Composite packaging film for fresh keeping of fresh bamboo fungus and preparation method of composite packaging film

Abstract

The invention provides a composite packaging film for fresh keeping of fresh bamboo fungi and a preparation method of the composite packaging film. The functional composite film is mainly prepared by taking gelatin and carrageenan as film-forming substrates and adding bamboo fungus support extracting solutions with different concentrations. The mechanical properties (tensile strength and elongation at break), gas permeability, color, ultraviolet absorbance and oxidation resistance of the composite film are explored. Results show that the dictyophora indusiata mushroom support extracting solution can be well blended with the film-forming substrate. Along with the increase of the content of the dictyophora indusiata mushroom support extracting solution in the composite film, the mechanical property of the composite film is enhanced, the water vapor transmission rate is increased, the light transmittance is reduced, and the composite film has a certain barrier function and relatively high oxidation resistance. The composite film is used for fresh keeping of fresh bamboo fungi, the rotting rate of the fresh bamboo fungi can be remarkably reduced, the reduction of the content of soluble solids is slowed down, and a certain inhibition effect on extracellular enzyme activity can be achieved. And a new method is provided for fresh keeping of the fresh bamboo fungus.

Description

Technical field:

[0001] The invention relates to the technical field of food preservation, and in particular to the preparation of a composite packaging film and application thereof in the preservation of fresh bamboo fungus. The composite film has certain antioxidant capacity, good ultraviolet blocking capacity, excellent mechanical strength and the like, can significantly inhibit the respiration intensity of the fresh bamboo fungus during storage, reduce the loss of nutrients, and effectively maintain the quality of the fresh bamboo fungus. Technical background:

[0002] Bamboo fungus, also known as bamboo fungus and bamboo ginseng, is a kind of precious large edible fungus, known as the "Queen of Fungi". It has high nutritional value, rich in polysaccharides, various amino acids and multiple trace elements, and has the effects of enhancing immunity, anti-tumor and anti-aging. However, fresh bamboo fungus has high water content, strong respiration, lack of tissue protection, and is easily susceptible to mechanical damage and microbial infection. Therefore, it is easy to have quality problems such as water loss, browning, and rotting during storage.

[0003] At present, the market mainly sells bamboo fungus as dried products. However, the drying process is carried out at high temperature, and some physiologically active substances and vitamin substances (such as vitamin C, etc.) in the bamboo fungus are easily damaged during the drying process, and soluble sugars are easily caramelized and lost. These factors have led to the loss of nutrition in the bamboo fungus, which is not conducive to the preservation of bamboo fungus nutrients. The preservation of fresh bamboo fungus has always been a problem that restricts the sale of bamboo fungus.

[0004] The existing preservation methods of edible fungi mainly include physical preservation and chemical preservation. Physical preservation includes low-temperature preservation, atmosphere-controlled refrigerated preservation, irradiation preservation, ultra-high pressure treatment preservation, etc. Although this method can achieve certain effects, most of them have the disadvantages of expensive facilities, strict operating requirements, high energy consumption, and unsuitable for promotion and use. Chemical preservation includes preservative preservation, acid electrolyzed water preservation, ozone preservation, etc. This method has the advantage of low price and significant effect on inhibiting the reproduction of microorganisms and bacteria. However, the chemical reagents used in preservative preservation or acid electrolyzed water preservation may leave residues on the surface of food, making the safety of this preservation method a matter of concern. Since the optimal treatment concentration of ozone has not yet been determined, its preservation effect is uncertain; and its preservation mechanism has not yet been determined, so its scientificity and safety cannot be guaranteed. At present, there are few preservation methods for fresh bamboo fungus on the market, and the main preservation methods used for edible fungi include low-temperature preservation (traditional ice bag foam box plus absorbent paper, refrigerator, cold storage, etc.), preservative preservation (1-MCP preservation, etc.) and ozone preservation, etc. These preservation technologies not only have the above shortcomings, but also have a short preservation time, and will rot and deteriorate in 2-7 days.

[0005] Therefore, how to overcome the shortcomings of existing bamboo fungus preservation methods and propose an economical, safe, pollution-free and widely applicable preservation method is an urgent problem to be solved. Biodegradable edible composite films have become a research hotspot in the field of edible fungus preservation packaging and are a potential way to solve this problem. Gelatin is a protein-based edible film material with good film-forming properties and biocompatibility, but a single gelatin film has the disadvantage of poor ductility; carrageenan has good gel properties and is usually used as a thickener, gelling agent, emulsifier and stabilizer in the food industry; compounding carrageenan with gelatin can produce a composite film with good performance. Bamboo fungus stipe is the main by-product of bamboo fungus. It is a natural barrier for the fruiting body to resist various external stresses (oxygen, water vapor, pathogens, etc.), and it transports nutrients to fresh bamboo fungus during its growth process. It is rich in protein, polysaccharides, polyphenols, flavonoids and other active substances. However, at present, bamboo fungus stipe is just discarded as waste and has not been fully utilized. Adding the natural antioxidant components in the bamboo fungus stipes into gelatin and carrageenan solutions can prepare a green and pollution-free composite film, which provides technical support for promoting the resource circulation of the bamboo fungus stipes, making the best use of them and preserving fresh bamboo fungus. Summary of the invention:

[0006] The present invention aims to disclose a method for preparing a safe, non-toxic and biodegradable composite film for preserving fresh bamboo fungus, so as to overcome the shortcomings mentioned in the above background technology.

[0007] To achieve this purpose, the present invention adopts the following technical scheme: gelatin-carrageenan is used as the main film-forming matrix, and different concentrations of bamboo fungus stalk extract are added as the main active ingredient, and the preservation and storage time of fresh bamboo fungus is extended by effective means such as reducing the respiration intensity, reducing the gas permeability, and anti-oxidation. The method has the characteristics of simple operation, low cost, and no pollution, and is a green and environmentally friendly preservation method.

[0008] The specific preparation process of the composite film (G-KC-DVE) is as follows:

[0009] (1) Weigh a certain amount of gelatin and dissolve it in 60 mL of distilled water. Stir at a certain temperature until it is completely dissolved.

[0010] (2) Weigh a certain amount of carrageenan and dissolve it in 60 mL of distilled water. Stir at a certain temperature until it is completely dissolved.

[0011] (3) The gelatin solution and the carrageenan solution were mixed evenly in a magnetic stirrer at 400 rpm.

[0012] (4) Add a certain amount of glycerol and stir at 80°C for 30 minutes to ensure that the solution is fully mixed.

[0013] (5) Add different concentrations of bamboo fungus stalk extract to the above solution, and stir at 80° C. for 30 minutes on a magnetic stirrer (400 rpm).

[0014] (6) The prepared solutions of different trophoside extract concentrations were cast onto an acrylic plate (16 cm-25 cm).

[0015] (7) Place in a forced air drying oven at a certain temperature for several hours.

[0016] (8) After drying, remove the film and place it in a desiccator for equilibrium.

[0017] Furthermore, in step 1, the amount of gelatin added is 3.60 g and the stirring temperature is 60°C.

[0018] Furthermore, in step 2, the amount of carrageenan added is 1.20 g, and the stirring temperature is 80°C.

[0019] Furthermore, the amount of gelatin added in step 4 is 1.20 g.

[0020] Furthermore, the concentration of the bamboo fungus stalk extract (DVE) added in step 5 is 0.00wt%, 3.00wt%, 5.00wt%, 10.00wt%, 15.00wt%, and 20.00wt%.

[0021] Furthermore, in step 7, the temperature of the blast drying oven is 60° C., and the drying time is 6-7 hours.

[0022] Furthermore, in step 8, the dryer balancing time is 2-3 days.

[0023] Beneficial technical effects:

[0024] (1) The present invention provides a functional composite film for preserving fresh bamboo fungus. Bamboo fungus stipes are the main by-products of bamboo fungus, accounting for 20%-30% of the fresh weight of the whole plant. Bamboo fungus stipe extract has a variety of nutrients, including polysaccharides, polyphenols, flavonoids and other substances, has a certain antioxidant capacity, and is a natural antioxidant active ingredient. Gelatin has good film-forming properties and a certain gas barrier capacity, but a single gelatin film has poor mechanical properties and is prone to breakage. Compounding with carrageenan can enhance the tensile strength of the film and has a certain UV barrier capacity. The bamboo fungus stipe extract-gelatin-carrageenan composite film has a certain antioxidant capacity, water vapor permeability, UV barrier capacity and has high mechanical properties.

[0025] (2) The present invention uses the bamboo fungus stalk extract-gelatin-carrageenan composite film for the preservation of fresh bamboo fungus, which can significantly reduce the decay rate of fresh bamboo fungus, slow down the decrease of soluble solid content and polyphenol flavonoid content, and can play a certain inhibitory effect on extracellular enzyme activity. Description of the drawings:

[0026] Figure 1 It is a comparison diagram of the appearance of six kinds of composite films prepared in the present invention.

[0027] Figure 2 Graph showing the moisture permeability of six composite films prepared in the present invention.

[0028] Figure 3 Graph showing light transmittance of six composite films prepared in the present invention.

[0029] Figure 4 Graph showing the antioxidant properties of six composite films prepared in the present invention.

[0030] Figure 5 It is a comparison chart of the storage effects and decay rates of the fresh bamboo fungus CK group, PE group, G-KC group, G-KC-10% DVE group and G-KC-15% DVE group at 4°C in the present invention.

[0031] Figure 6 This is a comparison chart of the malondialdehyde content of fresh bamboo fungus CK group, PE group, G-KC group, G-KC-10% DVE group and G-KC-15% DVE group stored at 4°C in the present invention.

[0032] Figure 7 It is a comparison chart of flavonoid contents of fresh bamboo fungus CK group, PE group, G-KC group, G-KC-10% DVE group and G-KC-15% DVE group stored at 4°C in the present invention.

[0033] Figure 8 It is a comparison chart of polyphenol oxidase activity of fresh bamboo fungus CK group, PE group, G-KC group, G-KC-10% DVE group and G-KC-15% DVE group stored at 4°C in the present invention. Specific implementation method:

[0034] Implementation Case 1:

[0035] Preparation of gelatin-carrageenan composite film (G-KC): Weigh 3.60g gelatin and dissolve it in 60mL distilled water, and stir at 60℃ until completely dissolved. Weigh 1.20g carrageenan and dissolve it in 60mL distilled water, and stir at 80℃ until completely dissolved. Mix the gelatin solution and carrageenan solution evenly in a magnetic stirrer at 400rpm, then add 1.20g glycerol and stir at 80℃ for 30 minutes to fully mix the solution. Finally, cast the prepared gelatin-carrageenan solution on an acrylic plate (16cm×25cm), dry it in a forced air drying oven at 60℃ for 6 to 7 hours, and after drying, remove the film and place it in a desiccator.

[0036] Implementation Case 2:

[0037] Preparation of a gelatin-carrageenan composite film (G-KC-3% DVE) with a bamboo fungus stalk extract concentration of 3.00wt%: Weigh 3.60g of gelatin and dissolve it in 60mL of distilled water, and stir it at 60°C until it is completely dissolved. Weigh 1.20g of carrageenan and dissolve it in 60mL of distilled water, and stir it at 80°C until it is completely dissolved. Mix the gelatin solution and the carrageenan solution in a magnetic stirrer at 400rpm, then add 1.20g of glycerol and stir it at 80°C for 30 minutes, add 3.00wt% of the bamboo fungus stalk extract to the above solution, and stir it in a magnetic stirrer (400rpm) for 30 minutes. Finally, cast the prepared 3.00wt% bamboo fungus stalk extract-gelatin-carrageenan solution on an acrylic plate (16cm×25cm), dry it at 60°C in a forced air drying oven for 6-7 hours, and after drying, remove the film and place it in a desiccator.

[0038] Implementation Case 3:

[0039] Preparation of a 5.00wt% gelatin-carrageenan composite film (G-KC-5% DVE) containing a bamboo fungus stalk extract: Weigh 3.60g of gelatin and dissolve it in 60mL of distilled water, and stir at 60°C until it is completely dissolved. Weigh 1.20g of carrageenan and dissolve it in 60mL of distilled water, and stir at 80°C until it is completely dissolved. Mix the gelatin solution and the carrageenan solution in a magnetic stirrer at 400rpm, then add 1.20g of glycerol and stir at 80°C for 30 minutes, add 5.00wt% of the bamboo fungus stalk extract to the above solution, and stir at a magnetic stirrer (400rpm) for 30 minutes. Finally, cast the prepared 5.00wt% bamboo fungus stalk extract-gelatin-carrageenan solution on an acrylic plate (16cm×25cm), dry it at 60°C in a forced air drying oven for 6 to 7 hours, and then remove the film and place it in a desiccator after drying.

[0040] Implementation Case 4:

[0041] Preparation of a gelatin-carrageenan composite film (G-KC-10% DVE) with a bamboo fungus stalk extract concentration of 10.00wt%: Weigh 3.60g of gelatin and dissolve it in 60mL of distilled water, and stir it at 60°C until it is completely dissolved. Weigh 1.20g of carrageenan and dissolve it in 60mL of distilled water, and stir it at 80°C until it is completely dissolved. Mix the gelatin solution and the carrageenan solution in a magnetic stirrer at 400rpm, then add 1.20g of glycerol and stir it at 80°C for 30 minutes, add 10.00wt% of the bamboo fungus stalk extract to the above solution, and stir it in a magnetic stirrer (400rpm) for 30 minutes. Finally, cast the prepared 10.00wt% bamboo fungus stalk extract-gelatin-carrageenan solution on an acrylic plate (16cm×25cm), dry it at 60°C in a forced air drying oven for 6-7 hours, and after drying, remove the film and place it in a desiccator.

[0042] Implementation Case 5:

[0043] Preparation of a gelatin-carrageenan composite film (G-KC-15% DVE) with a bamboo fungus stalk extract concentration of 15.00wt%: Weigh 3.60g of gelatin and dissolve it in 60mL of distilled water, and stir it at 60°C until it is completely dissolved. Weigh 1.20g of carrageenan and dissolve it in 60mL of distilled water, and stir it at 80°C until it is completely dissolved. Mix the gelatin solution and the carrageenan solution in a magnetic stirrer at 400rpm, then add 1.20g of glycerol and stir it at 80°C for 30 minutes, add 15.00wt% of the bamboo fungus stalk extract to the above solution, and stir it in a magnetic stirrer (400rpm) for 30 minutes. Finally, cast the prepared 15.00wt% bamboo fungus stalk extract-gelatin-carrageenan solution on an acrylic plate (16cm×25cm), dry it at 60°C in a forced air drying oven for 6-7 hours, and after drying, remove the film and place it in a desiccator.

[0044] Implementation Case 6:

[0045] Preparation of a gelatin-carrageenan composite film (G-KC-20% DVE) with a bamboo fungus pedicle extract concentration of 20.00wt%: Weigh 3.60g of gelatin and dissolve it in 60mL of distilled water, and stir it at 60°C until it is completely dissolved. Weigh 1.20g of carrageenan and dissolve it in 60mL of distilled water, and stir it at 80°C until it is completely dissolved. Mix the gelatin solution and the carrageenan solution in a magnetic stirrer at 400rpm, then add 1.20g of glycerol and stir it at 80°C for 30 minutes, add 20.00wt% of the bamboo fungus pedicle extract to the above solution, and stir it in a magnetic stirrer (400rpm) for 30 minutes. Finally, cast the prepared 20.00wt% bamboo fungus pedicle extract-gelatin-carrageenan solution on an acrylic plate (16cm×25cm), dry it at 60°C in a forced air drying oven for 6-7 hours, and after drying, remove the film and place it in a desiccator.

[0046] Implementation Case 7: Determination of the preservation effect of bamboo fungus stalk extract-gelatin-carrageenan composite film on fresh bamboo fungus.

[0047] Fresh bamboo fungi of the same size, maturity and no rot or deterioration were randomly divided into 5 groups, with 3-4 in each group. The first group was treated without film (CK) as a blank control experiment; the second group was sealed with commercially available plastic wrap (PE); the third group was sealed with gelatin-carrageenan composite film (G-KC); the fourth group was sealed with gelatin-carrageenan composite film (G-KC-10% DVE) with a bamboo fungus stalk extract concentration of 10.00wt%; the fifth group was sealed with gelatin-carrageenan composite film (G-KC-15% DVE) with a bamboo fungus stalk extract concentration of 15.00wt%. The five groups of samples were placed in a 4°C refrigerator, and samples were taken every three days to measure their preservation indicators (such as weight loss rate, decay rate, malondialdehyde content, polyphenol flavonoid content, extracellular enzyme activity, etc.).

[0048] The water vapor transmission rates (WVP) of the composite films prepared in Examples 1, 2, 3, 4, 5, and 6 were compared. The results are as follows: Figure 2 As shown, the overall WVP value of the composite film is low, but a higher extract concentration will increase the WVP value of the composite film, which may be related to the effect of the hydrophilic compounds in the extract.

[0049] The composite films prepared in Examples 1, 2, 3, 4, 5, and 6 were characterized by UV-Vis spectrophotometer (UV). Figure 3 As shown in the figure, in the range of 300-500nm, the transmittance decreases with the increase of the extract content. The light scattering of the extract increases the diffuse reflection of the composite film and reduces the transmittance of the film. This shows that the G-KC-DVE composite film can block ultraviolet rays to a certain extent.

[0050] The antioxidant properties of the composite films prepared in Examples 1, 2, 3, 4, 5, and 6 were measured by free radical scavenging experiments. The results are as follows: Figure 5 As shown, when the addition amount of bamboo fungus stalk extract was 5.00wt%, the DPPH radical scavenging rate of the composite membrane reached 29.83%; the DPPH radical scavenging rate of the G-KC-15%DVE composite membrane reached 47.41%; the composite membranes with bamboo fungus stalk extract content higher than 15.00wt% all had high DPPH scavenging activity.

[0051] The preservation effect and decay rate of the five fresh bamboo fungus preservation storage methods in implementation case 7 were measured. The results are as follows: Figure 6As shown in the figure, after the same storage days, the storage effect of the treatment group was significantly better than that of the CK group. On the 20th day, the decay rate of fresh bamboo fungus encapsulated by the 15% DVE group was only 39.47%.

[0052] The malondialdehyde content of the five fresh bamboo fungus preservation and storage methods in Example 7 was measured, and the results were as follows: Figure 7 As shown in the figure, the MDA content of fresh bamboo fungus showed an upward trend during the entire storage period. At 20 days of storage, the MDA content of fresh bamboo fungus in the CK group was significantly higher than that in the three groups of film treatments. This shows that G-KC-DVE composite film preservation can effectively reduce the respiration intensity of fresh bamboo fungus during storage.

[0053] The flavonoid content of the five fresh bamboo fungus preservation and storage methods in Example 7 was measured, and the results were as follows: Figure 8 As shown in the data, the flavonoid content of fresh bamboo fungus after harvest showed a downward trend throughout the storage period. After 20 days of storage, the flavonoid content of fresh bamboo fungus in the CK group dropped to 1.05 mg / g, while the flavonoid content of fresh bamboo fungus in the G-KC-10% DVE group and the G-KC-15% DVE group was higher, with the highest content in the G-KC-15% DVE group.

[0054] The polyphenol oxidase (PPO) activity of the five fresh bamboo fungus preservation storage methods in Example 7 was measured, and the results were as follows: Figure 8 As shown in the figure, the discoloration of edible fungi fruiting bodies is usually caused by the reaction between polyphenol oxidase and phenolic substances. During storage, the activity of polyphenol oxidase showed a trend of first increasing, then decreasing, and then increasing again. On the 20th day of storage, the PPO activity of the CK group was significantly higher than that of the composite film treatment group. This may be because the respiration of the CK group was not inhibited without preservation measures, and the oxidation rate was accelerated.

[0055] The present invention is described in detail by explaining the steps and implementation methods of the present invention. The technical solution of the present invention can be modified or replaced by equivalents, and these modifications or equivalent replacements also fall within the protection scope of the present invention.

Claims

1. A composite packaging film for preserving fresh bamboo fungus and a preparation method thereof, characterized in that The method comprises the following steps: weighing a certain amount of gelatin and dissolving it in 60 ml of distilled water, stirring it at a certain temperature until it is completely dissolved. Weighing a certain amount of carrageenan and dissolving it in 60 ml of distilled water, stirring it at a certain temperature until it is completely dissolved.

2. The gelatin and carrageenan solutions prepared in step 1 were mixed evenly in a magnetic stirrer at 400 rpm, and a certain amount of glycerol was added and stirred at 80°C for 30 min to fully mix the solution.

3. Add different concentrations of bamboo fungus stalk extract to the above solution and stir at 80°C for 30 minutes on a magnetic stirrer (400 rpm).

4. Cast the prepared solutions with different concentrations of trophoside extract onto acrylic plates.

5. Place the solution in a forced air drying oven at a certain temperature for several hours. After drying, remove the film and place it in a dryer for equilibrium.

6. The method for preparing a composite film according to claim 1, characterized in that: The amount of gelatin added was 3.60 g, and the stirring temperature was 60°C; the amount of carrageenan added was 1.20 g, and the stirring temperature was 80°C.

7. The method for preparing a composite film according to claim 2, characterized in that: The amount of glycerol added was 1.20 g.

8. The method for preparing the composite film according to claim 3, characterized in that: Add the concentrated DVE The concentration is 0.00wt%, 3.00wt%, 5.00wt%, 10.00wt%, 15.00wt%, and 20.00wt%.

9. The method for preparing the composite film according to claim 4, characterized in that: Acrylic sheet size (16cm×25cm).

10. The method for preparing the composite film according to claim 5, characterized in that: The temperature of the blast drying oven is 60°C, and the drying time is 6-7 hours; the equilibrium time in the dryer is 2-3 days.

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