Ultrasound-Assisted Submicron CRTO–Chitosan Coating Suppresses Lasiodiplodia theobromae Fruit Rot in ‘Ri 6’ Durian

Lasiodiplodia theobromae is an important postharvest fruit rot pathogen that reduces the shelf life and marketability of durian. This study developed an ultrasound-assisted submicron curcumin-removed turmeric oleoresin and chitosan coating and evaluated its antifungal activity against L. theobromae in ‘Ri 6’ durian. An optimum formulation of 250 g L−1 CRTO and 11.18 g L−1 chitosan was obtained using response surface optimisation and prepared with ultrasound energy input of 384 J mL−1. The optimised dispersion showed a hydrodynamic droplet size of 514 nm, a low polydispersity index of 0.16, a positive ζ-potential of +38 mV, and an emulsification efficiency of 86.16%; it retained one of the highest degrees of visual homogeneity among the 15 design formulations after 7 months of storage at 25 °C. In vitro assays showed strong dose-dependent inhibition of L. theobromae, with mycelial growth suppressed by 98.4–100% at 0.10 C0 and 0.20 C0; the two concentrations did not differ significantly (p > 0.05). Lesion development on wounded-inoculated fruit was reduced by 84.8–88.6% in CRTO–chitosan-coated fruit compared with the untreated control. Ultrasound-assisted submicron CRTO–chitosan coating is therefore a promising natural strategy for controlling postharvest fruit rot caused by L. theobromae in ‘Ri 6’ durian. The study was limited to one cultivar and one harvest batch, and postharvest quality, sensory attributes, and long-term dispersion stability were not assessed.