Time-resolved reflectance spectroscopy as a non-destructive tool to assess the maturity at harvest and to model the softening of nectarines

Background colour is a maturity index for the harvest of peaches and nectarines. In the new cultivars the background colour is masked by blush, preventing the identification of the maturity stage. A new non-destructive technique, Time-Resolved Reflectance Spectroscopy (TRS), can measure separately the optical properties of absorption and scattering at selected wavelengths in diffusive media. In a previous trial with nectarines, the absorption coefficient at 670 nm (mu(a)670) measured at harvest was correlated to fruit maturity and to softening after harvest. The aim of this research was to model the softening during shelf-life of 'Spring Bright' nectarines measured at harvest by TRS. Fruits of two sizes were picked on 16 July 2003, and ranked by decreasing mu(a)670 (increasing maturity). Ranked nectarines were randomly assigned to each sample for analysis at harvest and during shelf-life, in order to ensure that fruits from the whole range of mu(a)670 were available in each sample. Fruits were stored at 0 degrees C for 3 or 10 days, then at 20 degrees C for 5 days. Firmness was measured destructively (pressure test) at harvest and twice a day during shelf-life. Firmness did not change significantly during cold storage. Softening during shelf-life after cold storage was modelled by non linear regression analysis, following a logistic model in function of mu(a)670 at harvest and of time at 20 degrees C (R-2=0.85). The results of the previous trial were fully confirmed. The logistic model had already been used to model the colour evolution in horticultural products, but not yet, in our knowledge, to model fruit softening. By using this model and knowing the mu(a)670 at harvest of 'Spring Bright' nectarines, it is possible to predict their softening rate at 20 degrees C, and so to choose their marketing destination.