Biodegradable film and application thereof in preservation of picked small white apricots

Abstract

The invention discloses a biodegradable film and application thereof in fresh keeping of picked small white apricots. The biodegradable film is prepared from the following components in percentage by mass: 70 to 90 percent of PBAT (Poly (Butyleneadipate-co-Terephthalate)), 5 to 15 percent of PLA (Poly Lactic Acid) and 5 to 15 percent of CaCO3. The biodegradable film has any one of the following functions: 1) the color change of the small white apricots is delayed, so that the fruit quality is maintained; 2) the respiration rate of the small white apricots and the generation of ethylene are inhibited, so that the hardness of the fruits is maintained and the weight loss is reduced; and (3) the content of soluble solids and titratable acidity in the small white apricots is increased, so that the flavor of the fruits is maintained. As a biodegradable polymer, the PBAT / PLA / CaCO3 film disclosed by the invention represents a promising substitute for fresh agricultural product packaging, and provides the benefits of maintaining the product quality and reducing environmental pollution caused by a petroleum-based polymer.

Description

Technical Field

[0001] The invention relates to a biodegradable film and application thereof in post-harvest preservation of small white apricots, belonging to the technical field of post-harvest preservation of fruits and vegetables. Background Art

[0002] Small white apricots are beloved by consumers for their rich nutritional value and unique flavor. However, they mature in the hot summer, making the fruits highly susceptible to rot and spoilage after harvest, severely restricting their storage, transportation, and sales. Low-temperature refrigeration is often used to extend shelf life during production. However, prolonged refrigeration can lead to chilling damage, manifested by browning, sloughing, a sharp loss of aroma and flavor, and a decline in quality. This creates an industry dilemma for fruit farmers, with increased production but no corresponding increase in income, hindering the industry's large-scale development.

[0003] In current industry practice, while traditional preservation technologies (such as controlled atmosphere storage and low-temperature cold chains) can effectively extend the post-harvest storage period of small white apricots, their equipment investment and energy consumption significantly hinder their widespread adoption. Developing a novel preservation material system that maintains nutritional quality, protects commodity value, and offers comprehensive cost advantages, targeting the post-harvest physiological characteristics of respiratory climacteric fruits, has become a key breakthrough in improving the efficiency of the specialty fruit post-harvest supply chain. Summary of the Invention

[0004] The purpose of the invention is to provide a biodegradable film for preserving fruits after harvest. PBAT, PLA and CaCO3 are mixed as raw materials. The prepared biodegradable fresh-keeping bag can effectively reduce the weight loss rate of fruits, maintain the hardness of fruits, reduce the consumption of soluble solids in fruits, and improve the storage quality of fruits.

[0005] The biodegradable film for preserving fruits after harvest provided by the present invention is made of PBAT (polybutylene adipate / terephthalate), PLA (polylactic acid) and CaCO3, and their mass percentages are:

[0006] PBAT 70-90%, PLA 5-15%, CaCO35-15%.

[0007] Preferably, the mass percentages of the three are:

[0008] PBAT 80%; PLA 10%; CaCO3 10%;

[0009] Wherein, the particle size of the CaCO3 is ≤5 μm.

[0010] The biodegradable film provided by the invention has a thickness of 15-100 μm, a light transmittance of 50-80%, and a haze of ≥50%.

[0011] The oxygen permeability of the biodegradable film provided by the present invention is 1350-3550cm 3 / (m 2 ·24h·0.1MPa), water vapor transmission rate is 104-227g / (m 2 ·24h).

[0012] The biodegradable film provided by the invention has a tensile strength of 13-48 MPa, a tensile strain of 200-470%, and a Young's modulus of 3.5-24 MPa.

[0013] The thickness of the biodegradable film provided by the present invention is any of the following:

[0014] 1) 15.1±1.8μm;

[0015] 2) 49.3 ± 5.7 μm;

[0016] 3)97.3±8.8μm.

[0017] The present invention further provides a method for preparing the biodegradable film, comprising the following steps:

[0018] S1, PBAT, PLA and CaCO3 are mixed in proportion and prepared as a masterbatch by melt mixing;

[0019] S2, processing the masterbatch into a film by a blown film extrusion method.

[0020] The biodegradable film provided by the present invention can be used for post-harvest preservation of small white apricots.

[0021] The biodegradable film has any of the following functions:

[0022] 1) Delaying the color change of small white apricots and thus maintaining the fruit quality;

[0023] 2) Inhibit the respiration rate and ethylene production of small white apricots, thereby maintaining the firmness of the fruit and reducing weight loss;

[0024] 3) Increase the content of soluble solids and titratable acidity in small white apricots, thereby maintaining the flavor of the fruit.

[0025] Based on the above application, the present invention also provides a post-harvest preservation method for small white apricots, comprising the following steps:

[0026] The harvested small white apricots are packaged in biodegradable fresh-keeping bags and then refrigerated for storage;

[0027] The biodegradable fresh-keeping bag is made of the biodegradable film according to any one of claims 1 to 4.

[0028] Preferably, the refrigerated storage conditions are: temperature of 0±0.5°C and relative humidity of 85-90%.

[0029] The refrigerated storage time is not less than 30 days.

[0030] The PBAT / PLA / CaCO3 films provided by the present invention exhibit excellent physicochemical properties, particularly in terms of mechanical and barrier properties, while maintaining a cost comparable to commercial PE films. When used as packaging for apricots (Prunus armeniaca L.), the PBAT / PLA / CaCO3 films demonstrated significant advantages over traditional packaging (PE mesh) by effectively reducing the apricots' respiration rate and ethylene production, reducing weight loss, and maintaining the fruit's firmness during refrigerated storage. Furthermore, the PBAT / PLA / CaCO3 packaging of the present invention performed better in retaining key flavor and antioxidant components, including soluble solids content, titratable acidity, L-ascorbic acid, and total phenolic content.

[0031] The use of the present PBAT / PLA / CaCO3 film as apricot packaging significantly improved fruit quality preservation during cold storage. The use of a thicker film, likely due to its balanced moisture and gas barrier properties, further improved fruit quality. As a biodegradable polymer, the present PBAT / PLA / CaCO3 film represents a promising alternative for fresh produce packaging, offering the benefits of maintaining product quality and reducing environmental pollution caused by petroleum-based polymers. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 SEM images of the surface (a) and cross-section (b) of the PBAT / PLA / CaCO3 film (S2), and optical images of the PBAT / PLA / CaCO3 film and pure PE film (c).

[0033] Figure 2 DSC (Figure a) and TGA (Figure b) curves of PBAT / PLA / CaCO3 film.

[0034] Figure 3 Changes in appearance (Figure a), L* (Figure b), a* (Figure c), and b* (Figure d) of apricots during storage at 0±0.5℃ for 49 days.

[0035] Figure 4 Figure 3 Changes in respiration rate (a), ethylene production rate (b), firmness (c), and weight loss (d) of apricots during storage at 0±0.5℃ for 49 days.

[0036] Figure 5 Figure 3 Changes in total soluble solids content (Figure a), titratable acid content (Figure b), L-ascorbic acid content (Figure c), and total phenolic content (Figure d) of apricots during storage at 0±0.5℃ for 49 days.

[0037] Figure 6 An electronic nose and electronic tongue detected volatile (panels ac) and nonvolatile (panels df) organic compounds in apricots during 49 days of storage at 0±0.5°C. Electronic nose detection results on day 0 (panel a), day 14 (panel b), and day 35 (panel c). W1C: aromatic compounds; W5S: broad-spectrum nitrogen oxides; W3C: ammonia, aromatic compounds; W6S: hydrogen, hydrides; W5C: alkanes, aromatic compounds; W1S: broad-spectrum methane; W1W: sulfur organic compounds; W2S: broad-spectrum alcohols; W2W: sulfur-aromatic compounds; and W3S: methane. Electronic tongue detection results on day 0 (panel d), day 14 (panel e), and day 35 (panel f). The AHS, CTS, NMS, ANS, and SCS sensors represent sour, salty, umami, sweet, and bitter, respectively; the PKS and CPS sensors represent other complex flavors. DETAILED DESCRIPTION

[0038] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0039] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0040] Materials used in the following examples:

[0041] PLA resin (model: Revode 101, Zhejiang Hisun Biomaterials Co., Ltd., Zhejiang, China), PBAT resin (model: T18, Hubei Yihua Chemical Co., Ltd., China), CaCO3 particles (particle size ≤ 5 μm, model: XF-658, 2000 mesh, Quanzhou Xufeng Powder Co., Ltd., China), and aluminate coupling agent (model: DL-411, Shandong Chunchao Co., Ltd., China) were used. Chemicals used (analytical grade) included oxalic acid (Shanghai Qiushuang Biotechnology Co., Ltd., China), ethyl gallate (Shanghai Yuanye Biotechnology Co., Ltd., China), catechol, and phosphotungstic acid (Beijing Solaibao Technology Co., Ltd., China). Ascorbic acid standard solution was purchased from Shanghai Jiayi Biotechnology Co., Ltd., China.

[0042] All treatments in the following examples were repeated three times. Origin 2024 was used for plotting, and Excel 2024 was used for data processing. Statistical significance analysis was performed using SPSS 27.0. Different letters at the same sampling point indicate significant differences between groups (p < 0.05), and the same letter indicates no significant difference.

[0043] Example 1. Preparation of PBAT / PLA / CaCO3 film

[0044] First, a masterbatch containing 80% PBAT, 10% PLA and 10% CaCO3 (modified by high-temperature mechanical compounding) was prepared using a melt mixer, and then a film was made by blown film extrusion.

[0045] Three composite films with different thicknesses were further prepared and named S1 (15.1±1.8 μm, N=6), S2 (49.3±5.7 μm, N=6) and S3 (97.3±8.8 μm, N=6), and further made into bags with a size of 40×60 cm.

[0046] Example 2: Characterization of PBAT / PLA / CaCO3 Film

[0047] 1. Scanning electron microscope (SEM)

[0048] The surface and cross-sectional morphologies of the PBAT / PLA / CaCO3 films were observed using a SU8010 SEM (Hitachi, Japan) at an accelerating voltage of 10 kV. The film samples were freeze-fractured in liquid nitrogen and coated with a thin layer of platinum using a sputter coater.

[0049] 2. Light transmittance and haze

[0050] The optical properties of the PBAT / PLA / CaCO3 films were measured using an SGW-820 haze meter (Shanghai Yidian Physical Optical Instrument Co., Ltd., China), primarily measuring transmittance and haze. Each sample was tested in triplicate.

[0051] The results show:

[0052] Figure 1 (a and b) show SEM images of the surface and cross-section of the PBAT / PLA / CaCO3 film. The smooth and uniform morphology indicates good compatibility between PBAT and PLA. This improved interfacial compatibility can be attributed to the addition of CaCO3 particles, which act as a compatibilizer for the PBAT / PLA blend. The CaCO3 particles also exhibit good dispersion in the polymer matrix, as shown in Figure 2. Figure 1 As shown by the red circle in the figure. Although the addition of inorganic fillers such as CaCO3 usually reduces the transparency of the film, this optical defect can be alleviated by enhancing polymer miscibility and particle dispersion. Figure 1As shown in Figure c, the PBAT / PLA / CaCO3 film achieved relatively good transmittance compared to the commercial pure PE film (thickness: 28.1±4.6μm, N=6). The highest transmittance of the S1 film was 78.9%, which is equivalent to 90% of the pure PE film (91.1%). These optical measurements provide complementary evidence to the SEM images, verifying the optimized polymer miscibility and particle dispersion. As the film thickness increases, the transmittance values decrease, while the haze values show the opposite trend. The haze values of all PBAT / PLA / CaCO3 film samples exceeded 50%, significantly higher than the 14.0% of the pure PE film. The increase in haze value is mainly attributed to the light scattering of the opaque CaCO3 particles (10%) in the film.

[0053] 3. Tensile test

[0054] The mechanical properties of PBAT / PLA / CaCO3 films, including tensile strength (σ), tensile strain (ε), and Young's modulus (E), were evaluated using a universal testing machine (Model: WDW-5, Shanghai Sonton Instrument Manufacturing Co., Ltd., China). Film samples were cut into 100 mm × 20 mm strips and conditioned at 23°C and 50% RH for 24 h before testing.

[0055] Table 1 lists the tensile test results for the tensile strength, tensile strain, and Young's modulus of the PBAT / PLA / CaCO3 films. All film samples exhibited excellent tensile strength (13.6-47.9 MPa) and tensile strain (204.3-470.3%). These results suggest that, based on their mechanical properties, PLA / PBAT / CaCO3 films could serve as suitable alternatives to PE films for fresh produce packaging. Film S1 exhibited the highest tensile strength and Young's modulus values, followed by films S2 and S3, showing a decreasing trend in mechanical properties with increasing film thickness.

[0056] Table 1 Tensile properties of PBAT / PLA / CaCO3 films

[0057] sample Tensile strength (MPa) Tensile strain (%) Young's modulus (MPa) S1 47.9±4.2 204.3±4.2 23.51±2.1 S2 21.8±1.4 470.3±11.4 4.6±0.3 S3 13.6±0.8 355.6±34.4 3.9±0.4

[0058] 4. Thermal analysis

[0059] The thermal properties of PBAT / PLA / CaCO3 films were characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). -1 The rate of measuring glass transition temperature (T g ), melting temperature (T m ) and crystallinity (X cSTA 8000TGA (PerkinElmer, USA) was used under nitrogen atmosphere from 50°C to 800°C at a rate of 10°C min -1 The mass change of the film sample was recorded at a rate of . Before TGA measurement, the film sample was dried in a vacuum oven to remove free water and bound water.

[0060] Figure 2 Figure (a) shows the DSC curves of the PBAT / PLA / CaCO3 film samples. All samples exhibited different behaviors during the first and second heating processes, indicating the influence of polymer processing on the morphology of the composite films. The parameters related to thermal properties are summarized in Table 2. The T of PLA g The T value (measured during the first heating) was approximately 60°C. All samples, especially S1, showed a clear T g Endothermic peak ( Figure 2 This is related to the enthalpy relaxation of the amorphous region of PLA generated during polymer processing. During the second heating process, PBAT in all film samples showed a melting temperature (T m ), crystallinity (X c ) is about 5%. In contrast, PLA shows two distinct melting peaks (about 145°C and 153°C) during the second heating process, while there is only one peak (about 150°C) during the first heating process. The addition of CaCO3 as a heterogeneous nucleating agent may affect the arrangement of PLA chains during the rapid cooling and film stretching during the polymer processing stage, causing the two melting peaks to merge into one. The crystallinity of PLA (X c ) The crystallinity of all film samples calculated from the second heating process ranged from 1.4% to 5.6%, which was significantly lower than that of pure PLA.

[0061] Figure 2 Panel (b) shows the TGA curves of the PBAT / PLA / CaCO3 film samples. All curves exhibit similar degradation patterns within the tested temperature range. Significant weight loss (>80%) is observed between 300°C and 430°C, primarily attributable to the thermal decomposition of PBAT, while weight loss above 430°C is primarily attributed to the thermal decomposition of PLA. CaCO3 particles in the film samples contribute approximately 8% of the residual ash after 700°C.

[0062] Table 2 Thermal properties of PBAT / PLA / CaCO3 films

[0063]

[0064] 5. Water Vapor Transmission Rate (WVTR) and Oxygen Transmission Rate (OTR)

[0065] Water vapor transmission rate (WVTR) was recorded using a PERME W3 / 031 instrument (PERME Inc., China) at 38°C and 100% RH. Oxygen transmission rate (OTR) was recorded using a Brugger GDP-C instrument (Brugger Inc., Germany) at 23°C and 100% RH. All samples were conditioned at 23°C and 50% RH for 24 hours prior to analysis and tested in triplicate.

[0066] Table 3 lists the water vapor transmission rate (WVTR) and oxygen transmission rate (OTR) of PBAT / PLA / CaCO3 films. The measured WVTR and OTR values were 104.7-226.3 gm -2 24h and 1367 to 3536cm3 m -2 ·24h·0.1MPa. Both WVTR and OTR show a decreasing trend with increasing film thickness, which is attributed to the longer diffusion paths for water and gas molecules through the thicker polymer matrix. Compared to PE films widely used for food packaging, composite films exhibit higher water vapor transmission rates, with WVTR values 6 to 13 times higher, depending on film thickness. However, the OTR values of the two film types show little difference. Good water vapor permeability can reduce moisture accumulation within the package caused by respiration of fresh produce, thereby reducing spoilage.

[0067] Table 3 WVTR and OTR of PBAT / PLA / CaCO3 film and pure PE film

[0068]

[0069]

[0070] Example 3: PBAT / PLA / CaCO3 film for postharvest preservation of small white apricots

[0071] Apricots (Prunus armeniaca L. cv. "Xiaobai") were harvested from orchards in Luntai County, Xinjiang, China. After removing diseased and damaged fruits, apricots of relatively uniform maturity and size were selected and randomly divided into four groups. One group of fruits was wrapped in PE mesh (a common packaging material for Chinese apricots to protect their delicate skin from mechanical damage) and placed in plastic baskets (approximately 2 kg per basket), labeled CK (control group). The other three groups of fruits (also wrapped in PE mesh) were placed in PBAT / PLA / CaCO₃ bags, placed in plastic baskets (approximately 2 kg per basket), and labeled S1, S2, and S3, corresponding to film thicknesses of 15.1, 49.3, and 97.3 μm, respectively. All samples were pre-cooled overnight in a local cold storage and then transported via cold chain to the Western Agricultural Research Institute of the Chinese Academy of Agricultural Sciences and stored at 0±0.5°C and 85-90% relative humidity for 49 days. Parameters were measured every 7 days, with three replicates.

[0072] Example 4: Fresh-keeping effect of small white apricots

[0073] 1. Color

[0074] The color of 10 fresh apricots in each group was measured using a colorimeter (TS7700, Shenzhen Sanen Technology Co., Ltd., China). The color parameters were measured at three points on the equator of each fruit and recorded as L* (lightness), a* (redness), and b* (yellowness).

[0075] Analysis of the morphological and color characteristics of small white apricots:

[0076] Sensory attributes, such as appearance and color, are important indicators of fruit quality and influence consumers’ purchasing decisions. Figure 3 As shown in Figure (a), apricots packaged with PBAT / PLA / CaCO3 film showed a significant delay in yellowing compared to the control group. Slight yellowing was observed in all groups starting from the 7th day. However, apricots in the control group almost completely yellowed within 21 days, while apricots treated with PBAT / PLA / CaCO3 maintained minimal color change until the 49th day. More precise color changes are shown in Figure (a). Figure 3 As shown in Figures bd. Figure 3 Figure b shows that the L* value initially increased and then decreased during storage. During the rising stage, the L* value of the PBAT / PLA / CaCO3 treated fruit was always lower than that of the control, which may be due to the delay of fruit ripening, consistent with the morphological changes ( Figure 3 At the end of storage, fruits treated with PBAT / PLA / CaCO3 maintained better L* values, indicating improved storage quality. Figure 3 Figure c shows that the a* value continued to increase during the entire storage period ( Figure 3(Figure c), but the a* values of fruits treated with PBAT / PLA / CaCO3 were lower than those in the control. The differences between treatments were not significant (p < 0.05). For example, on day 49, the a* value of S3 (0.97 mm thickness) was 1.81% lower than that of CK. Figure 3 The middle d figure shows the b* value (blue-yellow), which increased more slowly in the PBAT / PLA / CaCO3 group. On the 49th day, the b* value of S3 was 50.76, which was 1.14% lower than that of the control group. Overall, Figure 3 Figure C and Figure 3 Figure d in the middle shows that PBAT / PLA / CaCO3 packaging effectively delayed the increase of a* and b* values, indicating that the transition of apricots from green to yellow was delayed, which is consistent with the Figure 3 The visual changes in Figure a are consistent.

[0077] 2. Hardness

[0078] The firmness of 10 fresh apricots per group was tested using a digital force tester (GY-4, Zhejiang Top Yunnong Technology Co., Ltd., China) equipped with a 7.99 mm diameter probe. Parameters were measured at three points along the equator of each peeled fruit. The maximum value during the test was recorded and expressed in Newtons.

[0079] 3. Weight loss

[0080] A random sample of 10 fresh apricots was randomly selected for weight loss testing. Specifically, the weight of each sample was measured at the initial stage and at each sampling interval. Weight loss was expressed as the ratio of the change in weight to the initial value.

[0081] Firmness is one of the most important parameters for evaluating the quality of fruit during ripening. Figure 4 As shown in Figure (c), fruit firmness decreased during storage. The trends were more pronounced for CK and S2 compared to S1 and S3. In particular, the values for CK, S1, S2, and S3 decreased by 3.17%, 1.33%, 2.96%, and 0.67%, respectively, after 49 days, indicating that the PBAT / PLA / CaCO3 film was effective in delaying softening. Fruit ripening is primarily associated with changes in cell wall structure and composition, which are caused by the degradative activity of related enzymes. The function of these enzymes (pectin methylesterase (PME), polygalacturonase (PG), etc.) is primarily affected by pathogens and respiration. Pathogens, for their part, can secrete enzymes such as PME, PG, and proteases to promote the degradation of cell wall polymers, and their growth can be enhanced in warm and humid environments. Respiration, for its part, synergizes with ethylene to accelerate the ripening process and increase the pectinase activity of the fruit itself, leading to softening. Therefore, the maintenance of firmness in S3 may be attributed to the correspondingly lower respiration and ethylene ( Figure 4However, the inconsistency between the characteristics of S1 and S2 samples may be related to the microenvironmental differences between O2, CO2 and water permeability. Figure 4 As shown in Figure d, the weight loss of all groups increased during storage. Figure 4 As shown in Figure d, weight loss increased in all groups during storage. On day 49, the weight losses of CK, S1, S2, and S3 were 15.21%, 9.71%, 8.61%, and 6.67%, respectively, with the lowest value (S3) being 8.54% lower than the highest value (CK). The lower weight loss in S3 may be due to the inhibitory effect on the respiratory rate ( Figure 4 Furthermore, the lower water vapor transmission rate (WVTR) of S3 in an appropriate oxygen and carbon dioxide environment also helps slow down moisture diffusion, retaining moisture on the fruit surface and in the packaging surroundings, leading to lower weight loss.

[0082] 4. Respiration rate and ethylene production rate

[0083] A gas analyzer (Felix F-950, Felix Instruments Inc., Washington, USA) was used to measure the respiration rate and ethylene production rate of 10 fresh apricots per group. After weighing, the fruits were placed in a chamber and left at room temperature for 2 hours. The chamber was connected to a digital gas sensor to record changes in CO2 and C2H4.

[0084] Postharvest respiration is closely related to nutrient metabolism, such as the degradation of polysaccharides, which may lead to fruit softening and accompanying ripening and even senescence. Ethylene production also plays an important role in accelerating this process, especially in the later stages. Figure 4 As shown in Figure 4a and Figure 4b, the respiration rate and ethylene production rate showed a similar trend of increasing from day 0 to day 28 and then decreasing. It can be seen that compared with the control group, the respiration and ethylene production rates of the PBAT / PLA / CaCO3 treated groups were inhibited, especially S3. On day 28, the respiration rate and ethylene production rate values of S3 were 12.2% and 0.53% lower than those of the control group, respectively. This may be due to the lower O2 permeability of the S3 film (Table 3), which promoted the formation of a low-oxygen, high-carbon dioxide microenvironment compared with the other films.

[0085] 5. Soluble solids content (SSC) and titratable acidity (TA)

[0086] SSC measurements were performed using a handheld sugar and acid analyzer (PAL-BX\ACID F5, Beijing Juhuatai Technology Co., Ltd.). 30 μL of juice was aspirated using a micropipette and diluted 50-fold with distilled water for TA measurements. Between measurements, the prism was cleaned with distilled water and dried with filter paper to avoid residual interference.

[0087] SSC and TA are important indicators of apricot taste. Figure 5 As shown in Figure a, the SSC of all groups first increased and then decreased during storage. The S3 content remained the highest throughout the treatment and storage period. On the 14th day, the S3 content peaked at 18.8%, 0.15% higher than the control group, and remained ahead by 1.19% on the 49th day. The results are consistent with the changes in respiration and ethylene. The TA of all samples showed a slight increase and then a decrease during storage ( Figure 5 Figure 2 (middle panel b), which may be due to the consumption of organic acids in metabolic pathways, especially during respiration. At the end of storage, the reductions in TA were 0.62% (CK), 0.44% (S1), 0.44% (S2), and 0.42% (S3), respectively, compared to the initial values of 1.79%, 1.75%, 1.69%, and 1.74%, respectively, fully demonstrating the effectiveness of the PBAT / PLA / CaCO3 film in reducing acidity.

[0088] 6. L-ascorbic acid

[0089] Weigh about 0.1g of frozen apricots into a 5ml centrifuge tube, then add 1mL of 50g L -1 TCA (trichloroacetic acid) solution and homogenize in an ice bath. -1 After centrifugation for 20 min, the supernatant was collected for analysis. L-ascorbic acid content was measured using a detection kit (Beijing Solaibao Technology Co., Ltd., China), and the results were expressed as mg g -1 express.

[0090] 7. Total phenol content

[0091] Weigh about 2 g of frozen apricots into a 20 ml centrifuge tube, then add pre-cooled 1% HCl-methanol solution and homogenize in an ice bath. -1 After centrifugation for 20 minutes, the supernatant was collected and stored in the dark before reading the absorbance at 280 nm.

[0092] L-ascorbic acid, a water-soluble vitamin and natural antioxidant, showed a slight increasing and then decreasing trend in apricots of all groups during storage ( Figure 5 (C) Apricots packaged with PBAT / PLA / CaCO3 (S3) film maintained a higher L-ascorbic acid content after 14 days compared to S1, S2, and CK. By day 28, L-ascorbic acid content had dropped dramatically in all treatments except S3, which retained a value of 4.97. This phenomenon may be attributed to the oxygen barrier properties of the S3 film, low respiration, and poor hydrolysis of individual sugars in the fruit. Figure 5Figure d (center) shows that the total phenolic content in apricots also showed an initial increase followed by a decrease during storage. As expected, the PBAT / PLA / CaCO3 packaging significantly promoted the accumulation of total phenols and delayed their degradation in the fruit. By day 49, the total phenolic contents of S1, S2, and S3 were 5.28, 7.17, and 5.83, respectively, representing 1.45, 1.98, and 1.60 times that of the control. These results indicate that the PBAT / PLA / CaCO3 films, especially S3, effectively slowed the physiological ripening of apricots, as evidenced by changes in color, firmness, weight loss, and respiration.

[0093] 8. Flavor

[0094] For electronic nose analysis, approximately 3 g of frozen apricots were weighed and placed in an electronic nose sampling bottle, which was immediately sealed. After 0.5 h of quiescence, the sampling bottle was filled with odorants and used for further aroma analysis. Volatility detection was performed using an electronic nose (PEN 3.5, Airsense Analysentechnik GmbH, Germany) under the following conditions: a rinse time of 180 s, a detection time of 10 s, and an injection flow rate of 1.0 L min. -1 .

[0095] For electronic tongue analysis, approximately 3 g of frozen apricots were weighed and placed in a 50 mL centrifuge tube, followed by addition of 30 mL of ultrapure water and ultrasonic oscillation for 15 min at 8000 rpm at 23 °C. -1 After centrifugation for 20 min, the supernatant was filtered through a 0.22 μm membrane and diluted to a final volume of 100 mL. The samples were immersed in a reference solution (0.3 mmol L -1 Tartaric acid and 30mmolL -1 The cells were fixed in a 5% sodium chloride solution and detected using an electronic tongue (AsrreeII / LS16 electronic tongue, Alpha MOS, France) for 120 s.

[0096] like Figure 6 As shown in Figures ac, the electronic nose analyzed the volatile components of apricots. On the 0th day, there was no significant difference in the ten response values of all apricots. From the 14th day to the 35th day, sensors W5S and W1W showed significant differences, indicating the production of organic compounds. The maximum response value of W5S came from S3, which was 2.58 on the 35th day. The highest response value of W1W came from S2, which was 2.62 on the 35th day. Overall, both W5S and W1W in the PBAT / PLA / CaCO3 film showed higher accumulation compared with CK. It is worth noting that sensor W6S (hydrogen) showed a downward trend during storage. Relatively high levels of W6S were also retained in apricots packaged with PBAT / PLA / CaCO3, especially S3. As Figure 6As shown in the figure df in the middle, the non-volatile components of apricots were analyzed by electronic tongue. Positive response values of ANS were observed in all groups, especially in the treatment group, indicating that the sweetness was better maintained in the PBAT / PLA / CaCO3 packaging compared with CK, which is also consistent with the change in SSC ( Figure 5 (Figure a). On day 35, the ANS values for S3 and CK were 9.36 and 8.10, respectively. Correspondingly, the AHS values for all groups showed a downward trend. On day 35, the values for S3 and CK were 4.39 and 4.08, respectively.

Claims

1. A biodegradable film for preserving postharvest fruit, comprising PBAT, PLA, and CaCO3, wherein the mass percentages thereof are: PBAT 70-90%, PLA 5-15%, CaCO3 5-15%.

2. The biodegradable film according to claim 1, wherein: The biodegradable film has a thickness of 15-100 μm, a light transmittance of 50-80%, and a haze of ≥50%; The oxygen permeability of the biodegradable film is 1350-3550cm 3 / (m 2 ·24h·0.1MPa), water vapor transmission rate is 104-227g / (m 2 ·24h).

3. The biodegradable film according to claim 1 or 2, characterized in that: The biodegradable film has a tensile strength of 13-48 MPa, a tensile strain of 200-470%, and a Young's modulus of 3.5-24 MPa.

4. The biodegradable film according to any one of claims 1 to 3, characterized in that: The thickness of the biodegradable film is any of the following: 1) 15.1±1.8μm; 2) 49.3 ± 5.7 μm; 3)97.3±8.8μm.

5. A method for preparing the biodegradable film according to any one of claims 1 to 4, comprising the following steps: S1, PBAT, PLA and CaCO3 are mixed in proportion and prepared as a masterbatch by melt mixing; S2, processing the masterbatch into a film by a blown film extrusion method.

6. Use of the biodegradable film according to any one of claims 1 to 4 in the post-harvest preservation of small white apricots.

7. The use according to claim 6, characterized in that: The biodegradable film has any of the following functions: 1) Delaying the color change of small white apricots and thus maintaining the fruit quality; 2) Inhibit the respiration rate and ethylene production of small white apricots, thereby maintaining the firmness of the fruit and reducing weight loss; 3) Increase the content of soluble solids and titratable acidity in small white apricots, thereby maintaining the flavor of the fruit.

8. A method for preserving small white apricots after harvest, comprising the following steps: The harvested small white apricots are packaged in biodegradable fresh-keeping bags and then refrigerated for storage; The biodegradable fresh-keeping bag is made of the biodegradable film according to any one of claims 1 to 4.

9. The post-harvest preservation method according to claim 8, characterized in that: The refrigerated storage conditions are: temperature of 0±0.5°C and relative humidity of 85-90%.

10. The post-harvest preservation method according to claim 8 or 9, characterized in that: The refrigerated storage time is not less than 30 days.

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