A possibility for non-invasive diagnosis of superficial scald in ‘Rocha’ pear based on chlorophyll a fluorescence, colorimetry, and the relation between α-farnesene and conjugated trienols

This study aimed to identify physiological markers in superficially scalded ‘Rocha’ pear (Pyrus communis L. ‘Rocha’) that would relate to chlorophyll a fluorescence (CF), allowing a non-invasive diagnosis of the disorder. Conditions chosen before shelf life provided two fruit groups with different developing patterns and severity of superficial scald: T fruit fully developed the disorder in storage, while C fruit developed it progressively throughout shelf life. Principal component analysis (PCA) of all the measured variables, and simple linear correlations among several major parameters and scald index (SI)/shelf life showed that scald and ripening/aging were concurring processes, and that it was not possible to isolate a particular variable that could deliver a direct non-invasive diagnosis of the disorder. For both fruit groups the SI resulted from the balance between the reducing power (OD200) and the content of conjugated trienols (CTos) and α-farnesene (α-Farn) in the fruit peel. At OD200 > 150 there was a linear relationship between CTos and OD200, suggesting that the level of antioxidants was self-adjusted in order to compensate the CTos level. However, at OD200 < 150 this relationship disappeared. A consistent linear relationship between CTos and α-Farn existed throughout shelf life in both fruit groups, contrarily to the early storage stage, when those compounds do not relate linearly. The CF variables F0, Fv/Fm, and the colorimetric variables, L* and h° were used in multi-linear regressions with other physiological variables. The regressions were made on one of the fruit groups and validated through the other. Reliable regressions to α-Farn and CTos were obtained (R ≈ 0.6; rmsec ≈ rmsep). Our results suggest that a model based on CF and colorimetric parameters could be used to diagnose non-invasively both the contents and the relationship between α-Farn and CTos and hence the stage of scald development.

► Scald and ripening/aging effects difficult to distinguish.
► Evidence for an antioxidant breakdown; scald enhancement occurs after.
► Linear relation CTos/α-Farn observed; it is non-linear in early storage.
► Good regressions of F0, Fv/Fm, and L* and h° to α-Farn and CTos were obtained.
► These parameters could assess the relation CTos/α-Farn and thus the scald stage.