Mapping the antioxidant activity of apple peels with soft probe scanning electrochemical microscopy

Article history: Received 26 September 2016 Received in revised form 3 January 2017 Accepted 4 January 2017 Available online 06 January 2017 We present a non-invasive electrochemical strategy for mapping the antioxidant (AO) activity of apple peels, which counterbalances oxidative stress caused by various external effectors. Soft carbon microelectrodes were used for soft probe scanning electrochemical microscopy (SECM) enabling the gentle and scratch-free contact mode scanning of rough and delicate apple peels in an electrolyte solution. The SECM feedbackmodewas applied using ferrocenemethanol (FcMeOH) as redoxmediator that gets electrochemically oxidized at the soft probe and diffuses towards the apple peel where it gets regenerated by certain AOs leading to a redox mediator recycling and increased current signal. The global AO activity in the apple peel including lenticels and regions with artificially degradedAOsweremappedusing the softmicroelectrodes. Finally, in an apple cross-section the higher and homogeneous AO concentration in the peel with a heterogeneously decaying AO gradient towards the apple inwardwas visualized, demonstrating the adequatemicrometer resolution of the SECMprobe and the possibility to get information of the interior AO activity of the apple. © 2017 Elsevier B.V. All rights reserved.