Analysis of phytochemical contributors to antioxidant capacity of the peel of Chinese mandarin and orange varieties.

The phytochemicals in the peel of six oranges and ten mandarins including seven wild varieties and three cultivars were systematically characterised using UHPLC-Q-TOF-MS, and the correlation analysis was performed between phytochemicals and antioxidant capacity in order to investigate the phytochemical contributors to antioxidant capacity. The gradient elution was completed within 16 min and 92 compounds were undoubtedly or tentatively identified. Furthermore, the antioxidant capacities were determined using ABTS, DPPH and FRAP methods. The number of compounds, their contents and the antioxidant capacities were sequenced in the same order of the wild mandarins > cultivated mandarins > oranges. The correlation analysis that showed five compounds were significantly correlated with the antioxidant capacity and can act as main contributors to the citrus varieties with high antioxidant capacities. This study is systematic for the metabolites identification of mandarins and oranges and provides valuable information for effective utilisation of citrus peel and their bioactive compounds.

Efficient analysis of phytochemical constituents in the peel of Chinese wild citrus Mangshanju (Citrus reticulata Blanco) by ultra high performance liquid chromatography-quadrupole time-of-flight-mass spectrometry.

An efficient ultra high-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry method was developed for separation and profiling of phytochemical constituents of Chinese wild mandarin Mangshanju (Citrus reticulata Blanco). All constituents were well separated within 16 min. Based on retention times, accurate mass, MSE fragments, and/or reference standards as well as databases, a total of 81 compounds were unambiguously identified or tentatively assigned including flavonoid glycosides, acylated flavonoid glycosides, flavones, polymethoxylated flavonoids, and limonoids as well as four other compounds. Among them, 22 polymethoxylated flavones and ten polymethoxylated flavanones/chalcones were identified in Mangshanju, more types than other citrus reported before. A basic procedure for identifying flavonoid-O-glycosides and the aglycones including polymethoxylated flavonoids was proposed. In addition, this method was successfully used to analyze another four mandarin germplasms, Cenxi suan ju, Xipi gousi gan, Nanfeng miju, and Or, showing that Mangshanju contained two characteristic compounds distinct from the other four citrus species. This study systematically profiled phytochemical constituents of Mangshanju, which was helpful for further utilization of Mangshanju owing to its abundant bioactive compounds.

Fast Separation and Sensitive Quantitation of Polymethoxylated Flavonoids in the Peels of Citrus Using UPLC-Q-TOF-MS.

A rapid, sensitive, and efficient ultraperformance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS) method has been developed to analyze polymethoxylated flavonoids (PMFs) in 14 Citrus peels, including 7 Citrus reticulata (C. reticulata) and 7 Citrus sinensis (C. sinensis). In this study, fast separation can be achieved within 12 min and 42 PMFs have been identified including 33 flavones and 9 flavanones. Most C. reticulata were shown to contain more than 20 PMFs, except Guangxihongpisuanju (GX) containing only 12 PMFs, while most C. sinensis contained fewer than 20 PMFs, except Edangan (EG) containing as many as 32 PMFs. To our knowledge, there are few reports about the quantitation of PMFs using the MS response. Here, a MS quantitative method was established and systematically validated in linearity, precision, and recovery. The linearity was from 1.25 ng/mL to 1.0 µg/mL with the limit of detection (LOD) as low as 75 pg/mL and the limit of quantitation (LOQ) as low as 0.25 ng/mL. Up to 13 PMFs, more types than ever before, were undoubtedly identified and quantitated according to the PMF standards. The results showed that the contents of PMFs in the C. reticulata were generally higher than those in the C. sinensis. This study is systematic for analyzing PMFs and is of great significance because it can provide guidance on utilization of both PMFs and citrus germplasm resources in the future.

Sodium hydroxide-mediated hydrogel of citrus pectin for preparation of fluorescent carbon dots for bioimaging.

The citrus process industry produces annually a huge amount of pomace, which is a rich source of citrus pectin. Here, we report the hydrogel of citrus pectin mediated by sodium hydroxide can be used to prepare fluorescent carbon dots (CDs). The introduction of hydrogel can not only make the temperature of the hydrothermal reaction down to 100 °C, but also avoid visually carbonized precipitates in the synthesis process even up to 180 °C. The as-synthesized CDs are well dispersed in water with an average size of 2.7 nm and show cyan fluorescence with high photostability, good biocompatibility. Furthermore, the CDs can act as a potential fluorescent probe for cell imaging. Citrus pectin as a non-toxic carbonaceous precursor for preparation of fluorescent CDs provides a new approach for the efficient utilization of citrus germplasm in future.