The benefits provided by antioxidant compounds are well known. They reduce the risk of cardiovascular disease and tumours in man and protect fruits against stressful conditions such as drought, cold temperatures, UV radiations or pathogen attacks.
In fruit, antioxidants are generally found in peel, this is why it represents one of its leading protective barriers. As a consequence, the concentration of antioxidants in peel is an indicator of the fruit's self-defence system.
Apples have a high antioxidant content and thus have great nutritional and nutraceutical value. This is why thousands of tons of apples are consumed all over the world every day.
Researchers from the Polytechnic School in Lausanne, in collaboration with the University of Taiwan, studied a non-invasive soft probe scanning microscopy technique to map the antioxidant activity of Gala apple peel.
Researchers used scanning electro-chemical microscopy (SECM), which measures the current flowing through carbon microelectrodes with a probe placed in proximity to the peel. This enables the assessment and mapping of the redox activity of antioxidants.
SECM microscopy enabled researchers to obtain chemical images, i.e. maps in which colour variations quantify different antioxidant concentrations - high (red), low (yellow) and very low (blue).
"This approach could be the basis for developing portable electrochemical probes and scanners that enable the monitoring of antioxidant levels during the cultivation, harvesting and storing phases as well as the early identification of diseases such as apple rot."
Source: Tzu-En Lin, Andreas Lesch, Chi-Lin Li, Hubert H. Girault, 'Mapping the antioxidant activity of apple peels with soft probe scanning electrochemical microscopy', 1 Febbraio 2017, Journal of Electroanalytical Chemistry, Vol. 786, pag. 120–128. www.sciencedirect.com/science/article/pii/S1572665717300152