Soursop fruit storage: Edible coating based on Hibiscus sabdariffa mucilage

Soursop fruit (Annona muricata L.) is a crop of important economic value for the state of Nayarit, however, it has a fast ripening that causes a short shelf life. Several post-harvest handling techniques have been applied to reduce its metabolic processes, such as refrigeration, the use of 1-methylcyclopropene (1-MCP) and controlled and modified atmospheres. In recent years, polysaccharide-based coatings have been applied to fruits. The aim of this research was to evaluate the physicochemical changes of soursop fruits coated with hibiscus calyx mucilage (2%), stored at 22 °C and 15 °C. Weight loss, firmness, pH, total soluble solids, acidity and colour were evaluated. Results for coated fruits stored at 15 °C showed lower weight loss (6.4%), lower firmness (29.7 N), higher TSS concentration (10.4 °Bx) and lower acidity (0.38%) compared to uncoated fruits. Coating with hibiscus mucilage and storage at 15 °C for four days decreased fruit weight loss. It was also observed that storage under these conditions allows a lower concentration of total soluble solids and organic acids. The coatings did not intervene in the decrease of fruit peel colour. Key words: coating, mucilage, soursop, postharvest. Introduction Mexico is the world's leading producer of soursop, with a national production of 30, 790 T in 2019. In this sense, the state of Nayarit was the largest producer of soursop with 23,230 T (Servicio de Información Agroalimentaria y Pesquera [SIAP], 2020). Soursop production contributes to the economic growth of Nayarit; however, there is a problem in the handling of the fruit due to the high respiration rate and ethylene production leading to softening of the fruit, resulting in a short post-harvest shelf life (Balois-Morales et al., 2019). Nayarit does not have an adequate postharvest system, which leads to inadequate fruit handling during handling (Jiménez-Zurita et al., 2016), causing production losses (Tovar-Gómez et al., 2011). Therefore, there is interest in investigating postharvest technologies that allow prolonging shelf life while maintaining the nutritional quality of the fruit (Moreno-Hernández et al., 2014). As an alternative to improve postharvest handling and maintain the quality of fruit and vegetable products, the use of edible coatings has been implemented (Park et al., 2014). Edible coatings based on polysaccharides have gained importance because they create a modified atmosphere through a semi-permeable layer in the fruit that allows gas exchange, reducing metabolic processes and prolonging the postharvest life of the fruit (Solano-Doblado et al., 2018). Among the polysaccharides of interest, mucilages have been used due to their highly branched structure, complex polymeric and hydrocarbon nature that allows modifying the rheology of a solution (Dugarte et al., 2019). Coatings made from mucilage allow a decrease in weight loss, delay in the concentration of total soluble solids, as well as colour improvement (Zambrano et al., 2017). In the above context, hibiscus mucilage could be used as a material for the preparation of an edible coating to prolong the shelf life of fruits. With this in mind, the effect of hibiscus mucilage-based coating (2%) on physicochemical changes during postharvest storage was evaluated in this study.