Application of rosin resin and zinc oxide nanocomposites to chitosan coatings for extending the shelf life of passion fruits

Passion fruit (Passiflora edulis Sims f. flavicarpa DEG) is a tropical fruit widespread in Brazil, the largest producer and consumer in the world. As a climacteric fruit, it continues the ripening process after being detached from the plant, resulting in a short shelf life, with post-harvest problems, such as wilting and susceptibility to attack by microorganisms such as fungi. Therefore, this work aimed to develop chitosan-based coatings to be applied on passion fruit to maintain its post-harvest quality. Film forming solutions were prepared using chitosan (C) as the main polymer, carnauba wax (W) or rosin (R) as a hydrophobicity promoting agent and zinc oxide (ZnO) nanoparticles as an antimicrobial agent. The solutions were applied to passion fruit surfaces and the fruits were stored for 10 days at 22.5 °C and 82 RH for continuous evaluation. To determine the coating effect on ripening evolution during storage, the fruits were analysed for mass loss, texture, colour, pH, acidity, total soluble solids, and sugar contents. The post-harvest loss index was also determined during storage. The results showed that C + R coatings were more effective in protecting the fruits against weight loss, injury appearance and microorganism attacks. The visual appearance was also maintained. Increasing the resin concentration in the film forming solution provided better protection for the fruits against excessive weight loss and delayed the physicochemical changes related to maturation (acidity, pH, soluble solids, and firmness). Therefore, rosin-containing coatings provided the best results in postharvest applications to control passion fruit storage problems.