Method for preparing amine-responsive nanofiber indicating membrane by electrospinning and application thereof in food freshness detection

Abstract

The application belongs to the field of food packaging and food detection, and particularly relates to a method for preparing an amine response type nanofiber indicating film by electrospinning and food freshness detection application thereof, and comprises the following steps: taking polycaprolactone as a film forming base material, polydiacetylene as an indicator, and polyacrylic acid as an auxiliary agent, preparing a nanofiber film by electrospinning technology, and preparing an amine response type nanofiber indicating film through ultraviolet lamp irradiation; the amine response type nanofiber indicating film prepared by the application has good biological safety and mechanical performance, the indicating film added with polydiacetylene and polyacrylic acid can produce obvious color change to low-concentration biological amine, and can effectively indicate the freshness change condition of shrimp and other meat food during transportation and storage. The food freshness intelligent indicating film prepared by the method has wide application value in the field of food intelligent packaging.

Description

Technical Field

[0001] This invention belongs to the field of food packaging and food testing, specifically relating to a method for preparing amine-responsive nanofiber indicator membranes by electrospinning and its application in food freshness detection. Background Technology

[0002] With rapid social and economic development and rising living standards, people are increasingly concerned about food quality and safety. During processing, packaging, storage, transportation, and sales, food is inevitably affected by changes in the external environment or microbial contamination. Taking meat products as an example, because most meat products are high in protein, they are highly susceptible to spoilage during processing or storage, affecting their sales value, processing value, and food safety, thus causing significant economic losses. Therefore, developing intelligent food packaging with real-time freshness detection can help avoid resource waste, reduce economic losses, and support the high-quality development of the food industry.

[0003] In recent years, thanks to the significant advantages of smart food packaging, its research has received widespread attention. Firstly, smart food packaging eliminates the need for any complex instruments for testing; consumers can quickly determine the freshness of food simply by visually observing the color change of the built-in color developer. Furthermore, adding biosafe antioxidants or antibacterial ingredients to the packaging can slow down food oxidation, maintain the food's appearance, and reduce the growth of spoilage-causing bacteria, thereby extending shelf life and reducing food waste.

[0004] During food spoilage, amino acids are converted into large amounts of biogenic amines by microbial decarboxylases. The amount of biogenic amines released is one of the indicators for judging food freshness. Polyacetylene (PDA) can undergo structural changes under the stimulation of biogenic amines, resulting in a blue shift in light absorption and thus inducing a color change. However, PDA has low mechanical properties and sensitivity, affecting monitoring results and limiting its large-scale application. Therefore, it is necessary to add other polymer materials and compounds to enhance its mechanical properties and sensitivity. Summary of the Invention

[0005] To address the problems existing in the prior art, a method for preparing amine-responsive nanofiber indicator membranes by electrospinning is provided, and its application in food freshness detection is also presented.

[0006] The objective of this invention is achieved through the following technical solutions: In a first aspect, the present invention provides a method for preparing an amine-responsive nanofiber indicator membrane by electrospinning, comprising the following steps: Step 1, Preparation of spinning solution: Weigh diacetylene monomer (DA), polycaprolactone (PCL), and polyacrylic acid (PAA) and dissolve them in solvent A, solvent B, and solvent C respectively to obtain DA solution, PCL solution, and PAA solution respectively; mix and stir the DA solution, PCL solution, and PAA solution evenly, and sonicate to obtain spinning solution; Step 2: Preparation of amine-responsive nanofiber indicator membrane: The spinning solution is used to prepare a nanofiber membrane with uniform thickness using a roller collection device. The nanofiber membrane on the receiver is removed and placed under ultraviolet light for irradiation to obtain the amine-responsive nanofiber indicator membrane.

[0007] Preferably, in step 1, solvent A is chloroform, and the concentration of DA is 10~50 mg / mL; solvent B is hexafluoroisopropanol, and the concentration of PCL is 0.1~10 mg / mL; solvent C is distilled water, and the mass concentration of PAA is 0%~20%; the stirring time is 10min~60min, the ultrasonic power is 300~500W, and the ultrasonic time is 30min~60min.

[0008] Preferably, in step 2, an appropriate amount of solution is drawn with a 10 mL syringe, fixed to the push pump, and the distance between the push pump and the roller is adjusted to 10~20 cm. The electrospinning parameters are: temperature (25±5)℃, relative humidity (40±10)%, push speed 0.1~1.0 mL / h, and spinning voltage 10~20 kV. The obtained nanofiber membrane is irradiated under ultraviolet light for 5~30 min and dried in a drying oven for 1~3 h to obtain a smart indicator membrane for food freshness.

[0009] Preferably, the thickness of the indicator film is between 10 micrometers and 200 micrometers.

[0010] Secondly, this invention provides an amine-responsive nanofiber indicator membrane prepared by electrospinning, which is applied to food freshness detection, comprising the following steps: An amine-responsive nanofiber indicator membrane is attached to the space of the sample to be tested. The color of the indicator membrane is observed. When the color is light blue, it indicates that the storage time is less than or equal to 8 hours and the sample is fresh. When the color turns light purple, it indicates that the storage time is greater than 8 hours but less than 14 hours and the sample has begun to spoil. When the color turns light pink or even pink, it indicates that the storage time is greater than or equal to 14 hours and the sample has completely spoiled. Experiments have confirmed that the indicator film prepared in this application is suitable for shrimp, salmon, chicken breast, pork, and other meat products that produce alkaline nitrogenous substances such as ammonia and amines during spoilage. The indicator film changes from light blue to pink as the food begins to spoil.

[0011] Taking shrimp as an example, the detection methods involved in this application are as follows: (1) Freshness detection of shrimp An amine-responsive nanofiber indicator membrane was attached to the space of the sample to be tested. The color of the indicator membrane was recorded at different times using a colorimeter. The color parameter of the indicator membrane at time 0 h was used as a control to calculate the color change of the indicator membrane during the storage process.

[0012] (2) Determination of volatile basic nitrogen The volatile basic nitrogen (TVB-N) of the sample during storage was determined by spectrophotometry as a basis for judging the freshness of the sample. The TVB-N value range of the sample under different storage time was compared with the color change of the indicator label under different storage time in step S1 (1) to evaluate the correlation between the two.

[0013] (3) Determination of microbial colony count The colony count (TVC) of the samples during storage was determined by plate count method as a basis for judging the freshness of the samples. The TVC values ​​of the samples at different storage times were compared with the color changes of the indicator labels at different storage times in step (1) S1 to evaluate the correlation between the two.

[0014] (4) Sensory rating The freshness of the samples was judged by sensory evaluation method. The texture, color and odor of the samples were scored at different storage times. The score value corresponds to the color change of the indicator label at different storage times in step (1) S1. The correlation between the two was evaluated.

[0015] Compared with the prior art, the present invention has the following beneficial effects: (1) Nanofiber membranes prepared by electrospinning technology have a large specific surface area and dense structure, and are widely used in the food packaging field. This invention prepares an indicator membrane by electrospinning technology, using polyacetylene as an amine-sensitive indicator and biodegradable polycaprolactone as a film-forming substrate. By optimizing and determining the optimal addition concentration of polyacrylic acid, an indicator membrane with higher sensitivity and better mechanical properties is obtained, realizing real-time, portable, and visual freshness detection of meat products.

[0016] (2) Traditional freshness detection techniques are cumbersome to operate and require high-quality experimental instruments. The amine-responsive nanofiber indicator membrane in this invention is portable, low-cost, and can intuitively, quickly, and sensitively determine the freshness of food, which is of great significance for ensuring food safety.

[0017] (3) This application does not require the use of ultraviolet lamps or other equipment for detection; the significant color change can be seen with the naked eye, making it more practical. This application uses polyacetylene (PDA) as an amine-responsive indicator. Its color-changing mechanism is based on the conjugated structure transformation induced by biogenic amines, directly targeting the characteristic biogenic amines (such as putrescine and histamine) produced during meat spoilage. Compared with traditional acid-base indicators (such as methyl red and bromothymol blue), it has higher specificity and sensitivity, and is especially suitable for food systems with high protein content. Attached Figure Description

[0018] Figure 1 The images are scanning electron microscope (SEM) images of amine-responsive nanofiber indicator membranes. a) PAA addition is 0%, b) PAA addition is 7%, c) PAA addition is 9%, d) PAA addition is 11%, e) PAA addition is 13%, and f) PAA addition is 15%. Figure 2 The images show actual images of shrimp stored at 25°C for 24 hours after the amine-responsive nanofiber indicator membrane was used. Image a shows the optical images of the shrimp at different storage times, and image b shows the color block images of the indicator membrane at different storage times. Figure 3 For the correlation analysis of color difference and TVB-N, a shows the change of color difference and volatile basic nitrogen over time (0 h-24 h), and b shows the correlation analysis of color difference and volatile basic nitrogen. Figure 4 For the correlation analysis between color difference and TCV, a shows the change of color difference and microbial colony count over time (0 h-24 h), and b shows the correlation analysis between color difference and microbial colony count. Figure 5 For the correlation analysis of color difference and sensory rating, a shows the changes in color difference and sensory rating over time (0 h-24 h), and b shows the correlation analysis between color difference and sensory rating. Detailed Implementation

[0019] The present invention will be described in detail below with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0020] Example 1: Preparation of amine-responsive nanofiber indicator membrane 1.1 Amine-responsive nanofiber indicator membrane without added PAA (1) Preparation of spinning solution Weigh 2 mg of PCL and dissolve it in 5 mL of hexafluoroisopropanol. Stir for 12 h and sonicate for 15 min to prepare the PCL spinning solution. Weigh 90 mg of DA and dissolve it in 3 mL of chloroform. Stir for 30 min and sonicate for 30 min. Mix the PCL spinning solution and the DA monomer solution, stir at room temperature for 1 h, and sonicate for 1 h to obtain the spinning solution.

[0021] (2) Preparation of indicator membrane The spinning solution was filled into a 10 mL syringe and fixed to the feed pump. The distance between the feed pump and the roller was adjusted to 10 cm. The electrospinning parameters were: temperature (25±5)℃, relative humidity (40±10)%, feed speed 0.3 mL / h, and spinning voltage 18 kV. The obtained nanofiber membrane was irradiated under a UV lamp for 10 min and then dried in a drying oven for 3 h to obtain an amine-responsive nanofiber indicator membrane.

[0022] 1.2 Amine-responsive nanofiber indicator membrane with 7% PAA addition Unlike 1.1, (1) the spinning solution preparation is as follows: Weigh 2 mg of PCL and dissolve it in 5 mL of hexafluoroisopropanol, stir for 12 h, and sonicate for 15 min to prepare the PCL spinning solution. Weigh 90 mg of DA and dissolve it in 3 mL of chloroform, stir for 30 min, and sonicate for 30 min. Weigh 140 mg of PAA and dissolve it in 2 mL of distilled water, stir for 30 min, and sonicate for 30 min. Mix the PCL spinning solution, DA monomer solution, and PAA solution, stir at room temperature for 1 h, and sonicate for 1 h to obtain the spinning solution; the rest is the same as in 2.1.

[0023] 1.3 Amine-responsive nanofiber indicator membrane with 9% PAA addition Unlike 1.1, (1) the spinning solution preparation is as follows: Weigh 2 mg of PCL and dissolve it in 5 mL of hexafluoroisopropanol, stir for 12 h, and sonicate for 15 min to prepare the PCL spinning solution. Weigh 90 mg of DA and dissolve it in 3 mL of chloroform, stir for 30 min, and sonicate for 30 min. Weigh 180 mg of PAA and dissolve it in 2 mL of distilled water, stir for 30 min, and sonicate for 30 min. Mix the PCL spinning solution, DA monomer solution, and PAA solution, stir at room temperature for 1 h, and sonicate for 1 h to obtain the spinning solution; the rest is the same as in 2.1.

[0024] 1.4 Amine-responsive nanofiber indicator membrane with 11% PAA addition Unlike 1.1, (1) the spinning solution preparation is as follows: Weigh 2 mg of PCL and dissolve it in 5 mL of hexafluoroisopropanol, stir for 12 h, and sonicate for 15 min to prepare the PCL spinning solution. Weigh 90 mg of DA and dissolve it in 3 mL of chloroform, stir for 30 min, and sonicate for 30 min. Weigh 220 mg of PAA and dissolve it in 2 mL of distilled water, stir for 30 min, and sonicate for 30 min. Mix the PCL spinning solution, DA monomer solution, and PAA solution, stir at room temperature for 1 h, and sonicate for 1 h to obtain the spinning solution; the rest is the same as in 2.1.

[0025] 1.5 Amine-responsive nanofiber indicator membrane with 13% PAA addition Unlike 1.1, (1) the spinning solution preparation is as follows: Weigh 2 mg of PCL and dissolve it in 5 mL of hexafluoroisopropanol, stir for 12 h, and sonicate for 15 min to prepare the PCL spinning solution. Weigh 90 mg of DA and dissolve it in 3 mL of chloroform, stir for 30 min, and sonicate for 30 min. Weigh 260 mg of PAA and dissolve it in 2 mL of distilled water, stir for 30 min, and sonicate for 30 min. Mix the PCL spinning solution, DA monomer solution, and PAA solution, stir at room temperature for 1 h, and sonicate for 1 h to obtain the spinning solution; the rest is the same as in 2.1.

[0026] 1.6 Amine-responsive nanofiber indicator membrane with 15% PAA addition Unlike 1.1, (1) the spinning solution preparation is as follows: Weigh 2 mg of PCL and dissolve it in 5 mL of hexafluoroisopropanol, stir for 12 h, and sonicate for 15 min to prepare the PCL spinning solution. Weigh 90 mg of DA and dissolve it in 3 mL of chloroform, stir for 30 min, and sonicate for 30 min. Weigh 300 mg of PAA and dissolve it in 2 mL of distilled water, stir for 30 min, and sonicate for 30 min. Mix the PCL spinning solution, DA monomer solution, and PAA solution, stir at room temperature for 1 h, and sonicate for 1 h to obtain the spinning solution; the rest is the same as in 2.1.

[0027] like Figure 1 As shown in Examples 1.1-1.6, the microstructure of six amine-responsive nanofiber indicator films was observed. After drying, the amine-responsive nanofiber indicator films were treated with vacuum sputtering gold, and the surface morphology of the samples was observed by field emission scanning electron microscopy (SEM). SEM images were obtained under accelerated decompression at 15 kV.

[0028] Example 2: Application of amine-responsive nanofiber indicator membrane in shrimp freshness detection 2.1 Preparation of spinning solution 2 mg of PCL was dissolved in 5 mL of hexafluoroisopropanol, stirred for 12 h, and sonicated for 15 min to prepare the PCL spinning solution. 90 mg of DA was dissolved in 3 mL of chloroform, stirred for 30 min, and then sonicated for 30 min. 220 mg of PAA was dissolved in 2 mL of distilled water, stirred for 30 min, and then sonicated for 30 min. The PCL spinning solution, DA monomer solution, and PAA solution were mixed, stirred at room temperature for 1 h, and sonicated for 1 h to obtain the spinning solution.

[0029] 2.2 Preparation of Amine-Responsive Nanofiber Indicator Membranes The spinning solution was filled into a 10 mL syringe and fixed to the push pump. The distance between the push pump and the roller was adjusted to 10 cm. The electrospinning parameters were: temperature (25±5)℃, relative humidity (40±10)%, push speed 0.3 mL / h, and spinning voltage 18 kV. The obtained nanofiber membrane was irradiated under ultraviolet light for 10 min and then dried in a drying oven for 3 h to obtain a smart indicator membrane for food freshness.

[0030] 2.3 Freshness testing of shrimp (1) Detection of color difference change of indicator film Fresh shrimp were placed in petri dishes, and amine-responsive nanofiber indicator membranes (2 cm × 2 cm) were adhered to the dishes. The dishes were then sealed with sealing film and stored at 25°C. Color changes in the shrimp and indicator membranes were recorded every 2 hours under natural light using a smartphone. Figure 2 As shown, when the storage time is 8 hours, the indicator film changes from light blue to light purple; when the storage time is 14 hours, the indicator film changes to light pink; and when the storage time is 24 hours, the indicator film changes to pink.

[0031] Preliminary experiments have confirmed that the indicator membrane prepared in this application is also applicable to salmon, chicken breast, and pork. The indicator membrane changes from blue to pink as the food begins to spoil.

[0032] Acquisitions were collected using a colorimeter from an amine-responsive nanofiber indicator membrane. L *, a *, b * Value: Data is collected every 2 hours for a total of 24 hours. The Δ value is calculated using the formula. E value: In the formula: L* is the brightness of the experimental histamine-responsive nanofiber indicator film, and L0 is the brightness of the control group amine-responsive nanofiber indicator film; a *Indicates the redness of the experimental histamine-responsive nanofiber indicator membrane. a 0* represents the redness of the amine-responsive nanofiber indicator membrane in the control group;b * indicates the blueness of the experimental histamine-responsive nanofiber indicator membrane. b 0* represents the blueness of the control group amine-responsive nanofiber indicator film.

[0033] (2) Detection of volatile basic nitrogen During storage, shrimp are tested for volatile basic nitrogen (TVB-N). Based on the TVB-N value, shrimp freshness is graded as follows: Grade 1 Freshness (<15 mg / 100 mg), corresponding to fresh and edible condition; Grade 2 Freshness (15-20 mg / 100g), corresponding to near spoilage and requiring prompt consumption; Grade 3 Freshness (20-30 mg / 100g) and completely spoiled (>30 mg / 100g), corresponding to inedible condition. Figure 3 As shown, after 14 hours of storage, the TVB-N level in shrimp meat increased to approximately 60 mg / 100 g, indicating that the shrimp meat was in a state of complete spoilage. Simultaneously, the TVB-N value of the shrimp meat correlated with the indicator membrane Δ... E They exhibit good consistency and show a positive correlation.

[0034] Combination Figure 2 and Figure 3 In curve a, ∆E shows that when the shrimp were stored for 8 hours, the color of the nanofiber membrane began to change, and ∆E also increased from 0 to 10.99. The membrane began to show a visible color change, from light blue to light purple, indicating that the shrimp had begun to spoil. When the storage time was 14 hours, ∆E increased to 25.09, and the nanofiber membrane turned light pink, at which point the shrimp had completely spoiled. When the storage time was 24 hours, ∆E increased to 36.85, and the color changed from light pink to pink.

[0035] (3) Total number of microorganisms During storage, the total microbial count of shrimp is performed, and the microbial count can be used as one of the indicators of shrimp freshness. When the colony count is ≤5.0 log... 10 CFU / g indicates Grade 1 freshness, with a total bacterial count between 5.0 and 5.7 log. 10 A CFU / g level indicates secondary freshness; when the bacterial count of shrimp is >5.7 mg / g... 10 A CFU / g level indicates that the shrimp meat is spoiled and should not be eaten. Figure 4 As shown, when the storage time was 0 h, the bacterial count of the shrimp was 2.5 log. 10 At this point, the shrimp were at Grade 1 freshness (CFU / g). The bacterial count showed an increasing trend with increasing storage time. When the storage time was 14 hours, the bacterial count exceeded 5.8 log₂ / g. 10 At CFU / g, the shrimp was in a state of complete spoilage. Simultaneously, the total bacterial count in the shrimp meat showed good consistency with the indicator membrane ΔE, exhibiting a positive correlation.

[0036] (4) Sensory rating Sensory evaluation is a common method used by consumers when purchasing aquatic products. It involves judging the freshness of shrimp by changes in their appearance, smell, and color. Figure 5 This refers to the changes in the sensory quality of shrimp during storage. Initially, the shrimp exhibit good overall quality, with a natural color, glossy shell, and a bluish-gray hue. They have a faint shrimp aroma without any other off-odors, scoring 10 points. As storage time increases, the shrimp develop a pungent odor, gradually lose their luster, turn red, and develop a pungent ammonia smell. After 14 hours of storage, black spots appear on the shrimp's surface, turning them red (color score 1.36 points). The meat becomes soft, inelastic, and sticky, and the head may detach (body shape score 1.41 points). An ammonia and foul odor also develops (odor score 1.06 points), resulting in an overall score less than 5 points, making it sensorily unacceptable and indicating complete spoilage. Furthermore, the sensory score of the shrimp meat shows a good consistency with the indicator membrane ΔE, exhibiting a negative correlation.

[0037] The above results demonstrate that the amine-responsive nanofiber indicator membrane of the present invention has high sensitivity, and can accurately determine the freshness of meat products in real time by visual observation. It has good portability and can be used to indicate the freshness of meat products.

Claims

1. A method for preparing an amine-responsive nanofiber indicator membrane by electrospinning, characterized in that, Includes the following steps: Step (1) Preparation of spinning solution: Weigh diacetylene monomer (DA), polycaprolactone (PCL), and polyacrylic acid (PAA) and dissolve them in solvent A, solvent B, and solvent C respectively to obtain DA solution, PCL solution, and PAA solution respectively; mix and stir the DA solution, PCL solution, and PAA solution evenly, and sonicate to obtain spinning solution; the solvent A is chloroform, the concentration of the DA solution is 10~50 mg / mL; the solvent B is hexafluoroisopropanol, the concentration of the PCL solution is 0.1~10 mg / mL; the solvent C is distilled water, and the mass concentration of the PAA solution is 7%~20%; Step (2) Preparation of amine-responsive nanofiber indicator membrane: The spinning solution is used to prepare a nanofiber membrane with uniform thickness using a roller collection device. The nanofiber membrane on the receiver is removed, irradiated under ultraviolet light for 5~30 min, and dried in a drying oven for 1~3 h to obtain the amine-responsive nanofiber indicator membrane. In step (1), the stirring time is 10 min to 60 min, the ultrasonic power is 300 to 500 W, and the ultrasonic time is 30 min to 60 min. In step (2), a suitable amount of solution is drawn with a 10 mL syringe, fixed to the push pump, and the distance between the push pump and the roller is adjusted to 10~20 cm. The push speed is 0.1~1.0 mL / h. The electrospinning parameters are: temperature 25±5℃, relative humidity 40±10%, and spinning voltage 10~20 kV. The thickness of the indicator film is between 10 micrometers and 200 micrometers.

2. An amine-responsive nanofiber indicator membrane prepared by electrospinning, characterized in that, It is prepared by the preparation method described in claim 1.

3. An application of an amine-responsive nanofiber indicator membrane prepared by electrospinning, characterized in that, The amine-responsive nanofiber indicator membrane of claim 1 is pasted in the space of the sample to be tested. The color of the indicator membrane is observed. When the color is light blue, it indicates that the storage time is less than or equal to 8 hours and the sample is fresh. When the color turns light purple, it indicates that the storage time is greater than 8 hours but less than 14 hours and the sample has begun to spoil. When the color turns light pink or even pink, it indicates that the storage time is greater than or equal to 14 hours and the sample has completely spoiled.

4. The application of the amine-responsive nanofiber indicator membrane prepared by electrospinning according to claim 3, characterized in that, The samples to be tested were meat products that produced ammonia and amine-like alkaline nitrogenous substances during the spoilage process.

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