Application of Photoacoustic Spectroscopy and Phase-Resolved Technique to the Study of Photoprotective Pigments in Golden Delicious Apple (Malus domestica)

We report on the application of the Photoacoustic Spectroscopy and the phase-resolved technique to analyze the presence and contribution of the photosensitive pigments to the photoacoustic signal of the peel in Golden Delicious Apple (Malus domestica), as well as the changes in the photoacoustic signal with maturation time. Unlike optical absorption spectra reported with conventional methods, the application of phase-resolved technique on the data of amplitude and phase measured with Photoacoustic Spectroscopy provides the spectral separation of absorption centers of the photosensitive pigments in the layers of the peel. The results obtained show a clear definition of the contributions to the photoacoustic signal associated with each one of the isolated absorption centers of the surface layers of the apple samples. A remarkable decrease in amplitude of the photoacoustic signal and its isolated contributions was observed with maturation time, showing the usefulness of the photoacoustic spectroscopy and phase-resolved technique to monitor the degradation of the photosensitive pigments in apple fruit peel with the maturation time.