A pH colorimetric film for indicating freshness of meat

Abstract

This invention discloses a pH colorimetric membrane for indicating meat freshness, obtained through the following steps: First, konjac glucomannan and polyvinyl alcohol are dissolved separately in distilled water and heated and stirred until dissolved; then, the konjac glucomannan aqueous solution and the polyvinyl alcohol aqueous solution are mixed to obtain a film-forming solution; curcumin and alizarin are added to the film-forming solution, homogenized using a homogenizer, and then ultrasonically treated to remove air bubbles; the solution is poured into a plastic petri dish and dried in an incubator to obtain the pH colorimetric membrane. This invention uses a 3:1 mass ratio of curcumin and alizarin as colorants, resulting in stronger pH sensitivity and more obvious color changes. Furthermore, all raw materials used are derived from natural substances, are safe and non-toxic, and edible. No complex processing of meat samples is required, making the operation simple and low-cost. It has great application potential in meat freshness monitoring and intelligent packaging, and can be applied to the freshness monitoring of various meat products.

Description

Technical Field

[0001] This invention belongs to the field of food monitoring technology, and specifically relates to a pH colorimetric membrane for indicating the freshness of meat. Background Technology

[0002] With the continuous improvement of living standards, meat has become an indispensable part of people's daily food consumption, and its consumption is constantly increasing. Meat contains a large amount of protein, fatty acids, vitamins, minerals, and other bioactive components. Precisely because it contains rich nutrients, it is extremely susceptible to microbial contamination during processing, storage, transportation, and sales, leading to spoilage and deterioration. This not only reduces the nutritional value and hygienic quality of the meat but may also endanger consumers' health.

[0003] With changing consumer habits and increased emphasis on food safety, real-time monitoring of meat freshness has become crucial, as it comprehensively reflects the product's nutritional safety. Meat, rich in protein and water, is prone to oxidation and spoilage during transportation and storage, producing volatile amines and causing an increase in pH levels within the packaging. pH colorimetric membranes utilize the volatile alkaline substances (such as dimethylamine, trimethylamine, and ammonia) produced during meat spoilage by microorganisms and enzymes as "information" to monitor meat freshness. Generally, pH colorimetric membranes consist of a solid carrier and a pH-sensitive dye. The solid matrix used for the membrane is mainly of two types: natural and synthetic. For safety and edibility considerations, natural polysaccharide polymers (such as starch and pectin) have been the most extensively studied.

[0004] Konjac glucomannan (KGM) is a natural polysaccharide and water-soluble dietary fiber derived from the tuber of the konjac plant. It is composed of β-1,4-linked D-mannose and D-glucose. KGM possesses excellent film-forming ability, good water absorption and gelling properties, and also exhibits special physiological functions such as lowering blood pressure and blood lipids, enhancing immunity, and inhibiting tumors. Furthermore, KGM has advantages such as good biocompatibility, non-toxicity, harmlessness, and biodegradability, making it widely used in food, pharmaceuticals, and materials, and possessing significant application value. pH-sensitive colorants are another important component of pH-matching films, including both natural and synthetic indicators. Natural pH-sensitive pigments mainly contain anthocyanins, curcumin, betaine, alizarin, etc. Currently, natural pigments are widely favored due to their non-toxicity, safety, and easy degradation. However, the instability of natural pigments under light and heat conditions limits the application of smart films. Studies have shown that mixed natural pigments are more sensitive to indicating meat freshness than individual natural pigments, and individual natural pigments used for meat freshness detection suffer from structural instability, monotonous color changes, and poor visual identification. Curcumin is a natural pigment extracted from the rhizomes of plants such as turmeric (Zingiber officinale). It is yellow under neutral and acidic conditions and reddish-brown under alkaline conditions. It is highly stable to reducing agents, has strong coloring properties, and does not easily fade after coloring. Alizarin is a natural pigment extracted from the roots of the madder plant. It is yellow under acidic conditions, red under weakly alkaline conditions, and blue-purple under strongly alkaline conditions. Summary of the Invention

[0005] The purpose of this invention is to provide a pH colorimetric membrane that is more sensitive to meat freshness and shows obvious color changes.

[0006] To achieve the above objectives, the pH colorimetric membrane used in this invention is prepared by the following steps:

[0007] Step 1: Add konjac glucomannan and polyvinyl alcohol to distilled water separately, heat and stir until dissolved;

[0008] Step 2: Mix the konjac glucomannan solution and polyvinyl alcohol solution obtained in Step 1 to obtain a film-forming solution;

[0009] Step 3: Add a mixture of curcumin and alizarin in a mass ratio of 3:1 as a colorant to the film-forming solution obtained in step 2, and then homogenize it with a homogenizer and sonicate it to remove air bubbles in the solution to obtain a uniform film-forming mixture.

[0010] Step 4: Pour the film-forming mixture obtained in Step 3 into a petri dish and place it in an oven to dry. After drying, a pH colorimetric membrane is obtained.

[0011] In step 1 above, the preferred addition amount of konjac glucomannan in the distilled water is 4.0-5.0 g / mL, the preferred addition amount of polyvinyl alcohol is 2.0-2.5 g / mL, the preferred heating temperature is 90-100℃, and the preferred stirring time is 30-40 minutes.

[0012] In step 2 above, the volume ratio of the konjac glucomannan solution to the polyvinyl alcohol solution is preferably 1:1 to 1:1.5.

[0013] In step 3 above, it is preferred that the mass ratio of curcumin to alizarin in the colorant is 3:1, and it is even more preferred that the amount of colorant added is 3.0% to 4.0% of the volume of the film-forming solution.

[0014] In step 3 above, it is preferred that the rotation speed of the homogenizer is 10,000 to 11,000 rpm and the homogenization time is 5 to 8 minutes.

[0015] In step 3 above, the preferred time for the ultrasonic treatment is 5 to 10 minutes.

[0016] In step 4 above, the drying temperature is preferably 35-45°C and the drying time is 20-24 hours.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0018] 1. The konjac glucomannan, curcumin and alizarin used in this invention are all derived from natural substances, are safe and non-toxic, and are edible.

[0019] 2. In this invention, curcumin and alizarin are compounded in a mass ratio of 3:1 as coloring agents, which are more sensitive to pH and show obvious color changes.

[0020] 3. This invention requires no complicated processing of meat samples, is simple to operate, low in cost, and does not require special or expensive instruments and equipment, making it easy to promote and apply.

[0021] 4. The konjac glucomannan used in this invention has special physiological effects such as lowering blood pressure, lowering blood lipids, enhancing immunity, and inhibiting tumors.

[0022] 5. This invention can be applied to the monitoring of the freshness of various meat products. Attached Figure Description

[0023] Figure 1 These are water solubility diagrams of the pH colorimetric membranes obtained in Example 1 and Comparative Examples 1-4.

[0024] Figure 2 These are the pH colorimetric membranes obtained in Example 1 and Comparative Examples 1-4, used to monitor the freshness of pork and the changes in TVB-N. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments, but the scope of protection of the present invention is not limited to these embodiments.

[0026] Example 1

[0027] Step 1: Add 3.2g of konjac glucomannan and 1.6g of polyvinyl alcohol to 70mL of distilled water respectively, and stir at 95℃ for 30 minutes to dissolve them;

[0028] Step 2: Mix the konjac glucomannan solution and polyvinyl alcohol solution obtained in Step 1 to obtain a film-forming solution;

[0029] Step 3: Add 5 mL of colorant to the film-forming solution obtained in Step 2, homogenize at 10,000 rpm for 5 minutes using a homogenizer, and then sonicate for 10 minutes to remove air bubbles from the solution to obtain a uniform film-forming mixture; wherein, the colorant is a mixture of 0.5 g / L curcumin ethanol solution and 0.5 g / L alizarin ethanol solution in a volume ratio of 3:1;

[0030] Step 4: Take 20 mL of the film-forming mixture obtained in Step 3 and pour it into a 9 cm diameter petri dish. Place the petri dish in an oven and dry it at 40 °C for 24 hours to obtain a pH colorimetric membrane.

[0031] Comparative Example 1

[0032] In step 3 of Example 1, 5 mL of 0.5 g / L curcumin ethanol solution was added as a coloring agent, and the other steps were the same as in Example 1 to obtain a pH colorimetric membrane.

[0033] Comparative Example 2

[0034] In step 3 of Example 1, 5 mL of 0.5 g / L alizarin ethanol solution was added as a coloring agent, and the other steps were the same as in Example 1 to obtain a pH colorimetric membrane.

[0035] Comparative Example 3

[0036] In step 3 of Example 1, the colorant is prepared by mixing 0.5 g / L curcumin ethanol solution and 0.5 g / L alizarin ethanol solution in a volume ratio of 1:3. The other steps are the same as in Example 1 to obtain a pH colorimetric film.

[0037] Comparative Example 4

[0038] In step 3 of Example 1, the colorant is prepared by mixing 0.5 g / L curcumin ethanol solution and 0.5 g / L alizarin ethanol solution in a volume ratio of 1:1. The other steps are the same as in Example 1 to obtain a pH colorimetric film.

[0039] The water solubility of the pH colorimetric membranes obtained in Example 1 and Comparative Examples 1-4 above, and various indicators for monitoring pork freshness were determined. The specific determination methods and results are as follows:

[0040] 1. Water solubility analysis of colorimetric membranes

[0041] Cut the pH colorimetric membrane into 2cm × 2cm slices and dry at 50°C for 30 minutes. Record the weight (w0) of each dried membrane, then immerse it in 80mL of distilled water at room temperature for 1 hour. Finally, dry it in a hot air oven at 100°C until a constant weight (w1) is achieved. Water solubility (WS) is calculated using the following formula:

[0042] WS(%)=(w0-w1 / w0)×100

[0043] As a packaging material, the lower its water solubility, the better it is for the transportation and storage of food. Figure 1 As can be seen, although the water solubility of the pH colorimetric membranes of Example 1 and Comparative Examples 1-4 showed significant differences in significance analysis, the values ​​were distributed between 60% and 70%, which is not significant. This indicates that the addition of the mixed colorant of curcumin and alizarin did not increase the water solubility of the colorimetric membrane.

[0044] 2. Application of colorimetric membrane in monitoring pork freshness

[0045] Five pH colorimetric membranes were used to detect the freshness of pork. The specific method was as follows: 30g of fresh pork and a pH colorimetric membrane (2cm×2cm) were placed in a petri dish (12cm in diameter) and stored in a constant temperature incubator at 25℃ for 28 hours. The color change of the membrane was recorded with a camera, and the TVB-N of the sample was determined using an automatic Kjeldahl nitrogen analyzer. TVB-N is expressed as mg / 100g.

[0046] Depend on Figure 2As can be seen, the colorimetric membranes of Comparative Examples 1 and 2 only exhibited a uniform color change from light to dark, while the pH colorimetric membrane of Example 1 showed a color change from yellow to red, a change easily identifiable to the naked eye. When the TVB-N content was 9.84 mg / 100g, the pH colorimetric membrane of Example 1 changed from yellow to red, while the pH colorimetric membranes of Comparative Examples 2 and 3 only showed a color change when the TVB-N content was 16.09 mg / 100g. This indicates that the pH colorimetric membrane of Example 1 is more sensitive to volatile ammonia substances produced during meat spoilage, and the color change is more obvious, making it easier for consumers to visually identify the color change. The national standard GB / T 5009.228–2016 classifies meat freshness based on the TVB-N content. When the TVB-N content is less than 15mg / 100g, it is classified as Grade 1 fresh meat; when the TVB-N content is between 15 and 25mg / 100g, it is classified as Grade 2 fresh meat; and when the TVB-N content is greater than 25mg / 100g, it is classified as spoiled meat. When the pH colorimetric membrane of Example 1 of this invention is applied to the detection of pork freshness, the color change is most obvious. When the storage time is 0-8 hours, the TVB-N content is less than 15 mg / 100g, and the pH colorimetric membrane is yellow, indicating that the pork is Grade 1 fresh meat. When the storage time is 20-24 hours, the TVB-N content is in the range of 15-25 mg / 100g, and the pH colorimetric membrane is already reddish-brown, indicating that the pork is Grade 2 fresh meat. When the storage time is greater than 28 hours, the TVB-N content exceeds 25 mg / 100g, and the pH colorimetric membrane is already dark brown, visibly darker than Grade 1 fresh meat, indicating that the pork has spoiled and is inedible.

Claims

1. A pH colorimetric membrane for indicating the freshness of meat, characterized in that, The pH colorimetric membrane was prepared by the following steps: Step 1: Add konjac glucomannan and polyvinyl alcohol to distilled water separately, heat and stir until dissolved; Step 2: Mix the konjac glucomannan solution and polyvinyl alcohol solution obtained in Step 1 to obtain a film-forming solution; Step 3: Add a colorant to the film-forming solution obtained in Step 2, homogenize using a homogenizer, and then sonicate to remove air bubbles from the solution to obtain a uniform film-forming mixture; the colorant is prepared by mixing a 0.5 g / L curcumin ethanol solution and a 0.5 g / L alizarin ethanol solution at a volume ratio of 3:1; the amount of colorant added is 3.0% to 4.0% of the volume of the film-forming solution; Step 4: Pour the film-forming mixture obtained in Step 3 into a petri dish and place it in an oven to dry. After drying, a pH colorimetric membrane is obtained.

2. The pH colorimetric membrane for indicating meat freshness according to claim 1, characterized in that, In step 1, the amount of konjac glucomannan added to the distilled water is 4.0–5.0 g / mL, the amount of polyvinyl alcohol added is 2.0–2.5 g / mL, the heating temperature is 90–100℃, and the stirring time is 30–40 minutes.

3. The pH colorimetric membrane for indicating meat freshness according to claim 2, characterized in that, In step 2, the volume ratio of the konjac glucomannan solution to the polyvinyl alcohol solution is 1:1 to 1:1.

5.

4. The pH colorimetric membrane for indicating meat freshness according to claim 1, characterized in that, In step 3, the homogenizer rotates at 10,000 to 11,000 rpm, and the homogenization time is 5 to 8 minutes.

5. The pH colorimetric membrane for indicating meat freshness according to claim 1, characterized in that, In step 3, the ultrasonic treatment time is 5 to 10 minutes.

6. The pH colorimetric membrane for indicating meat freshness according to claim 1, characterized in that, In step 4, the drying temperature is 35-45°C and the time is 20-24 hours.

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