Kinectics of calcium diffusion and associated physical changes in papaya fruit

Calcium-based treatments are recognized for their effectiveness in preserving the postharvest quality of papaya; however, the mechanisms and kinetics of calcium diffusion within the fruit pulp remain insufficiently characterized. This study aimed to characterize the calcium diffusion parameters in ‘Golden’ papaya subjected to postharvest immersion in calcium chloride solutions. The transient diffusion model provided the best fit when the Freundlich isotherm was used to estimate the equilibrium calcium concentration at the fruit surface. The peel exhibited greater resistance to mass transfer, with a lower diffusivity (2.9 × 10 ⁻⁹  m ² s ⁻¹ ) than the outer pulp layer (2.4 × 10 ⁻⁷  m ² s ⁻¹ ), confirming its role as a diffusion barrier. Calcium treatments significantly improved pulp firmness, particularly in fruits immersed for 60 min in solutions containing at least 1% Ca ²⁺ . Additionally, immersion in 1% Ca ²⁺ for ≥30 min slightly delayed peel color change after 12 days of storage at 23 °C and 90% relative humidity.