Estimation of phenolic compounds and antioxidant capacity in leaves of fruit species using near-infrared spectroscopy and a chemometric approach

Description of the subject. Phenolic compounds are very important to the antioxidant capacity of plant species. Phenolic compounds and hence antioxidant capacity are commonly measured in the laboratory using indirect methods that involve several stages and chemicals. Objectives. This study aims to identify species with high content of phenolic compounds and antioxidant capacity and to measure these parameters in the leaves of fruit species using near-infrared spectroscopy (NIRS). Method. A total of 68 samples of different varieties of Prunus avium, Prunus cerasus, Malus domestica, Prunus domestica, Pyrus communis, Vitis vinifera, Ficus carica and Corylus avellana were investigated. The dried ground leaves were scanned in reflectance mode and the phenolic compound content (total phenolic compounds, total flavanols and total flavonols) and antioxidant capacity (2-2-diphenyl-1-picrylhydazil [DPPH] and oxygen radical absorbance capacity [ORAC]) were determined. Results. Great variability of phenolic compound content and antioxidant capacity was observed between species (inter-species) and between varieties (intra-species). The spectra with and without pre-treatments were tested to correlate with the phenolic compound content and antioxidant capacities. The pre-treatments tested showed a slight improvement in statistical parameters (R²CAL > 0.75; R²CV > 0.21; RPD > 1.1). Conclusions. The results suggest that NIR spectroscopy with chemometric approaches could be used to rapidly estimate the phenolic compound content and antioxidant capacity of the leaves of fruit species. The species evaluated in this study were shown to be a rich source of phenolic compounds and antioxidants.