Preparation and characterization of ultrasound-assisted essential oil-loaded nanoemulsions stimulated pullulan-based bioactive film for strawberry fruit preservation.

Ultrasound is a high-energy approach that can help with homogenization and dispersion in cavitation. In this study, nanoemulsions of curcumin and orange essential oil were prepared with ultrasound treatment at different times. The ultrasound-treated nanoemulsions for 10 min exhibited the smallest droplet size, the best storage, and higher thermal stability. The pullulan-based film with ultrasound-assisted nanoemulsions exhibited improved water vapor permeability and moisture content and the highest tensile strength and elongation at break. The structural analysis showed that ultrasonic treatment enhanced the H-bond, resulting in a more orderly molecular arrangement and intermolecular compatibility. Furthermore, the bioactive film had the maximum oil retention time. It possessed excellent bacteriostatic properties against Escherichia coli and Staphylococcus aureus due to the smallest oil droplets and uniform distribution in the film matrix. Besides, the weight loss and deterioration of the strawberry fruit were effectively reduced, thus prolonging the shelf life.

Ultrasound-assisted development and characterization of novel polyphenol-loaded pullulan/trehalose composite films for fruit preservation.

A novel food packaging film was developed by incorporating a tea polyphenols-loaded pullulan/trehalose (TP@Pul/Tre) into a composite film with ultrasound-assisted treatment of dual-frequency (20/35 kHz, 40 W/L) for 15 min to assess the physicochemical and mechanical properties of a composite film. The optimized ultrasound-assisted significantly increases elongation at break, tensile strength, and improves the composite film's UV/water/oxygen barrier properties. Structure analysis using attenuated total reflectance-Fourier transform infrared, X-ray diffraction and thermal stability revealed that these improvements were achieved through ultrasound-enhanced H-bonds, more ordered molecular arrangements, and good intermolecular compatibility. Besides, the ultrasound-assisted TP@Pul/Tre film has proven to have good antibacterial performance against Escherichia coli and Staphylococcus aureus, with approximately 100 % lethality at 4 h and 8 h, respectively. Moreover, the ultrasound-assisted TP@Pul/Tre film effectively delayed moisture loss, oxidative browning, decay, and deterioration in fresh-cut apples and pears, thereby extending their shelf life. Thus, ultrasound has proved to be an effective tool for improving the quality of food packaging films, with a wide range of applications.

Insights into ultrasonic treatment on the properties of pullulan/oat protein/nisin composite film:mechanical, structural and physicochemical properties.

This study developed two novel food packaging films, oat protein/pullulan (Op/Pul) and Nisin-loaded oat protein/pullulan (Nis@Op/Pul) films. Ultrasound was introduced to improve its mechanical, structural and physicochemical properties. The Op/Pul film has lower light transmittance, water vapour and oxygen permeability (OP) and improved film uniformity than pure oat protein and pullulan film. The addition of Nisin led to a significant decrease in the composite films' transparency, moisture content, and total soluble matter (TSM). The ultrasound treatment significantly increased the elongation at break and transparency of Nis@Op/Pul film by 18.37% and 8.03% and decreased its TSM and OP by 8.33% and 2.78%, respectively, compared to the conventional method. The structure analysis shows ultrasound enhances intermolecular hydrogen bonding, reduces the crystallinity and formed a more regular, uniform surface. Moreover, the Nis@Op/Pul film prepared by ultrasound treatment could effectively delay the decay and deterioration of fresh strawberries and prolong their shelf life.