Preparation method and application of waxberry composite preservative film

Abstract

The invention discloses a preparation method of a waxberry composite preservative film, which comprises the following steps: adding waxberry anthocyanin, waxberry carbon dots and a plasticizer into a gelatin-K-carrageenan solution, uniformly stirring and mixing, ultrasonically degassing, forming a film by using a mixed solution, and drying at room temperature to obtain the waxberry composite preservative film, the preservative film has good water vapor and oxygen barrier property and excellent mechanical property; in addition, the film shows freshness indicating ability through pH responsiveness; meanwhile, the adopted preparation method is easy to operate and free of special equipment requirements, high-value utilization of waxberry waste is achieved, and the prepared composite preservative film 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] This invention belongs to the field of food preservation film application, specifically relating to a pH-responsive intelligent active bayberry composite food preservation film and its application in the preservation of fresh shrimp. Background Technology

[0002] Fresh shrimp contains a high amount of protein, trace elements, and essential amino acids, making it a delicious and nutritious aquatic product with both economic and nutritional value. However, due to the unique physiological and biochemical characteristics of shrimp—namely, their high protein and water content, and the presence of a large amount of highly active polyphenol oxidase—dead shrimp are susceptible to contamination from microorganisms on their body surface and digestive organs, as well as from external microorganisms, leading to spoilage during storage. Simultaneously, the polyphenol oxidase within the shrimp catalyzes substances such as tyrosine, producing a series of biochemical reactions that generate melanin, resulting in black spots on the shrimp's surface, a phenomenon known as melanosis.

[0003] In practical applications of fresh shrimp storage and preservation, traditional methods commonly use petroleum-based plastic films for packaging. However, these petrochemical-derived packaging materials are difficult to biodegrade and can persist in the natural environment for hundreds of years, leading to significant ecological accumulation and pollution problems. Meanwhile, as consumers increasingly demand freshness, safety, and quality in food, the development of environmentally friendly and sustainable new bio-based packaging materials has become a crucial need for the packaging industry.

[0004] Waxberries are rich in nutrients, containing anthocyanins, flavonols, ascorbic acid (vitamin C), and various amino acids and vitamins, giving them high nutritional and health value. However, the processing generates a large amount of byproducts—waxberry pomace. Utilizing this pomace for high-value purposes not only transforms waste into high-value-added products, creating significant economic benefits, but also effectively alleviates the environmental pressure caused by its accumulation. Gelatin is a protein extracted from animal slaughter and processing byproducts. Due to its excellent film-forming properties, edibility, biodegradability, abundant sources, and low cost, its application in the food packaging industry is becoming increasingly widespread. Carrageenan is a linear sulfated polysaccharide derived from red algae, composed of repeating alternating disaccharide units of d-galactose and 3,6-anhydrous d-galactose linked by α-1,3 and β-1,4-glycosidic bonds. However, both gelatin and κ-carrageenan, as matrices, face common limitations such as poor thermal stability, insufficient mechanical strength, susceptibility to humidity, and limited functionality of pure components (e.g., weak antibacterial and antioxidant capabilities). Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a method for preparing a pH-responsive bayberry composite preservation film and its application in the preservation of fresh shrimp. This invention uses gelatin and k-carrageenan as the matrix, and adds anthocyanins and carbon dots extracted from bayberry pomace as active fillers to prepare an intelligent active preservation film. This film has good water vapor and oxygen barrier properties and excellent mechanical properties. Furthermore, this film exhibits freshness indication capabilities through pH responsiveness.

[0006] The preparation method of the intelligent food preservation film based on bayberry pomace of this invention is as follows: (1) Preparation of Myrica rubra anthocyanins The washed, dried and pulverized bayberry residue was mixed with an acidified 70-80% ethanol solution. After extraction at 20-30℃ under ultrasonic conditions for 20-30 min, the reaction product was allowed to stand at room temperature in the dark for 2-4 h. The solid and liquid were separated, and the liquid was concentrated and dried to obtain the product. The acidified 70-80% ethanol solution is prepared by mixing a 70-80% ethanol solution with glacial acetic acid in a volume ratio of 5-7:1. (2) Preparation of carbon dots in bayberry Wash and dry the solid after solid-liquid separation in step (1) of anthocyanin extraction. Disperse the dried solid in distilled water, stir thoroughly, and carry out the mixture in an oil bath at 180-220℃ for 5-7 hours. After cooling, separate the solid and liquid, collect the supernatant, filter the supernatant through a 0.22μm membrane filter, and freeze dry to obtain the final product. (3) Add bayberry anthocyanins, bayberry carbon dots and plasticizer to gelatin-K-carrageenan solution, stir and mix well, degas by ultrasonication, form a film of the mixture, and dry at room temperature to obtain bayberry composite preservation film. The mass-volume concentration (g:mL) of gelatin and K-carrageenan (mass ratio 1:1) in the gelatin-K-carrageenan solution is 1-3%. For every 100mL of gelatin-K-carrageenan solution, add 100-300mg of myrica anthocyanin, 10-30mg of myrica carbon dots, and 0.3-0.5g of plasticizer.

[0007] Another objective of this invention is to apply the bayberry composite preservation film prepared by the above method to the preservation of fresh shrimp.

[0008] Compared with the prior art, the advantages and technical effects of the present invention are as follows: (1) The method for preparing the smart food preservation film of the present invention is simple, green and environmentally friendly, and does not require complicated instruments and equipment. It is highly operable and easier to promote. (2) The gelatin and k-carrageenan used in this invention are abundant, low-cost and biodegradable raw materials, which are green and environmentally friendly and in line with the concept of sustainable development. The preparation of bayberry anthocyanins and carbon dots from bayberry residue realizes the high-value utilization of waste, which is of great significance for reducing environmental pollution and recycling resources. (3) The preservation film prepared by this invention has good water vapor and oxygen barrier properties, good mechanical properties, and good stability, and is less affected by changes in the surrounding environment. The preservation film can effectively inhibit oxidation, inhibit microbial reproduction, delay the spoilage process of shrimp, and extend its storage period. At the same time, the preservation film has pH response capability, which can visually assess the freshness of food and monitor the freshness of food in real time. Attached Figure Description

[0009] Figure 1 The color changes of the composite preservation films prepared in the control example and Examples 1-3 under different pH conditions; Figure 2 The results show the effects of composite preservation film, PE film and unpackaged treatment on the pH of shrimp. Figure 3 The results show the effects of composite preservation film, PE film and unpackaged treatment on the total viable bacteria count of shrimp. Figure 4 The results show the effects of composite preservation film, PE film, and unpackaged treatment on the total volatile basic nitrogen content of shrimp. Detailed Implementation

[0010] The present invention will be further described in detail below with reference to embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto. Unless otherwise specified, the reagents in the embodiments are all conventional commercially available reagents; In the following examples, the waste material, bayberry residue, is the residue from the production of bayberry juice; Example 1

[0011] (1) Collect bayberry waste, bayberry residue, wash bayberry residue three times with distilled water, air dry naturally, and then crush it through an 80-mesh sieve to obtain bayberry residue powder; (2) Mix the bayberry residue powder with an acidified 75% ethanol solution (6:1 acidification) at a solid-liquid ratio of 1:1.5 g:mL. After extraction at 25℃ and under ultrasound for 30 min, let it stand at room temperature in the dark for 2 hours. Filter and collect the supernatant. Concentrate the supernatant at 40℃ using a rotary evaporator. Freeze-dry the concentrate to prepare bayberry anthocyanin powder. (3) The solid filtered in step (2) was washed with water and dried. 4g of solid was dispersed in 70mL of distilled water and stirred thoroughly. Then it was transferred to a 100mL reaction vessel and reacted in an oil bath at 200℃ for 6 hours. After cooling, it was centrifuged at 8000 rpm for 20 minutes and the supernatant was collected. The supernatant was filtered through a membrane filter with a pore size of 0.22μm and freeze-dried to obtain the carbon dots of bayberry. (4) Add 1g gelatin and 1g K-carrageenan to 100mL of distilled water, stir in a 70℃ water bath until completely dissolved, then add 0.4g glycerol and continue stirring for 30min; then add 100mg bayberry anthocyanin, stir and mix well, then add 10mg bayberry carbon dots, stir and mix well, pour the mixture into a glass plate to form a film, and let it dry naturally at room temperature to obtain bayberry composite preservation film. Example 2

[0012] (1) The preparation of bayberry residue powder is the same as step (1) in Example 1; (2) Mix the bayberry residue powder with an acidified 70% ethanol solution (5:1 acidification) at a solid-liquid ratio of 1:3 g:mL. After extraction at 20℃ and under ultrasound for 30 min, let it stand at room temperature in the dark for 3 hours. Filter and collect the supernatant. Concentrate the supernatant at 40℃ using a rotary evaporator. Freeze-dry the concentrate to prepare bayberry anthocyanin powder. (3) The solid filtered in step (2) was washed with water and dried. 6g of solid was dispersed in 70mL of distilled water and stirred thoroughly. Then it was transferred to a 100mL reaction vessel and reacted in an oil bath at 190℃ for 6 hours. After cooling, it was centrifuged at 8000 rpm for 20 minutes and the supernatant was collected. The supernatant was filtered through a membrane filter with a pore size of 0.22μm and freeze-dried to obtain the carbon dots of bayberry. (4) Add 1g gelatin and 1g K-carrageenan to 100mL of distilled water, stir in a 70℃ water bath until completely dissolved, then add 0.4g glycerol and continue stirring for 30min; then add 200mg bayberry anthocyanin, stir and mix well, then add 20mg bayberry carbon dots, stir and mix well, pour the mixture into a glass plate to form a film, and let it dry naturally at room temperature to obtain bayberry composite preservation film. Example 3

[0013] (1) The preparation of bayberry residue powder is the same as step (1) in Example 1; (2) Mix the bayberry residue powder with an acidified 80% ethanol solution (7:1 acidification) at a solid-liquid ratio of 1:4.5 g:mL. After extraction at 30℃ and under ultrasound for 20 min, let it stand at room temperature in the dark for 4 hours. Filter and collect the supernatant. Concentrate the supernatant at 40℃ using a rotary evaporator. Freeze-dry the concentrate to prepare bayberry anthocyanin powder. (3) The solid filtered in step (2) was washed with water and dried. 8g of solid was dispersed in 70mL of distilled water and stirred thoroughly. Then it was transferred to a 100mL reaction vessel and reacted in an oil bath at 210℃ for 6 hours. After cooling, it was centrifuged at 8000 rpm for 20 minutes and the supernatant was collected. The supernatant was filtered through a membrane filter with a pore size of 0.22μm and freeze-dried to obtain the carbon dots of bayberry. (4) Add 1g gelatin and 1g K-carrageenan to 100mL of distilled water, stir in a 70℃ water bath until completely dissolved, then add 0.4g glycerol and continue stirring for 30min; then add 300mg bayberry anthocyanin, stir and mix well, then add 30mg bayberry carbon dots, stir and mix well, pour the mixture into a glass plate to form a film, and let it dry naturally at room temperature to obtain bayberry composite preservation film.

[0014] Comparative example: Add 1g of gelatin and 1g of K-carrageenan to 100mL of distilled water, stir in a 70℃ water bath until completely dissolved, then add 0.4g of glycerin and continue stirring for 30min; pour the mixture into a glass plate to form a film, and let it dry naturally at room temperature to obtain a plastic wrap.

[0015] Example 4: pH response performance test of the plastic wrap prepared in Examples 1-3 and the control example The composite plastic wraps of Examples 1-3 and the control plastic wrap were subjected to pH response testing. The color change of the composite plastic wrap samples in phosphate buffer solutions with pH 2.0-12.0 was recorded, and a control (the color of the plastic wrap before it was placed in the buffer solution) was set up. See results Figure 1 ,from Figure 1 As can be seen, the control film showed no change, while Examples 1-3 all showed clear and distinguishable color responses. The film was pink at pH 2-4, light brown at pH 5-9, and green at pH 10-12.

[0016] Example 5: Water vapor transmission rate, oxygen transmission rate, and mechanical properties tests of the composite preservation films of Examples 1-3 The water vapor transmission rate, oxygen transmission rate, and mechanical properties of the plastic wrap prepared in Examples 1-3 and the comparative examples were tested. The water vapor transmission rate was tested according to the method in GB1037-1988; the oxygen transmission rate was tested according to the method in GB / T19789-2005; and the tensile strength was tested according to the method in GB13022-91. The results are shown in Tables 1 and 2. Table 1. Water vapor transmission rate and oxygen transmission rate of plastic wrap

[0017] As can be seen from Table 1, the plastic wrap prepared by the method of the present invention has low water vapor permeability and oxygen permeability. Table 2 Mechanical properties of plastic wrap

[0018] As can be seen from Table 2, the multifunctional composite food preservation film prepared by the method of the present invention has strong mechanical properties.

[0019] Example 6: To further verify the preservation effect of the above-mentioned plastic wrap on shrimp, the plastic wrap prepared in Examples 1-3 was applied to shrimp preservation. Unpackaged shrimp (Control) and shrimp packaged in commercially available PE plastic bags were used as controls. The shrimp were stored at 4°C for 5 days, and the pH value, total viable bacteria (TVC) and total volatile alkaline nitrogen (TVB-N) of the shrimp were measured on days 0, 1, 2, 3, 4 and 5.

[0020] 1. The pH of shrimp was determined by potentiometry. The pH of each group of samples was measured during storage using a pH meter. Shrimp spoilage was largely attributed to bacterial proliferation and degradation of muscle protein and connective tissue, which led to changes in pH value. The results are as follows Figure 2 As shown, the pH value dropped sharply on day 1, possibly due to the activity of acid-producing bacteria. From day 2 onwards, the pH value increased, which is related to the accumulation of degradation byproducts (such as ammonia and other volatile basic nitrogen compounds). The pH value of the control group and the PE group exceeded 7.7 on day 3, indicating that the shrimp had spoiled to the point of being inedible. However, the pH value of Example 3 was still below 7.7 on day 5. This is because the preservation film prepared in Example 3 has a low water vapor permeability and oxygen permeability, which can effectively slow down the exchange of oxygen and carbon dioxide, thus slowing down respiration to a certain extent and effectively reducing bacterial proliferation and degradation of muscle protein and connective tissue in shrimp during storage.

[0021] 2. The changes in the total aerobic bacterial count were detected using the method specified in GB 4789.2-2010 "Determination of Total Colony Count". The total bacterial count is one of the indicators that determine food hygiene. According to data from the International Committee on Microbiological Standards for Foods, the acceptable total bacterial count for meat products is 7 log CFU / g. Figure 3 The study showed the changes in total viable bacteria (TVC) during the preservation of fresh shrimp. The initial TVC of the fresh shrimp samples was recorded as 3.5 log CFU / g; the TVC value steadily increased with the extension of storage time. The control group and the PE group exceeded the microbial threshold on day 3, while the composite preservation films of Examples 2 and 3 remained below the threshold until day 5.

[0022] 3. The semi-micro Kjeldahl method was used to determine the changes in volatile basic nitrogen (TVB-N) content in pork during preservation, according to GB5009.228-2016 "Determination of Volatile Basic Nitrogen in Food". TVB-N is mainly composed of ammonia and amine compounds and is a key indicator of spoilage in aquatic products. A TVB-N level exceeding 20 mg / 100g indicates that freshwater fish and shrimp have spoiled.

[0023] See results Figure 4 The control group and the PE group exceeded the threshold on the third day, while the composite preservation film of Examples 2 and 3 effectively delayed the spoilage of shrimp until the fifth day.

Claims

1. A method for preparing a composite preservation film for bayberries, characterized in that: The waxberry compound preservative film is prepared by adding waxberry anthocyanin, waxberry carbon dots and plasticizer into a gelatin-K-carrageenan solution, stirring and mixing, ultrasonic degassing, film forming, drying at room temperature. The waxberry anthocyanin is prepared by mixing the cleaned, dried and crushed waxberry residue powder with acidified 70-80% ethanol solution with a volume concentration, stirring and mixing, extracting at 20-30 ℃ under ultrasonic for 20-30 min, placing the reaction product at room temperature in dark for 2-4 h, solid-liquid separation, liquid concentration and drying. The waxberry carbon dots are prepared by washing and drying the solid after the solid-liquid separation in the preparation of the waxberry anthocyanin, dispersing the dried solid in distilled water, stirring, heating in an oil bath at 180-220 ℃ for 5-7 h, cooling, solid-liquid separation, collecting the supernatant, filtering the supernatant with a 0.22 μm membrane filter and freeze-drying.

2. The method for preparing the bayberry composite preservation film according to claim 1, characterized in that: The mass concentration of gelatin and K-carrageenan in the gelatin-K-carrageenan solution is 1-3%, 100-300 mg of waxberry anthocyanin, 10-30 mg of waxberry carbon dots and 0.3-0.5 g of plasticizer are added into 100 mL of the gelatin-K-carrageenan solution.

3. The method for preparing the bayberry composite preservation film according to claim 2, characterized in that: The plasticizer is glycerol.

4. The method for preparing the bayberry composite preservation film according to claim 2, characterized in that: The acidified 70-80% ethanol solution is prepared by mixing 70-80% ethanol solution with glacial acetic acid at a volume ratio of 5-7:

1.

5. The waxberry compound preservative film prepared by the preparation method of any one of claims 1-4 is used for fresh shrimp preservation.

Images