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During the postharvest stage, fruits are susceptible to various pathogens, including bacteria and fungi, which leads to spoilage during transportation and storage. Packaging materials are widely recognized for their crucial role in preventing food from deteriorating due to physical, chemical, or biological factors and ensuring overall quality and safety. However, traditional petroleum - based synthetic packaging materials have numerous drawbacks, such as non - biodegradability, non - sustainability, and the presence of toxic plasticizers, posing a serious threat to the environment. Therefore, biodegradable food packaging materials have emerged as a sustainable alternative to address the problems associated with conventional plastic packaging. A team led by Yiting Ye, Jiaqi Liu, Tingzi Yan, etc. from the College of Life Science, Zhejiang Chinese Medical University, focused on poly(lactic - co - caprolactone)/Gelatin/Tannic acid (PLCL/GEL/TA) nanofibrous membranes and deeply explored their excellent properties and application potential in the field of blueberry preservation.
Poly(lactic - co - caprolactone) (PLCL) is a biodegradable and environmentally friendly material widely used in fields such as medicine and packaging. However, it does not have inherent antibacterial properties and requires the addition of antibacterial agents for food packaging applications. Among many antibacterial agents, natural antibacterial substances have attracted much attention due to their good inhibitory effects on food - borne bacteria and fungi and high biosafety. Tannic acid (TA), a natural polyphenol, not only has strong antibacterial, antioxidant, and anti - inflammatory properties but is also an FDA - approved additive, widely used in the food and medical industries. Gelatin (GEL), a biopolymer derived from collagen, is inexpensive, biodegradable, has good water - binding ability, film - forming capacity, and excellent biocompatibility, making it an ideal material for food packaging.
In this study, the electrospinning technique was used. First, PLCL and GEL were dissolved in specific solvents respectively, mixed evenly, and then electrospun using an electrospinning machine to obtain PLCL/GEL nanofibers. Subsequently, these nanofibers were immersed in TA solutions with different concentrations for a certain period, then taken out, rinsed, and freeze - dried to obtain PLCL/GEL/TA membranes with different TA contents.
Scanning electron microscope (SEM) images show that all electrospun membranes have a smooth and uniform microstructure. As can be clearly seen from Figure 1 below, with the increase of TA content, the diameter of the nanofibers gradually increases, and when the TA concentration is 10%, the diameter distribution of the nanofibers is the most uniform.
Through Fourier - transform infrared spectroscopy (FTIR) analysis, it was confirmed that TA was successfully incorporated into the PLCL/GEL nanofibers. In terms of mechanical properties, as can be seen from the stress - strain diagram (b) and elastic modulus diagram (c) in Figure 2, with the increase of TA content, the elastic modulus of the membrane increases. From the elongation - at - break diagram (d), although the elongation at break decreases, all PLCL/GEL/TA membranes can still be stretched to about three times their original length, showing good flexibility. The contact angle measurement results (the water contact angle diagram (e) and the quantified water contact angle values (f) in Figure 2) indicate that the addition of TA significantly improves the wettability of the membrane, and the wettability is positively correlated with the TA content.
In the in-vitro degradation experiment, as can be seen from Figure 3 (a), all membranes show rapid degradation in the first week, with a weight loss of nearly 50%, and then the degradation rate slows down. The higher the TA content, the stronger the degradation ability of the membrane. The TA release experiment in Figure 3 (b) shows that the fiber membrane releases TA rapidly within the first 20 minutes and then releases it slowly and continuously. This release pattern can provide a rapid antibacterial effect in the initial stage and a long - term antibacterial effect in the later stage. Moreover, the higher the TA content, the faster the release rate.
The antioxidant capacity of the membrane was evaluated by the DPPH radical scavenging assay. The results show that the antioxidant capacity of the membrane modified with TA is significantly enhanced. As can be seen from Figure 4 (a), the color change of DPPH in ethanol after adding different PLCL/GEL/TA membranes, and the change of the DPPH radical scavenging rate with the membrane concentration in Figure 4 (b) can intuitively reflect this. Antibacterial experiments show that the PLCL/GEL membrane has no inhibitory effect on Escherichia coli and Staphylococcus aureus, while the PLCL/GEL/TA membrane has a significant inhibitory effect on both bacteria. As can be seen from the inhibition zone method evaluation of antibacterial activity diagram (c) and the analysis of the inhibition radius as a function of TA concentration in different PLCL/GEL/TA membranes (d) in Figure 4, the radius of the inhibition zone increases with the increase of TA concentration, and the inhibitory effect on Staphylococcus aureus is more significant. The cytotoxicity of the membrane was analyzed by the CCK - 8 method using NIH/3T3 cells. As can be seen from the cell viability diagram (f) in Figure 4, the cell survival rates of PLCL/GEL and PLCL/GEL/TA₁₀ membranes at different time points are close to 100%, indicating good biocompatibility of the membrane.
Blueberries were used as a model fruit to evaluate the preservation performance of the membrane. As can be seen from the physical pictures (a) and morphological change pictures (b) in Figure 5, blueberries covered with the PLCL/GEL/TA₁₀ membrane show almost no color and structural changes after 5 days of storage, with only a few mold spots. In contrast, blueberries in the control group and the PLCL/GEL/TA₀ group show signs of decay on the 1st - 2nd day and completely decay after 5 days. In terms of weight loss, as can be seen from the weight loss diagram (d) in Figure 5, the blueberries in the PLCL/GEL/TA₁₀ group have the highest retention rate after 5 days, reaching 89%±2.13%, effectively reducing the water loss of blueberries during storage.
In this study, PLCL/GEL/TA nanofibrous membranes with different TA concentrations were prepared by electrospinning and then cross - linked with TA. The cross - linking bonds between TA and GEL maintained a stable release of TA. In addition, with the increase of TA concentration, the mechanical properties, hydrophilicity, biodegradability, antioxidant, and antibacterial abilities of the membrane were all improved. Moreover, the cytotoxicity test results show that the survival rate of the electrospun membranes against NIH/3T3 cells is about 100%, indicating their good biocompatibility. Particularly, when the TA content reaches 10%, the PLCL/GEL/TA membrane effectively inhibits the decay degree and weight loss of blueberries, significantly extending the shelf life of blueberries. It can be seen that the electrospun PLCL/GEL/TA nanofibrous membranes have great potential in the application of packaging materials in the fields of active packaging and food preservation. They can not only reduce the loss of fruits during transportation and storage but also reduce the impact on the environment.
In future research, the preparation process of the membrane can be further optimized, and the effects of different TA contents on the preservation of other fruits can be explored to broaden its application range. It is also possible to study the combination of other bioactive substances with PLCL/GEL/TA membranes to develop preservation materials with more functions. It is believed that in the near future, this new - type preservation material will be widely used in the fruit preservation industry, contributing significantly to reducing fruit waste and promoting the development of packaging.
Literature source: https://doi.org/10.1016/j.lwt.2025.117388
