Multiple bioactive guar gum/pullulan based composite films incorporated co-stabilized nanoemulsions of melatonin and carvacrol for mangoes preservation.

Active films displayed substantial prospects to maintain quality of tropical fruits during storage and transportation. This study developed multifunctional composite films loaded with melatonin/carvacrol nanoemulsions (MCNE) in guar gum/pullulan polysaccharide (GP) matrixes. The SEM analysis showed that MCNE was uniformly dispersed in GP film matrixes, and formed dense and continuous phase structure. The FTIR, XPS and XRD results indicated that MCNE was linked with GP matrixes through hydrogen bonds. Incorporation of MCNE reduced the density, hydrophobicity and gas permeability of composite films, while improved the mechanical properties and UV shielding ability. The MCNE/GP films displayed excellent DPPH and ABTS antioxidant activities (85.92 % and 93.21 %), and antimicrobial activities against E. coli, S. aureus and B. cinerea, also the low hemolysis rate confirmed the film biosafety. The release mechanism of active substance from the films in water was in accordance with Fickian diffusion, and the diffusion process was not depended on MCNE concentration. Especially, the mangoes treated with MCNE/GP films effectively maintained changes of weight loss, firmness, pH and soluble solids, decreased MDA content (40.11 %), increased proline content (44.83 %), and increased preservation time by 50 % compared to control samples at 4 °C storage. The results suggested that the multiple bioactive MCNE/GP films have potential application in delaying maturity and defensing chilling stress of tropical fruits.