Antioxidant potential and authenticity of some commercial fruit juices studied by EPR and IRMS

Abstract

AbstractAntioxidant status of foods, plant, or fruit products is generally characterized by means of spectroscopic methods. Methods like HPLC, UV-VIS, or MS spectroscopy are used to understand the chemical and physical properties of different samples, and also EPR spectroscopy seems to be a valuable tool to characterize antioxidant activity of juice beverages. In this technique, certain antioxidants present in fruit juices interact with free radicals interrupting the chain reaction that can possibly damage essential molecules. Recording the EPR signal decay caused by the reaction with a natural or artificial reducing agent, it is possible to draw conclusions about the antioxidant capability of materials. IRMS is a powerful tool to distinguish between an authentic fruit juice and a juice obtained by concentrate dilution. This technique allows also the detection of commercial C4 cane or corn derived sugar syrups in C3 fruit juices. In the present study, four commercial fruit juices were investigated using stable isotope measurements (oxygen, hydrogen, and carbon) and EPR measurements in order to check the correct labeling in the Romanian markets and to compare antioxidant activity of the studied juices and the reference. It was proven that the number of paramagnetic species decreases in time with different reaction rates and this was correlated with the antioxidant activity of the studied juices. Stable isotope ratio measurements have demonstrated that the fruit juices studied were reconstructed from concentrates with tap water, according to their label.