Nonthermal processing technologies have been researched in lab scale for more than 15 years. In this study, the influence of sonification and high voltage electrical discharge—plasma treatment of water on the formation and stabilization of hydroxyl radicals has been investigated by electron paramagnetic resonance (EPR) spectroscopy and spin‐trapping method. As analysis tool, an agglomerative hierarchical clustering was used in grouping samples recorded by EPR and near infrared spectroscopy (NIR) spectroscopy. Also, the multivariate analysis was performed using the principal component analysis (PCA) and Principal Regression models (PCR). Results for ultrasound‐treated samples showed that number of radicals is increasing with treatment time and increase in amplitude. High‐voltage electrical discharge treatment at 120 Hz resulted in the formation of the largest number of hydroxyl radicals. Developed PCR models are highly effective in prediction of NIR spectra, regardless the sample treatment what is an additional step forward in green technology. Practical applications Usage of electron paramagnetic resonance measurement can be used in laboratory and scale‐up treatments by nonthermal processing. It is of outmost importance to monitor the production of free radicals, from starting of processing, in order to avoid overtreatment of foods and to avoid possible oxidation and unwanted radical chain reactions. Monitoring of processing can be used to optimize nonthermal processing and to avoid production of unwanted oxidative products and compounds.

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Dynamic properties of the first stable l-alanine radical, SAR1, induced by gamma-irradiation of l-alanine crystals, have been investigated by the electron nuclear double resonance technique (ENDOR). The study focuses on the dynamic properties of the alpha-proton hyperfine splitting in the temperature range from 180 to 320 K. In this region the motion of the NH(3)(+) and CH(3) groups exhibits slow and fast motional dynamics in comparison to the nuclear and electron Larmor frequencies, respectively. Evidence for different conformations of the SAR1 center is presented on the basis of thermodynamic properties of the alpha-hyperfine splitting. The activation processes causing the broadening of the ENDOR lines are studied. At room temperature the motional dynamics of the SAR1 center are modulated by the dynamics of the charged, neighboring NH(3)(+) group.

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