As described by Assiry et al. (2003) one of the main reactions influencing degradation is the electrolysis of water, which yields hydrogen at the cathode and oxygen at the anode. Since

alternating current is used in the system both reactions occur at each electrode. equation(4) Cathode:2H+(aq)+2e−→H2(g) equation(5) Anode:2H2O(l)→O2(g)+4H+(aq)+4e− equation(6) Overall:2H2O(l)→2H2(g)+O2(g) According to the authors, the molecular oxygen generated by water electrolysis causes additional oxidation of the ascorbic acid. The presence of molecular oxygen in the system presented in this work could be related to the observed anthocyanin degradation. Another important reaction, also described by Assiry et al. (2003), is electrode corrosion. These reactions may happen in the ohmic heating systems either by direct metal oxidation or by electrochemical generation of corroding chemicals. The direct MAPK inhibitor metal oxidations yields hydrogen and metal ions, these ions migrate into the medium

and can be oxidized and undergo other secondary reactions. In an agitated system, like the apparatus used in this work, the products of the previously described reactions could have dispersed in the pulp, where further reactions may have occurred, enhancing degradation. The frequency of electrochemical reactions is greater when higher voltages are used, as observed in the experiments of Içier and Ilicali selleck inhibitor (2005), Palaniappan and Sastry (1991) and Qihua, Jindal, and Van Winden (1993). In the last mentioned work, bubbles were produced during the ohmic heating of orange juice as a result of electrochemical reactions. Like ascorbic acid, anthocyanins are effective antioxidants and therefore oxidize easily (Skrede et al., 2000).

The unsaturated nature of anthocyanins makes them prone to attack by molecular oxygen; consequently, anthocyanins are likely to undergo similar chemical reactions, and these reactions may explain the observed behavior. When metallic electrodes are used, electrochemical reactions must always Bcl-w be taken into account when frequencies between 50 and 60 Hz are used (Ruan et al., 2002). In the present study, it was possible to observe the deposition of black materials on the electrodes during the use of the experimental apparatus, and the Pt-100 m lost their black color due to the dissociation of the nickel–phosphorous alloy coating. According to the literature, the use of inert materials for the electrodes and the use of high frequencies are able to prevent electrochemical reactions (Içier & Ilicali, 2005). These effects can be observed in the study of Jun, Sastry, and Samaranayake (2007), who showed that retort pouches used with stainless steel electrodes and high frequencies can minimize bubble formation.