Optical properties, ethylene production and softening in mango fruits

Firmness decay, chlorophyll breakdown and carotenoid accumulation, controlled by ethylene, are major ripening events in mango fruit. Pigment content and tissue structure affect the optical properties of the mesocarp, which can be measured nondestructively in the intact fruit by time-resolved reflectance spectroscopy (TRS). This work is aimed at improving the maturity assessment in mango (Mangifera indica L. cv Haden) from Brazil, using TRS absorption in both the carotenoid and chlorophyll regions in order to develop a model for fruit ripening. Scattering and absorption in the 540–900 nm spectral range by TRS, ethylene production and respiration rate, and firmness, were measured in one day on each individual fruit of a sample covering the range of maturity. The fruit displayed a variability which was attributed to the different biological age. Absorption spectra showed two peaks at 540 and 670 nm, corresponding respectively to the tail of carotenoid absorption and to chlorophyll-a absorption. Carotenoids increased substantially only in fruit where chlorophyll had almost disappeared. The absorptions at 540 and 670 nm, which described the maturity state of each fruit relative to the range of each wavelength, were combined in one index of biological age (biological shift factor) for each fruit and used in logistic models of ethylene increase and firmness decay respectively. The model explained about 80% of the variability in ethylene production rate. A similar result was obtained for firmness when scattering was added in the model. The combination of absorption at 540 and 670 nm measured by TRS in the intact fruit can be used to classify mango fruit according to maturity and to predict the ripening of individual fruit.