Utilization of watermelon peel as a pectin source and the effect of ultrasound treatment on pectin film properties

The objectives of this study were to prepare a biofilm from watermelon peel pectin and to improve the commercial value and performance of the pectin film using ultrasound treatment. The results showed that ultrasound treatment decreased the particle size and turbidity of the film-forming solutions and changed the rheological properties, including a decrease in the viscosity, storage modulus (G′), and loss modulus (G″), and an increase in the phase angle. The digital photos and micrographs of films showed that the watermelon peel pectin had good film-forming properties. A low ultrasonic treatment time (<10 min) dispersed the pectin molecules and increased the hydrogen bonding interactions, as shown by Fourier-transform infrared spectroscopy (FTIR). This caused the thickness, oxygen permeability (OP), water vapor permeability (WVP), transmittance, and tensile strength (TS) to decrease and the density and elongation at break (EAB) to increase; however, the physical, barrier, and mechanical properties declined when the ultrasonic treatment time was increased to 15 min due to small cavities in the film matrix formed by cavitation effects. These results suggest that the developed biodegradable films can be used as food-grade edible films and may potentially replace existing conventional synthetic plastic packages.