Evaluation of Phenolic Compound Content and Antioxidant Capacity in Citrus Byproducts from the Yucatán Peninsula

Abstract

The Yucatán Peninsula produces 45.6 % of all citrus fruits grown in Mexico, offering a wide variety of fruits. The most common include lime, mandarin, grapefruit, Yucatecan lime, and sour orange. Ten percent of these citrus fruits are used for juice and concentrate production, while the remaining 90 % are consumed unprocessed. The citrus fruits studied in this research were sweet orange (Citrus sinensis), grapefruit (Citrus paradisi), lime (Citrus limon), and sour orange (Citrus aurantium), recognized for their high secondary metabolite content in the peel and pulp, particularly phenolic compounds. The peels were dried to obtain citrus flour (CF), which was analyzed for total polyphenol (TP) and total flavonoid (TF) concentrations and antioxidant capacity (AC). The factors evaluated through a factorial design (3 × 3 × 2) were: 1) solvent type: water and 50 % ethanol; 2) drying methods: freeze-drying, oven, and trays; and 3) citrus type: grapefruit, sweet orange, lime. The response variables analyzed included polyphenol, flavonoid concentrations, and antioxidant capacity. The CFs with the highest metabolite concentrations were grapefruit, with TP of 181.65 ± 15 mg gallic acid equivalents (GAE)/100 g CF, AC of 89.07 ± 1 % inhibition, and TF of 113.62 ± 3 mg catechin equiva- lents (CE)/100 g CF, as well as lime, which recorded TP of 126.62 ± 9 mg GAE/100 g CF, AC of 85.93 ± 2 % inhibition, and TF of 99.76 ± 17 mg CE/100 g CF. The best treatment for TP extraction was achieved us- ing ethanol with freeze-drying, while for TF, it was achieved with ethanol and oven or tray drying (p < 0.05). Water extraction combined with any drying method positively influenced CF antioxidant capacity. The factors evaluated showed significant effects (p < 0.05) on TF and AC. These citrus peels indicate they are an important source of natural antioxidants, which can be used for developing functional foods and as metabolites for pharmaceutical or nutraceutical applications targeting cardiovascular disease treatments.