Preparation method and application of composite preservative film based on stropharia rugoso-annulata

Abstract

The invention discloses a preparation method of a composite preservative film based on stropharia rugoso-annulata, which specifically comprises the following steps: adding aldehyde modified stropharia rugoso-annulata polysaccharide, stropharia rugoso-annulata polyphenol and a plasticizer into a gelatin solution with the mass volume concentration of 1-3%, uniformly stirring and mixing, ultrasonically degassing, and drying the prepared film at room temperature to obtain the composite preservative film, the preservative film disclosed by the invention has relatively high oxidation resistance and excellent antibacterial property, and also has relatively good water vapor barrier property and mechanical property; the preservative film can effectively inhibit oxidation, inhibit microbial reproduction, delay the decay process of fresh pork and prolong the storage period of the pork; meanwhile, the adopted preparation method is easy to operate, no special equipment requirement exists, high-value utilization of the stropharia rugoso-annulata waste is achieved, and the prepared composite preservative film with the excellent oxidation resistance and antibacterial performance has a huge application market prospect in the field of fresh-keeping packaging of meat which is prone to oxidation and microorganism breeding.

Description

Technical Field

[0001] The invention belongs to the technical field of cling film, and in particular relates to a preparation method of a composite cling film based on Stropharia rugosa and application of the composite cling film in pork preservation. Background Art

[0002] Pork is a common food, which is favored by consumers because of its delicious taste, relatively low price, and rich protein, fat, carbohydrates, calcium, phosphorus, iron and other ingredients. It has the functions of nourishing the body, nourishing yin and moistening dryness, and nourishing the muscles and skin. However, pork has a short shelf life. During storage, lipid oxidation and microbial growth and reproduction will occur, which makes it very easy to spoil.

[0003] In storage and preservation practices, the traditional method is to use petroleum-based plastic film to package pork. However, this non-biodegradable packaging material extracted from petroleum takes hundreds of years to decompose, causing serious environmental pollution. Moreover, consumers' growing preference for fresh, safe and high-quality food highlights the urgent need for innovative bio-based and sustainable packaging materials. Gelatin, an animal protein extracted from the by-products of animal slaughter and processing, is becoming increasingly popular in food packaging due to its excellent film-forming ability, edibility, biodegradability, abundance and cost-effectiveness. Despite these advantages, pure gelatin film still has some limitations, such as poor antioxidant, antibacterial ability, poor mechanical strength, low barrier properties and poor water resistance, which hinder its effectiveness in food packaging applications.

[0004] Stropharia Stropharia rugosoannulata ) is a major wild mushroom in Yunnan with a large yield. The Stropharia rugosa is rich in essential amino acids for the human body. The polysaccharides and some minerals it contains can clean up cholesterol in the blood, purify the blood, soften blood vessels, prevent coronary heart disease, hyperlipidemia, arteriosclerosis and other diseases, relieve neurasthenia, and it is known as the "meat among vegetarians". Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention provides a method for preparing a composite cling film of Stropharia capensis with excellent antioxidant and antibacterial properties and its application in pork preservation. The present invention uses gelatin as a matrix and adds aldehyde-modified Stropharia capensis polysaccharides and Stropharia capensis polyphenols extracted from Stropharia capensis waste as active substances to prepare a multifunctional composite cling film, which has good antioxidant and antibacterial properties, good mechanical properties, good transparency, and good water vapor and oxygen barrier properties.

[0006] The preparation method of the composite fresh-keeping film based on Stropharia rugosa of the present invention is as follows: (1) Preparation of aldehyde-modified Stropharia rugosa polysaccharide The washed, dried and crushed Stropharia capensis powder was added to distilled water, and the mixture was placed in a water bath at 65-75°C for 1-2 hours, filtered, anhydrous ethanol was added to the extract, precipitated at 4°C, the precipitate was collected and dissolved in distilled water, free protein in the precipitate was removed by Sevag reagent, and the mixture was precipitated again by anhydrous ethanol, and the solid was separated and the solid was freeze-dried to obtain Stropharia capensis polysaccharide; after dissolving Stropharia capensis polysaccharide in distilled water, anhydrous ethanol was added and stirred for 3 hours, sodium periodate was added, and oxidation was carried out in the dark for 4-6 hours, ethylene glycol was added, stirred for 30 minutes, anhydrous ethanol was added, stirred for 5 minutes, and the mixture was allowed to stand for 30 minutes, centrifuged and the supernatant was discarded, the precipitate was redissolved in ultrapure water, and dialyzed in water for 3 days using a dialysis bag, and the dialyzed solution was freeze-dried to obtain aldehyde-modified Stropharia capensis polysaccharide; The mass ratio of the Stropharia capensis polysaccharide to sodium periodate is 2-3:1; the mass volume ratio of the Stropharia capensis polysaccharide to ethylene glycol is 1:1-3.

[0007] (2) Preparation of Stropharia rugosa polyphenols The powder of Stropharia capensis was added into an ethanol solution with a volume concentration of 95%, and ultrasonic extraction was performed at 30-50°C for 20-40 minutes. The supernatant was obtained by centrifugation, rotary evaporation, and freeze-drying to obtain Stropharia capensis polyphenols. (3) adding aldehyde-modified Stropharia polysaccharide, Stropharia polyphenol and a plasticizer to a gelatin solution with a mass volume concentration of 1 to 3%, stirring and mixing, ultrasonically degassing and drying at room temperature to obtain a composite preservative film; To every 100 mL of gelatin solution, 20-60 mg of aldehyde-formulated Stropharia capitis polysaccharide, 20-60 mg of Stropharia capitis polyphenol, and 0.2-0.4 g of plasticizer were added.

[0008] Another purpose of the present invention is to use the composite fresh-keeping film prepared by the above method in the preservation of pork.

[0009] Compared with the prior art, the advantages and technical effects of the present invention are as follows: (1) The preparation method of the composite cling film of the present invention is simple, green and environmentally friendly, does not require complex instruments and equipment, has strong operability, and is easier to promote; (2) The gelatin used in the present invention is a resource-rich, low-cost and degradable raw material, which is green and environmentally friendly and conforms to the concept of sustainable development. Extracting Stropharia polysaccharides and polyphenols from Stropharia waste realizes the high-value utilization of waste, which is of great significance to reducing environmental pollution and recycling resources; (3) The composite cling film prepared by the present invention has high antioxidant and excellent antibacterial properties, and its water vapor barrier performance and mechanical properties are also good, and it has good stability and is less affected by changes in the surrounding environment; the cling film can effectively inhibit oxidation, inhibit microbial reproduction, delay the corruption process of fresh pork, and extend its storage period; the prepared composite cling film with excellent antioxidant and antibacterial properties provides a new idea and approach in the field of fresh-keeping packaging of meat that is easily oxidized and microbially reproduced, and has a huge application market prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 The results of the effects of composite cling film, PE film and no packaging on the weight loss of pork at room temperature; Figure 2 The results of the effects of composite cling film, PE film and no packaging on pork hardness at room temperature; Figure 3 The results show the effects of composite cling film, PE film and no packaging on the volatile basic nitrogen content of pork at room temperature. Figure 4 The results show the effects of composite cling film, PE film and no packaging treatments on the total aerobic colony count of pork at room temperature. DETAILED DESCRIPTION

[0011] The present invention is further described in detail below with reference to the examples and drawings, but the embodiments of the present invention are not limited thereto. The reagents in the examples are all conventional commercially available reagents unless otherwise specified; Example 1

[0012] (1) Collect the waste of Stropharia rugosa, wash the Stropharia rugosa with distilled water for 3 times, dry them in an oven at 60°C for 24 h, and then crush them through an 80-mesh sieve to obtain Stropharia rugosa powder; (2) Take 20g of Stropharia capillaris powder and place it in 300mL of distilled water, heat it in a water bath at 65℃ and stir it for 2h, let it stand and filter to collect the upper extract, add 4 times its volume of anhydrous ethanol to the extract, let it stand at 4℃ for 24h, filter to collect the precipitate, dissolve the precipitate in 10mL of distilled water, add 2mL of Sevag reagent (chloroform: n-butanol volume ratio = 4:1), shake vigorously for 3min, let it stand for 10min, centrifuge at 5000rpm for 15min, collect the upper extract, add 4 times its volume of anhydrous ethanol to the extract, let it stand at 4℃ for 24h, filter to collect the lower precipitate, and freeze-dry to obtain Stropharia capillaris polysaccharide; 2g of Stropharia capensis polysaccharide was dispersed in 20mL of distilled water and stirred for 30min. After the powder was completely dissolved, 40mL of anhydrous ethanol was added and stirred for 3h, then 0.6g of sodium periodate was added, and stirred for 4h in a dark place, and then 4mL of ethylene glycol was added and stirred for 30min to terminate the reaction. Finally, 20mL of anhydrous ethanol was added, and stirred for 5min, and then allowed to stand for 30min, centrifuged at 1500 rpm for 5min, and the supernatant was discarded. The precipitate was redissolved in ultrapure water, and dialyzed in water for 3 days using a dialysis bag (MD3544 dialysis bag), and the dialyzed solution was freeze-dried to obtain the aldehyde-modified Stropharia capensis polysaccharide. (3) Take 20 g of Stropharia capillaris powder and add 500 mL of 95% ethanol solution, ultrasonically treat at 30°C for 40 min, then centrifuge at 3000 rpm for 10 min, take the supernatant and rotary evaporate at 60°C, and freeze-dry to obtain Stropharia capillaris polyphenols; (4) Add 2 g of gelatin to 100 mL of distilled water and stir in a 50°C water bath until completely dissolved. Then, add 0.2 g of glycerol as a plasticizer and continue stirring for 30 min. Then, add 20 mg of aldehyde-modified Stropharia capillaris polysaccharide and stir to mix. Then, add 20 mg of Stropharia capillaris polyphenol and stir to mix. After that, degas by ultrasonication. Pour the mixture into a glass plate to form it. Then, dry it naturally at room temperature to form a film to obtain a composite cling film. Example 2

[0013] (1) Take 20g of Stropharia capillaris powder and dissolve it in 400mL of distilled water, heat it in a water bath at 70℃ and stir it for 1.5h, let it stand and filter to collect the upper extract, add 4 times its volume of anhydrous ethanol to the extract, let it stand at 4℃ for 24h, filter to collect the lower precipitate, dissolve the precipitate in 10mL of distilled water, add 2mL of Sevag reagent (chloroform: n-butanol = 4:1), shake it vigorously for 3min, let it stand for 10min, centrifuge it at 5000rpm for 15min, collect the upper extract, add 4 times its volume of anhydrous ethanol to the extract, let it stand at 4℃ for 24h, filter to collect the lower precipitate, and freeze-dry to obtain Stropharia capillaris polysaccharide; 2 g of Stropharia capensis polysaccharide was dispersed in 20 mL of distilled water and stirred for 30 min until the powder was completely dissolved. Then, 40 mL of anhydrous ethanol was added and stirred for 3 h. Then, 0.8 g of sodium periodate was added and stirred for 5 h in a dark environment. Then, 4 mL of ethylene glycol was added and stirred for 30 min to terminate the reaction. Finally, 20 mL of anhydrous ethanol was added and stirred for 5 min. Then, the mixture was allowed to stand for 30 min and centrifuged at 1500 rpm for 5 min to discard the supernatant. The precipitate was redissolved in ultrapure water and dialyzed in water for 3 days using a dialysis bag (MD3544 dialysis bag). The dialyzed solution was freeze-dried to obtain the aldehyde-modified Stropharia capensis polysaccharide. (2) Take 20 g of Stropharia capillaris powder and add 600 mL of 95% ethanol solution, ultrasonically treat at 40 °C for 30 min, then centrifuge at 3000 rpm for 10 min, take the supernatant and rotary evaporate at 60 °C, and freeze-dry to obtain Stropharia capillaris polyphenols; (3) Add 2 g of gelatin to 100 mL of distilled water, stir in a 50°C water bath until completely dissolved, then add 0.3 g of glycerol as a plasticizer, and continue stirring for 30 min; then add 40 mg of aldehyde-modified Stropharia polysaccharide, stir and mix, then add 40 mg of Stropharia polyphenol, stir and mix, pour the mixture into a glass plate to form, and dry it naturally at room temperature to form a film to obtain a composite cling film; Example 3

[0014] (1) Take 20g of Stropharia capillaris powder and dissolve it in 500mL of distilled water, heat it in a water bath at 75℃ and stir it for 1h, let it stand and filter to collect the upper extract, add 4 times its volume of anhydrous ethanol to the extract and let it stand at 4℃ for 24h, filter and collect the lower precipitate, dissolve the precipitate in 10mL of distilled water, add 2mL of Sevag reagent (chloroform: n-butanol = 4:1), shake it vigorously for 3min, let it stand for 10min, centrifuge it at 5000rpm for 15min, collect the upper extract, add 4 times its volume of anhydrous ethanol to the extract and let it stand at 4℃ for 24h, filter and collect the lower precipitate, and freeze-dry to obtain Stropharia capillaris polysaccharide; 2g of Stropharia capensis polysaccharide was dispersed in 20mL of distilled water and stirred for 30min. After the powder was completely dissolved, 40mL of anhydrous ethanol was added and stirred for 3h. Then, 1g of sodium periodate was added and stirred for 6h in a dark place. Then, 4mL of ethylene glycol was added and stirred for 30min to terminate the reaction. Finally, 20mL of anhydrous ethanol was added and stirred for 5min. The mixture was allowed to stand for 30min and centrifuged at 1500rpm for 5min to discard the supernatant. The precipitate was redissolved in ultrapure water and dialyzed in water for 3 days using a dialysis bag (MD3544 dialysis bag). The dialyzed solution was freeze-dried to obtain the aldehyde-modified Stropharia capensis polysaccharide. (2) Take 20 g of Stropharia capillaris powder and add 600 mL of 95% ethanol solution, ultrasonically treat at 50°C for 20 min, then centrifuge at 3000 rpm for 10 min, take the supernatant and rotary evaporate at 60°C, and freeze-dry to obtain Stropharia capillaris polyphenols; (3) Add 2 g of gelatin to 100 mL of distilled water, stir in a 50°C water bath until completely dissolved, then add 0.4 g of glycerol as a plasticizer, and continue stirring for 30 min; then add 60 mg of aldehyde-modified Stropharia polysaccharide, stir and mix, then add 60 mg of Stropharia polyphenol, stir and mix, pour the mixture into a glass plate to form, and dry it naturally at room temperature to form a film to obtain a composite cling film.

[0015] Comparative Example 1 Add 2 g of gelatin to 100 mL of distilled water, stir in a 50°C water bath until completely dissolved, then add 0.4 g of glycerol as a plasticizer, and continue stirring for 30 minutes; after stirring and mixing, pour the mixture into a glass plate to form it, and naturally dry it at room temperature to form a film to obtain a plastic wrap.

[0016] Comparative Example 2 The preparation of aldehyde-modified Stropharia capitis polysaccharide was the same as in Example 3. 2 g of gelatin was added to 100 mL of distilled water, and the mixture was stirred in a 50°C water bath until completely dissolved. Then, 0.4 g of glycerol was added as a plasticizer, and stirring was continued for 30 min. Then, 60 mg of aldehyde-modified Stropharia capitis polysaccharide was added, and after stirring and mixing, the mixture was poured into a glass plate to form a composite preservative film, and naturally dried at room temperature to form a film.

[0017] Example 4: Antioxidant and antibacterial properties of the composite cling film prepared in Examples 1-3 and Comparative Examples 1-2 The composite cling film prepared in Examples 1-3 was tested for its antioxidant and antibacterial properties; the antioxidant properties were measured by IC scavenging of ABTS and DPPH free radicals. 50 The antibacterial property is characterized by the inhibition rate of the composite film against Staphylococcus aureus and Escherichia coli; Table 1 Antioxidant test results of cling film

[0018] It can be seen from Table 1 that the cling film has good antioxidant properties. Table 2 Antibacterial test results of cling film

[0019] It can be seen from Table 2 that the plastic wrap has a significant inhibitory effect on Staphylococcus aureus and Escherichia coli, and can reduce the reproduction of microorganisms during storage to a certain extent, thereby extending the shelf life.

[0020] Example 5: Performance test of the composite cling film prepared in Examples 1-3 The water vapor permeability, oxygen permeability, mechanical properties and oxidation resistance of the cling films prepared in Examples 1-3 and Comparative Examples 1-2 were tested; the water vapor permeability was tested with reference to the method in GB1037-1988; the oxygen permeability was tested with reference to the method in GB / T19789-2005; the tensile strength was tested with reference to the method in GB13022-91; the results are shown in Tables 3 to 5; Table 3 Water vapor permeability and oxygen permeability of cling film

[0021] It can be seen from Table 3 that the cling film prepared by the method of the present invention has lower water vapor permeability and oxygen permeability; Table 4 Mechanical properties of cling film

[0022] It can be seen from Table 4 that the multifunctional composite fresh-keeping film prepared by the method of the present invention has strong mechanical properties.

[0023] Example 6: In order to further verify the preservation effect of the above-mentioned cling film on pork, the cling film prepared in the above-mentioned Examples 1-3 was used to preserve pork, and unpackaged pork (Control) and pork packaged in conventional commercially available PE fresh-keeping bags were used as controls. The pork was stored at 4°C, and the changes in weight loss, hardness, volatile basic nitrogen content and total aerobic colony count were measured on the 0th, 2nd, 4th, 6th, 8th and 10th days. Three replicates were made for each sample. 1. The weight loss rate of pork was measured by weight method. The weight of each group of samples during storage was weighed with an electronic balance and the weight loss rate was calculated. The results are as follows: Figure 1 As shown, the loss of moisture in pork during storage is an important indicator for evaluating the preservation effect of the composite film, and the main manifestation of weight loss is the respiration of pork. With the increase of storage time, the weight loss rate of each group is constantly increasing. Compared with the blank control, the cling film prepared in Examples 1-3 of the present invention has a lower weight loss rate. The cling film prepared by the present invention has a lower water vapor permeability and oxygen permeability, which can effectively slow down the exchange of oxygen and carbon dioxide gases, slow down the respiration to a certain extent, and effectively reduce the loss of nutrients and moisture content in pork during storage. The weight loss rate of pork that has not been packaged is the highest, and the weight loss rate of the PE group is the lowest. This is because of the airtightness of the PE film, but it also aggravates the growth of microbial colonies therein (caused by Figure 4 can be known).

[0024] 2. Use TA.XTplus type physical structure analyzer to test hardness, select P / 36R probe and TPA mode, test parameters: pre-test rate 2mms, test rate 1mms, post-test rate 2mms, compression ratio 50%, press down dwell time 5s, trigger type automatic, trigger force 5g. The results of the pork hardness test are shown in Figure 2One of the main indicators for determining pork quality and post-harvest shelf life is the rate and degree of hardness loss during storage. Hardness can reflect the texture of pork during storage. With the increase in storage days, the hardness of all treatment groups showed an overall downward trend. Compared with the PE group and the unpackaged group, the cling film prepared in Examples 1-3 effectively delayed the decline in pork hardness, especially the cling film in Example 3, which still maintained a high hardness after 10 days of storage. This is because the cling film prepared in Example 3 has good antioxidant and antibacterial properties, low water vapor and oxygen permeability, which effectively prevents the loss of moisture in pork during storage and maintains the hardness of pork.

[0025] 3. Use the semi-micro Kjeldahl method to determine the changes in the volatile basic nitrogen content of pork during the preservation process in accordance with GB5009.228-2016 "Determination of Volatile Basic Nitrogen in Foods". Volatile basic nitrogen is one of the physical and chemical indicators for evaluating meat spoilage. During storage, pork is exposed to the action of microorganisms and protein enzymes, and the protein in the pork undergoes deamination and deamination reactions to produce amines, nitrogen and other alkaline substances. The content of these substances has a great influence on the freshness of pork. If the volatile basic nitrogen value is greater than 15mg / 100g, it is spoiled meat. Figure 3 It can be seen that within 0-10 days, the volatile basic nitrogen content of pork processed by different packaging methods gradually increased, among which the volatile basic nitrogen content of unpackaged and PE-packaged pork increased the fastest, but the volatile basic nitrogen content of pork packaged with plastic wrap in Examples 1-3 was lower than that of the unpackaged group and the PE group. In contrast, the volatile basic nitrogen content of pork packaged in Example 3 was well suppressed, which can effectively inhibit the corruption and deterioration of pork, thereby extending the shelf life of pork.

[0026] 4. Use GB 4789.2-2010 "Determination of total bacterial count" method to detect changes in total aerobic bacterial count. The total bacterial count is one of the indicators that determine food hygiene. Figure 4 The changes in the total aerobic colony count during the preservation of pork are shown. The total aerobic colony counts of all treatment groups showed an upward trend, among which the total colony counts of the unpackaged group and the PE group were the highest, higher than those of Examples 1-3. At present, 7.0 log CFU / g of the total aerobic bacteria count is considered to be the tolerance limit for evaluating microbial quality. On the 10th day, the total aerobic bacteria counts of the unpackaged group and the PE group exceeded 7.0 log CFU / g; the total aerobic bacteria count of the packaged group in Example 3 increased the slowest, which can effectively extend the shelf life of pork.

[0027] The above embodiments are only preferred implementation modes of the present invention and are only used to explain the present invention rather than to limit the present invention. Any changes, substitutions, modifications, etc. made by those skilled in the art without departing from the spirit of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for preparing a composite preservative film based on Stropharia rugosa, characterized in that: Adding aldehyde-modified Stropharia polysaccharide, Stropharia polyphenol and plasticizer to a gelatin solution with a mass volume concentration of 1-3%, stirring and mixing, ultrasonic degassing, and drying at room temperature to obtain a composite fresh-keeping film; The aldehyde-modified Stropharia polysaccharide is prepared by adding dried and crushed Stropharia powder to distilled water, bathing at 65-75°C for 1-2 hours, filtering, adding anhydrous ethanol to the extract, precipitating at 4°C, collecting the precipitate and dissolving it in distilled water, removing free protein in the precipitate with Sevag reagent, precipitating with anhydrous ethanol again, separating the solid and the liquid, and freeze-drying the solid to obtain the Stropharia polysaccharide; after dissolving the Stropharia polysaccharide in distilled water, adding anhydrous ethanol and stirring for 3 hours, adding sodium periodate, oxidizing in the dark for 4-6 hours, adding ethylene glycol, stirring for 30 minutes, adding anhydrous ethanol, stirring and standing, centrifuging and discarding the supernatant, re-dissolving the precipitate in ultrapure water, dialyzing it in water with a dialysis bag for 3 days, and freeze-drying the dialyzed solution to obtain the Stropharia polysaccharide; Stropharia polyphenols are prepared by adding Stropharia powder to an ethanol solution with a volume concentration of 95%, ultrasonically extracting at 30-50°C for 20-40 minutes, centrifuging to obtain the supernatant, rotary evaporating, and freeze-drying.

2. The method for preparing the composite preservative film based on Stropharia officinalis according to claim 1, characterized in that: To every 100 mL of gelatin solution, 20-60 mg of aldehyde-formulated Stropharia capitis polysaccharide, 20-60 mg of Stropharia capitis polyphenol, and 0.2-0.4 g of plasticizer were added.

3. The method for preparing the composite preservative film based on Stropharia rugosa according to claim 1, characterized in that: The plasticizer is glycerol.

4. Use of the composite preservative film prepared by the method for preparing the composite preservative film based on Stropharia officinalis according to any one of claims 1 to 3 in preserving pork.

Images