A composite food packaging film resistant to oxidation degradation

Abstract

The present invention discloses an antioxidant and degradable composite food packaging film. The composite food packaging film uses sodium carboxymethyl cellulose and cassava starch as film-forming matrices and uses defatted Antarctic krill meal antioxidant peptides as an antioxidant. By adding defatted Antarctic krill meal antioxidant peptides to a bio-based film, the present invention reduces the water contact angle and crystallinity, increases the water vapor permeability, enhances the antioxidant capacity, thermal stability and mechanical properties, changes the color of the composite film, and improves the barrier property to ultraviolet light.

Description

Technical Field

[0001] The invention belongs to the technical field of food packaging, and in particular relates to a composite food packaging film that is resistant to oxidation and degradation. Background Art

[0002] Food is susceptible to oxidation and deterioration during sales, storage, and transportation, and food packaging is one of the most effective means of addressing this problem. Currently, fossil-based plastics dominate the packaging industry due to their outstanding advantages such as high strength, flexibility, durability, impermeability, and lightness, but they are not easily degraded and pose a significant threat to the ecological environment. Biopolymers have garnered significant attention in the packaging industry due to their excellent film-forming properties, biodegradability, and wide availability, and are expected to become an effective alternative to fossil-based plastics. Furthermore, the addition of natural antioxidants to the biopolymer matrix can enhance the oxidative stability of food. The development of bioactive, biodegradable films is one of the most promising technologies in the current food packaging field and an important approach to ensuring food quality and safety.

[0003] Biodegradable packaging has garnered significant attention in the packaging industry due to its environmentally friendly, safe, and non-toxic properties. Natural polymers such as polysaccharides and proteins are promising sources of biodegradable materials. Polysaccharides are complex biomacromolecules composed of repeating monosaccharides or disaccharides linked by glycosidic bonds. Polysaccharide derivatives such as cellulose, starch, alginate, and chitin are isolated from natural, renewable resources and can be used as matrices for active food packaging applications. By incorporating various types of plasticizers, nanofillers, and antioxidants, a variety of polysaccharide-based active films have been developed for food packaging applications to extend the shelf life of food.

[0004] Antioxidants are the primary active substances in antioxidant films. These active substances migrate into food or absorb oxidative free radicals within it, thereby improving food quality and extending shelf life. Currently, a variety of synthetic antioxidants have been used in food, for example, butylated hydroxytoluene, butylated hydroxyanisole, and tert-butylhydroquinone have been developed for use in active packaging films to preserve oxygen-sensitive foods. However, these synthetic antioxidants pose potential risks to human health. Therefore, there is a need to identify novel, healthy, and non-toxic natural antioxidants for use in the preparation of antioxidant films.

[0005] Antioxidant peptides are a well-studied class of biological peptides. They are generally composed of 3-16 amino acid residues, primarily histidine or tyrosine residues, as well as methionine, cysteine, tryptophan, and lysine. Due to their safe sources, abundant variety, and strong stability, antioxidant peptides have been widely studied and applied as natural antioxidants in recent years.

[0006] Animal protein is rich in protein and is a key source of antioxidant peptides. Defatted Antarctic krill meal, a byproduct of krill oil extraction, is inexpensive, high-yield, and contains 65-75% protein. Enzymatic hydrolysis is a key method for preparing defatted Antarctic krill antioxidant peptides. Antioxidant peptides can exert antioxidant activity by reducing hydrogen peroxide, scavenging free radicals, and chelating metal ions, thereby extending the shelf life of food.

[0007] Antioxidant active films are packaging materials that incorporate antioxidants into a polymer matrix and release them onto the food surface through food packaging, extending shelf life and maintaining food sensory quality. These films primarily consist of a film-forming matrix and antioxidants. As people demand higher levels of food quality, antioxidant active films are gaining increasing attention and have been applied to a variety of food preservation applications. Black bean extract-carrageenan films can delay oxidation of cheese stored at 4°C, Indian gooseberry puree / methylcellulose composite films can extend the shelf life of roasted cashews to 90 days, and clove essential oil-basil seed films improve the oxidative stability and sensory properties of camel minced meat stored at 4°C for 20 days. These bio-based antioxidant active films, with their readily biodegradable and effective ability to extend food shelf life, show great potential for application in food packaging. Summary of the Invention

[0008] In view of the problems existing in the prior art, the present invention aims to provide an antioxidant and degradable composite food packaging film and its application.

[0009] The present invention is specifically implemented through the following technical solutions:

[0010] An antioxidant and degradable composite food packaging film, comprising sodium carboxymethyl cellulose and cassava starch as film-forming matrices and defatted Antarctic krill meal antioxidant peptides as antioxidants, wherein the specific preparation process comprises the following steps:

[0011] 1) Dissolve cassava starch in distilled water, heat in a water bath to obtain a starch solution, and cool for use;

[0012] 2) After the starch solution is cooled to room temperature, sodium carboxymethyl cellulose, glycerol and sorbitol are added to the starch solution, and mixed and stirred until clear and transparent to prepare a composite membrane solution;

[0013] 3) adding defatted Antarctic krill powder antioxidant peptides to the composite membrane solution, mixing evenly, filtering, and ultrasonically degassing to obtain a degassed composite membrane solution;

[0014] 4) Pour the degassed composite film liquid into a plastic dish and form a film at 25° C. to prepare a composite food packaging film.

[0015] Furthermore, defatted Antarctic krill antioxidant peptides were prepared by the following method: defatted Antarctic krill powder was dispersed in distilled water to form a solution, the pH value was adjusted to the optimal pH value of the protease, the protease was added, and the solution was placed in a constant temperature oscillating water bath for enzymatic hydrolysis. After the enzymatic hydrolysis was completed, the solution was inactivated by boiling water bath for 15 minutes, cooled to room temperature, filtered, and the residue was discarded to obtain a filtrate. The filtrate was centrifuged and filtered, the supernatant was collected, and freeze-dried to obtain a defatted Antarctic krill hydrolysate.

[0016] Furthermore, the protease is a neutral protease, the enzyme addition amount is 2945 U / g, the material-liquid ratio is 1:9.4 (w / v), the enzymolysis temperature is 48° C., and the enzymolysis time is 9.2 h.

[0017] Furthermore, per 100 mL of distilled water, the amount of cassava starch added was 0.5 g, the amount of sodium carboxymethyl cellulose added was 1 g, the amount of glycerol added was 0.3 g, and the amount of sorbitol added was 0.3 g.

[0018] Furthermore, the water bath temperature in step 1) is 95° C., and the water bath time is 10 min.

[0019] Furthermore, the power of mixing and stirring in step 2) is 300 μm / min.

[0020] Furthermore, in step 3), the amount of antioxidant peptides added from defatted Antarctic krill meal is 10-30% (w / w).

[0021] The present invention reduces the water contact angle and crystallinity, increases the water vapor permeability, enhances the antioxidant capacity, thermal stability and mechanical properties, changes the color of the composite film and improves the barrier property to ultraviolet light by adding defatted Antarctic krill powder antioxidant peptides to the bio-based film. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is the total antioxidant capacity of different protease hydrolysis products;

[0023] Figure 2 The effects of enzyme addition amount, material-liquid ratio, enzymolysis temperature and enzymolysis time on the total antioxidant capacity of enzymolysis products;

[0024] Figure 3 The interaction of various factors in the enzymatic hydrolysis of defatted Antarctic krill meal and their effects on the total antioxidant capacity;

[0025] Figure 4 (A) HPLC elution chromatogram and (B) molecular weight distribution of APA;

[0026] Figure 5 (A) Appearance and (B) transmittance of TC, TC-A10, TC-A20, and TC-A30;

[0027] Figure 6 XRD patterns of CMC-Na, TP, APA, TC, TC-A10, TC-A20 and TC-A30;

[0028] Figure 7 Thermogravimetric curves of APA, TC, TC-A10, TC-A20 and TC-A30;

[0029] Figure 8 The infrared spectra of CMC-Na, TP, APA, TC, TC-A10, TC-A20 and TC-A30 are shown;

[0030] Figure 9 Surface and cross-sectional scanning electron microscopy images of TC, TC-A10, TC-A20, and TC-A30. DETAILED DESCRIPTION

[0031] The present invention is further described below in conjunction with specific embodiments and accompanying drawings to facilitate a better understanding of the present technical solution.

[0032] Example 1: Preparation of defatted Antarctic krill hydrolysate

[0033] Weigh 5.0 g of defatted Antarctic krill meal and disperse it in 50 mL of distilled water to prepare a solution. Adjust the pH to the optimal pH for the protease using NaOH (1 mol / L) and HCl (1 mol / L). Add neutral protease and react in a constant-temperature shaking water bath for 8 hours. After enzymatic hydrolysis, inactivate the enzyme in a boiling water bath for 15 minutes. Cool to room temperature, filter, and discard the residue to obtain the filtrate. Centrifuge the filtrate at 10,000 rpm for 20 minutes, collect the supernatant, and freeze-dry to obtain the defatted Antarctic krill hydrolysate.

[0034] Example 2: Preparation of composite food packaging film

[0035] Weigh 0.5g of TP and dissolve it in 100mL of distilled water. Heat in a 95°C waterbath for 10 minutes. After cooling to room temperature, add 1g of CMC-Na, 0.3g of glycerol, and 0.3g of sorbitol. Stir at 300 rpm until clear and transparent. Add 0%, 10%, 20%, and 30% (w / w) of APA to the composite membrane solution, mix thoroughly, filter, and ultrasonically degas. Pour 40mL of the prepared composite membrane solution into a 100mm plastic dish and form films at 25°C. Label them as TC, TC-A10, TC-A20, and TC-A30, respectively. The prepared composite membranes are equilibrated at a relative humidity of 50±4% and a temperature of 25±2°C for 48 hours, and the properties of the composite membranes are measured.

[0036] Test example

[0037] The selection of protease types in the preparation of defatted Antarctic krill hydrolysate: Different proteases have different specificities and cleavage sites. Therefore, even if the substrate is the same, the amino acid composition and molecular weight of the hydrolysate produced will be different, which can ultimately manifest as differences in activity. Figure 1 As shown, the enzymatic hydrolysis product of neutral protease possessed the strongest antioxidant capacity (15.27±0.91 U / mL), significantly higher than the enzymatic hydrolysis products of the other six proteases (p<0.05). Neutral protease is specific for hydrolyzing carboxyl-terminal aromatic hydrophobic amino acids, and the antioxidant activity of peptides is often associated with the exposure of hydrophobic and aromatic hydrophobic amino acid groups. Therefore, neutral protease was selected as the optimal protease for the preparation of antioxidant peptides from enzymatically degreased Antarctic krill meal in this study.

[0038] Determination of total antioxidant capacity of defatted Antarctic krill enzymatic hydrolysate: The total antioxidant capacity was determined using a total antioxidant capacity kit (T-AOC). Each group of samples was measured three times and the average value was taken.

[0039] Example 1 Screening of proteases during the preparation of defatted Antarctic krill hydrolysate:

[0040] Defatted Antarctic krill meal was used as raw material, and enzymatic hydrolysis was carried out using composite protease, trypsin, neutral protease, papain, alkaline protease, acid protease and bromelain at their respective optimal temperatures and pH values. The enzyme dosage was set at 2000U / g, the material-liquid ratio was 1:10, and the enzymatic hydrolysis time was 8h. The total antioxidant capacity was used as an indicator to select the optimal protease.

[0041] Single factor experiment: Taking total antioxidant capacity as an indicator, the effects of enzyme addition amount (2000U / g, 2500U / g, 3000U / g, 3500U / g, 4000U / g), material-liquid ratio (1:6, 1:8, 1:10, 1:12, 1:14), enzymolysis time (4h, 6h, 8h, 10h, 12h), and enzymolysis temperature (40℃, 45℃, 50℃, 55℃, 60℃) on total antioxidant capacity were explored.

[0042] Effects of enzyme addition amount, material-liquid ratio, enzymatic hydrolysis temperature and enzymatic hydrolysis time on the total antioxidant capacity of enzymatic hydrolysis products Figure 2 As shown in the figure, under the conditions of a material-liquid ratio of 1:10, a hydrolysis temperature of 50°C, and a hydrolysis time of 8 hours, the total antioxidant capacity of the hydrolysis product first increases and then decreases with increasing neutral protease levels within the enzyme dosage range of 2000-4000 U / g. The total antioxidant capacity reaches its highest level at an enzyme dosage of 3000 U / g. This may be because increasing the enzyme dosage increases the mass transfer efficiency between the enzyme and the substrate, which in turn increases the reaction rate. Excessive enzyme dosage may cause the enzymes to adhere to each other, reducing the mass transfer efficiency between the enzyme and the substrate and slowing the reaction rate.

[0043] Under the conditions of an enzyme dosage of 3000 U / g, a hydrolysis temperature of 50°C, and a hydrolysis time of 8 hours, the total antioxidant capacity of the enzymatic hydrolysis product showed a trend of first increasing and then decreasing with the increase of the liquid-to-liquid ratio in the range of 1:6-1:14. The total antioxidant capacity reached its highest level at a liquid-to-liquid ratio of 1:10. This may be because water facilitates the movement and diffusion of molecules in the enzymatic hydrolysis reaction. When the liquid-to-liquid ratio is too small, the enzyme and substrate cannot fully combine, and inactive intermediates will be generated. When the liquid-to-liquid ratio is too large, the protease and the enzymatic substrate are not in sufficient contact, the degree of protein hydrolysis is reduced, and the concentration of the enzymatic hydrolysis product will also decrease.

[0044] Under the conditions of a material-liquid ratio of 1:10, an enzyme dosage of 3000 U / g, and an enzymatic hydrolysis time of 8 hours, and within the reaction temperature range of 40-60°C, the total antioxidant capacity of the enzymatic hydrolysis product first increased, then decreased, and then leveled off with increasing temperature. The total antioxidant capacity reached its highest level at 45°C. This may be because the catalytic reaction of proteases requires an appropriate temperature. Within this temperature range, the catalytic efficiency increases with increasing temperature. When the temperature exceeds the optimal reaction temperature of the protease, the activity of the protease is inhibited or even inactivated, reducing the degree of protein hydrolysis.

[0045] Under the conditions of a material-liquid ratio of 1:10, an enzyme dosage of 3000 U / g, and a hydrolysis temperature of 45°C, with reaction times ranging from 4 to 12 hours, the total antioxidant capacity of the hydrolysis product initially increased and then decreased with increasing hydrolysis time. The total antioxidant capacity reached its highest level at 8 hours. This may be because the substrate is fully hydrolyzed as the hydrolysis time increases, and over-hydrolysis may occur with extended time, leading to a decrease in antioxidant capacity.

[0046] Response surface optimization experiment: Based on the Box-Behnken experimental design principle, with total antioxidant capacity as the response value, a four-factor three-level experimental design was performed using Design-Expert software to determine the optimal enzymatic hydrolysis process for the preparation of defatted Antarctic Krill antioxidant peptides (APA). The specific experimental design is shown in Table 1.

[0047] Table 1: Response surface experiment factor level table

[0048]

[0049] Response surface model development: Based on the single-factor experimental results, four factors (enzyme dosage (A, U / g), solid-liquid ratio (B, w / v), hydrolysis temperature (C, °C), and hydrolysis time (D, h)) were selected as the evaluation indicators, and total antioxidant capacity was used as the response value. A four-factor, three-level Box-Behnken experimental design was conducted using Design Expert 8.0.6 software. The experimental design and results are shown in Table 2.

[0050] Table 2: Response surface design and results of enzymatic hydrolysis conditions of defatted Antarctic krill meal

[0051]

[0052]

[0053] The experimental data were subjected to regression fitting analysis using Design Expert.8.0.6 software, and the quadratic regression equation for the total antioxidant capacity of the enzymatic hydrolysate of defatted Antarctic krill meal versus the variables was obtained as follows:

[0054] Y=15.29+0.67A-2.68B+0.63C+0.94D-5.000E-003AB-0.23AC-1.3

[0055] 9AD-1.55BC+1.20BD+1.60CD-1.26A 2 -4.55B 2 -1.94C 2 -1.33D 2 .

[0056] The regression equation was subjected to a significance test (ANOVA), and the results are shown in Table 3. The regression model was significant (p = 0.0247 < 0.05), and the lack-of-fit term was not significant (p = 0.238 > 0.05). Both the primary and secondary factors of B showed extremely significant influencing factors. Comparison of F values ​​revealed that the order of influence of each factor on the total antioxidant capacity of the enzymatic hydrolysis product was: B > D > A > C, i.e., material-to-liquid ratio > enzymatic hydrolysis time > enzyme addition > enzymatic hydrolysis temperature.

[0057] Table 3: Analysis of variance for the quadratic polynomial model

[0058]

[0059]

[0060] Note: * indicates significant difference (p<0.05); ** indicates extremely significant difference (p<0.01)

[0061] Note:*means significant difference (p<0.05); **means extremely significant difference (p<0.01)

[0062] The three-dimensional surface plot between the independent variable and the response value is as follows Figure 3 , showing the effect of the interaction term on the total antioxidant capacity when one factor remains unchanged at an intermediate level and two factors change. In the 3D graph, the slope of the graph indicates the sensitivity of the response value to the response factor. Figures 3A, D, and E show the effect of the interaction between the solid-liquid ratio and the other three factors on the total antioxidant capacity. From the slope, it can be seen that the effect of the solid-liquid ratio on the change of total antioxidant capacity is relatively significant compared with the other three factors. The 3D graphs of the other three factors interacting with each other are relatively flat, and their effects on the total antioxidant capacity are not significant. These results are consistent with the results of the variance analysis, and their optimal levels are all within the experimental range.

[0063] Model Validation Experiment: Based on the results of the above experiments, the theoretically optimal enzymatic hydrolysis conditions were determined to be: enzyme dosage of 2945.03 U / g, material-liquid ratio of 1:9.35 (w / v), hydrolysis temperature of 47.68°C, and hydrolysis time of 9.19 h. The predicted total antioxidant capacity was 16.1163 U / mL. To verify the feasibility of the experiment, the validation experiment conditions were set to 2945 U / g enzyme dosage, material-liquid ratio of 1:9.4 (w / v), hydrolysis temperature of 48°C, and hydrolysis time of 9.2 h. The actual measured antioxidant peptide content of defatted Antarctic krill meal was 16.67±0.88 U / mL, with a relative error of less than 5% between the measured and theoretical values. This demonstrates that the parameters for the enzymatic hydrolysis process of defatted Antarctic krill meal derived from the response surface analysis have practical application value. The antioxidant peptides from defatted Antarctic krill meal prepared under the conditions of enzyme addition amount 2945 U / g, material-liquid ratio 1:9.4 (w / v), enzymatic hydrolysis temperature 48°C, and enzymatic hydrolysis time 9.2 h are referred to as APA.

[0064] Amino acid composition determination: The amino acid composition of APA was determined using an amino acid analyzer.

[0065] The amino acid composition of APA is shown in Table 4. Glutamic acid (13.76%) is the highest content, followed by aspartic acid (10.09%). Both are acidic amino acids. It has been reported that acidic amino acids, due to the presence of amino or carboxyl groups in their side chains, have the ability to chelate metal ions and act as proton donors. Their content can influence the antioxidant capacity of a peptide. For example, glutamic acid residues in antioxidant peptides from red snapper and Pacific herring contribute to their excellent antioxidant activity. Studies have shown that hydrophobic amino acids are a key factor in the free radical scavenging and antioxidant capacity of peptides. These amino acids help antioxidant peptides approach free radicals, donating protons or electrons to them to stabilize reactive oxygen species, and thus play a positive role in scavenging free radicals and inhibiting lipid oxidation. APA contains a large amount of hydrophobic amino acids (42.89%), which may be related to its strong antioxidant activity.

[0066] Table 4: APA amino acid composition

[0067]

[0068]

[0069] Note: a: essential amino acid; b: acidic amino acid; c: hydrophobic amino acid

[0070] Molecular weight distribution determination: The molecular weight distribution of APA was determined according to the high performance size exclusion chromatography method in accordance with GB 31645-2018.

[0071] Molecular weight distribution of APA: The molecular weight distribution of peptides can reflect the enzymatic hydrolysis process of proteases. The retention time (min) of elution of 5 standards (cytochrome C, aprotinin, bacitracin, tetrapeptide Gly-Gly-Tyr-Arg and tripeptide Gly-Gly-Gly) is used as the ordinate and the logarithm of molecular weight (lg(Mw)) is used as the abscissa. The linear equation is y=-3.5858x+25.986, R 2 =0.9726.

[0072] Figure 4The molecular weight distribution of APA prepared under optimal enzymatic hydrolysis conditions. The results showed that 90.75% of APA had a molecular weight below 2000Da, of which peptides with a molecular weight range of 100-2000Da accounted for approximately 86.15%, and peptides with a molecular weight less than 100Da accounted for approximately 4.5%. Studies have shown that low-molecular-weight peptides have strong antioxidant activity. Liu Xiaoyi et al. used a composite protease to enzymatically dehull safflower seed meal. The ultrafiltration fraction was divided into four components: SSPH-Ⅰ (<3kDa), SSPH-Ⅱ (3-5kDa), SSPH-Ⅲ (5-10kDa), and SSPH-Ⅳ (>10kDa). The results showed that SSPH-Ⅰ had a significantly higher scavenging rate for DPPH free radicals than the other groups. APA contains a large amount of small-molecule peptides, which is consistent with the results of previous studies.

[0073] Peptide sequence identification: The peptide sequence of APA was determined by high performance liquid chromatography-mass spectrometry.

[0074] The peptide sequences of APA were analyzed using liquid chromatography-mass spectrometry. Based on the identification results, peptides with an ALC > 95% were first selected, followed by the top 20 peptides based on their abundance. The results are shown in Table 5. The molecular weights of the 20 most abundant peptides primarily ranged from 500 to 2000 Da and consisted of 4 to 14 amino acids. The antioxidant activity of peptides is closely related to the proportion of hydrophobic amino acids, primarily Ala, Val, Met, Ile, Leu, Phe, Pro, and Trp. These hydrophobic amino acids account for over 50% of the total amino acid content in these 20 peptides. Numerous studies have shown that the antioxidant activity of peptides is related to their amino acid composition, type, and order. Ala, Val, Phe, and Pro enhance the solubility of peptides in fats, thereby improving their interaction with lipid free radicals. Peptides with Leu and Val at the N-terminus generally exhibit excellent antioxidant activity. In this study, the amino acids with higher frequencies at the N-termini of the 20 peptides were Leu, Phe, and Val, which were correlated with the strong antioxidant activity of APA.

[0075] Table 5: The 20 most abundant peptide sequences in APA

[0076]

[0077] This study optimized the enzymatic hydrolysis process for preparing antioxidant peptides from defatted Antarctic krill meal. Using defatted Antarctic krill meal as the raw material and total antioxidant capacity as the indicator, the optimal enzymatic hydrolysis process was determined using single-factor and response surface methodology: neutral protease as the optimal protease, enzyme dosage of 2945 U / g, material-liquid ratio of 1:9.4 (w / v), hydrolysis temperature of 48°C, and hydrolysis time of 9.2 hours. The total antioxidant capacity of APA produced under these conditions was 16.67±0.88 U / mL.

[0078] Antioxidant properties of composite membranes

[0079] Preparation of membrane extract: weigh 0.5 g of composite membrane sample, add 15 mL of distilled water, soak for 3 h, centrifuge at 8000 rpm for 10 min, and take the supernatant to obtain the membrane extract.

[0080] The total antioxidant activity was determined using the same method as above.

[0081] DPPH free radical scavenging rate: 2 mL of membrane extract was mixed with 1 mL of 0.1 mmol / L 1,1-diphenyl-2-trinitrophenylhydrazine (DPPH) anhydrous ethanol solution, and allowed to stand in the dark for 30 minutes. The absorbance of the mixture was measured at 517 nm using a UV-visible spectrophotometer. The absorbance of the mixture of membrane extract and DPPH anhydrous ethanol solution was A1. At the same time, the absorbance value A2 of the mixture of membrane extract and an equal volume of anhydrous ethanol and the absorbance value A0 of the mixture of DPPH and an equal volume of anhydrous ethanol were measured. Each sample was measured 3 times and the average value was taken. The DPPH free radical scavenging rate was calculated as follows:

[0082]

[0083] Anti-superoxide anion ability: The inhibition and generation of superoxide anion free radical assay kit (A052-1-1) produced by Nanjing Jiancheng was used for determination. Each group of samples was measured 3 times and the average value was taken.

[0084] Mechanical properties of the composite film: The composite film was cut into 10 mm x 70 mm pieces and the tensile strength and elongation at break were measured using an electric tensile tester at a rate of 50 mm / min. The thickness of the composite film was measured using a thickness gauge, and the average value of the measurements obtained at six random points on the composite film was used as the result.

[0085] Determination of physical properties of composite films

[0086] Water vapor permeability: Water vapor permeability was determined according to the method in the literature. The composite film was cut into a circular shape with a diameter of 100 mm and sealed on the top of a weighing bottle containing 5 g of anhydrous silica gel desiccant. The weighing bottle was placed in a desiccator containing 100 mL of saturated NaCl solution. The weight was recorded every 24 hours. The water vapor permeability (WVP) was calculated as follows:

[0087]

[0088] Where Δm is the mass of water vapor transferred (g); d is the film thickness (mm); s is the permeation area (m 2 ); t is the permeation time (h); Δp is the water vapor pressure difference across the composite membrane (kPa). WVP is expressed as g·mm / (m 2·h·kPa).

[0089] Water contact angle: The water contact angle was determined using the method of Lopes et al. with slight modifications. The water contact angle of the composite films was measured using an optical contact angle meter. A 10 μL drop of deionized water was placed on the air surface of the membrane (20 mm × 20 mm) using a microsyringe. A high-speed camera recorded the instantaneous droplet image, and the Laplace-Young equation was used to fit the droplet profile data. Six measurements were performed for each composite film.

[0090] Light transmittance: The light transmittance of the composite film sample (10 mm × 40 mm) was measured in the wavelength range of 200 to 600 nm using a UV-visible spectrophotometer, and an empty cuvette was used as a control.

[0091] Color: Use a handheld colorimeter to measure the surface color (L*, a*, and b*) of the composite film, using a standard white plate as the background to measure the color parameters of the composite film. The total color difference (ΔE) is calculated as follows:

[0092]

[0093] Where L, a, and b are the color parameters of a standard white board, and L*, a*, and b* are the color parameters of the film (the a value represents redness and greenness, the b value represents yellowness and blueness, and L represents brightness).

[0094] Characterization of composite membranes

[0095] Thermogravimetric determination: The thermal stability of the composite film was determined using a thermogravimetric thermal analyzer (TGA). 5 mg of the composite film sample was placed in a ceramic crucible and heated from 30° C. to 500° C. at a rate of 10° C. / min.

[0096] X-ray diffraction: The crystal structure of the composite film was determined using X-ray diffraction (XRD) following the method of Huntrakul et al. with slight modifications. Data were collected in continuous mode at a scan rate of 2° / min over an angular range of 5° to 50° (2θ).

[0097] Attenuated total reflection Fourier transform infrared spectroscopy: The attenuated total reflection Fourier transform infrared spectrum of the composite film was measured using an attenuated total reflection infrared spectrometer with a wave number range of 4000 to 650 cm -1 , with 4cm -1 32 scans were performed at a resolution of 100 nm.

[0098] Microstructure: Film morphology was observed using a Zeiss scanning electron microscopy (SEM). The composite film was cut into 1 mm x 3 mm rectangular sections and sprayed with a thin layer of gold to obtain high-resolution images. Cross-sectional images of the sample were also taken by placing the composite film vertically on a sample holder.

[0099] Data were analyzed using IBM SPSS Statistics 26 software. One-way ANOVA was used to test for statistical significance, with p < 0.05 considered statistically significant. Graphs were constructed using Origin 8 software. Data are presented as mean ± standard deviation.

[0100] Test results

[0101] Effect of APA on the Antioxidant Capacity of Composite Membranes: TC, TC-A10, TC-A20, and TC-A30 represent APA / CMC-Na / TP composite membranes with APA additions of 0%, 10%, 20%, and 30%, respectively. Table 6 shows that with increasing APA addition, the DPPH radical scavenging rate, anti-superoxide anion activity, and total antioxidant capacity of the composite membranes increased accordingly. TC exhibited extremely low DPPH radical scavenging rate (8.15%) and total antioxidant capacity (0.43 U / mL), and showed no anti-superoxide anion activity. TC-A30, on the other hand, exhibited the highest DPPH radical scavenging rate (75.09%), anti-superoxide anion activity (67.55 U / L), and total antioxidant capacity (7.26 U / mL), significantly exceeding those of TC-A10 (p < 0.05). This study is consistent with the findings of Kang et al., showing that the antioxidant capacity of the composite membranes gradually increased with increasing amounts of antioxidant.

[0102] Table 6: Effect of APA addition on the antioxidant activity of composite films

[0103]

[0104] Note: Different letters indicate statistically significant differences (p<0.05).

[0105] Effect of APA on the Mechanical Properties of Composite Films: Tensile strength and elongation at break are important parameters for measuring the mechanical properties of food packaging. Bio-based films should possess a certain degree of compressive strength to maintain the integrity of food during transportation and handling. Table 7 shows the effect of APA addition in the range of 0%-30% on the mechanical properties of composite films. With increasing APA addition, elongation at break and thickness continue to increase, while tensile strength only slightly increases. The thickness of the composite film increases significantly (p < 0.05). This may be because the total solute content in the film-forming solution increases, resulting in an increase in the polymer content per unit volume.

[0106] Table 7: Effect of APA addition on the mechanical properties of composite films

[0107]

[0108]

[0109] Note: Different letters indicate statistically significant differences (p<0.05).

[0110] Effects of APA on the physical properties of composite membranes

[0111] Water Contact Angle and Water Vapor Permeability: The water contact angle reflects the surface hydrophilicity / hydrophobicity of a film. A contact angle less than 90° indicates hydrophilicity, while a contact angle greater than 90° indicates hydrophobicity. The effect of APA addition on the water contact angle is shown in Table 8. The contact angle of TC is 50.24°. With a significant increase in APA addition (p < 0.05), the water contact angle gradually decreases (TC-A30 contact angle is 38.62°). This may be because the addition of APA increases the number of hydrophilic groups, increasing the hydrophilicity of the composite film.

[0112] Table 8: Effect of APA addition on water contact angle, WVP and color of composite films

[0113]

[0114] Note: Different letters indicate statistically significant differences (p<0.05).

[0115] WVP is an indicator of how easy it is for water vapor to pass through a film. This property has a great impact on the shelf life of food. Table 8 shows the water vapor transmission rate values ​​of the composite films. The water vapor transmission rate of TC is 0.53 g·mm / (m 2 ·h·kPa), TC-A30 water vapor transmission rate is 0.72 g·mm / (m 2h·kPa), and the water vapor transmission rate value was significantly increased compared with TC (p<0.05). Salgado et al. also showed similar properties in soybean and sunflower protein-based films containing bovine plasma hydrolysate, which may be due to the hydrophilicity of the peptides.

[0116] Color and transmittance analysis: The surface color of the composite film can directly affect the appearance of food and is an important parameter in practical applications. L*, a*, and b* are the color properties of the film, and ΔE is the total color difference. The L* value defines the lightness or darkness, a* represents red or green, and b* represents yellow or blue. The changes in L*, a*, b*, and total color difference (ΔE) of the composite film caused by the addition of APA are shown in Table 8 and Figure 5 (A) With the increase of APA addition, the L* value decreased, and the L* value of TC and TC-A30 * The values ​​of a* were 93.43 and 92.60, respectively. The a* values ​​decreased significantly (p < 0.05) to -0.95, -1.24, -1.69, and -1.73 for TC, TC-A10, TC-A20, and TC-A30, respectively. The b* values ​​increased significantly (p < 0.05) to 2.07, 4.02, 6.21, and 7.05 for TC, TC-A10, TC-A20, and TC-A30, respectively. ΔE values ​​ranged from 1.40 to 6.05. These results indicate that the addition of APA significantly (p < 0.05) altered the color of the composite film, and this color change may be related to the pigments contained in the APA.

[0117] The addition of APA improves the film's UV light blocking performance. Figure 5 (B) shows that TC-A30 has a transmittance of less than 10% in the wavelength range of 200-280 nm, while the transmittance of TC-A30 increases from 0% to over 60%, indicating its excellent UV shielding properties. Mu et al. also observed similar UV barrier properties in protein-based films. This may be due to the presence of UV-absorbing aromatic amino residues in proteins. Discoloration and oxidation in food are associated with high-energy UV radiation, which can shorten the retail life of food. Therefore, from an application perspective, effective UV barrier properties are crucial for safe food packaging.

[0118] Characterization of composite membranes

[0119] X-ray diffraction: The crystallinity of the film is a parameter that reflects the compatibility and intermolecular interaction between different film components. The peak of a substance with high crystallinity is narrow and high, while the peak of a substance with low crystallinity is broad. Figure 6As shown in the figure, the XRD pattern of APA has a broad diffraction peak near 20.36° (2θ), indicating that APA is amorphous. In the XRD pattern of cassava starch, narrow diffraction peaks appeared near 17.58° (2θ), 19.84° (2θ), 20.96° (2θ) and 23.36° (2θ), which is similar to previously reported studies. In the spectrum of sodium carboxymethyl cellulose, a diffraction peak appeared at 19.96° (2θ). TC showed a broad diffraction peak at 19.96° (2θ), indicating that the interaction between cassava starch and sodium carboxymethyl cellulose caused the crystallinity to decrease. With the increase of APA content, the diffraction peak near 20.56° (2θ) gradually became wider, indicating that the addition of APA reduced the crystallinity of the composite film to a certain extent.

[0120] Thermogravimetry: The weight loss of the composite film during heating is as follows: Figure 7 As shown, the thermal decomposition of the composite membrane can be divided into three stages. The first stage, from 30-95°C, is likely due to the evaporation of free water in the composite membrane. The second stage, from 120-300°C, shows a high weight loss, which is likely due to the decomposition of the polysaccharide chains. The cleavage of peptide bonds leads to deamination, decarboxylation, and depolymerization, resulting in the loss of physically and chemically bound water. The third stage, from 300-500°C, is associated with the decomposition of carbonaceous materials. The four films exhibit similar decomposition curves. In the third stage, the decomposition temperature of TC-A30 (316°C) is slightly higher than that of TC (300°C). This is likely due to the interaction between APA and the polymer matrix through hydrogen bonding and van der Waals interactions, which enhances the thermal stability of the composite membrane.

[0121] Attenuated total reflection Fourier transform infrared spectroscopy: Infrared spectroscopy can be used to analyze the molecular conformation and interactions of different components in a film. Figure 8 The ATR-FTIR spectra of cassava starch, sodium carboxymethyl cellulose, APA, TC, TC-A10, TC-A20 and TC-A30 are shown. The ATR-FTIR spectra of cassava starch at 3275 cm -1 The absorption band near 996 cm is related to the stretching vibration of -OH. -1 The peak at 1412 cm is related to the CO stretching vibration of the COC bond in the glycosidic bond. -1 The peak at 1587 cm is attributed to the asymmetric stretching of -COO-. -1 The peak at 1023 cm is due to the stretching vibration of C–O. -1 The peak at 1524 cm is related to the stretching vibration of C–H in the aromatic ring skeleton. -1 and 1396cm -1Two characteristic peaks correspond to amine II (N–H bending and C–N stretching vibrations) and amine III (bound to the plane vibrations of the C–N and N–H groups of amide or the CH2 group vibrations of glycine). -1 The absorption peak intensity at 3273 cm -1 and 2927cm -1 The characteristic peaks appearing near the amide-B bands are related to the -OH stretching vibration and -CH asymmetric stretching vibration, respectively, indicating that there may be an interaction between sodium carboxymethyl cellulose and cassava starch.

[0122] SEM: Microstructure is the main indicator of the membrane, reflecting the surface morphology and internal structure. Figure 9 The surface and cross-sectional microstructures of TC, TC-A10, TC-A20, and TC-A30 are shown. The surface of TC is smooth and dense, without micropores or cracks, indicating good compatibility between cassava starch and sodium carboxymethyl cellulose. Some agglomerated particles were observed in the cross-section of TC, which may be due to the presence of gelatinized starch molecules. Some tiny embedded pores were also observed, which may be due to the evaporation of water during the film formation of the hydrophilic starch, thus forming such a microporous structure. After the addition of APA, there was no obvious change on the surface of TC-A10, TC-A20, and TC-A30. The small white spots and tiny embedded pores in the cross-section disappeared, which may be because APA is composed of hydrophilic and hydrophobic amino acids, which may make APA show good dispersion in the matrix. However, raised wrinkles can also be observed, which may be caused by the aggregation of polypeptide molecules.

Claims

1. An antioxidant and degradable composite food packaging film, characterized in that: The composite food packaging film uses sodium carboxymethyl cellulose and cassava starch as film-forming matrices and defatted Antarctic krill powder antioxidant peptides as antioxidants. The specific preparation process includes the following steps: 1) Dissolve cassava starch in distilled water, heat in a water bath to obtain starch solution, and cool for later use; 2) After the starch solution is cooled to room temperature, sodium carboxymethyl cellulose, glycerol and sorbitol are added to the starch solution and mixed and stirred until clear and transparent to prepare a composite membrane solution; 3) adding defatted Antarctic krill meal antioxidant peptide to the composite membrane liquid, mixing evenly, filtering, and ultrasonically degassing; obtaining a degassed composite membrane liquid, wherein the defatted Antarctic krill meal antioxidant peptide is prepared by the following method: dispersing defatted Antarctic krill meal in distilled water to form a solution, adjusting the pH to the optimal pH of the protease, adding the protease, and placing the solution in a constant temperature oscillating water bath for enzymatic hydrolysis; after the enzymatic hydrolysis is completed, boiling water bath for 15 minutes to inactivate the enzyme, cooling to room temperature, filtering, discarding the filter residue to obtain a filtrate, centrifuging the filtrate, collecting the supernatant, and freeze-drying to obtain a defatted Antarctic krill hydrolysate; the protease is a neutral protease, the enzyme amount is 2945 U / g, the material-liquid w / v ratio is 1:9.4, the enzymatic hydrolysis temperature is 48°C, and the enzymatic hydrolysis time is 9.2 hours; 4) Pour the degassed composite film liquid into a plastic dish and form a film at 25°C to prepare a composite food packaging film.

2. The antioxidant and degradable composite food packaging film according to claim 1, characterized in that The amount of cassava starch added to 100 mL of distilled water was 0.5 g, the amount of sodium carboxymethyl cellulose added was 1 g, the amount of glycerol added was 0.3 g, and the amount of sorbitol added was 0.3 g.

3. The antioxidant and degradable composite food packaging film according to claim 1, characterized in that The water bath temperature in step 1) is 95° C., and the water bath time is 10 min.

4. The antioxidant and degradable composite food packaging film according to claim 1, characterized in that The mixing speed in step 2) is 300 μm / min.

5. The antioxidant and degradable composite food packaging film according to claim 1, characterized in that In step 3), the amount of antioxidant peptides added from defatted Antarctic krill meal is 10-30% (w / w).

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