Production of smart film based on gelatin/chitosan nanofibers containing common poppy petals anthocyanins to monitor shrimp spoilage

Introduction: In recent years, researchers have focused on production of active and smart packaging due to the increasing interest of consumers in biodegradable packaging (Hashem et al., 2022; Zhang et al., 2022). Smart films are a category of biodegradable films that convey visual information to consumers (Dong et al., 2020). Anthocyanins are a group of flavonoids that are responsible for the red, blue and purple colors of plants. The color of anthocyanins changes in different pH (Wang et al., 2021). Common poppy belongs to the poppy family, which have several health benefits. Common poppy petals are red in color due to the anthocyanins in their composition (Katarzyna et al., 2021). The use of anthocyanins from different plants in combination with biopolymers has attracted increasing interest in the food industry. One of these biopolymers is gelatin (Xu et al., 2022). Gelatin is widely used in food packaging due to its abundant resources, non-toxicity and inexpensive price (Wang et al., 2022). However, gelatin is used in combination with other biopolymers or nanofillers due to its high-water solubility and poor mechanical properties (Rangaraj et al., 2022). One of these nanofillers is chitosan nanofibers. Chitosan nanofibers are used to improve the properties of films due to their biodegradability, non-toxicity, antibacterial properties and biocompatibility (Amjadi et al., 2019).
Material and methods: In this study, common poppy extract was prepared using the solvent extraction method. Then, the obtained extract was used to prepare a smart film based on gelatin/chitosan nanofibers. Afterward, Surface morphology was analyzed using scanning electron microscope, chemical structure using Fourier transmission infrared spectrometer and crystal structure using X-ray diffractometer. The antioxidant property of the films was tested using the DPPH method. Also, UV-vis absorption and transmission in the range of 200-800 nm was evaluated using a spectrophotometer. In addition, the samples were cut in a dumbbell shape and investigated using a tissue analyzer to evaluate the mechanical properties of the films. The sensitivity of films to ammonia and acidic vapors was evaluated using ammonia and acetic acid solutions. Also, the transparency of smart films was evaluated at a wavelength of 600 nm using a spectrophotometer. In addition, the package containing the indicator film and shrimp was kept in the refrigerator for 7 days in order to monitor shrimp spoilage. The color changes of smart film at the beginning and end of storage were recorded using a digital camera in order to investigate shrimp spoilage.
Results: The addition of common poppy extract increased the thickness of the smart film due to the increase in solid content. Also, the pure gelatin film had the highest transparency, which significantly decreased the transparency of the films by adding chitosan nanofibers and common poppy extract. In addition, the color change of common poppy extract at different pH was evaluated. The color changes at different pH values were as follows: red at pH = 2, coral at pH = 4, peach puff at pH = 6-8, goldenrod at pH = 10 and dark goldenrod at pH = 12. In addition, the color change of the smart film at different pH was also evaluated. The results showed that the smart film at pH = 2 has a crimson color, at pH = 4 it has an indian red color, at pH 6, 7 and 8 it has a coral color, at pH = 10 it is dark salmon color and at pH = 12 it has It was dark goldenrod color. Furthermore, the results of UV-Vis light absorption and transmission characteristics of the films showed that pure gelatin film and gelatin/chitosan nanofibers
have low UV-Vis absorption and high transmission. However, the addition of common poppy extract significantly increased the UV-Vis absorption and decreased the transmission of the films, which could be due to the light absorbing property of common poppy anthocyanins. Also, X-ray diffraction results showed that the pure gelatin film had a peak at 2θ = 12.16°, which did not change significantly with the addition of common poppy. In addition, the results of the food packaging showed that the color of the smart film changed from bright coral to goldenrod after 7 days, which was caused by the increase in pH from 8.3 to 10.5 and the production of ammonia compounds. Also, the SRGB of the smart film increased to 13.20%.
Conclusion: Smart film based on gelatin/chitosan nanofiber containing common poppy extract was produced by casting method. The results showed that the smart film had the lowest amount of transparency. Also, the smart film had the lowest UV-Vis transmission and the highest absorption, which indicated the film's potential to be used for light-sensitive food packaging. In addition, the smart film color changed from coral to dark red, and its SRGB reached 38.17%, when it was exposed to acid vapors. Moreover, when the smart film was exposed to ammonia vapor, its color changed from coral to dark olive and the SRGB of the film reached 61.14%. The results of the food packaging showed that the color of the smart film changed from coral to goldenrod, which was caused by the decomposition of shrimp tissues and the production of ammonia-containing compounds and the increase in pH from 8.3 to 10.5. This result showed that smart film has the potential to be used to monitor food (shrimp) spoilage.