Unconventional application of FLIM and phasor analysis to monitor phenolic content in natural extracts: A FLIM- φ approach to track the ripening of olive drupes

Olive fruits are rich in some specific phenols belonging to the classes of flavones, phenolic acids, phenolic alcohols, lignans, and secoiridoids, such as hydroxytyrosol, tyrosol, caffeic acid, oleocanthal, oleacein, oleuropein, verbascoside, and some of their derivatives. Due to their high degree of molecular conjugation, some of these compounds —primarily flavones, and to a small extent caffeic acid and verbascoside— can show intrinsic fluorescence even upon visible-light excitation. Given the relationship between the phenolic profile and the growth of olive fruit, their overall fluorescence can serve as a marker for the degree of ripeness and for the expected quality of the final products and derivatives. This work explores an unconventional detection method for olive phenols based on fluorescence lifetime imaging coupled to the phasor analysis (FLIM-φ). This approach could reveal possible trends that can be used to discriminate between different phenolic compositions to improve quality assessments in the olive value chain, considered part of the Italian excellence in food production and often protected by the “Made in Italy” certification.