An innovative single step of cross-linked alginate-based edible coating for maintaining postharvest quality and reducing chilling injury in rose apple cv. 'Tabtimchan' (Syzygium samarangenese)

Chilling injury, a major problem for tropical fruits, can be reduced by a modified atmosphere. Edible coatings including alginate are able to form a barrier against gasses and moisture. Apart from traditional alginate coatings using two steps and take long time, innovative method can be developed. The aims of this study were to investigate the properties of modified film by a crosslinking in single step of sodium alginate-based edible coating and apply coating solutions for reducing the chilling injury and maintaining the postharvest quality of 'Tabtimchan' rose apple stored at low temperature. Edible coating formulations were based on mixed sodium alginate (SA) solution with various amount of CaCl2 solution; SA, 20 SAC and 40 SAC. Mechanical and barrier properties of alginate films were determined before applying the coating on the fruit surface. The results show that the 40 SAC improved the mechanical and barrier properties of alginate films, which resulted in increased tensile strength and elongation at break (1.5- and 2.4-fold, respectively) and decreased water vapor permeability and oxygen permeability (5.3- and 5-fold, respectively) compared with the alginate stand-alone films. Thereafter, edible coatings were applied on fruit surface. The 40 SAC coating significantly reduced the respiration rate and the weight loss of the rose apple throughout the 10 days of cold storage. They significantly improved the visual appearance and retarded the chilling injury (CI) of rose apple by reducing the malondialdehyde (MDA) and hydrogen peroxide (H2O2) contents and lipoxygenase (LOX) activity. In addition, the activities of catalase (CAT) and ascorbate peroxidase (APX) in fruits coated with 40 SAC were 3.69- and 3.33-fold higher than those in the control fruits after 10 days of storage. Moreover, the total phenolic content and antioxidant activity in fruits coated with 40 SAC were 1.46- and 1.48-fold higher than those of the control on days 10. The alginate-Ca2+cross-linking is expected to be a novel single step for coating fruits, which not only improved the efficacy of inhibiting CI but also maintained the postharvest quality of rose apple fruits during cold storage, in addition to being eco-friendly.