Differentiating Tangerine Peels from Other Citrus reticulata through GC-MS, UPLC-Q-Exactive Orbitrap-MS, and HPLC-PDA

The nonvolatile and volatile compounds in the peels of 13 Citrus reticulata cultivars (4 mandarins, 5 tangerines, and 4 hybrids) and 5 Citrus sinensis (sweet oranges) cultivars were analyzed. Initially, 66 volatile compounds were detected using gas chromatography-mass spectrometry (GC-MS). Tangerines were distinguished from other citrus cultivars (mandarins, sweet oranges, hybrids) by having higher volatile oil extraction rates and higher relative contents of o-Cymene, α-Terpinene, d-α-Pinene, Terpinolene, γ-Terpinene, l-β-Pinene, and 3-Thujene. Additionally, 115 nonvolatile compounds were tentatively identified using ultraperformance liquid chromatography-Q-Exactive Orbitrap tandem mass spectrometry (UPLC-Q-Exactive Orbitrap-MS). C. sinensis contained fewer compounds than did C. reticulata. Pterostilbene was detected in all tangerines but not in mandarins and hybrids, suggesting its potential as a marker compound for differentiating tangerines from other C. reticulata. Lastly, a high-performance liquid chromatography-photodiode array (HPLC-PDA) was used to quantify 9 major nonvolatile components. Heat map and principal component analysis showed that the contents of tangerines differed from other cultivars (sweet oranges, mandarins, and hybrids). It may be caused by the higher content of synephrine, nobiletin, tangeretin, and 5-hydroxy-6,7,8,3',4'-pentamethoxyflavone in tangerines. The study may obtain information for the application of different types of C. reticulata (tangerines, mandarins, or hybrids) and C. sinensis peels, thereby promoting their recycling.