Highland barley vinasse prolamin-based fresh-keeping coating liquid and preparation method thereof

Abstract

The invention relates to the field of food preservation, and particularly discloses a highland barley vinasse prolamin-based preservation coating liquid and a preparation method, and every 100 mL of the preservation coating liquid comprises 1800-2200 mg of highland barley vinasse prolamin, 1.3-1.6 mL of a humectant, 2.2-2.7 g of vitamin C and 75-85 mL of an alcoholic solution. The prepared film coating liquid can obviously reduce the weight loss rate of the fruits in the storage period and effectively reduce the water loss; the decay rate is obviously inhibited, and an experimental group does not have a decay phenomenon within a 28-day storage period; the fruit hardness is effectively maintained, and the hardness reduction speed is slowed down; change of titratable acid content is controlled, organic acid reduction is delayed, and fruit flavor is reserved; the activity of polyphenol oxidase is obviously inhibited, the enzymatic browning reaction is retarded, and the color and quality of fruits are maintained; the total number of bacterial colonies is greatly reduced, and growth and reproduction of microorganisms are inhibited, so that the shelf life of fruits is effectively prolonged.

Description

Technical Field

[0001] The present application relates to the field of food preservation, and more specifically, to a prolamine-based fresh-keeping coating solution from hulless barley distiller's grains and a preparation method thereof. Background Art

[0002] In the field of food preservation, although traditional preservation methods (such as chemical preservative treatment, low-temperature storage, etc.) can extend the storage period of fruits to a certain extent, they generally have problems such as high cost, high risk of environmental pollution, and high energy consumption. In recent years, with the continuous improvement of people's requirements for food safety and quality, the development of efficient and environmentally friendly preservation technologies has become the key direction of the industry's development. Coating preservation, as an environmentally friendly technology, has attracted much attention. Through the synergistic effect of physical barrier and active ingredients, a protective film is formed on the surface of fruits, effectively reducing water evaporation, inhibiting the growth of microorganisms, and delaying the respiration of fruits, thereby achieving the preservation effect.

[0003] However, existing coating preservation solutions mostly use a single film-forming matrix, such as preservatives mainly composed of chitosan, gelatin, or pectin. These substances have certain film-forming properties and antibacterial properties. In addition, some studies have tried to add active ingredients such as antioxidants and antibacterial agents to the coating solution to enhance the preservation effect. However, these methods usually have problems such as single composition and limited functions, and it is difficult to fully meet the needs of fruit preservation. For example, although chitosan coating has good antibacterial properties, its film-forming strength is poor; pectin coating is prone to rupture due to insufficient stability, resulting in poor preservation effect.

[0004] The functions of such coating preservation solutions are limited and single. Especially when facing fruits that are prone to water loss and decay, traditional coating solutions are difficult to simultaneously achieve multiple functions such as water retention, anti-corrosion and antibacterial, and quality maintenance, resulting in limited preservation effect. Therefore, how to develop a composite coating solution that can comprehensively solve the above problems has become an urgent technical problem to be solved. Summary of the Invention

[0005] The present application provides a prolamine-based fresh-keeping coating solution from hulless barley distiller's grains and a preparation method thereof. The prepared coating solution can significantly reduce the weight loss rate of fruits during storage, effectively reduce water loss; significantly inhibit the decay rate, and no decay phenomenon occurred in the experimental group during the 28-day storage period; effectively maintain the fruit firmness and slow down the rate of firmness decline; control the change of titratable acid content, delay the reduction of organic acids, and retain the fruit flavor; significantly inhibit the activity of polyphenol oxidase, slow down the enzymatic browning reaction, and maintain the fruit color and quality; greatly reduce the total number of colonies, inhibit the growth and reproduction of microorganisms, thereby effectively extending the shelf life of fruits.

[0006] In the first aspect, a prolamine-based fresh-keeping coating solution from hulless barley distiller's grains provided by the present application adopts the following technical scheme:

[0007] A prolamine-based fresh-keeping coating solution from highland barley distillers' grains, wherein each 100 mL of the fresh-keeping coating solution comprises: 1800 - 2200 mg of prolamine from highland barley distillers' grains, 1.3 - 1.6 mL of a humectant, 2.2 - 2.7 g of vitamin C, and 75 - 85 mL of an alcohol solution.

[0008] By adopting the above technical solution, the present application uses prolamine from highland barley distillers' grains as a film-forming matrix, which is naturally biodegradable and rich in hydrophobic amino acids. It forms a dense protective layer through hydrogen bonds and hydrophobic interactions, enhancing the anti-water vapor permeability of the film, reducing water evaporation and oxygen penetration; the addition of the humectant further optimizes the performance of the coating solution, maintains the water balance of the fruit, and helps to maintain the fruit hardness and appearance quality. Vitamin C, as an antioxidant, scavenges free radicals, inhibits enzymatic browning, and cooperates with prolamine from highland barley distillers' grains to inhibit the growth of microorganisms. The alcohol solution, as a solvent, can not only promote protein dissolution but also play a certain antibacterial role, destroying the cell membranes of microorganisms.

[0009] With the above components acting together in a specific ratio, a highly efficient fresh-keeping coating solution is formed. This coating solution can significantly reduce the weight loss rate of fruits during storage, effectively reduce water loss; significantly inhibit the spoilage rate, and no rotting phenomenon occurred in the experimental group during the 28-day storage period; effectively maintain the fruit hardness and slow down the rate of hardness decline; control the change of titratable acid content, delay the reduction of organic acids, and retain the fruit flavor; significantly inhibit the activity of polyphenol oxidase, slow down the enzymatic browning reaction, and maintain the fruit color and quality; greatly reduce the total number of colonies, inhibit the growth and reproduction of microorganisms, thereby effectively extending the shelf life of fruits.

[0010] Preferably, the molecular weight of the prolamine from highland barley distillers' grains is below 20 kDa.

[0011] Further, the molecular weight of the prolamine from highland barley distillers' grains is preferably 11 - 17 kDa.

[0012] By adopting the above technical solution, the molecular weight of the prolamine from highland barley distillers' grains is limited to below 20 kDa, which has high solubility in the alcohol solution, can significantly improve the film-forming performance and uniformity of the fresh-keeping coating solution, so that it is easier for the prolamine to form a dense and stable protective layer on the fruit surface, and enhance the binding force between the film and the fruit epidermis, effectively reducing the water evaporation rate and reducing the possibility of microbial infection, thereby further enhancing the fresh-keeping effect on fruits. At the same time, the prolamine within this molecular weight range has better solubility and dispersibility, which helps to improve the overall stability and use convenience of the coating solution.

[0013] Preferably, the alcohol solution is one of an ethanol solution and an isopropanol solution.

[0014] By adopting the above technical solution, the alcohol solution selects ethanol solution or isopropanol solution as the solvent, which can effectively adjust the dissolution performance and penetration ability of the fresh-keeping coating solution, improve the solubility of the alcohol-soluble protein in hulless barley distillers' grains, and enhance the uniformity and stability of the coating solution. Ethanol and isopropanol have good volatility and permeability, which helps to form a dense and uniform protective film on the fruit surface, reduce water evaporation, inhibit the growth of microorganisms, and thus significantly improve the fresh-keeping effect. Considering from the perspectives of cost and food application safety, the preferred alcohol solution is ethanol solution.

[0015] Preferably, the mass concentration of the alcohol solution is 70-95%.

[0016] By adopting the above technical solution, optimizing the mass concentration of the alcohol solution further optimizes the performance of the coating solution. Through experimental research, it is found that the alcohol solution within this concentration range can better synergistically act with the alcohol-soluble protein in hulless barley distillers' grains, the humectant, and vitamin C to form a uniform and stable protective film, effectively reducing the water evaporation rate on the fruit surface and reducing water loss; at the same time, this concentration range helps to inhibit the growth of microorganisms, reduce the total number of colonies, and maintain the color and quality of the fruit.

[0017] Preferably, the humectant is one of glycerol, propylene glycol, and sorbitol.

[0018] By adopting the above technical solution, the humectant can play a role in regulating the water evaporation rate. Glycerol has good hygroscopicity and moisture retention, which can significantly reduce water evaporation, thereby reducing the weight loss rate of fruits during storage; propylene glycol and sorbitol also have excellent moisture retention effects, which can form a uniform protective layer in the coating solution, further enhancing the physical barrier effect of the coating, effectively maintaining the hardness of the fruit and delaying its softening process. In addition, the addition of the humectant also helps to control the change in the content of titratable acids, slow down the reduction of organic acids, and thus retain the flavor of the fruit.

[0019] Specifically, the preferred humectant is glycerol. Glycerol inserts between the protein molecular chains, reducing the brittleness of the film, improving the flexibility and adhesion, and can regulate the porosity of the film after binding with the alcohol-soluble protein in hulless barley distillers' grains, balancing the barrier property and air permeability.

[0020] In the second aspect, the present application provides a preparation method of an alcohol-soluble protein-based fresh-keeping coating solution for hulless barley distillers' grains, adopting the following technical solution:

[0021] A preparation method of an alcohol-soluble protein-based fresh-keeping coating solution for hulless barley distillers' grains, comprising the following steps:

[0022] Extraction of prolamin from highland barley distillers' grains: The dried highland barley distillers' grains sample is pulverized and then added to a solvent. After magnetic stirring, it is ultrasonically treated at 350 - 450 W and 40 - 60 °C for 1.5 - 2.5 h. The ultrasonically treated sample is centrifuged, and the supernatant of the centrifugation is taken and the protein is precipitated with water. The protein is dialyzed, rotary evaporated to remove water and solvent, and then freeze-dried to constant weight to obtain prolamin from highland barley distillers' grains; among them, 90 - 120 g of highland barley distillers' grains sample is added to every 300 mL of solvent;

[0023] Preparation of fresh-keeping coating solution: The prolamin from highland barley distillers' grains, a humectant, vitamin C, and an alcohol solution are stirred and mixed evenly to obtain the fresh-keeping coating solution.

[0024] By adopting the above technical solution, during the extraction process of prolamin from highland barley distillers' grains, the ratio range of the sample to the solvent is strictly controlled and ultrasonic treatment is carried out under specific power and temperature conditions. Through steps such as centrifugation, precipitation, dialysis, rotary evaporation, and freeze-drying, it is ensured that the extracted prolamin has high purity and activity. This extraction method can effectively retain the prolamin with a molecular weight below 20 kDa in highland barley distillers' grains, providing a key raw material for the subsequent preparation of the fresh-keeping coating solution. The fresh-keeping coating solution prepared by mixing the extracted prolamin from highland barley distillers' grains, a humectant, vitamin C, and an alcohol solution evenly according to a specific ratio can form an effective protective film on the surface of fruits, significantly reducing the water evaporation rate, inhibiting the respiratory effect, delaying fruit softening, controlling the change of titratable acid content, inhibiting the activity of polyphenol oxidase, reducing microbial contamination, thereby effectively prolonging the flavor, quality, and color of fruits, and further extending the shelf life of fruits.

[0025] Preferably, the solvent is one of an ethanol solution, a propanol solution, and an isopropanol solution with a mass concentration of 70 - 85%.

[0026] By adopting the above technical solution, selecting an ethanol solution, a propanol solution, or an isopropanol solution with a specific concentration range as the solvent can effectively extract the prolamin from highland barley distillers' grains, improve the extraction efficiency and purity, and ensure that the subsequent prepared fresh-keeping coating solution has better stability and fresh-keeping effect.

[0027] Preferably, after the dried highland barley distillers' grains sample is pulverized, it is passed through a 60 - 80 mesh sieve and then added to the solvent.

[0028] By adopting the above technical solution, after the highland barley distillers' grains sample is pulverized and passed through a 60 - 80 mesh sieve treatment, the contact area between the highland barley distillers' grains and the solvent is improved, promoting the dissolution and release of prolamin. It can not only effectively improve the extraction efficiency of prolamin in the subsequent extraction process, but also improve the content of effective components in the fresh-keeping coating solution, and further enhance the fresh-keeping performance of the coating solution.

[0029] In summary, the present application has the following beneficial effects:

[0030] This application uses hordeum vulgare distillers' soluble protein, a humectant, vitamin C, and an alcohol solution to act together in a specific ratio to form an efficient fresh-keeping coating solution. This coating solution can significantly reduce the weight loss rate of fruits during storage, effectively reduce water loss; significantly inhibit the spoilage rate, and no rotting phenomenon occurred in the experimental group during the 28-day storage period; effectively maintain the fruit firmness and slow down the rate of firmness decline; control the change of titratable acid content, delay the reduction of organic acids, and retain the fruit flavor; significantly inhibit the activity of polyphenol oxidase, slow down the enzymatic browning reaction, and maintain the fruit color and quality; greatly reduce the total number of colonies, inhibit the growth and reproduction of microorganisms, and thus effectively extend the shelf life of fruits. Description of the Drawings

[0031] Figure 1 It is a graph showing the influence results of different soluble protein concentrations on the weight loss rate.

[0032] Figure 2 It is a graph showing the influence results of different dosages of vitamin C on the weight loss rate.

[0033] Figure 3 It is a graph showing the influence results of different dosages of glycerol on the weight loss rate.

[0034] Figure 4 It is a graph showing the influence results of different dosages of ethanol on the weight loss rate.

[0035] Figure 5 It is a general graph showing the influence results of the fresh-keeping coating solution on the weight loss rate of Huangguan pears.

[0036] Figure 6 It is an experimental graph showing the influence of the fresh-keeping coating solution on the spoilage rate of Huangguan pears.

[0037] Figure 7 It is a general graph showing the influence results of the fresh-keeping coating solution on the firmness of Huangguan pears.

[0038] Figure 8 It is a graph showing the influence results of the fresh-keeping coating solution on the titratable acid content of Huangguan pears.

[0039] Figure 9 It is a graph showing the influence results of the fresh-keeping coating solution on the PPO activity of Huangguan pears.

[0040] Figure 10 It is a graph showing the influence results of the fresh-keeping coating solution on the total number of colonies of Huangguan pears. Detailed Embodiments

[0041] The embodiments of the present invention will be described in detail below in conjunction with examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. The specific conditions not specified in the examples are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used without indicating the manufacturer are all conventional products that can be purchased commercially.

[0042] Highland barley lees are the main byproduct of highland barley wine fermentation, with a huge annual output, but there is a lack of high-value utilization methods in the existing technology; currently, highland barley lees are mostly used directly as animal feed or discarded, which not only causes waste of nutrients such as protein and polysaccharides, but also causes environmental pollution due to pile fermentation. Highland barley lees are rich in alcohol-soluble proteins (content up to 15-20%), which have good film-forming properties, biocompatibility and antibacterial activity, and are ideal raw materials for developing natural coating materials. However, there are no reports in the existing technology on the extraction of alcohol-soluble proteins from highland barley lees and their application in fruit coating preservation, and there is also a lack of systematic research on its functional properties and synergistic formula.

[0043] Therefore, how to efficiently utilize the alcohol-soluble protein resources in highland barley grains to construct a composite coating system with physical barrier, antioxidant and antibacterial functions to break through the technical bottleneck of the existing coating liquid with single function and insufficient preservation effect, and at the same time realize the high-value utilization of agricultural by-products, has become a key issue to be urgently solved in this field. This application is based on this.

[0044] Example

[0045] A fresh-keeping coating liquid based on highland barley lees alcohol-soluble protein, wherein each 100 mL of the fresh-keeping coating liquid comprises: 1986 mg of highland barley lees alcohol-soluble protein, 1.47 mL of a moisturizing agent, 2.49 g of vitamin C and 80.2 mL of an alcohol solution; specifically, the molecular weight of the highland barley lees alcohol-soluble protein is 11 kDa, the moisturizing agent is glycerol, and the alcohol solution is an ethanol solution with a mass concentration of 85%.

[0046] In other embodiments, the dosage of highland barley wine grains alcohol-soluble protein can be 1900 mg, 1950 mg, 2036 mg, 2108 mg, 2130 mg, 2185 mg, 2200 mg, etc.

[0047] In other embodiments, the molecular weight of highland barley lees alcohol-soluble protein can be 17kDa, 12kDa, 15kDa, 18kDa, etc.

[0048] In other embodiments, the moisturizing agent may also be propylene glycol or sorbitol, and the amount of the moisturizing agent may be.

[0049] In other embodiments, the dosage of vitamin C can be 2.2 g, 2.3 g, 2.4 g, 2.5 g, 2.6 g, 2.7 g, etc.

[0050] In other embodiments, the alcohol solution can also be isopropyl alcohol.

[0051] In other embodiments, the dosage of the alcohol solution can be 75 mL, 78 mL, 80 mL, 81 mL, 83 mL, 85 mL, etc.

[0052] A method for preparing a prolamine-based fresh-keeping coating solution from hulless barley distillers' grains comprises the following steps:

[0053] Extracting prolamine from hulless barley distillers' grains: Crushing a dried hulless barley distillers' grains sample and sieving it through a 60-mesh sieve to obtain hulless barley distillers' grains powder. Adding 200 g of the hulless barley distillers' grains powder to 600 mL of an ethanol solution with a mass concentration of 80%, magnetically stirring for 20 min, and then ultrasonically treating the sample at 400 W and 50 °C for 120 min; After ultrasonic treatment, centrifuging the sample at 8000 xg for 20 min, pouring the supernatant into a 5-L beaker, then adding 1.8 L of water to precipitate the protein, and finally dialyzing the obtained precipitate. After dialysis, removing water and ethanol by rotary evaporation and freeze-drying to constant weight;

[0054] Preparing the fresh-keeping coating solution: Stirring and mixing prolamine from hulless barley distillers' grains, a humectant, vitamin C, and the alcohol solution evenly to obtain the fresh-keeping coating solution.

[0055] In other embodiments, in the step of extracting prolamine from hulless barley distillers' grains, the solvent can be propanol or isopropyl alcohol.

[0056] In other embodiments, in the step of extracting prolamine from hulless barley distillers' grains, 90 g or 120 g or 110 g of hulless barley distillers' grains sample is added to every 300 mL of the solvent.

[0057] In other embodiments, in the step of extracting prolamine from hulless barley distillers' grains, the ultrasonic conditions can be: 350 W, 60 °C, ultrasonic treatment for 1.5 h.

[0058] In other embodiments, in the step of extracting prolamine from hulless barley distillers' grains, the ultrasonic conditions can be: 450 W, 40 °C, ultrasonic treatment for 2.5 h.

[0059] Weight loss rate test

[0060] In this application, Crown pears are selected as the experimental objects, and other products that are prone to water loss and decay can also be used as fresh-keeping objects, including but not limited to strawberries, blueberries, apples, bananas, melons, rock sugar oranges, crispy red plums, honey peaches, cucumbers, etc. 400 mL of the fresh-keeping coating solution is prepared, and the selected Crown pears are immersed in the fresh-keeping coating solution for 10 s and placed on a plate for the test.

[0061] Specifically, to explore the influence of the dosage of each raw material component on the weight loss rate of Crown pears, the dosage of each raw material component was changed singly, and the weight loss rate of Crown pears was recorded every 7 days.

[0062] Among them, the influence results of different concentrations of prolamine on the weight loss rate are as Figure 1 shown, and the prolamine concentration is shown in Table 1.

[0063] Table 1

[0064]

[0065] Among them, the influence results of different dosages of vitamin C on the weight loss rate are as Figure 2 shown, and the dosage of vitamin C is shown in Table 2.

[0066] Table 2

[0067]

[0068] Among them, the influence results of different dosages of glycerol on the weight loss rate are as Figure 3 shown, and the dosage of glycerol is shown in Table 3.

[0069] Table 3

[0070]

[0071] Among them, the influence results of different dosages of ethanol on the weight loss rate are as Figure 4 shown, and the dosage of ethanol is shown in Table 4.

[0072] Table 4

[0073]

[0074] Combined with Figures 1-4 Tables 1 - 4, it can be seen that only by the combined action of prolamine from hulless barley distillers grains, glycerol, vitamin C and ethanol solution in a specific ratio can an efficient fresh-keeping coating solution be formed, significantly reducing water loss and the weight loss rate of fruits during storage.

[0075] 400 mL of the fresh-keeping coating solution in the above-mentioned embodiment of this application was prepared, and the selected Crown pears were immersed in the fresh-keeping coating solution for 10 s, placed on a plate and marked as the experimental group, and the Crown pears not treated with the fresh-keeping coating solution were used as the control group. They were stored at 25 ± 2 °C for 28 d, and the weight loss rate, spoilage rate, hardness, titratable acid content, polyphenol oxidase activity, and total colony count were measured every 7 d. The results are as Figures 5-10 shown.

[0076] Through Figure 5It can be seen that, compared with the blank control group, the weight loss rate of the Crown pears treated with the fresh-keeping coating solution was significantly reduced during storage. This is attributed to the formation of a multifunctional protective film on the surface of the Crown pear fruits by the fresh-keeping coating solution. From the perspective of water evaporation, this protective film effectively reduced the water vapor exchange rate between the fruits and the external environment, reducing water loss; in terms of respiration, it blocked the entry of part of the oxygen, inhibited the respiratory metabolism of the fruits, thereby reducing the material consumption and water loss caused by respiration.

[0077] It can be seen that Figure 6 during the storage process, the decay rate of the Crown pears showed a gradually increasing trend with the extension of time. In the middle and late stages of storage (the 21st day), the blank control group without any treatment began to show decay. By the 28th day of storage, the decay rate of the blank control group had climbed to 100%. In sharp contrast, in the experimental group treated with the fresh-keeping coating solution, although a certain degree of shrinkage appeared on the surface of the Crown pear fruits, no decay occurred, indicating that the treatment with the fresh-keeping coating solution could effectively delay the increase in the decay rate of the Crown pear fruits. The fresh-keeping coating solution used in the experiment successfully constructed a uniform and stable protective film on the surface of the Crown pear fruits, which could significantly reduce the invasion of microorganisms in the external environment into the fruits and effectively delay the decay rate of the fruits.

[0078] Fruit firmness is one of the key indicators to measure fruit quality, and its change reflects the changes in the internal structure and physiological state of the fruits; it can be seen that Figure 7 this coating solution could significantly improve the fruit firmness of the Crown pears, which benefited from its effective protection of the fruit cells. It can be seen that Figure 7 the firmness of both groups of Crown pears gradually decreased with the extension of storage time. The firmness of the Crown pears treated with the coating solution was always higher than that of the control group, and the decreasing trend of the experimental group was the slowest. From the initial stage of storage to the 28th day of the Crown pears, the firmness of the Crown pears in the blank control group decreased from 8.28 N to 4.70 N, and the firmness of the Crown pears in the experimental group decreased from 9.04 N to 6.19 N. This is due to the effective protection of the fruit cells by the fresh-keeping coating solution. The fresh-keeping coating solution can form a physical barrier on the fruit surface, which can regulate the water loss rate of the fruits, reduce the water content of the cells, and maintain the integrity of the cell structure. In addition, this coating solution can also inhibit the respiration and bacterial proliferation of the Crown pears, reduce the degradation of cell walls and cellulose, thereby slowing down the softening process of the Crown pears.

[0079] The titratable acid content is one of the important indicators to measure fruit quality and flavor, and its change reflects the dynamic changes of a series of physiological and biochemical processes inside the fruits. It can be seen from Figure 8It can be seen that during the storage process, the titratable acid content of Huangguan pears shows a trend of first increasing and then decreasing, and the overall titratable acid content of the control group is relatively low. The results show that this fresh-keeping coating solution can effectively reduce cell necrosis caused by bacterial damage to the root stalk, delay the reduction of organic acids, extend the shelf life of Huangguan pears, and retain their flavor.

[0080] As Figure 9 shown, during the storage period, the activity of polyphenol oxidase (PPO) in Huangguan pears shows a dynamic change trend of first increasing and then decreasing with time. Among them, in the experimental group treated with the fresh-keeping coating solution based on hulless barley distillers grains protein, the PPO activity is always lower than that of the untreated control group throughout the storage process. On the 28th day of storage, the PPO activity of the control group reaches 126.6 U / gFW, while that of the treated group is only 86.9 U / g FW.

[0081] As the key enzyme causing fruit browning, the level of its activity directly affects the quality of fruits. The lower PPO activity in the experimental group indicates that the fresh-keeping coating solution based on hulless barley distillers grains protein has a significant inhibitory effect on the PPO activity of Huangguan pears. This inhibitory effect effectively slows down the enzymatic browning reaction of fruits, which is of great significance for maintaining the color, flavor and other quality characteristics of Huangguan pears, and plays an active and important role in the fruit fresh-keeping process.

[0082] The total number of colonies is a key indicator to measure the microbial contamination status of Huangguan pears, and its value is positively correlated with the possibility of sample spoilage and deterioration. In this study, the samples after 28 days of storage were detected. As Figure 10 shown, in the experimental group treated with the fresh-keeping coating solution based on hulless barley distillers grains protein, the total number of colonies is significantly lower than that of the untreated blank control group. This result shows that the fresh-keeping coating solution can effectively inhibit the growth and reproduction of microorganisms and reduce the number of microorganisms. Therefore, it is proved that the composite coating solution based on hulless barley distillers grains protein has good antibacterial properties, thus extending the shelf life of Huangguan pears.

[0083] In summary, during the storage period of Huangguan pears treated with the fresh-keeping coating solution, the weight loss rate is significantly reduced, effectively reducing water loss; the spoilage rate decreases significantly. At the 28th day of storage, the spoilage rate of the blank control group reaches 100%, while no spoilage occurs in the experimental group; the fruit firmness is effectively maintained. From the initial stage of storage to the 28th day, the decrease in the firmness of Huangguan pears in the experimental group is less than that in the control group; the change in the titratable acid content is effectively controlled, delaying the reduction of organic acids and retaining the fruit flavor; the activity of polyphenol oxidase (PPO) is significantly inhibited, slowing down the enzymatic browning reaction of fruits and maintaining the color and quality of fruits; the total number of colonies is significantly lower than that of the untreated blank control group, inhibiting the growth and reproduction of microorganisms and extending the shelf life of fruits.

[0084] This specific embodiment is only an interpretation of the present application and does not limit the present application. After reading this specification, those skilled in the art can make modifications to this embodiment that do not contribute creatively as needed, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. A highland barley lees alcohol-soluble protein-based fresh-keeping coating liquid, characterized in that: Every 100 mL of the fresh-keeping coating liquid includes: 1800-2200 mg of highland barley lees alcohol-soluble protein, 1.3-1.6 mL of a moisturizer, 2.2-2.7 g of vitamin C and 75-85 mL of an alcohol solution.

2. The highland barley lees alcohol-soluble protein-based fresh-keeping coating liquid according to claim 1, characterized in that: The molecular weight of the highland barley lees alcohol-soluble protein is below 20 kDa.

3. The highland barley lees alcohol-soluble protein-based fresh-keeping coating liquid according to claim 1, characterized in that: The alcohol solution is one of an ethanol solution and an isopropanol solution.

4. The highland barley lees alcohol-soluble protein-based fresh-keeping coating liquid according to claim 3, characterized in that: The mass concentration of the alcohol solution is 70-95%.

5. The highland barley lees alcohol-soluble protein-based fresh-keeping coating liquid according to claim 1, characterized in that: The moisturizing agent is one of glycerin, propylene glycol and sorbitol.

6. The method for preparing the highland barley lees alcohol-soluble protein-based fresh-keeping coating liquid according to any one of claims 1 to 5, characterized in that: The following steps are involved: Extracting highland barley lees alcohol-soluble protein: grinding a dried highland barley lees sample and adding it to a solvent, subjecting it to magnetic stirring and ultrasonic treatment for 1.5-2.5 hours at 350-450W and 40-60°C, centrifuging the ultrasonically treated sample, taking the supernatant from the centrifuge and precipitating the protein with water, dialyzing the protein, rotary evaporating to remove water and solvent, and then freeze-drying to constant weight to obtain highland barley lees alcohol-soluble protein; wherein 90-120 g of highland barley lees sample is added to every 300 mL of solvent; Preparation of fresh-keeping coating liquid: stir and mix highland barley lees alcohol-soluble protein, moisturizer, vitamin C and alcohol solution to obtain fresh-keeping coating liquid.

7. The method for preparing the highland barley lees alcohol-soluble protein-based fresh-keeping coating liquid according to claim 6, characterized in that: The solvent is one of an ethanol solution, a propanol solution and an isopropanol solution with a mass concentration of 70-85%.

8. The method for preparing the highland barley lees alcohol-soluble protein-based fresh-keeping coating liquid according to claim 6, characterized in that: The dried highland barley lees sample is crushed, passed through a 60-80 mesh sieve, and then added to the solvent.

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