Physicochemical characterization of red pitaya (Hylocereus sp.) peel flour using FT-IR, Raman, and EPR spectroscopy: Effects of γ-irradiation on its intrinsic properties

To ensure food and fruit safety, it is essential to use accurate and appropriate techniques that allow irradiated products to be identified and labelled, thereby preventing their adulteration and that of their derivatives. In this context, in this study, we evaluated the physicochemical properties of γ-irradiated red pitaya peel flour from lab-prepared (PT) and commercial (PC) samples, using X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier transform infrared (FT-IR), Raman, and electron paramagnetic resonance (EPR) spectroscopic techniques, as well as thermal analysis (TGA/DSC). The moisture content ranged from 8.01% to 16.38%, with the highest values being 16.38% for the PC sample at 3.5 kGy and 10.56% for the PT sample at 7.5 kGy. FT-IR and Raman spectroscopy revealed differences in betalain concentrations, indicating that irradiation did not significantly alter the spectral profiles. However, chemical changes were detected in the PC sample compared to the PT sample. In the PT sample, at least three distinct paramagnetic centers were identified. A six-line EPR spectrum was assigned to Mn²⁺ ions (center I). Center II arises from at least two radical species, with the dominant radical exhibiting hyperfine interaction with one α-type and two nearly equivalent β-type protons and characterized by a g-value of 2.0023. The cellulosic component of the pitaya contributes to the formation of center III, which exhibits a g-value of 2.0027. In the PC sample, only center III was detected, with no evidence of Mn²⁺ signals.