Electrochemical determination of the procyanidins in peanut skin using a carbon nanotube electrode.

We demonstrated the electrochemical detection of procyanidins in peanut skin, which is often a waste product of the food industry, using a carbon nanotube electrode. Procyanidins, the main ingredients of peanut skin, are oligomers of catechin or epicatechin; therefore, they have various forms such as dimers, trimers, and a different number of linkages between monomers. Quantification using traditional high-performance liquid chromatography-mass spectroscopy (HPLC-MS) is tedious, because many peaks can be traced. The use of CNT electrodes for procyanidin sensing is promising, because CNT's properties, such as high conductivity, catalytic ability, and special geometry (high ratio of surface area to volume), enable common and specific profiles of the cyclic voltammograms (CVs) of procyanidins. Furthermore, the intensity of the anodic peaks (+ 0.32 V) due to the oxidation of catechol groups is proportional to the concentration of procyanidin (linear rang: 2.8-88 mg L, sensitivity: 1.4 mA mg L cm), and does not depend on the type of procyanidin. The amount of procyanidins in the peanut skin estimated by CV was similar to that estimated by HPLC-MS. This study may contribute to accelerating the utilization of peanut skin for animal food, drugs, and supplementation.