapid application on site or production line; (4) Destructive or invasive: Most existing testing methods require opening the bottle for sampling, which is a destructive test and cannot be used for follow-up of the same product or for non-destructive screening of the final product. Summary of the Invention

[0007] The purpose of this invention is to provide a real-time visual detection method for the freshness of coconut water, which solves the problems of high cost, complex operation, low accuracy, and inability to detect in real time in existing methods.

[0008] The technical solution adopted in this invention is a real-time visual detection method for coconut water freshness, which is implemented according to the following steps: Step 1: Prepare colored shrimp skin using black tiger shrimp shells; Step 2: Immerse the colored shrimp shells obtained in Step 1 completely in coconut water and monitor the freshness of the coconut water in real time.

[0009] The invention is further characterized by: In step 1, the main component of the colored shrimp shells is chitosan, and the chitosan is arranged in a chiral nematic helical structure. The iridescent color on the surface of the colored shrimp shells is the structural color.

[0010] In step 1, the shells of black tiger shrimp are treated with NaOH solution and HCl solution to remove protein, calcium and acetylate, so that the chitin in the shrimp shell is converted into chitosan, and colored shrimp skin is obtained.

[0011] Step 1 is as follows: Wash and drain the black tiger prawn shells, then soak them in a 5% NaOH solution. After removing them, rinse them with water and drain them again. Repeat this treatment step three times. Next, soak the NaOH-treated prawn shells in a 0.1M HCl solution, then rinse them with water and drain them again. Repeat this treatment step three times. Finally, soak the HCl-treated prawn shells in a 50% NaOH solution, then rinse them with water and drain them again. Repeat this treatment step three times to obtain black tiger prawn shells with stable iridescent structural colors, i.e., colored prawn shells.

[0012] When soaking dried shrimp in a 5% NaOH solution, the temperature should be 80-100℃ and the time should be 6-8 hours.

[0013] The shrimp shells were soaked in a 0.1M HCl solution at room temperature for 2-3 hours.

[0014] When soaking dried shrimp in a 50% NaOH solution, the temperature should be 85-95℃ and the time should be 8-10 hours.

[0015] In step 2, the coconut water is judged by whether the color of the colored shrimp shells has changed to red. If a red shift occurs, the water has spoiled; otherwise, it has not spoiled.

[0016] The beneficial effects of this invention are: (1) The method of the present invention uses acid and alkali to deproteinize and decalcify the shell of black tiger shrimp, and converts the chitin in the shrimp shell into chitosan as much as possible through deacetylation to obtain colored shrimp skin. The preparation method is simple to operate, low in cost and can be mass-produced. At the same time, it effectively recycles marine biological waste such as shrimp shells, realizing the high-value utilization of marine resources. (2) The main component of the colored shrimp shell prepared by the method of the present invention is chitosan. The nano-chitosan in the shrimp shell is arranged in a chiral nematic helical structure and contains a large number of free active amino groups. It has color-changing response to the acid and aldehyde substances produced after the coconut water deteriorates. When it is placed in the coconut water, the deterioration of the coconut water can be indicated by the color change on the surface of the shrimp shell. Real-time and visual detection of the freshness of coconut water is achieved, and the detection accuracy is high. (3) The method of this invention utilizes the shells of black tiger prawns to prepare colored shrimp skin. Black tiger prawn shells are thick, flexible, and have a large surface area. The colored shrimp skin prepared from them can be soaked in coconut water for a long time without deformation. The film surface has a large pore size, making it easier to respond to the spoilage products of coconut water. Furthermore, the colored shrimp skin made from black tiger prawn shells has a predominantly blue-purple hue, allowing for a larger red shift in color, which is more conducive to a noticeable color change during coconut water detection. In addition, the shrimp shells have high safety and can directly contact food. This invention is a low-cost, green, consumer-oriented real-time detection method. Attached Figure Description

[0017] Figure 1 This is a photograph of the colored shrimp shells prepared according to an embodiment of the present invention; Figure 2 These are scanning electron microscope (SEM) images of the surface and cross-section of the colored shrimp shells prepared according to embodiments of the present invention; Figure 3 This is a comparison of the Fourier transform infrared spectra of black tiger shrimp shells and colored shrimp shells in an embodiment of the present invention. Figure 4 These are X-ray diffraction comparison images of black tiger shrimp shells and colored shrimp shells in an embodiment of the present invention; Figure 5 This is a comparison chart of thermogravimetric analysis of black tiger shrimp shells and colored shrimp shells in an embodiment of the present invention; Figure 6 This is the nitrogen adsorption-desorption curve of the colored shrimp shells prepared in the embodiments of the present invention; Figure 7 This is a pore size distribution diagram of the colored shrimp shells prepared according to an embodiment of the present invention; Figure 8 This is a circular dichroism chromatogram of the colored shrimp shells prepared according to an embodiment of the present invention; Figure 9 This is a polarized light microscope image of the colored shrimp shells prepared according to an embodiment of the present invention; Figure 10 This is a color change response diagram of the colored shrimp shells prepared according to the embodiments of the present invention to acid; Figure 11 This is a color change response diagram of the colored shrimp shells prepared according to the embodiments of the present invention to aldehydes; Figure 12 This is a color change diagram of the colored shrimp shells prepared according to the embodiments of the present invention during the storage process in coconut water; Figure 13 This is a graph showing the changes in the physicochemical properties of coconut water during storage in an embodiment of the present invention. Detailed Implementation

[0018] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0019] The present invention provides a real-time visual detection method for coconut water freshness, which is implemented according to the following steps: Step 1, Prepare colored shrimp shells: First, wash and drain the black tiger shrimp shells. Soak them in a 5% NaOH solution at 80-100℃ for 6-8 hours in a constant temperature water bath. Remove, rinse thoroughly with water, and drain. Repeat the 5% NaOH treatment three times. Next, soak the NaOH-treated shrimp shells in a 0.1M HCl solution at room temperature for 2-3 hours. Remove, rinse thoroughly with water, and drain. Repeat the 0.1M HCl treatment three times. The repeated NaOH and HCl treatments remove proteins and calcium carbonate from the inside of the shrimp shells. Finally, soak the shrimp shells in a 50% NaOH solution at 85-95℃ for 8-10 hours in a constant temperature water bath. Remove, rinse thoroughly, and drain. Repeat the 50% NaOH treatment three times to obtain black tiger shrimp shells with stable iridescent structural colors, i.e., colored shrimp shells.

[0020] Step 2: Use the colored shrimp shells obtained in Step 1 to detect the freshness of the coconut water in real time. Colored shrimp shell film is fixed inside the coconut water packaging container, ensuring it is completely submerged in the coconut water. During the distribution, storage, and sale of the coconut water, the color change of the colored shrimp shell is observed visually. A red shift in the structural color of the shrimp shell surface is used to determine whether the coconut water has spoiled.

[0021] The main component of the colored shrimp shells prepared by the method of this invention is chitosan, which exhibits a chiral nematic helical structure, and the iridescent color on the film surface is a structural color. Because the interchain hydrogen bonds and free amino groups of chitosan have strong reactivity, they can react with the products of spoiled coconut water, thereby changing the color of the shrimp shells. Therefore, this method can be used to detect the freshness of coconut water.

[0022] Furthermore, the colored shrimp shells prepared by the method of this invention through deproteinization, decalcification, and deacetylation reactions are mainly composed of chitosan nanofibers arranged in parallel in a layered structure. Continuous layers rotate around the normal axis at a certain angular increment. After a 360° rotation, the vertical distance between two layers is one pitch. This helical layered structure is called a chiral nematic helical structure. This structure can generate structural color on the shrimp shell surface by reflecting visible light, and the reflection principle follows Bragg's law. Because chitosan has active amino groups and strong hydrogen bonding forces, the chitosan in the colored shrimp shells can react with acids and aldehydes, changing the color of the shrimp shell surface by altering the pitch of the chiral nematic helical structure. Simultaneously, since acids and aldehydes are important metabolic products in coconut water, the spoilage of coconut water is usually accompanied by the accumulation of large amounts of acid and aldehyde products. Therefore, the method of this invention can achieve real-time visual detection of coconut water freshness through the dual responsiveness of colored shrimp shells to acids and aldehydes.

[0023] Example 1: This embodiment demonstrates a natural colored shrimp shell film material that can detect the freshness of coconut water. The material is derived from the shells of black tiger shrimp, which undergo corresponding deproteinization and decalcification treatments. Furthermore, the chitin in the shrimp shells is converted into chitosan as much as possible through deacetylation.

[0024] Wash and drain the black tiger shrimp shells. Soak them in a 5% NaOH solution at 90℃ for 6 hours, then rinse and drain. Soak them in a 0.1M HCl solution at room temperature for 2 hours, then rinse and drain. Repeat the treatment with 5% NaOH and 0.1M HCl three times to remove proteins and calcium carbonate from the inside of the shells. Soak the resulting shrimp shells in a 50% NaOH solution at 90℃ for 8 hours, then rinse and drain. Repeat the 50% NaOH treatment three times to obtain black tiger shrimp shells with stable iridescent structural colors, i.e., colored shrimp shells.

[0025] Figure 1 The image shown is of the actual product of the colored shrimp shells prepared in this embodiment. It can be seen that the colored shrimp shells mainly exhibit purple and green colors. This color is a purely physical optical effect, without the use of any natural or artificial pigments or other chemical substances. Furthermore, the color of the colored shrimp shells also changes due to the variation in the pitch of the spiral structure inside the shrimp shells.

[0026] The content of each element and the degree of deacetylation (DD) of the raw material black tiger shrimp shells and the obtained colored shrimp shells used in this embodiment were detected. The results are shown in Table 1. The results in Table 1 are expressed as mean ± standard deviation (n=3). There are significant differences between different letters in the same column (P<0.05).

[0027] Table 1. Elemental composition and degree of deacetylation of black tiger prawn shells and colored prawn shells

[0028] As shown in Table 1, the contents of carbon, nitrogen, hydrogen, oxygen and calcium in the colored shrimp shells are 39.55%, 7.58%, 7.47%, 42.84% and 0.02%, respectively. The degree of deacetylation of the colored shrimp shells is as high as 83.93%, which proves that its composition is basically chitosan.

[0029] Figure 2 The images show scanning electron microscope (SEM) images of the surface (Fig. a, b) and cross-section (Fig. c, d) of the colored shrimp shells prepared in this embodiment. It can be seen that the shrimp shell surface has many small pores, which facilitates the entry and reaction of coconut water residue into the shrimp shell. The surface texture is mainly composed of stacked chitosan nanofibers. The cross-sectional SEM image of the shrimp shell reveals a unique layered structure, indicating that the interior of the shrimp shell is composed of a chiral nematic helical structure arranged with chitosan nanofibers. It is precisely because of the presence of this layered structure that the shrimp shell reflects visible light, thus forming a colored shrimp shell.

[0030] Figures 3-5 The images show a comparison of Fourier transform infrared (FTIR) spectra, X-ray diffraction (XRD), and thermogravimetric analysis (TGA) results for black tiger shrimp shells and colored shrimp shells, respectively. It can be seen that colored shrimp shells are mainly composed of chitosan, as the FTIR, XRD, and TGA results for colored shrimp shells are very close to those for natural chitosan. Furthermore, the TGA results indicate that colored shrimp shells only degrade at around 325°C, demonstrating their good thermal stability.

[0031] Figure 6 , Figure 7 The figures show the nitrogen adsorption-desorption curves and pore size distribution of colored shrimp shells. It can be seen that there are many small pores on the surface of the shrimp shells, with the pore size mainly within 40 nm, which to some extent increases the adsorption capacity of the colored shrimp shells.

[0032] Figure 8 , Figure 9 The images show a circular dichroism spectrum and a polarizing microscope image of colored shrimp shells. These two images demonstrate, from an optical perspective, that the color on the surface of the shrimp shell is a structural color, caused by the left-handed chiral nematic helical structure within the shrimp shell.

[0033] The color change response of the colored shrimp shells prepared in this embodiment to acid and aldehyde was tested. (1) Color change response to acid: Using water as a control, the acid response of colored shrimp shells was studied using 5 mL of aqueous solutions of 11 different organic or inorganic acids (lactic acid, formic acid, acetic acid, propionic acid, butyric acid, valeric acid, malic acid, citric acid, succinic acid, hydrochloric acid, and sulfuric acid). The results are as follows: Figure 10 As shown, dried colored shrimp shells exhibit purple, blue, and green hues. When immersed in water, the colors undergo varying degrees of red shift. This difference between the different colored shrimp shells is due to their heterogeneity as biological materials. The color changes of the colored shrimp shells in acidic solutions at pH 4 and 5 are the same as in water. However, at pH 3, the shrimp shells show a more pronounced red shift after immersion in all acidic solutions for 1 hour. This is mainly due to the protonation of amino groups in the colored shrimp shells, leading to the adsorption of acidic media in the form of chitosan-acid salts, resulting in an increase in the helical pitch. Furthermore, the hygroscopic nature of chitosan-acid salts allows for the adsorption of more water molecules into the chiral nematic helical structure, also contributing to the increase in pitch. Compared to other acidic solutions, the red shift of the shrimp shells immersed in acetic acid, propionic acid, butyric acid, and valeric acid solutions at pH 3 is more pronounced, causing the color to completely disappear.

[0034] (2) Color change response to aldehydes: Using water as a control, the aldehyde response of colored shrimp shells was studied by using 5 mL of 100 μmol / mL aqueous solutions of three aldehydes (acetaldehyde, malondialdehyde, and hexanal). The results are as follows: Figure 11As shown.

[0035] It can be seen that compared to the color of the colored shrimp shells in water, the shrimp shells soaked in these aldehyde solutions showed varying degrees of red shift. This indicates that aldehyde molecules are incorporated into the chiral nematic helical structure, leading to an increase in pitch. The colored shrimp shells showed the most rapid red shift after soaking in hexanal solution, and the color quickly disappeared completely; while acetaldehyde and malondialdehyde only caused a red shift in color. This may be because hexanal molecules are larger than the other two aldehydes, resulting in a greater increase in pitch and a more intense red shift.

[0036] The color change response of the colored shrimp shells prepared in this embodiment to coconut water was tested. In this embodiment, colored shrimp shells are fixed onto a black filter screen, and then the shrimp shells and filter screen are fixed together in a transparent container, ensuring that the shrimp shells are positioned between the filter screen and the inner wall of the container to prevent them from shifting. Coconut water is poured into the container, completely submerging the colored shrimp shells. During the storage of coconut water, samples are taken at five time points (0h, 6h, 12h, 18h, and 24h) to determine the total bacterial count, pH value, total titratable acidity, and conductivity, thus assessing the freshness of the coconut water. The results of the physicochemical property tests are compared with the results based on the color change of the shrimp shells to evaluate the effectiveness of this visual detection method.

[0037] The changes in the color of the colored dried shrimp with the freshness of the coconut water and the changes in their physicochemical properties with the freshness of the coconut water are respectively shown in the figures. Figure 12 and 13 As shown in the figure, the colored shrimp shells began to change color after coconut water had spoiled for more than 12 hours, and the color change was obvious after 18 hours, at which point the coconut water was no longer suitable for use. Furthermore, as the coconut water further deteriorated, the color of the colored shrimp shells gradually shifted to red and even disappeared. This change can effectively indicate the degree of spoilage of the coconut water in real time. The results indicate that colored shrimp shells can effectively indicate the spoilage of coconut water through color changes.

[0038] Example 2: The method for real-time visual detection of coconut water freshness in this embodiment is implemented according to the following steps: Step 1: First, wash and drain the black tiger shrimp shells. Soak them in a 5% NaOH solution at 80℃ for 8 hours in a constant temperature water bath. Remove, rinse thoroughly with water, and drain. Repeat the 5% NaOH treatment three times. Next, soak the NaOH-treated shrimp shells in a 0.1M HCl solution at room temperature for 2 hours. Remove, rinse thoroughly with water, and drain. Repeat the 0.1M HCl treatment three times. The repeated NaOH and HCl treatments remove proteins and calcium carbonate from the inside of the shrimp shells. Finally, soak the shrimp shells in a 50% NaOH solution at 85℃ for 9 hours in a constant temperature water bath. Remove, rinse thoroughly, and drain. Repeat the 50% NaOH treatment three times to obtain black tiger shrimp shells with stable iridescent structural colors, i.e., colored shrimp shells.

[0039] Step 2: Secure the colored shrimp film inside the coconut water packaging container, ensuring it is completely submerged in the coconut water. During the distribution, storage, and sale of the coconut water, visually observe the color changes of the colored shrimp film. Determine if the coconut water has spoiled by observing whether the structural color on the shrimp shell surface has shifted to red.

[0040] Example 3: The method for real-time visual detection of coconut water freshness in this embodiment is implemented according to the following steps: Step 1: First, wash and drain the black tiger shrimp shells. Soak them in a 5% NaOH solution at 80℃ for 6 hours in a constant temperature water bath. Remove, rinse thoroughly with water, and drain. Repeat the 5% NaOH treatment three times. Next, soak the NaOH-treated shrimp shells in a 0.1M HCl solution at room temperature for 3 hours. Remove, rinse thoroughly with water, and drain. Repeat the 0.1M HCl treatment three times. The repeated NaOH and HCl treatments remove proteins and calcium carbonate from the inside of the shrimp shells. Finally, soak the shrimp shells in a 50% NaOH solution at 85℃ for 10 hours in a constant temperature water bath. Remove, rinse thoroughly, and drain. Repeat the 50% NaOH treatment three times to obtain black tiger shrimp shells with stable iridescent structural colors, i.e., colored shrimp shells.

[0041] Step 2: Secure the colored shrimp film inside the coconut water packaging container, ensuring it is completely submerged in the coconut water. During the distribution, storage, and sale of the coconut water, visually observe the color changes of the colored shrimp film. Determine if the coconut water has spoiled by observing whether the structural color on the shrimp shell surface has shifted to red.

[0042] Example 4: The method for real-time visual detection of coconut water freshness in this embodiment is implemented according to the following steps: Step 1: First, wash and drain the black tiger shrimp shells. Soak them in a 5% NaOH solution at 90℃ for 8 hours in a constant temperature water bath. Remove, rinse thoroughly with water, and drain. Repeat the 5% NaOH treatment three times. Next, soak the NaOH-treated shrimp shells in a 0.1M HCl solution at room temperature for 2 hours. Remove, rinse thoroughly with water, and drain. Repeat the 0.1M HCl treatment three times. The repeated NaOH and HCl treatments remove proteins and calcium carbonate from the inside of the shrimp shells. Finally, soak the shrimp shells in a 50% NaOH solution at 85℃ for 9 hours in a constant temperature water bath. Remove, rinse thoroughly, and drain. Repeat the 50% NaOH treatment three times to obtain black tiger shrimp shells with stable iridescent structural colors, i.e., colored shrimp shells.

[0043] Step 2: Secure the colored shrimp film inside the coconut water packaging container, ensuring it is completely submerged in the coconut water. During the distribution, storage, and sale of the coconut water, visually observe the color changes of the colored shrimp film. Determine if the coconut water has spoiled by observing whether the structural color on the shrimp shell surface has shifted to red.

[0044] Example 5: The method for real-time visual detection of coconut water freshness in this embodiment is implemented according to the following steps: Step 1: First, wash and drain the black tiger shrimp shells. Soak them in a 5% NaOH solution at 90℃ for 7 hours using a constant temperature water bath. Remove, rinse thoroughly with water, and drain. Repeat the 5% NaOH treatment three times. Next, soak the NaOH-treated shrimp shells in a 0.1M HCl solution at room temperature for 2 hours. Remove, rinse thoroughly with water, and drain. Repeat the 0.1M HCl treatment three times. The repeated NaOH and HCl treatments remove proteins and calcium carbonate from the inside of the shrimp shells. Finally, soak the shrimp shells in a 50% NaOH solution at 95℃ for 9 hours using a constant temperature water bath. Remove, rinse thoroughly, and drain. Repeat the 50% NaOH treatment three times to obtain black tiger shrimp shells with stable iridescent structural colors, i.e., colored shrimp shells.

[0045] Step 2: Secure the colored shrimp film inside the coconut water packaging container, ensuring it is completely submerged in the coconut water. During the distribution, storage, and sale of the coconut water, visually observe the color changes of the colored shrimp film. Determine if the coconut water has spoiled by observing whether the structural color on the shrimp shell surface has shifted to red.

[0046] Example 6: The method for real-time visual detection of coconut water freshness in this embodiment is implemented according to the following steps: Step 1: First, wash and drain the black tiger shrimp shells. Soak them in a 5% NaOH solution at 90℃ for 8 hours using a constant temperature water bath. Remove, rinse thoroughly with water, and drain. Repeat the 5% NaOH treatment three times. Next, soak the NaOH-treated shrimp shells in a 0.1M HCl solution at room temperature for 2.5 hours. Remove, rinse thoroughly with water, and drain. Repeat the 0.1M HCl treatment three times. The repeated NaOH and HCl treatments remove proteins and calcium carbonate from the inside of the shrimp shells. Finally, soak the shrimp shells in a 50% NaOH solution at 95℃ for 10 hours using a constant temperature water bath. Remove, rinse thoroughly, and drain. Repeat the 50% NaOH treatment three times to obtain black tiger shrimp shells with stable iridescent structural colors, i.e., colored shrimp shells.

[0047] Step 2: Secure the colored shrimp film inside the coconut water packaging container, ensuring it is completely submerged in the coconut water. During the distribution, storage, and sale of the coconut water, visually observe the color changes of the colored shrimp film. Determine if the coconut water has spoiled by observing whether the structural color on the shrimp shell surface has shifted to red.

Claims

1. A method for real-time visual detection of coconut water freshness, characterized in that, The specific steps are as follows: Step 1: Prepare colored shrimp skin using black tiger shrimp shells; Step 2: Immerse the colored shrimp shells obtained in Step 1 completely in coconut water and monitor the freshness of the coconut water in real time.

2. The method for real-time visual detection of coconut water freshness according to claim 1, characterized in that, In step 1, the main component of the colored shrimp shell is chitosan, and the chitosan is arranged in a chiral nematic helical structure. The iridescent color on the surface of the colored shrimp shell is a structural color.

3. The method for real-time visual detection of coconut water freshness according to claim 1, characterized in that, In step 1, the shells of black tiger shrimp are treated with NaOH solution and HCl solution to remove protein, calcium and acetylate, so that the chitin in the shrimp shell is converted into chitosan, and colored shrimp skin is obtained.

4. The method for real-time visual detection of coconut water freshness according to claim 1, characterized in that, Step 1 is as follows: Wash and drain the black tiger prawn shells, then soak them in a 5% NaOH solution. After removing them, rinse them with water and drain them again. Repeat this treatment step three times. Next, soak the NaOH-treated prawn shells in a 0.1M HCl solution, then rinse them with water and drain them again. Repeat this treatment step three times. Finally, soak the HCl-treated prawn shells in a 50% NaOH solution, then rinse them with water and drain them again. Repeat this treatment step three times to obtain black tiger prawn shells with stable iridescent structural colors, i.e., colored prawn shells.

5. The method for real-time visual detection of coconut water freshness according to claim 4, characterized in that, When soaking dried shrimp in a 5% NaOH solution, the temperature should be 80-100℃ and the time should be 6-8 hours.

6. The method for real-time visual detection of coconut water freshness according to claim 4, characterized in that, The shrimp shells were soaked in a 0.1M HCl solution at room temperature for 2-3 hours.

7. The method for real-time visual detection of coconut water freshness according to claim 4, characterized in that, When soaking dried shrimp in a 50% NaOH solution, the temperature should be 85-95℃ and the time should be 8-10 hours.

8. The method for real-time visual detection of coconut water freshness according to claim 1, characterized in that, In step 2, the coconut water is judged by whether the color of the colored shrimp shells has changed to red. If a red shift occurs, the water has spoiled; otherwise, it has not spoiled.

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