Effect of gamma radiation on freeze-dried red pitaya (Hylocereus costaricensis) skin powder: An EPR study to assess the original dose

The integral use of some fruits is an alternative for sustainable production from an environmental, social, and economic point of view, so activities that promote the sustainability of the food production chain, such as fruits waste irradiation, are being carried out. For control and safety purposes with irradiated products, it is necessary to use precise and adequate techniques that allow the marking and unequivocal identification of these products. Among these techniques, electron paramagnetic resonance (EPR) spectroscopy has stood out for its high sensitivity in detecting paramagnetic species generated during irradiation. The pitaya fruit has as its processing residue its skin, which represents 33 % of its total weight. In addition, studies carried out with pitaya reveal the presence of bioactive compounds, including phenolic compounds, that contribute to its antioxidant capacity. With this perspective, in the present work, we investigated the paramagnetic centers induced by gamma irradiation in powdered red pitaya skin products by means of the EPR technique, with the purpose of using them as indicators and/or dosimetric material for the determination of the absorbed dose in irradiated pitaya skin products. EPR experiments indicate the presence of at least three paramagnetic species. One of the centers (center I) exhibits six hyperfine lines with g = 2.0050 and is attributed to the Mn2+ ion. Center II has contributions from at least two radicals, and the dominant radical displays hyperfine interaction with one alpha-type and two nearly equivalent beta-type protons with g = 2.0042. Center III has g = 2.0029 and results from the cellulosic part of the pitaya fruit. The intensity of centers II and III increases linearly with increasing gamma irradiation doses in the dose range from 500 Gy to 30 kGy. In addition, the fading results with storage time at room temperature of centers II and III show a 20 % decay in the first 21 days and then stabilize. Also, complementary studies of the morphology and degree of crystallinity of the pitaya skin powder were carried out by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively.