Analysis of polyphenols content and antioxidant capacity from hybrids mandarin peel

Mandarin cultivars (Citrus reticulata) represent 22% of the total citrus fruit crops¹. Mandarin fruit residues (peel, seeds, and pulp) are usually discarded without regard to potential nutritional and commercial value. Mandarin peels are an abundant source of natural flavonoids² and other antioxidants. The aim is to determine the polyphenols content and antioxidant capacity from hybrid mandarins peel from Valencia province (Spain). A 33 samples of hybrid mandarins (´Clemenvilla`, ´Nadorcott` and ´Ortanique`), procured by citrus farmers of the province of Valencia (Spain), were selected. Fresh mandarin peel extracts were prepared by ultrasound assisted extraction (400 W, 80% v/v duty cycle, 40 ºC) at 30 min employing ethanol 50% (v/v) as solvent in 1:10 (w/v) solid-liquid ratio. Total polyphenols (TP), and total flavonoids (TF) content were determined by spectrophotometry<sup>3</sup> and, 2,2-diphenyl-1-picrylhydryzyl (DPPH) and Trolox equivalent antioxidant capacity (TEAC) assays<sup>3,4</sup> were employed to determine the antioxidant capacity. Before the chromatographic analysis, C<sub>18</sub> cartridges (200 mg) were employed for the Solid Phase Extraction clean-up process<sup>5</sup>. A ultra-performance liquid chromatography system coupled with a quadrupole time-of-flight mass spectrometer was used to identify and quantify the main polyphenols in samples. TP and TF content varied according to the mandarin variety (p<0.05). TP was higher in ´Ortanique` samples (1155±171 mg GAE/100 g), while ´Clemenvilla` samples had the highest values of TF (90 ± 16 mg catechin/100 g). ´Clemenvilla` and ´Ortanique` extracts showed the highest antioxidant capacity by DPPH (14±4.8 mmol Trolox/100 g) and TEAC (32±3.8 mmol Trolox/100 g) assays, respectively. The main polyphenol present in samples was hesperidin being higher in ´Nadorcott` peel (72±7.0 µg/g). Narirutin and rutin were higher in ´Ortanique` and ´Clemenvilla` peel (33±6.3 and 7.3±3.8 µg/g, respectively). Analyzed mandarin peels are an important source of polyphenol compounds with high antioxidant capacity. Results suggest that hesperidin, narirutin and rutin are the main polyphenols in hybrid mandarin peel.