Synthesis of pullulan derivatives: Postharvest application in fruit preservation

The preservation of postharvest fruit is a major challenge in contributing to food security. Biopolymer-based coatings offer sustainable alternatives to reduce postharvest losses. This study aimed to evaluate the effect of pullulan (PU) oxidation and acetylation on its physicochemical properties and ability to preserve fruits postharvest quality. The derivatives obtained by chemical modification were pullulan dialdehyde (OxP) and pullulan acetate (PA), respectively. The degree of substitution (DS) was highest for OxP1 and PA1, with values of 36.8 % and 2.8 (no unit), respectively. Spectroscopic analysis revealed characteristic signals corresponding to aldehyde groups in the OxP derivatives and to acetyl groups in PA. Thermal analysis showed that PA increased thermal stability compared to PU (T_d of 238.8 °C). Conversely, OxPs showed lower values than PU. OxP compounds increased hydrophilicity compared to PU, whereas PA exhibited hydrophobic behavior. This effect is attributed to aldehyde groups promoting hydrogen bond formation with water, while acetyl groups reduce it. Water vapor and oxygen permeability were higher in PU, in contrast to OxP and PA. For mechanical properties, OxP3, the least oxidized compound, showed superior mechanical performance compared to PU, OxP1, OxP2, and PA. PA coatings resulted in the lowest ripening index in both blueberries and strawberries compared to the control and PU. The preservation of the sensory quality of the fruits was superior in OxP1, unlike PA1. Therefore, PU derivatives are a promising option to extend fruit postharvest quality.