Optimization of microwave-assisted extraction of phenolic compounds from tomato: Characterization by FTIR and HPLC and comparison with conventional solvent extraction

© 2021 Elsevier B.V.In the extraction of phenolic compounds from tomato, Microwave-Assisted Extraction (MAE) was used as a novel technology in this study and compared to conventional solvent extraction (CSE). The optimal extraction conditions for tomato were determined using the multi-level factorial design. For this purpose, different powers (360, 600 and 900 W) and times (30, 60 and 90 s) were used for MAE and also different temperatures (40, 50 and 60 °C) and times (10, 20 and 30 min) were used for CSE. Total phenolic content (TPC), antioxidant activity (AA), and morphological changes were measured by the Folin–Ciocalteu assay, DPPH-scavenging activity, scanning electron microscopy (SEM) respectively. Phenolic compounds of tomato extracts were determined by using Fourier transform infrared (FTIR) spectroscopy and high performance liquid chromatography (HPLC). According to the results, MAE increased TPC and AA compared to CSE. The highest TPC (436.20 ± 4.34 mg GAE/kg FW) and antioxidant activity (39.15 ± 0.91 % of DPPH inhibition) was observed for MAE at 900 W, 90 s which was related with morphological changes, determined by SEM. Multivariate analysis (PCA and PLS) were used to discriminate and construct chemometric models in order to predict AA or TPC of the extracts using IR spectra. The bands found in the FTIR spectrum were found to be associated with chlorogenic acid and ferulic acid. Furthermore, chlorogenic acid, caffeic acid, p-coumaric acid, and ferulic acid were quantified with HPLC. Chlorogenic acid was detected as the main phenolic compound in tomato extracts. The highest amount of chlorogenic acid, caffeic acid, p-coumaric acid, and ferulic acid was found as 52.33 ± 0.80, 5.03 ± 0.37, 0.803 ± 0.017 and 0.506 ± 0.013 mg/kg FW, respectively with MAE at 900 w 90 s