Fluorescence Fingerprinting of Bulgarian Satureja hortensis L. Samples from Different Ecological Regions

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Abstract
In the present study, the fluorescence spectra of summer savory ( Satureja hortensis L. ) samples originating from ten different regions of Bulgaria were investigated, and the relationship between optical parameters, phenolic composition, and environmental factors (altitude, solar radiation, etc.) was evaluated. The samples were finely ground, and fluorescence spectra were recorded without extraction or dilution using the spectrophotometers AvaSpec-2038 (Avantes), Ocean Optics USB2000. The main phenolic compounds were identified by HPLC, while the total phenolic content and antioxidant activity were determined using the standard spectrophotometric assays as previously reported. Three main excitation–emission regions were distinguished in the obtained excitation–emission matrices (EEMs): λ_ex = 310 nm, λ_em ≈ (330–360) nm – associated with phenolic components; λ_ex = (440–450) nm, λ_em ≈ (455–465) nm – associated with flavonoids; λ_ex = 420 nm, λ_em ≈ (680–730) nm – associated with the state of chlorophyll a and oxidized phenolic compounds, reflecting the presence of photosynthetic pigments and plant metabolic activity. Principal component analysis (PCA) and cluster analysis based on the intensities of the above-mentioned fluorescence maxima revealed two main clusters. The first cluster included samples exhibiting strong “red” fluorescence, whereas the second consisted of samples with lower but relatively uniform fluorescence in the blue–green region. Furthermore, samples originating from higher altitudes showed stronger fluorescence in the blue–green region, suggesting enhanced biosynthesis of phenolic compounds under conditions of increased UV radiation. The obtained results demonstrated that fluorescence spectroscopy using excitation–emission matrices provided an informative spectral fingerprint of phenolic compounds in Bulgarian summer savory samples.

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