Preparation and characterization of soy hull nanocellulose composite film and its preservation for cold fresh chicken

With its high aspect ratio and renewable characteristics, nanocellulose not only exhibits excellent biodegradability, but also forms hydrogen bonds between abundant hydroxyl groups (-OH) on the surface and group materials when used as a reinforcing filler. It can also significantly enhance the mechanical properties and thermal stability of the composites. In this work, soy hull nanocellulose (SHNC) was prepared by ultrasonic-assisted acid hydrolysis, and PVA/PUL/SHNC composite film were prepared by solution casting method using soy hull nanocellulose, polyvinyl alcohol (PVA) and pullulan (PUL) as raw materials. The chemical structure of the composite film was characterized by Fourier transform infrared spectroscopy (FT-IR), and the changes of the vibration peaks of the characteristic functional groups were analyzed to verify the molecular interaction and chemical compatibility between the components. The crystallinity of the composite film was tested by X-ray diffractometer (XRD), and the microscopic morphology of the composite film was observed by scanning electron microscope (SEM), including key morphological parameters such as surface uniformity, phase separation phenomenon and cross-sectional layered structure. In terms of thermal stability evaluation. The thermogravimetric analyzer (TGA) was used to test the temperature programmed test of the material. The thickness, mechanical properties, contact angle, water content, water vapor permeability, storage stability and bacteriostatic effect on Escherichia coli of the composite film were tested. Finally, the composite film was applied to the preservation of chilled chicken at 4 ℃ to verify the preservation effect of the composite film on chilled chicken. The results of FT-IR and XRD showed that there was a strong hydrogen bond between SHNC and PVA, PUL, and no crystal was formed. SEM analysis showed that there was a good compatibility between SHNC and the composite film components. The surface and cross section showed a dense structure, and no phase separation or structural defects, such as rupture and holes, were observed. At the same time, SHNC increased the tensile strength and elongation at break of the composite film by 67.1% and 100.7%, respectively, indicating that SHNC had a significant enhancement effect on the mechanical properties of the composite film (P<0.05). TGA test results showed that the maximum thermal degradation temperature of PVA/PUL/SHNC-3 composite film containing SHNC was 317.58 ℃, which was significantly higher than that of PVA/PUL/SHNC-0 (302.41℃) (P<0.05). This is due to the formation of intermolecular hydrogen bonds between SHNC and PVA, PUL to stabilize the structure of the composite film. In addition, SHNC also significantly improved the hydrophobicity of the composite film (P<0.05). The water contact angle experiment showed that SHNC increased the water contact angle of the composite film from 38.8° to 66.4°, confirming the significant optimization of its hydrophobicity (P<0.05). Similarly, SHNC was uniformly dispersed in the composite film, creating a curved channel for the movement of water, which could effectively hinder the migration of water. Therefore, the water vapor permeability of the composite film was reduced from 0.408 8 (g·mm)/(m²·h·kpa) without SHNC to 0.271 5 (g·mm)/(m²·h·kpa), showing excellent water vapor barrier properties. Bacteriostatic experiments showed that the minimum inhibitory concentration of PVA/PUL/SHNC composite film against Escherichia coli was 3 % SHNC. Moreover, the preservation experiment showed that the PVA/PUL/SHNC-3 composite film separated cold fresh chicken from the outside world through its excellent barrier properties, effectively prevented the raw contact with bacteria in the air and slowed down the protein and lipid oxidation of cold fresh chicken, effectively slowed down the growth of the total number of colonies in cold fresh chicken, the increase of TVB-N value and pH value, maintained the freshness of cold fresh chicken and significantly prolonged the shelf life (P < 0.05). Therefore, the composite film prepared by blending SHNC with PVA and PUL has the potential to be developed as a packaging material for cold fresh chicken, and provides a reference for the development of new methods for the preservation and storage of cold fresh meat.