CN114034697A

CN114034697A - Preparation method of anthocyanin-betanin-k-carrageenan freshness indicating membrane

Info

Publication number: CN114034697A
Application number: CN202111182867.XA
Authority: CN
Inventors: 高莉; 刘盼盼; 刘琳琳; 李伊芸; 张书俐; 郭建峰; 史楠; 王芳; 赵英虎
Original assignee: North University of China
Current assignee: North University of China
Priority date: 2021-10-11
Filing date: 2021-10-11
Publication date: 2022-02-11

Abstract

The invention provides a preparation method of an anthocyanin-betanin-k-carrageenan freshness indicating membrane; the method comprises the following steps: step 1, extracting raw materials: extracting anthocyanin and beet element, and drying for later use; step 2, preparing a freshness indicating film: magnetically stirring anthocyanidin, betanin and 1.5g k-carrageenan, pouring on a polyethylene tetrafluoro plate, and drying. The anthocyanin is used for monitoring the pH change caused by the existence of phenol or a conjugated substance, and the substituent of the betanin is easily oxidized under the alkaline condition, so that the color of the betanin is changed.

Description

Preparation method of anthocyanin-betanin-k-carrageenan freshness indicating membrane

Technical Field

The invention belongs to the technical field of food packaging, storage and detection; in particular to a preparation method of an anthocyanin-betanin-k-carrageenan freshness indicating membrane.

Background

Today, food packaging is not limited to extending the shelf life of the product, but also has intelligent properties. Active and smart packaging technology is an inventive food packaging application that combines active and smart functions in the packaging to improve the safety and quality of packaged food and to monitor the quality of food by sensing external and internal conditions of the packaged food. Due to their efficiency and simplicity, pH sensitive indicator films have been used to monitor and indicate the freshness of food in storage, as spoilage processes are often accompanied by changes in pH. In this way, the consumer can distinguish between fresh and spoiled food products based on the visual difference without opening the package.

The main components of the pH sensitive indicator film are a pH sensitive dye and a solid matrix. Chemical agents such as methylene blue have been used as pH indicators to detect lean freshness, however, synthetic compounds are not ideal pH indicators because of their potentially harmful effects on the human body. In recent years, natural pH indicators have become more and more popular because of their non-toxicity and safety. Some natural pH indicators are used in the preparation of pH sensitive indicators. Anthocyanins and betaines are two different types of natural plants, and have antioxidant, anticancer, antiinflammatory, antibacterial and neuroprotective effects. Anthocyanins are a large class of natural dyes used to monitor pH changes due to the presence of phenols or conjugates. The betalain is prepared from arecolic acid and free radical R₁Or R₂Compositionally, these substituents are readily oxidized under alkaline conditions, resulting in a change in the color of the betalains. The combination of the two with polymer has potential value in developing food packageThe value is obtained.

Food packaging plays a key role in protecting the product from external conditions, making it easy to transport, store and deliver. The synthetic polymer film occupies a large proportion in the field of food packaging due to the advantages of low cost, good durability, good barrier property, good mechanical property and the like. However, in recent years, requirements for safety and biodegradability of food packaging have been increasing. Carrageenan has the advantages of being renewable, biodegradable, good in biocompatibility, good in film forming property and the like, is one of the most widely applied biopolymers at present, and can be used in the fields of food packaging, biomedicine and the like. The k-carrageenan is used as a nontoxic polymer matrix for food packaging and is used for manufacturing edible films so as to improve the food safety and prolong the shelf life.

Disclosure of Invention

The invention aims to provide a preparation method of an anthocyanin-betanin-k-carrageenan freshness indicating membrane. The pH color response type novelty indicator film is prepared by blending anthocyanin extracted from purple sweet potatoes, betanin extracted from pitaya peel and k-carrageenan.

The invention is realized by the following technical scheme:

the invention relates to a preparation method of an anthocyanin-betanin-k-carrageenan freshness indicating membrane, which comprises the following steps:

step 1, extraction of raw materials

And (3) extracting anthocyanin: taking purple sweet potato powder as a raw material, 0.1% HCl-absolute ethyl alcohol as an extracting agent, cellulase as a catalyst (the enzyme addition amount is 54U/mL), the material-liquid ratio is 1:20, the extraction temperature is 50 ℃, the ultrasonic power is 100W, the ultrasonic time is 30min, centrifuging, rotating and evaporating to obtain a concentrated solution, and drying for later use;

extracting betanin: cutting fresh pitaya peel into small pieces with the size of 2-3cm, putting the small pieces into a material machine, and uniformly stirring to obtain pitaya peel pulp; adding the dragon fruit peel pulp and distilled water (mass ratio is 1:5) into a beaker, adjusting pH to 5, extracting in water bath at 40 ℃ for 1.4h, centrifuging at 8000rpm/min for 5min, collecting supernatant, and drying for later use;

step 2, preparation of freshness indicating film

Preparing a composite membrane by adopting a solution casting method;

respectively dispersing the anthocyanin and the betanin prepared in the step 1 in deionized water to respectively obtain a 0.3 w/v% anthocyanin solution and a betanin solution;

mixing the anthocyanin solution and the betanin solution according to the volume ratio of 3:1, 3:2, 1:1, 2:3 or 1:3 to obtain a mixed solution, soaking 1.5g of k-carrageenan by 0.5g of glycerol, adding 50mL of the mixed solution to dissolve the k-carrageenan, magnetically stirring for 30min, then finishing, pouring the film forming solution on a polyethylene tetrafluoro plate, and drying at room temperature. The dried film was treated at 25 ℃ and 50% RH for at least 24 h.

The volume ratio of the anthocyanin solution to the betanin solution is 3:1, 3:2, 1:1, 2:3 and 1:3, and the correspondingly prepared films are kC-A3B1, kC-A3B2, kC-A1B1, kC-A2B3 and kC-A1B3 respectively.

The anthocyanin and the betanin are two different types of natural plants, and have the effects of oxidation resistance, cancer resistance, inflammation resistance, bacteria resistance and neuroprotection. Among them, anthocyanins are a large class of natural dyes used to monitor pH changes due to the presence of phenols or conjugates.

Betalains consist of betacyanin and betaxanthin. Betacyanin is stable under acidic conditions and extremely unstable under alkaline conditions, and is gradually degraded into betaxanthin, thereby causing a change in the color of betalain.

The phenolic substance in the anthocyanin is composed of one or more aromatic ring connected hydroxyl groups, free radicals can be eliminated by forming phenoxy, and the glucosylated phenolic hydroxyl group and cyclic amino group in the betanin are good electron donors and have strong antioxidation effect.

The k-carrageenan has the advantages of being renewable, biodegradable, good in biocompatibility, good in film forming property and the like, and is used for the fields of food packaging, biomedicine and the like. The k-carrageenan is a nontoxic polymer matrix used for food packaging and used for manufacturing edible films so as to improve the food safety and prolong the shelf life.

The invention has the following advantages:

the invention introduces anthocyanin and beet element; the freshness indicating membrane is prepared by mixing anthocyanin, betanin and k-carrageenan; the present invention utilizes anthocyanins for monitoring pH changes due to the presence of phenols or conjugates. The substituent of the betalain is easy to oxidize under alkaline conditions, thereby causing the color change of the betalain, and the invention combines the betalain and the polymer to enhance the pH response discoloration sensitivity of the natural pigment and improve the chemical stability of the natural pigment. Therefore, the efficient and stable freshness indicating film is obtained and applied to food packaging to monitor the freshness and the spoilage degree of packaged products and provide safety guarantee for consumers to purchase high-protein and high-fat packaged foods.

Drawings

FIG. 1 is a graph showing the structural changes of anthocyanins at different pH values;

FIG. 2 is a graph showing the structural changes of betalains at different pH values;

FIG. 3 is a graph of the UV absorption spectrum of anthocyanins at different pH values;

FIG. 4 is a graph of UV absorption spectra of betalains at different pH values;

FIG. 5 is a graph of infrared spectroscopic analysis of several indicator films made in accordance with the present invention;

FIG. 6 is a graph of the effect of the addition of anthocyanins and betaines on the mechanical properties of the indicator films;

FIG. 7 is a graph of an indicator film thermal degradation analysis of the present invention;

FIG. 8 is an analysis graph of the antioxidant activity of the thin film of the present invention;

FIG. 9 is a graph of the sensitivity of the film of the present invention to ammonia vapor;

FIG. 10 is a graph of the effect of the inventive film on pork deterioration;

fig. 11 is a graph indicating the change in total color difference of the film during storage of pork.

Detailed Description

The present invention will be described in detail with reference to specific examples. It should be noted that the following examples are only illustrative of the present invention, but the scope of the present invention is not limited to the following examples.

Examples

The embodiment relates to a preparation method of an anthocyanin-betanin-k-carrageenan freshness indicating membrane, which comprises the following steps:

step 1, extraction of raw materials

And (3) extracting anthocyanin: taking purple sweet potato powder as a raw material, taking 0.1% HCl-absolute ethyl alcohol as an extracting agent, taking cellulase as a catalyst (the enzyme addition amount is 54U/mL), carrying out ultrasonic treatment for 30min at the extraction temperature of 50 ℃ and the ultrasonic power of 100W in a material-liquid ratio of 1:20, carrying out centrifugal rotary evaporation to obtain a concentrated solution, and drying for later use;

step 2, preparation of freshness indicating film

Preparing a composite membrane by adopting a solution casting method;

mixing the anthocyanin solution and the betanin solution according to the volume ratio of 3:1, 3:2, 1:1, 2:3 and 1:3 respectively to obtain a mixed solution, soaking 1.5g of k-carrageenan by using 0.5g of glycerol, adding 50mL of the mixed solution to dissolve the k-carrageenan, magnetically stirring for 30min, then finishing, pouring the film forming solution on a polyethylene tetrafluoro plate, and drying at room temperature. The dried film was treated at 25 ℃ and 50% RH for at least 24 h. The films prepared by the experiment are respectively named as kC-A3B1, kC-A3B2, kC-A1B1, kC-A2B3 and kC-A1B3 according to the proportion of anthocyanin or/and betanin.

Second, performance test

1. Purple potato extract and dragon fruit peel extract were scanned at 200 to 800nm using a ReadMax1900 microplate reader for solutions of pH 2-13. And observing the color change and taking a picture for evidence.

2. Characterization of the Infrared Spectrum

And performing infrared spectroscopy (FIIR) characterization on the purple sweet potato extract, the dragon fruit peel extract and the film. Membrane is dryAfter drying, scanning infrared spectrum in transmission mode by an FTIR instrument, wherein the wave number range is 4000-400 cm^-1Resolution 2cm^-1。

3. Thickness and mechanical properties

The thickness was measured with a digital micrometer to a precision of 0.001mm, 5 points were randomly taken for each film, and the average was calculated in μm.

Tensile Strength (TS) and elongation at break (EB) were measured using a universal tester, and 5 films (100X 15mm) were taken for each type, and the average value was calculated.

4. Water vapor transmission rate

The film samples were cut into squares (6 cm. times.6 cm) and 1g of completely dried anhydrous calcium chloride was sealed in a transparent bottle having an inner diameter of 120mm and covered with a film. The clear vials were stored in a desiccator at 25 ℃ and 100% RH and weighed every 12 hours for 7 consecutive days. The calculation formula is as follows:

Δ m represents the increase in mass g over time t; l represents a film thickness m; a represents an effective area mm²(ii) a t represents the interval time h between two times after stabilization; Δ P represents the difference in water vapor pressure inside and outside the cup.

Note: saturated vapor pressure of water 3170Pa at 25 ℃.

5. Thermal stability

The thermal stability of the membrane was determined by thermogravimetric analysis.

Drying the prepared sample in vacuum (50 ℃, 48h) to constant weight, weighing 5-10mg of the dried sample, placing the sample into a crucible, adopting high-purity nitrogen with the flow of 30mL/min for protection, wherein the temperature scanning range is from room temperature to 600 ℃, and the heating speed is 10 ℃/min.

6. Antioxidant activity

The antioxidant activity of the film was evaluated by DPPH radical scavenging method and ABTS radical scavenging method. To 0.3mL of the film-forming solution was added 2.7mL of a DPPH ethanol solution (0.1mmol/L), and the mixture was reacted at room temperature with light for 30 min. The absorbance value A was measured at 517nm using a microplate reader, as V_cFor positive control, ethanol solution as blank control, 3mL ABTS solution (prepared from 7mM ATBTS ethanol solution and 2.45mM potassium persulfate, OD at 734nm of 0.7 + -0.02) was added to 1mL of the film forming solution, and left at room temperature in the dark for 6 min. OD was measured at 734nm using a microplate reader. Water blank control, V_cIs a positive control.

7. Sensitivity to ammonia

The film samples were cut into squares of 2cm by 2cm diameter and suspended in a small beaker containing ammonia solution (8mm, 80mL) and held at 25 ℃ for 30 min. The distance between the ammonia solution and the film was kept at 1 cm. The color change of the color indicating film was recorded every 5 min. The R, G and B values for the film were measured using a color difference meter, and the sensitivity of the film to volatile ammonia vapor was calculated as follows:

wherein R is₀、G₀、B₀And R₁、G₁、B₁Initial and final values for red, green and blue, respectively, of the film.

Third, the application of the anthocyanin-betanin-k-carrageenan freshness indication film prepared in the embodiment in the pork deterioration process

Taking pork purchased in the day, selecting pork with uniform appearance, dividing the pork into small blocks of about 10g, and putting 10g of fresh pork into a PE box. The indicating film prepared by the embodiment of the invention is cut into a square with the diameter of 2cm multiplied by 2cm and is attached to the box cover, and the indicating film does not contact pork. The color change of the film was recorded at 25 ℃ for 3 days. And taking out the pork samples at intervals to respectively measure the pH value, TVBN value, acidity and other physical and chemical indexes of the pork samples.

1. Determination of the pH value

Mincing 10g of pork, adding 90mL of distilled water, homogenizing, standing, performing suction filtration, measuring the pH value of the filtrate, and repeating the test for 3 times.

2、TVB-N

The determination is carried out according to the method mentioned in the national standard GB5009.228-2016 of the people's republic of China, and the TVB-N content is determined by a full-automatic Kjeldahl method.

3. Acidity/oxidation coefficient

Acidity (° T) (mL/100g) is defined as the volume of NaOH solution (mL) used for 100g of pork samples. Adding 40mL of distilled water into 10mL of prepared pork immersion liquid, then dropwise adding five drops of phenolphthalein reagent, titrating with 0.1M NaOH solution, and calculating the volume number of the consumed NaOH solution when the solution is reddish, namely the acidity value. And sequentially adding 50mL of distilled water, 5mL of 0.2M sulfuric acid and 1 drop of 0.02M potassium permanganate solution into the conical flask, mixing and heating, adding 10mL of meat immersion liquid, and titrating with 0.02M potassium permanganate until the solution is rose red and does not change color within half a minute, thus obtaining the titration end point. The volume of the solution which consumes the high potassium manganese is the oxidation value, and the calculation method is as the formula:

4. thiobarbituric acid number

10g pork samples were homogenized with 30mL of 7.5% trichloroacetic acid, centrifuged at 3000rpm for 5 minutes, and then filtered. To 2mL of the filtrate was added 2mL of 0.02M thiobarbituric acid solution, and the mixture was heated in a boiling water bath for 40min and cooled. The absorbance was measured at 530nm and the value is expressed in mg of Malondialdehyde (MDA) per kg of product (mg MDA/kg).

Fourth, analysis results

1. pH sensitivity of anthocyanins, betaines

As shown in fig. 1: the purple sweet potato extract anthocyanin has obvious color change under different pH values, because the anthocyanin has four structures of yellow molten salt ions, pseudoalkaloid, chalcone and quinoid alkali under different pH environments. When the pH value is less than 4, the purple sweet potato extract solution is red, and the molecular structure exists in a yellow molten salt ion form; when the pH is less than 7, the purple sweet potato extract solution presents light purple and exists in the form of chalcone or alcohol type pseudobase; when the pH value is more than 7, the purple sweet potato extract solution changes from blue to yellow green and exists in the form of quinoid alkali.

As shown in figure 3, in the range of pH2-13, the color of the purple sweet potato anthocyanin finally changes into yellow green from red to purple to blue along with the increase of the pH value, and the maximum absorption peak of an ultraviolet-visible spectrum moves from 530nm to 550nm and finally to 600 nm.

As shown in fig. 2, the solution color changed from red to colorless and finally to yellow as the pH of the pitaya peel extract betalain changed from 2 to 13. Accordingly, the UV-visible spectrum is also changed.

As shown in FIG. 4, the absorbance of the solution varied with increasing pH, and the maximum absorption peak was red-shifted from 536nm to 546nm and the absorbance gradually decreased at pH > 8. When the pH is between 11 and 13, the maximum absorption peak is blue-shifted to 408nm again, and the absorbance is also gradually decreased as the pH is increased. At p H > 11, the yellowing of the solution is due to the hydrolysis of betacyanin to betaxanthin under alkaline conditions.

2. Infrared spectroscopic analysis

As shown in FIG. 5, the purple sweet potato extract is at 3448cm^-1The peak of absorption was strong and broad, and it is presumed that the peak might be the stretching vibration of a hydrogen-bonded hydroxyl group (OH) between anthocyanin molecules, 1635cm^-1The absorption peak at (a) may be due to the C ═ C stretch, 1035cm, of the aromatics in the anthocyanin^-1The absorption peak is C-O stretching vibration.

The extract of pericarp of Pitaya canna is 3369 and 3481cm^-1Absorption peak at 1629cm corresponding to stretching vibration of hydroxyl (OH)^-1Corresponds to CN elongation of 1024cm^-1The absorption peak of (a) corresponds to the C-O-C stretch.

k-carrageenan film at 3413cm^-1The band of (2) is due to-OH stretching vibration, 2852, 2922cm^-1Corresponds to C-H stretching vibration, 1649cm^-1The absorption peak appeared in relation to the O-H bend of the absorbed water, 1265cm^-1、1041cm^-1、918cm^-1The absorption peaks correspond to the sulfate bond, the glycoside bond in carrageenan and the pyran ring in polysaccharide.

Therefore, the spectrum of the film is not obviously changed after a small amount of purple sweet potato extract and dragon fruit peel extract are added. Carrageenan film containing purple sweet potato extract and dragon fruit peel extract and having increased-OH stretching zoneStrong and moved to 3413-3336 cm^-1. In conclusion, from the FT-IR spectrum, the substance structure is mainly influenced by intermolecular forces, and the chemical composition is not changed.

3. Analysis of thickness and mechanical Properties

Shown by fig. 6, in which (a) indicates a thickness influence diagram of the film; (B) indicating tensile strength impact profile of the film; (C) graph indicating the effect of elongation at break of the film; (D) water vapor permeability impact plot of the indicated membranes. As can be seen from (A) (B) (C) in FIG. 6, the addition of anthocyanins and betaines had no significant effect on the thickness of the film (p > 0.05). The tensile strength is related to the acting force of substance crystal form and intermolecular hydrogen bond, the elongation at break can reflect the flexibility of the material, and the addition of anthocyanin and betanin obviously improves the tensile strength and the elongation at break (P is less than 0.05) of the film.

4. Water vapor permeability

The water vapor transmission rate is an important parameter for researching the compactness of the membrane material. As shown in the graph indicating the influence of water vapor permeability of the membrane in FIG. 6 (D), the water vapor permeability of the kC membrane was 2.01X 10^-9g·m/h·pa·m²The addition of anthocyanins and betaines significantly reduced the water vapor permeability of the membrane (P < 0.05).

5. Analysis of thermal stability

As can be seen from fig. 7, the thermal degradation of the film is divided into three stages: the initial weightlessness of the carrageenan film and the composite film is within the range of 60-70 ℃, mainly due to the evaporation of water; the second decomposition starts around 150 ℃ and reaches a maximum of 190 ℃ due to the evaporation of glycerol; the final weight drop occurred at 250 ℃ and 300 ℃ due to the breakdown of carrageenan. The slight mass loss from 500 ℃ to 600 ℃ is that the addition of the compounded indicator, which gradually changes the film ingredients to a semi-char state, increases the thermal stability of the film, probably because the interaction between the pigment and carrageenan can increase the thermal stability of the film.

6. Antioxidant activity

As shown in fig. 8, wherein(A) To characterize its radical scavenging rate by DPPH antioxidant properties,(B) characterizing the free radical clearance diagram for the antioxidant properties of ABTS; from FIG. 8, it can be seen thatThe carrageenan film without the anthocyanin extract and the betanin extract has weak oxidation resistance, the oxidation resistance of the composite film added with the anthocyanin and the betanin is obviously improved (P is less than 0.05), and when the addition amount of the anthocyanin or the betanin is 0.3 w/v%, the clearance rates of the carrageenan film on DPPH and ABTS are respectively improved from 7.75% and 6.88% to 40.39%, 57.67% and 42.32% and 66.80%. Because the phenolic substance in the anthocyanin is composed of one or more aromatic ring connecting hydroxyl groups, the free radical can be eliminated by forming phenoxy, and the glucosylated phenolic hydroxyl group and cyclic amino group in the betanin are good electron donors and have stronger antioxidation.

7. Ammonia sensitivity assay

As can be seen from FIG. 9, as time increases, the NH in the headspace₃The concentration is increasing, A) in FIG. 9 is the RGB change rate (S)_RGB) Fig. B) is a color change diagram of the indicating film. Wherein kC-A3B2 and kC-A1B3 both reduced SRGB and then increased SRGB at 15min, probably due to NH₃Can be combined with water molecules on the surface of the membrane and hydrolyzed to obtain NH₄+ and OH^-However, NH₄ ⁺The increase of the ions can greatly improve the hydrophilicity of the carrageenan in the membrane, so that the composite membrane absorbs water and swells to cause the fluctuation of the pH value of the anthocyanin environment.

8. Application of indicating film in pork deterioration process

(1) pH value

The pH value is an important index for evaluating the meat quality, and is an important index indicating the freshness of meat. As shown in fig. 10(a), the pH of the pork showed an overall increase (p < 0.05) in the pH change graph of the pork during storage, and the pH of the meat at the initial stage of storage was 5.74, indicating that the pork had a good nutritional status. The pH increased slowly to 6.44 after 12h of storage, at which point the pH increased probably because the protein started to decompose, producing alkaline amines and the pH started to rise. On day 3 of storage, the pH increased to 6.89, indicating that the muscle proteins were enzymatically decomposed to produce alkaline substances that caused the pH to rise, resulting in gradual spoilage of pork.

(2) TVB-N value

Microbial spoilage of protein and fat in pork produces large amounts of volatile nitrogen compounds (TVB-N), resulting in pork spoilage and pH changes. The Chinese standard (GB2707-2016) specifies that the upper limit of the TVB-N value of fresh pork is 15mg/100 g. As shown in FIG. 10B, the TVB-N value of pork in storage showed a marked increase in TVB-N value (P < 0.05) with the increase in storage time. The initial TVB-N value of the meat was 6.81mg/100g, and the TVB-N value increased to 14.67mg/100g after 12h of storage. At the 18 th hour, the TVB-N value is 19.24, which exceeds the upper limit of the Chinese standard. The TVB-N value of the pork is 33.51 when the pork is stored for 72 hours, and the pork is rotten.

(3) Acidity/oxidation coefficient

The acidity/oxidation coefficient of pork is shown in fig. 10(C) a graph of the acidity/oxidation coefficient of pork during storage. The acidity/oxidation coefficient during storage shows a slightly decreasing trend (P > 0.05). This is because the acidity of meat decreases during storage, and the acidity/oxidation coefficient as a whole tends to decrease.

(4)TBARS

Lipid oxidation is an important factor leading to the deterioration of fresh meat and TBARS is used to assess the freshness and degree of lipid oxidation of fresh meat, expressed as mg Malondialdehyde (MDA)/kg meat. The upper limit of the TBARS value of the fresh pork is 0.664. As seen from the TBARS of pork in FIG. 10(D) during storage, the TBARS showed an increasing trend (P < 0.05) with increasing storage time. The TBARS of the initial pork was 0.13mgMDA/kg, and on day 3, the TBARS was 1.41mgMDA/kg, at which time the unsaturated fatty acids in the pork reacted with oxygen to produce an unpleasant volatile odor and the meat spoiled.

(5) Change in total color difference of indicator film during pork storage

The color change of the indicating film should be significant in three periods of freshness date, middle freshness date and deterioration date, but not in the same period. As shown in fig. 11, (a) is a plot of the total color difference (Δ Ε) of the meat spoilage indicator film; (B) the color change diagram of the indicating film of the pork deterioration test at 25 ℃; wherein in the (A) storage and preservation period (0-12 h) of the pork, the delta E value of each index label is lower. The indexes kC-A3B2 and kC-A1B3 have higher delta E values in the middle fresh stage (18 th h) and the deterioration stage (24 th to 72 th h) than other indexes. The delta E value has strict correlation with freshness in the whole storage process, and the change of the delta E value of kC-A1B3 in the fresh-keeping period and the deterioration period is small. As shown in FIG. 11(B), the anthocyanidin was red at pH4-7 and at pH < 4, blue to yellowish green at pH > 7, betalain was red at pH8 and at pH < 8, and yellow at pH > 8. The mixed index can expand the color variation range compared to a single index. The anthocyanin and the betanin are mixed in a ratio of 3:2 and added into the membrane, so that the color change range is expanded. Thus, kC-A3B2 is best suited for identifying fresh, medium fresh and spoiled pork near the liriope putrefaction threshold.

In a change area (6-8) of pork deterioration pH value concentration, delta E of the indicating film is larger than 5, which indicates that the difference from fresh to deteriorated can be visually identified by the color of the indicating film. The particularly preferred kC-A3B2 indicates that the film varies most significantly within this range. The kC-A3B2 film exhibited an effective color change for each time period of meat. Therefore, the freshness indicating film can monitor changes in freshness of meat in real time.

The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention.

Claims

1. A preparation method of an anthocyanin-betanin-k-carrageenan freshness indicating membrane is characterized by comprising the following steps:

step 1, extraction of raw materials

And (3) extracting anthocyanin: taking purple sweet potato powder as a raw material, taking 0.1% HCl-absolute ethyl alcohol as an extracting agent and cellulase as a catalyst, extracting according to a material-liquid ratio of 1:20, performing ultrasonic treatment, performing centrifugal rotary evaporation to obtain a concentrated solution, and drying for later use;

extracting betanin: cutting peel of fresh dragon fruit into small pieces of 2-3cm, and stirring to obtain dragon fruit peel pulp; adding the dragon fruit peel pulp and distilled water into a beaker according to the mass ratio of 1:5, adjusting the pH to 5, extracting in water bath at 40 ℃ for 1.4h, centrifuging at 8000rpm/min for 5min, taking supernatant, and drying for later use;

step 2, preparation of freshness indicating film

Respectively dispersing anthocyanin and betanin in deionized water to respectively prepare 0.3 w/v% anthocyanin solution and betanin solution; mixing the anthocyanin solution and the beet pigment solution to obtain a mixed solution; soaking 1.5g of k-carrageenan in 0.5g of glycerol, adding 50mL of the mixture solution, magnetically stirring for 30min, pouring the film forming solution on a polyethylene tetrafluoro plate, drying at room temperature, and treating at 25 ℃ and 50% RH for at least 24h to obtain the anthocyanin-betanin-k-carrageenan freshness indicating film.

2. The method for preparing the anthocyanin-betanin-k-carrageenan freshness indicating membrane of claim 1, wherein the extraction temperature in step 1 is 50 ℃.

3. The method for preparing the anthocyanin-betanin-k-carrageenan freshness indicating membrane of claim 1, wherein in the step 1, the ultrasonic power is 100W, and the ultrasonic time is 30 min.

4. The method for preparing the anthocyanin-betanin-k-carrageenan freshness indicating membrane of claim 1, wherein in the step 2, the volume ratio of the anthocyanin solution to the betanin solution is 3:1, 3:2, 1:1, 2:3 or 1: 3.

5. The method for preparing the anthocyanin-betanin-k-carrageenan freshness indicating membrane of claim 1, wherein in the step 2, the anthocyanin-betanin-k-carrageenan freshness indicating membrane is kC-A3B1, kC-A3B2, kC-A1B1, kC-A2B3, kC-A1B 3.