Investigation of limonene recovery process through optimization and characterization studies

The optimization of automatic solvent extraction (ASE) for obtaining grapefruit ( Citrus paradisi ) peel extract was conducted by Box-Behnken design under statistical experimental design approach (response surface method-RSM). The optimization is based on the D-limonene concentration since it is the major volatile compound of the grapefruit essential oil. The optimum conditions were attained with almost 7.5 g fresh grapefruit peel, and ~11 min immersion time and ~10 min washing time by application of ASE. The maximum yield was 4.91 mg D-limonene per gram fresh grapefruit peel. The reliability of the study was satisfactory (the difference between the experimental and calculated values<2%). Depending on ANOVA findings of RSM, the second power effect of mass was the most significant, followed by the second power effects of immersion time and washing time, and the linear effect of immersion time ( p <0.0001). On the other hand, ~96% of the total volatile composition belong to the D-limonene depending on gas chromatography-mass spectrometry (GC-MS) measurements. Additionally, myrcene, decanal, and β-ocimene were also determined as the main flavor components in grapefruit peel extract. Moreover, the related componenens were also characterized by using nuclear magnetic resonance ( 1 H- and 13 C-NMR) techniques as well as Fourier transform infrared (FTIR) spectroscopy technology. Graphical abstract