Research Article Bioactive Flavonoids, Antioxidant Behaviour, and Cytoprotective Effects of Dried Grapefruit Peels (Citrus paradisi Macf.) Lucia Castro-Vazquez, 1 María Elena Alañón, 2 Virginia Rodríguez-Robledo, 1 María Soledad Pérez-Coello, 1,2 Isidro Hermosín-Gutierrez, 2 María Consuelo Díaz-Maroto, 1,2 Joaquín Jordán, 3 María Francisca Galindo, 1 and María del Mar Arroyo-Jiménez 1 1 Analytical Chemistry and Food Technology Area, Faculty of Pharmacy, University of Castilla-La Mancha, 02071 Albacete, Spain 2 Food Technology Area, Faculty of Chemistry, University of Castilla-La Mancha, 02071 Ciudad Real, Spain 3 Medical Sciences Department, Faculty of Medicine, University of Castilla-La Mancha, 02071 Albacete, Spain Correspondence should be addressed to Lucia Castro-Vazquez; luciaisabel.castro@uclm.es Received 11 October 2015; Revised 30 November 2015; Accepted 1 December 2015 Academic Editor: Denis Delic Copyright © 2016 Lucia Castro-Vazquez et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Grapefruit (Citrus paradisi Macf.) is an important cultivar of the Citrus genus which contains a number of nutrients benefcial to human health. Te objective of the present study was to evaluate changes in bioactive favonoids, antioxidant behaviour, and in vitro cytoprotective efect of processed white and pink peels afer oven-drying (45 ∘ C–60 ∘ C) and freeze-drying treatments. Comparison with fresh grapefruit peels was also assessed. Signifcant increases in DPPH, FRAPS, and ABTS values were observed in dried grapefruit peel samples in comparison with fresh peels, indicating the suitability of the treatments for use as tools to greatly enhance the antioxidant potential of these natural byproducts. A total of thirteen favonoids were quantifed in grapefruit peel extracts by HPLC-MS/MS. It was found that naringin, followed by isonaringin, was the main favonoid occurring in fresh, oven-dried, and freeze-dried grapefruit peels. In vivo assay revealed that fresh and oven-dried grapefruit peel extracts (45 ∘ C) exerted a strong cytoprotective efect on SH-SY5Y neuroblastoma cell lines at concentrations ranging within 0.1–0.25mg/mL. Our data suggest that grapefruit (Citrus paradisi Macf.) peel has considerable potential as a source of natural bioactive favonoids with outstanding antioxidant activity which can be used as agents in several therapeutic strategies. 1. Introduction Today, there is increasing demand for natural bioactive compounds as people express more concern about their health, especially in connection with health-giving diets. Epidemiological studies suggest that high dietary intake of phytochemicals, in particular of polyphenols, is associated with a reduced risk of a multitude of chronic diseases. In this connection, fruits of the Citrus genus are recog- nized as being a healthful source of bioactive compounds such as vitamins, carotenoids, fbre, and phenolic compounds [1–3]. Worldwide agricultural citrus production, including oranges, mandarins, lemons, bergamots, limes, pummelos, and grapefruits, has been increasing strongly in the last decades, reaching over 100 million metric tons per year [4]. About a third of citrus fruits go to produce fresh juice or citrus-based drinks. Te juice yield of citrus fruits accounts for half of the fruit weight, and hence a very large amount of pulp and peel waste is produced worldwide every year [5]. It has been found that peels are the main sources of polyphenols in citrus fruits [6]. Peel residues from sweet and bitter oranges, lemons, and mandarins have proved to Hindawi Publishing Corporation Oxidative Medicine and Cellular Longevity Volume 2016, Article ID 8915729, 12 pages http://dx.doi.org/10.1155/2016/8915729