Recovery of citrus volatile substances from orange juice waste: Characterization with GC-MS, FTIR, ¹H- and ¹³C-NMR spectroscopies

One of the most abundant agri-food waste is citrus peel derived from particularly fruit juice processing. In this study, waste of orange juice (orange peel) was used as a source of volatile-rich extract. Using the gas chromatography-mass spectroscopy (GC-MS) analysis, D-limonene was the major component with 89 % yield. Automatic solvent extraction (ASE) was used to extract D-limonene rich extract from orange peels. Optimum conditions of the ASE system based on the Box-Behnken design of Response Surface Method (RSM) was determined as 5.86 g fresh peel, similar to 12 min immersion time and similar to 10 min washing time in order to obtain 59.58 mg D-limonene per gram fresh mass (maximum). All the selected process parameters, their interactions and their second powers were found statistically significant, except for the linear effect of washing time (p > 0.05). The amount of raw material was the most significant parameter (p < 0.0001). The orange peel extract was analyzed by Fourier transform infrared (FTIR) spectroscopy to clarify the unique functional groups. The nuclear magnetic resonance (H-1- and C-13 NMR) spectroscopies were also applied for the characterization of the volatile-rich extract from orange peel.