Solid-phase microextraction-gas chromatography and ultra-high performance liquid chromatography applied to the characterization of lemon wax, a waste product from citrus industry

A novel application of SPME-GC and UHPLC is presented for the elucidation of an unexplored citrus by-product, namely lemon wax. In view of the current environmental protection strategies, directed toward reuse and/or recovery of waste products, this study aimed to evaluate a possible utilization of a discarded fraction from citrus fruits processing. Headspace SPME coupled with GC–MS and GC-FID allowed determining a residual amount (162.25 mg kg−1) of lemon volatiles, by means of accurate calibration of 38 terpenoids through linear regression analysis (R2 = 0.99). SPME method development, was supported by statistical analysis, consisting of experimental design and multisample comparison, where parameters such as type of coating, temperature and time of fiber exposure, were manipulated towards optimization. The optimized method was validated, showing limits of quantification (LOQ) and of detection (LOD) in the ranges 0.24 – 2.65 ng g−1 and 0.11 – 0.87 ng g−1, respectively; recoveries ranged from 84.9% to 111.5%. After optimization and validation, the UHPLC-PDA method revealed the presence in lemon wax samples of six coumarins, the most abundant being bergamottin (964 mg kg−1), followed, in decreasing amount, by citropten, 8-geranyloxypsoralen, biacangelicin, oxypeucedanin, 5-geranyloxy-7-methoxycoumarin; each analyte was calibrated by external standard methodology. Sensitivity (LOD, 31 – 112 ng g−1; LOQ, 102–370 ng⋅ g−1), accuracy (recovery, 81–94%), and precision (Retention time RSD, 0.03 – 0.09%; peak area RSD, 1.03–2.92%), were also measured.