Biomass antioxidant, method of preparation and use in food packaging

Abstract

The present application relates to the field of new food packaging materials, and discloses a biomass antioxidant, a preparation method thereof and application of the biomass antioxidant in food packaging, the preparation method of the biomass antioxidant comprises the following steps: S1: after the agricultural processing byproduct raw material is wetted, steam explosion treatment is carried out, the steam explosion treatment product is collected after instant pressure relief, and the steam explosion treatment product is dried; S2: the steam explosion treatment product after drying is ball milled under low temperature conditions; S3: the product after ball milling is screened, and the undersize is collected to obtain the biomass antioxidant, and the application of the biomass antioxidant in food packaging film is also disclosed, and a starch / biodegradable polyester-based antioxidant packaging film is prepared by the method. The biomass antioxidant prepared by the present application can play the interface enhancement and antioxidant functions in the polymer matrix, so that the prepared packaging film has good mechanical properties, processing performance and antioxidant activity.

Description

Technical Field

[0001] This invention relates to the field of new food packaging materials, specifically to a biomass antioxidant, its preparation method, and its application in food packaging. Background Technology

[0002] Globally, a significant amount of agricultural and food processing byproducts fail to be effectively utilized for high-value purposes each year, resulting in severe resource waste. Simultaneously, growing global concern about plastic pollution has accelerated the demand for low-cost and biodegradable materials. Existing technologies, such as Chinese Patent Publication No. CN108530855A, disclose a cellulose / starch-based biodegradable plastic film material. This material uses sweet potato residue, processed through simple physical methods such as soaking, crushing, and sieving, as a filler added to a starch-based system. However, this processing method only reduces the size of the raw material; it fails to disrupt the dense plant cell wall structure, making it difficult to release internal active ingredients. Therefore, the sweet potato residue merely serves as an inert filler to reduce costs, failing to substantially enhance the film's antioxidant functions and thus failing to meet the needs of high-value applications such as green food preservation. Chinese invention patent CN109354722A discloses a method for preparing a modified nanocellulose-reinforced thermoplastic starch food packaging film, and discloses a scheme for extracting nanocellulose by treating cassava residue with acid and alkali reagents. Although this technology improves the mechanical properties and interfacial compatibility of the composite film and can be applied to food packaging fields such as candy, pastries and instant noodles, this method requires a large amount of acid and alkali reagents to treat biomass raw materials during the preparation process, which is prone to generating chemical waste liquid and poses a certain risk of environmental pollution, which is not conducive to green and sustainable production.

[0003] As can be seen from the above, although existing technologies have made some progress in the modification of biomass raw materials and the preparation of starch-based biodegradable films, they still have shortcomings such as the difficulty in releasing intrinsic active ingredients through ordinary pulverization and the serious environmental pollution caused by chemical acid and alkali reagent treatment. This makes it difficult for existing films to simultaneously achieve good processing performance, mechanical properties, biodegradability, and antioxidant activity. Therefore, developing a greener, more efficient, lower-cost technology solution without secondary pollution is of great significance for promoting the development of green food packaging materials. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention employs steam explosion treatment to disrupt the cell wall structure of agricultural byproducts such as wheat bran and corn husks, promoting the release of active components like polyphenols. This is combined with low-temperature ball milling and fine sieving to obtain modified biomass antioxidants with uniform particle size and good activity retention. Subsequently, a stepwise plasticizing process is used: starch, biodegradable polyester, and plasticizer are melt-extruded to prepare a basic polymer masterbatch, which is then blended with the biomass antioxidant and blow-molded into a film. Steam explosion treatment exposes more polar groups such as hydroxyl groups on the surface of the biomass antioxidant, enhancing hydrogen bonding and interfacial bonding between the filler and the polymer matrix. Simultaneously, it reduces thermal degradation and activity loss of the active filler during high-temperature processing, resulting in a packaging film with excellent processing performance, mechanical properties, biodegradability, and antioxidant activity. This invention provides a simple, low-cost, and pollution-free technical solution for the high-value utilization of agricultural processing byproducts and the preparation of green food packaging materials, showing promising application prospects in the packaging and preservation of easily oxidized foods.

[0005] To achieve the above objectives, the present invention adopts the following technical solution.

[0006] On one hand, the present invention provides a method for preparing a biomass antioxidant, comprising the following steps:

[0007] S1: After wetting the agricultural processing by-product raw materials, steam explosion treatment is carried out. After instantaneous depressurization, the steam explosion treatment material is collected and dried.

[0008] S2: The dried steam explosion treatment material is ball-milled and pulverized under low temperature conditions;

[0009] S3: The product after ball milling is sieved, and the undersize material is collected to obtain the biomass antioxidant.

[0010] Preferably, the agricultural processing by-product raw materials in S1 are selected from agricultural processing by-products rich in cellulose and natural phenolic substances, including one or more of bran, corn husk, soybean husk, rice husk, sugarcane bagasse, and fruit and vegetable processing residues.

[0011] In step S1, the moisture content of the agricultural processing by-product raw material is maintained at 20% to 40% after wetting. The pressure of the steam explosion treatment is 1.0 to 2.0 MPa, and the pressure holding time is 60 to 120 s. After the steam explosion treatment is completed, the pressure is released instantly, and the collected steam explosion treatment material is dried to constant weight.

[0012] Preferably, in step S2, a ball milling device with cooling and temperature control function is used for ball milling, the ball milling speed is 80-100 rpm, the ball milling time is 20-30 min, and the material temperature during the ball milling process does not exceed 30℃.

[0013] Preferably, in step S3, the product after ball milling is sieved through a 300-500 mesh standard sieve, and the undersize material is collected.

[0014] On the other hand, this solution also provides a biomass antioxidant, which is prepared by the above-described preparation method.

[0015] In another aspect, the present invention also provides a food packaging film containing a biomass antioxidant, wherein, by weight parts, the raw materials of the food packaging film include: 20-30 parts of starch; 70-80 parts of biodegradable polyester; 7-11 parts of plasticizer; and 1-5 parts of the biomass antioxidant as described in claim 6.

[0016] The starch is selected from one or more of oxidized starch, carboxymethyl starch, hydroxypropyl starch, cationic starch, and esterified starch.

[0017] The biodegradable polyester is selected from one or more of polybutylene adipate / terephthalate, polylactic acid, polybutylene succinate, polycaprolactone, and polyhydroxyalkanoates.

[0018] The plasticizer is selected from one or more of glycerol, sorbitol, polyethylene glycol, citric acid, epoxidized soybean oil, and choline chloride.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) Balancing the antioxidant properties and performance of the film.

[0021] The film prepared by this invention can not only utilize the natural active components in biomass antioxidants to scavenge free radicals or delay oxidation reactions, but also maintain good mechanical properties, flexibility, continuous film-forming performance and processing stability through the synergistic control of raw material ratio, filler particle size and step-by-step plasticizing molding process.

[0022] (2) It helps to retain natural antioxidant active components.

[0023] This invention employs low-temperature cold air ball milling, controlling the material temperature below 30°C during the milling process. This reduces the oxidation and degradation of heat-sensitive active components such as polyphenols and phenolic acids during the pulverization process. Simultaneously, a stepwise plasticizing molding process is used to add the biomass antioxidant during the second blending and blowing stage, avoiding its participation in the prolonged melting and plasticizing process of the base masterbatch. This further reduces the loss of active components under high-temperature, high-shear conditions.

[0024] (3) Improve the functional utilization value of agricultural processing by-products and reduce secondary pollution.

[0025] This invention does not use agricultural processing byproducts as inert fillers to simply reduce costs. Instead, it uses steam explosion to destroy their cell wall structure, promoting the release and exposure of natural active components such as polyphenols and phenolic acids. This allows agricultural processing byproducts to simultaneously perform structural filling and antioxidant functions, transforming them from ordinary filler materials into functional packaging components. The entire process does not require the use of large amounts of strong acids, strong alkalis, or organic solvents, which can reduce the consumption of chemical reagents and waste liquid discharge, and reduce the difficulty of post-processing and environmental burden.

[0026] In summary, this invention effectively disrupts the cell wall structure of agricultural by-products through steam explosion treatment, promoting the release of antioxidant active components such as polyphenols. Simultaneously, it exposes abundant hydroxyl groups on the filler surface, significantly enhancing interfacial compatibility with the polymer matrix through hydrogen bonding. Furthermore, the combination of low-temperature cold air ball milling and stepwise plasticizing molding processes minimizes the thermal degradation and loss of heat-sensitive active components during high-temperature, high-shear processing. This solution not only endows the packaging film with excellent mechanical properties, processing stability, and significant antioxidant function, but also achieves the green, high-value utilization of agricultural waste. It is low-cost and produces no secondary pollution, making it a promising candidate for widespread application in the field of green preservation packaging for easily oxidized foods. Attached Figure Description

[0027] Figure 1 This is a comparison chart of the free radical scavenging capabilities of the food packaging film of the present invention;

[0028] Figure 2 This diagram shows the changes in color difference and polyphenol oxidase activity of potatoes during packaging with the food packaging film of this invention. Detailed Implementation

[0029] The following examples are provided to further illustrate the present invention, but should not be construed as limiting the scope of protection of the present invention. Unless otherwise specified, all raw materials used are commercially available products, and all equipment and testing methods used are conventional equipment and methods in the art; the amounts of each raw material are based on dry weight. Before use, the agricultural processing by-products are cleaned of stones, metals, and other foreign matter.

[0030] This invention provides a method for preparing a biomass antioxidant, comprising the following steps:

[0031] S1: After wetting the agricultural processing by-product raw materials, steam explosion treatment is carried out. After instantaneous depressurization, the steam explosion treatment material is collected and dried.

[0032] The moisture content of the agricultural processing by-product raw material after wetting and before steam explosion treatment is controlled at 20-40%, and the pressure of the steam explosion treatment is 1.0-2.0 MPa, so that the high temperature and high pressure steam can fully penetrate into the interior of the biomass raw material, and the pressure maintenance time is 60-120 s;

[0033] After the steam explosion treatment is completed, the pressure is released instantly to obtain the steam-exploded biomass raw material. The collected steam-exploded material is then dried at a temperature controlled between 40 and 60°C until it reaches a constant weight, in order to reduce the moisture content of the raw material and improve the stability of the subsequent crushing process.

[0034] S2: The dried steam explosion treatment material is ball-milled under low temperature conditions. Specifically, ball milling is carried out using ball milling equipment with cooling and temperature control function. The ball milling speed is 80-100 rpm, the ball milling time is 20-30 min, and the material temperature during the ball milling process does not exceed 30℃.

[0035] S3: The product after ball milling is sieved, and the undersize material is collected to obtain the biomass antioxidant.

[0036] Preferably, the agricultural processing by-product raw materials in S1 are selected from agricultural processing by-products rich in cellulose and natural phenolic substances, including one or more of bran, corn husk, soybean husk, rice husk, sugarcane bagasse, and fruit and vegetable processing residues.

[0037] In step S1, the moisture content of the agricultural processing by-product raw material is maintained at 20% to 40% after wetting. The pressure of the steam explosion treatment is 1.0 to 2.0 MPa, and the pressure holding time is 60 to 120 s. After the steam explosion treatment is completed, the pressure is released instantly, and the collected steam explosion treatment material is dried to constant weight.

[0038] Preferably, in step S2, a ball milling device with cooling and temperature control function is used for ball milling, the ball milling speed is 80-100 rpm, the ball milling time is 20-30 min, and the material temperature during the ball milling process does not exceed 30℃.

[0039] Preferably, in step S3, the product after ball milling is sieved through a 300-500 mesh standard sieve, and the undersize material is collected.

[0040] This solution also provides a biomass antioxidant, which is prepared by the above-described preparation method.

[0041] The present invention also provides a food packaging film containing a biomass antioxidant, wherein, by weight parts, the raw materials of the food packaging film include: 20-30 parts of starch; 70-80 parts of biodegradable polyester; 7-11 parts of plasticizer; and 1-5 parts of the biomass antioxidant as described in claim 6.

[0042] The starch is selected from one or more of oxidized starch, carboxymethyl starch, hydroxypropyl starch, cationic starch, and esterified starch.

[0043] The biodegradable polyester is selected from one or more of polybutylene adipate / terephthalate, polylactic acid, polybutylene succinate, polycaprolactone, and polyhydroxyalkanoates.

[0044] The plasticizer is selected from one or more of glycerol, sorbitol, polyethylene glycol, citric acid, epoxidized soybean oil, and choline chloride.

[0045] This invention provides a method and equipment requirements for preparing food packaging films containing biomass antioxidants:

[0046] S1: Mix starch, plasticizer and biodegradable polyester evenly using a high-speed mixer to obtain a basic polymer mixture, and seal and let it stand for 12-24 hours.

[0047] S2: The base polymer mixture is added to a co-rotating twin-screw extruder for melt blending and extrusion granulation. The temperature of each zone of the twin-screw extruder is controlled at 105–135°C according to the melting and plasticizing state of the raw material, and the screw speed is 100–150 rpm. The extruded strip is cooled by air cooling and then pelletized to obtain a base polymer masterbatch without biomass antioxidants.

[0048] S3: Weigh 1-5 parts of the biomass antioxidant according to the specified mass ratio and mix it with the base polymer masterbatch obtained in step S2. Add the mixture to a single-screw blown film mill for melt blending and blown film forming. The extrusion temperature during the blown film process is controlled at 110-155℃, and the screw speed is 30-50 rpm.

[0049] Preferably, the length-to-diameter ratio of the single-screw extruder is 30:1 to 40:1.

[0050] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0051] Example 1: A method for preparing a food packaging film based on biomass antioxidants, the specific steps of which are as follows:

[0052] (1) Weigh 1000g of wheat bran and add 30% of the dry weight of the bran with deionized water, i.e., add 300g of deionized water. After mixing thoroughly, seal and let stand for 2 hours to allow the moisture to be evenly distributed inside the bran. Load the moistened bran into a steam explosion device and maintain the pressure at 2.0MPa steam pressure for 90s. Then release the pressure instantly and collect the exploded material.

[0053] (2) Spread the obtained material evenly in a tray and dry it with hot air at 50°C until constant weight. Send the dried material into a ball mill with a cold air circulation system for crushing. The ball mill speed is 100 rpm and the ball milling time is 30 min. The material temperature is controlled to not exceed 30°C by cold air circulation. After the ball milling is completed, use a 500-mesh standard sieve to screen and collect the undersize material to obtain the biomass antioxidant. Seal and store it in the dark for later use.

[0054] (3) Weigh 200g of hydroxypropyl starch, 800g of polybutylene adipate / terephthalate (hereinafter referred to as PBAT) and 90g of glycerol. Add hydroxypropyl starch, PBAT and glycerol to a high-speed mixer and mix for 8min to obtain a uniform basic polymer mixture; seal the mixture and let it stand for 12h to allow the glycerol to fully penetrate and distribute in the starch phase.

[0055] (4) The settled basic polymer mixture is added to a co-rotating twin-screw extruder for melt blending. The temperature of the twin-screw extruder from the feed section to the die head is set to 105℃, 115℃, 125℃, 135℃, 125℃ and 110℃ respectively, and the screw speed is 120 rpm. The extruded strip is cooled by air cooling and then pelletized to obtain basic polymer masterbatch without biomass antioxidants.

[0056] (5) The above-mentioned basic polymer masterbatch and 10g of steam explosion modified bran were added to a single-screw blown film machine with a screw diameter of 25mm and a length-to-diameter ratio of 30:1. The temperature of each temperature zone and the die head of the single-screw blown film machine were set to 110℃, 130℃, 150℃, 155℃, 135℃ and 125℃ respectively, and the screw speed was 40rpm. The film thickness was about 60μm.

[0057] Example 2: A method for preparing a food packaging film based on biomass antioxidants, the specific steps of which are as follows:

[0058] Weigh out 250g of hydroxypropyl starch, 750g of PBAT, 9g of glycerol, and 30g of steam-explosion modified wheat bran. The preparation of biomass antioxidants and basic polymer masterbatch and subsequent blown film operation are the same as in Example 1, except for the amount of steam-explosion modified wheat bran added. The resulting film thickness is approximately 40μm.

[0059] Example 3: A method for preparing a food packaging film based on biomass antioxidants, the specific steps of which are as follows:

[0060] (1) Weigh 1000g of corn husks and add 25% of deionized water relative to its dry basis weight, i.e., add 250g of deionized water. After mixing thoroughly, seal and let stand for 2 hours to allow the moisture to be evenly distributed inside the bran. Load the moistened bran into a steam explosion device and maintain the pressure at 2.0MPa steam pressure for 120s. Then release the pressure instantly and collect the exploded material.

[0061] (2) Spread the obtained material evenly in a tray and dry it with hot air at 50°C until constant weight. Then, send the dried material into a ball mill with a cold air circulation system for crushing. The ball mill speed is 90 rpm and the ball milling time is 30 min. The material temperature is controlled to be no higher than 30°C by cold air circulation. After the ball milling is completed, use a 400-mesh standard sieve to screen the material and collect the sieve material to obtain the biomass antioxidant. Store it in a sealed, light-proof container for later use.

[0062] (3) Weigh 300g of oxidized starch, 70g of PBAT and 110g of glycerol. Add the oxidized starch, PBAT and glycerol to a high-speed mixer and mix for 10min to obtain a uniform basic polymer mixture. Seal and let stand for 12h.

[0063] (4) The settled basic polymer mixture is added to a co-rotating twin-screw extruder for melt blending. The temperature of the twin-screw extruder from the feed section to the die head is set to 105℃, 120℃, 125℃, 130℃, 120℃ and 105℃ respectively, and the screw speed is 100 rpm. The extruded strip is cooled by air cooling and then pelletized to obtain basic polymer masterbatch without biomass antioxidants.

[0064] (5) The above-mentioned basic polymer masterbatch and 50g of steam explosion modified corn husks were added to a single-screw blown film machine with a screw diameter of 25mm and a length-to-diameter ratio of 35:1. The temperature of each temperature zone and the die head of the single-screw blown film machine were set to 115℃, 130℃, 145℃, 155℃, 140℃ and 125℃ respectively, and the screw speed was 30rpm. The film thickness was about 55μm.

[0065] Example 4: A method for preparing a food packaging film based on biomass antioxidants, the specific steps of which are as follows:

[0066] (1) Weigh 500g each of corn husks and soybean husks, add 25% of their dry weight of deionized water (i.e., add 250g of deionized water), mix thoroughly, seal and let stand for 2 hours to allow the moisture to be evenly distributed inside the material. Load the moistened material into a steam explosion device, maintain the pressure at 2.0MPa steam pressure for 60s, then release the pressure instantly and collect the exploded material.

[0067] (2) Spread the obtained material evenly in a tray and dry it with hot air at 50°C until constant weight. Then, send the dried material into a ball mill with a cold air circulation system for crushing. The ball mill speed is 80 rpm and the ball milling time is 24 min. The material temperature is controlled to be no higher than 30°C by cold air circulation. After the ball milling is completed, use a 300-mesh standard sieve to screen and collect the sieve material to obtain the biomass antioxidant. Seal and store it in the dark for later use.

[0068] (3) Weigh 200g of carboxymethyl starch, 800g of PBAT and 90g of glycerol. Add carboxymethyl starch, PBAT and glycerol to a high-speed mixer and mix for 9 minutes to obtain a uniform basic polymer mixture. Seal the mixture and let it stand for 12 hours to allow the glycerol to fully penetrate and distribute in the starch phase.

[0069] (4) The settled basic polymer mixture is added to a co-rotating twin-screw extruder for melt blending. The temperatures of the twin-screw extruder from the feed section to the die head are set to 105℃, 120℃, 125℃, 135℃, 125℃ and 105℃ respectively, and the screw speed is 130 rpm. The extruded strip is cooled by air cooling and then pelletized to obtain basic polymer masterbatch without biomass antioxidants.

[0070] (5) The above-mentioned basic polymer masterbatch and 100 g of the above-mentioned composite biomass antioxidant were added to a single-screw blown film extruder with a screw diameter of 25 mm and a length-to-diameter ratio of 30:1. The temperature zones and die head of the single-screw blown film extruder were set to 110℃, 135℃, 145℃, 155℃, 135℃ and 125℃ respectively, and the screw speed was 45 rpm, resulting in a film thickness of approximately 65 μm.

[0071] Example 5: A method for preparing a food packaging film based on biomass antioxidants, the specific steps of which are as follows:

[0072] (1) Weigh 500g each of corn husks and soybean husks, add 25% of their dry weight of deionized water (i.e., add 250g of deionized water), mix thoroughly and seal, and let stand for 2 hours to allow the moisture to be evenly distributed inside the bran. Load the moistened bran into a steam explosion device, maintain the pressure at 1.5MPa steam pressure for 120s, then release the pressure instantly and collect the exploded material.

[0073] (2) Spread the obtained material evenly in a tray and dry it with hot air at 50°C until constant weight. Then, send the dried material into a ball mill with a cold air circulation system for crushing. The ball mill speed is 95 rpm and the ball milling time is 28 minutes. The material temperature is controlled to be no higher than 30°C by cold air circulation. After the ball milling is completed, use a 300-mesh standard sieve to screen the material and collect the undersize material to obtain the biomass antioxidant. Store it in a sealed, light-proof container for later use.

[0074] (3) Weigh 150g each of hydroxypropyl starch and corn starch, 600g of PBAT, 100g of polylactic acid (PLA), and 80g of glycerol. Add corn starch, PBAT, PLA and 80g of glycerol to a high-speed mixer and mix for 9 minutes to obtain a uniform basic polymer mixture. Seal and let stand for 24 hours.

[0075] (4) The settled base polymer mixture is added to a co-rotating twin-screw extruder for melt blending. The temperatures of the twin-screw extruder from the feed section to the die head are set to 110℃, 120℃, 130℃, 135℃, 120℃ and 115℃ respectively, and the screw speed is 150 rpm. The extruded strip is cooled by air cooling and then pelletized to obtain base polymer masterbatch without biomass antioxidants.

[0076] (5) The above-mentioned basic polymer masterbatch and 30g of the above-mentioned composite biomass antioxidant were premixed in a high-speed mixer for 5 minutes, and then added to a single-screw blown film extruder with a screw diameter of 25mm and an aspect ratio of 35:1. The temperature zones and die head temperatures of the single-screw blown film extruder were set to 120℃, 135℃, 145℃, 150℃, 145℃ and 125℃ respectively, and the screw speed was 50rpm, resulting in a film thickness of approximately 40μm.

[0077] Comparative Example 1: A method for preparing a basic packaging film without biomass antioxidants, the specific steps of which are as follows:

[0078] It was prepared using the same method as in Example 1, except that no steam-explosion modified biomass antioxidant was added. All other components and processes were the same as in Example 1.

[0079] Comparative Example 2: A method for preparing a basic packaging film containing unmodified biomass antioxidants, the specific steps of which are as follows:

[0080] It was prepared using the same method as in Example 2, except that an unmodified biomass antioxidant was added. All other components and processes were the same as in Example 2.

[0081] Comparative Example 3: An antioxidant packaging film prepared by directly mixing a film-forming matrix and a modified biomass antioxidant, the specific steps of which are as follows:

[0082] All raw materials were added to a high-speed mixer at once, mixed evenly, and then sealed and left to stand for 12 hours. The remaining components and processes were the same as in Example 3.

[0083] Comparative Example 4: An antioxidant packaging film that does not employ low-temperature ball milling to treat biomass antioxidants, the specific steps of which are as follows:

[0084] (1) Weigh 500g each of corn husk and sugarcane bagasse, add 20% of their dry weight of deionized water (i.e., add 200g of deionized water), mix thoroughly and seal, and let stand for 2 hours to allow the moisture to be evenly distributed inside the bran. Load the moistened bran into a steam explosion device, maintain the pressure at 1.0MPa steam pressure for 90s, then release the pressure instantly and collect the exploded material.

[0085] (2) Spread the obtained material evenly in a tray and dry it with hot air at 50°C until constant weight. Then, put the dried material into a ball mill and grind it at 90 rpm for 20 minutes. After the ball milling is completed, use a 300-mesh standard sieve to sieve and collect the sieve-underfill material to obtain the biomass antioxidant. Store it in a sealed, light-proof container for later use.

[0086] The remaining components and processes are the same as in Example 3.

[0087] Example 1: Antioxidant Activity. The film was cut into 1cm × 5cm pieces, and 10mL of 50% (v / v) ethanol aqueous solution was added. Extraction was carried out at 25℃ under light-protected conditions with shaking for 24h. The extract was mixed with DPPH working solution, reacted in the dark for 30min, and the absorbance at 517nm was measured. Separately, the extract was mixed with ABTS free radical working solution, reacted for 60min, and the absorbance at 734nm was measured. The corresponding solvent was used as a blank, and sample background correction was set. The free radical scavenging rate was calculated using the formula R = [1(A0-A1) / A0] × 100%, where A0 is the absorbance of the blank reaction solution and A1 is the absorbance of the film reaction solution. Antioxidant capacity was calculated using quinoline dimethacrylate (Trolox) as a standard and expressed as mmol Trolox equivalent per kilogram of biomass antioxidant dry weight. All measurements were repeated three times.

[0088] like Figure 1 As shown, the antioxidant capacity of Examples 1–5 showed a significant stepwise increase, all superior to the comparative examples. Specifically, Comparative Example 1, without any added biomass antioxidants, had the lowest free radical scavenging rate, reflecting only the extremely weak antioxidant capacity of the pure polymer substrate. Although Comparative Example 2 included biomass raw materials, due to the lack of steam explosion modification, the dense cell walls of the plants were not effectively destroyed, making it difficult to fully release the internal active components such as polyphenols; therefore, its antioxidant capacity improvement compared to Comparative Example 1 was extremely limited. Although the values ​​of Comparative Examples 3 and 4 were improved, they were still far inferior to the examples: Comparative Example 3 used a one-step blending process, which caused severe thermal degradation of the highly active biomass antioxidants under prolonged high-temperature melting and strong shearing; Comparative Example 4 did not control the low-temperature ball milling of the biomass antioxidants, and the local high temperature generated during the pulverization process also destroyed the heat-sensitive antioxidant components. In contrast, Examples 1–5 exhibited excellent antioxidant capacity in both tests, with DPPH· scavenging capacity maintained at approximately 3.7–5.0 mmol / kg and ABTS· ＋The scavenging capacity is approximately 4.5~5.8 mmol / kg. This comparative result fully demonstrates the necessity and advancement of the core process combination of this invention: effective destruction of plant cell walls through steam explosion to release natural antioxidant active substances, supplemented by low-temperature cold air ball milling to avoid thermal oxidative damage during the pulverization process, and combined with a stepwise plasticizing molding process to successfully avoid severe thermomechanical damage during the granulation stage of the base masterbatch. These three elements are indispensable and work synergistically to ultimately maximize the retention of natural antioxidant components in agricultural by-products, endowing the composite film with excellent and stable antioxidant function.

[0089] Example 2: Potatoes of similar maturity, size, and appearance without mechanical damage were selected, washed, peeled, and cut into strips 6 cm long with a cross-section of approximately 2 cm × 2 cm. The potato strips were quickly rinsed with sterile water to remove surface free starch and drained for 10 minutes. 100 g of potato strips were placed into a packaging bag made of the film from Examples 3 and 4, ensuring the inner surface of the film was in contact with the potato strips, and then heat-sealed. The packaging bag made of the film from Comparative Example 1 served as a control, with at least 3 independent replicates for each group.

[0090] The L*, a*, and b* values ​​of the potato strips were measured on days 1, 2, 3, 4, and 5 of storage, and the color difference changes were calculated. Simultaneously, polyphenol oxidase activity was measured, and the appearance was photographed. By comparing the color retention and polyphenol oxidase activity of each group during storage, the inhibitory effect of the packaging film of this invention on enzymatic browning and quality deterioration of fresh-cut potatoes was evaluated.

[0091] like Figure 2 As shown, the color difference change and polyphenol oxidase activity data together verify the excellent preservation effect of the packaging film of the present invention on fresh-cut potatoes. Color difference is a key indicator that directly reflects the degree of enzymatic browning on the potato surface. Taking the potatoes packaged in Comparative Example 1 as an example, its color difference value steadily increased in the early stage of storage, and deteriorated sharply after the 3rd day, reaching over 22 by the 5th day. This rapid deterioration in appearance quality is consistent with the loss of control of its biochemical indicators: the PPO enzyme activity of Comparative Example 1 increased rapidly in the early and middle stages of storage, reaching a peak of about 174 U / g on the 3rd day. In contrast, the browning process of potatoes was significantly inhibited after packaging with the films of Examples 3 and 4 containing biomass antioxidants. During the entire 5-day storage period, the color difference value of the Example group only showed a slow linear increase, eventually remaining at 10-11, less than half that of Comparative Example 1. This superior preservation effect is attributed to the strong inhibition of key browning enzymes by the natural antioxidant active ingredients in the composite film: the example group not only reduced the peak PPO enzyme activity to 139-145 U / g, but also delayed the peak appearance time to the 4th day. Therefore, the antioxidant food packaging film prepared by this invention has excellent antioxidant activity, providing an efficient and green preservation technology solution for easily oxidized foods.

Claims

1. A method for preparing a biomass antioxidant, characterized in that, Includes the following steps: S1: After wetting the agricultural processing by-product raw materials, steam explosion treatment is carried out. After instantaneous depressurization, the steam explosion treatment material is collected and dried. S2: The dried steam explosion treatment material is ball-milled and pulverized under low temperature conditions; S3: The product after ball milling is sieved, and the undersize material is collected to obtain the biomass antioxidant.

2. The method for preparing the biomass antioxidant according to claim 1, characterized in that, The agricultural processing by-product raw materials in S1 are selected from agricultural processing by-products rich in cellulose and natural phenolic substances, including one or more of the following: wheat bran, corn husk, soybean husk, rice husk, sugarcane bagasse, and fruit and vegetable processing residues.

3. The method for preparing the biomass antioxidant according to claim 1 or 2, characterized in that, In step S1, the moisture content of the agricultural processing by-product raw material is maintained at 20% to 40% after wetting. The pressure of the steam explosion treatment is 1.0 to 2.0 MPa, and the pressure holding time is 60 to 120 s. After the steam explosion treatment is completed, the pressure is released instantly, and the collected steam explosion treatment material is dried to constant weight.

4. The method for preparing the biomass antioxidant according to claim 1, characterized in that, In S2, a ball mill with cooling and temperature control function is used for ball milling. The ball milling speed is 80-100 rpm, the ball milling time is 20-30 min, and the material temperature during the ball milling process does not exceed 30℃.

5. The method for preparing the biomass antioxidant according to claim 1, characterized in that, In step S3, the product after ball milling is sieved through a 300-500 mesh standard sieve, and the undersize material is collected.

6. A biomass antioxidant, characterized in that, The biomass antioxidant is prepared by the preparation method according to any one of claims 1 to 5.

7. A food packaging film containing biomass antioxidants, characterized in that, The raw materials, by weight, include: 20-30 parts starch; 70-80 parts biodegradable polyester; 7-11 parts plasticizer; and 1-5 parts of the biomass antioxidant as described in claim 6.

8. The food packaging film containing biomass antioxidants according to claim 7, characterized in that, The starch is selected from one or more of oxidized starch, carboxymethyl starch, hydroxypropyl starch, cationic starch, and esterified starch.

9. The food packaging film containing biomass antioxidants according to claim 7, characterized in that, The biodegradable polyester is selected from one or more of polybutylene adipate / terephthalate, polylactic acid, polybutylene succinate, polycaprolactone, and polyhydroxyalkanoates.

10. The food packaging film containing biomass antioxidants according to claim 7, characterized in that, The plasticizer is selected from one or more of glycerol, sorbitol, polyethylene glycol, citric acid, epoxidized soybean oil, and choline chloride.

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