Design and characterization of an integrate dialytic system coupled with amperometric microsensors for the dynamic quantification of ascorbic acid and total polyphenols in the Pompia fruits.

Several studies have been carried out to highlight the importance of the biological and nonbiological role of antioxidant compounds present in foods, in counteracting oxidative stress and the different diseases associated with it, such as atherosclerosis, diabetes mellitus, chronic inflammation and neurodegenerative disorders: these studies aimed to quantify the antioxidant capacity of various compounds and substances in a standardized way (Carlsen et al 2010, Del Rio et al 2004). The aim of the present work was to study the total antioxidant capacity in the whole fruit of Pompia Citrus limon var. pompia Camarda), a variety of endemic lemon from Sardinia, by quantifying ascorbic acid and polyphenols content in the endocarp of the mature fruit by means of a microdialytic system coupled to an amperometric microsensor. The use of small microdialysis probes, determining a minimum invasiveness on the fruit, and the high temporal resolution of the electrochemical analysis allow an in-situ analysis of the sample (user-free sample) and an almost real-time monitoring of it. The device consisted in a microdialysis probe inserted in the endocarp of the fruit, that was connected through polyethylene tubes to a miniaturized electrochemical cell of a volume of about 100 µl. By means of a microinfusion pump, connected to the probe, an acetate buffer solution was perfused. The evaluation of the total antioxidant capacity of the fruit, due to the content of ascorbic acid and of total polyphenols, was electrochemically obtained using graphite microsensors by applying different potentials. In particular, a fixed potential of +150 mV was applied for the detection of ascorbic acid alone and +500 mV for monitoring the total antioxidant capacity (polyphenols plus ascorbic acid). Data were calculated in equivalents of ascorbic acid. The amount of ascorbic acid was calculated being around 1.36 ± 0.16 mM, while the total antioxidant capacity was 1.65 ± 0.18 mM. From those values the concentration of polyphenols was derived by difference (0.29 ± 0.05 mM). The integrated microdialysis/microsensor system has proved to be an effective, reliable and repeatable tool, able to provide an extraction of the ascorbic acid and the polyphenols from the matrix in a short time and, in the experimental configuration used in this work, with rapid monitoring and, in the experimental configuration used in this work, with rapid monitoring and in “real-time”