Evaluation of mandarin peel as an alternative source of limonene: identification with GC-MS, FTIR and NMR studies

In this study, mandarin peel rich in limonene was the feedstock as citrus essential oil source. Box-Behnken design of Response Surface Method was used to optimize the solid mass, immersion time and washing time of the automatic solvent extraction for the maximum D-limonene yield. The proposed conditions as the optimum were calculated as 8.63 g mandarin peel, 8.5 min immersion time and 8 min washing time to achieve the greatest D-limonene yield (~ 75 mg/g). The proposed conditions were reliable depending on the difference between the actual and predicted values (1.7%). With solid-phase microextraction gas chromatography-mass spectrometry (SPME-GC-MS), 19 components were identified in the mandarin peel. D-limonene was the most abundant volatile compound (91.56%), whereas the other main volatile compounds were identifed as myrcene (4.93%), α-pinen (1.69%) and sabinene (0.85%) in the mandarin peel. Additionally, fourier transform infrared (FTIR) and nuclear magnetic resonance ( 1 H– and 13 C-NMR) spectroscopies were also applied for the verification of GC-MS findings. Graphical abstract