engleski

Abrasive stripping square-wave voltammetry of fruits and vegetables

Abrasive stripping voltammetry is the technique in which microcrystals of compounds are mechanically immobilized on the surface of graphite electrode and immersed into an aqueous electrolyte to be studied by the voltammetric methods. In the present communication it will be shown that this method can be used for quick estimation of electrochemical properties of blackberry, raspberry, strawberry, pomegranate and sweet and blue potatoes. A certain berry is squashed and smeared over a circular surface of graphite rod or the graphite surface is pressed into a slice of potato tuber. Then the rod is used as a working electrode and the oxidation of various components of the smear is measured by square-wave voltammetry. The responses of investigated plants are characterized by two peaks with maxima at 0.45 V and 0.55 V vs. Ag/AgCl, respectively. Both electrode reactions appear reversible at the frequency of 8 Hz. They can be ascribed to anthocyanins, anthocyanidins and ellagic acid as electroactive components. The first group of compounds are glycosylated derivatives of the flavylium cations, or anthocyanidins. The red-violet colour of fruits and vegetables is derived mainly from anthocyanins. Aglycones that appear in higher plants most frequently are pelargonidin, cyanidin and delphinidin. Ellagic acid is a dimeric derivative of gallic acid. It is found in numerous fruits and vegetables. There, it is mostly esterified to glucose in hydrolysable ellagitannins. The content of ellagic acid is preserved in the food products, such as jams and juices. Its daily intake is estimated to 90 mg. By the proposed method an antioxidative capacity of a certain plant can be quickly estimated. Its advantage is that no extraction of electroactive components is necessary. Figure 1. Abrasive stripping square-wave voltammetry of raspberry (1), garden strawberry (2) and pomegranate (3) on the paraffin-impregnated graphite electrode in 0.1 mol/L KNO3 at pH 2. The frequency is 8 Hz, the pulse amplitude is 50 mV, the potential increment is 2 mV, the starting potential is 0 V vs. Ag/AgCl and the scan direction is positive. Figure 2. Abrasive stripping square-wave voltammetry of cyanidin (1), ellagic acid (2), the sum of these responses (3) and the blackberry (4). All experimental data are as in Fig. 1.

Graphite electrode; square-wave voltammetry; ellagic acid; anthocyanins; anthocyanidins; strawberry; raspberry; blackberry; sweet potato; blue potato

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