Nondestructive application of laser-induced fluorescence Spectroscopy for quantitative analyses of phenolic compounds in strawberry fruits (Fragaria x ananassa)

Laser-induced fluorescence spectroscopy (LIFS) was nondestructively applied on strawberries (EX=337 nm, EM=400-820 nm) to test the feasibility of quantitatively determining native phenolic compounds in strawberries. Eighteen phenolic compounds were identified in fruit skin by UV and MS spectroscopy and quantitatively determined by use of rp-HPLC for separation and diode-array or chemical reaction detection. Partial least-squares calibration models were built for single phenolic compounds by means of nondestructively recorded fluorescence spectra in the blue-green wavelength range using different data preprocessing methods. The direct orthogonal signal correction resulted in r(2)=0.99 and rmsep < 8% for p-coumaroyl-glucose, and r(2)=0.99 and rmsep < 24% for cinnamoyl-glucose. In comparison, the correction of the fluorescence spectral data with simultaneously recorded reflectance spectra did not further improve the calibration models. Results show the potential of LIFS for a rapid and nondestructive assessment of contents of p-coumaroyl-glucose and cinnamoyl-glucose in strawberry fruits.