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

Abstract

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 feedback mode was applied using ferrocene methanol (FcMeOH) as redox mediator 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 degraded AOs were mapped using the soft microelectrodes. Finally, in an apple cross-section the higher and homogeneous AO concentration in the peel with a heterogeneously decaying AO gradient towards the apple inward was visualized, demonstrating the adequate micrometer resolution of the SECM probe and the possibility to get information of the interior AO activity of the apple.

Reactive oxygen species metabolism and phenylpropanoid pathway involved in disease resistance against Penicillium expansum in apple fruit induced by ϵ‐poly‐l‐lysine

“…2 Antioxidants in apple fruit are beneficial for health with respect to diabetes, obesity and chronic heart and vascular disorders. 3,4 Other bioactive substances such as ursolic acid are found with antimicrobial, anti-inflammatory and antitumor activities. 5 However, postharvest losses can be up to 30-50% because of a lack of refrigeration and poor sanitation in developing countries.…”

“…Apple fruits are welcomed by consumers because they are rich in fiber, sugar, vitamins, minerals and phenolic compounds . Antioxidants in apple fruit are beneficial for health with respect to diabetes, obesity and chronic heart and vascular disorders . Other bioactive substances such as ursolic acid are found with antimicrobial, anti‐inflammatory and antitumor activities .…”

Biological imaging with scanning electrochemical microscopy

“…The versatility of the proposed methodology allows in-depth characterization of enzymatic activity under different and controlled conditions. Moreover, by using soft carbon microelectrodes as SECM tips, it was possible to evaluate the antioxidant activity of apple peel under a contact-scanning mode [118]. The use of soft probes made of flexible polymeric materials with built-in microelectrodes provides the possibility for a simple analysis of corrugated biological surfaces by working under constant gentle contact with the sample.…”

Advances and Perspectives in Chemical Imaging in Cellular Environments Using Electrochemical Methods

“…Single soft probes were developed by Girault and coworkers (for antioxidant mapping) [44] that were capable of tracing the contours of a soft surface. These probes were developed into soft linear array probes, in an approach that allows scanning over a large area in a shorter time than for a single electrode probe to achieve high-throughput imaging (Figure 1d) [45].…”