Abstract
A flow injection system using an unmodified gold screen-printed electrode was employed for total phenol determination in black and green teas. In order to avoid passivation of the electrode surface due to the redox reaction, preoxidation of the sample was realized by hexacyanoferrate(III) followed by addition of an EDTA solution. The complex formed in the presence of EDTA minimizes or avoids polymerization of the oxidized phenols. The previously filtered tea sample and hexacyanoferrate(III) reagent were introduced simultaneously into two-carrier streams producing two reproducible zones. At confluence point, the pre-oxidation of the phenolic compounds occurs while this zone flows through the coiled reactor and receives the EDTA solution before phenol detection. The consumption of ferricyanide was monitorized at 360 mV versus Ag/AgCl and reflected the total amount of phenolic compounds present in the sample. Results were reported as gallic acid equivalents (GAEs). The proposed system is robust, versatile, environmentally-friendly (since the reactive is used only in the presence of the sample), and allows the analysis of about 35–40 samples per hour with detection limit = 1 mg/L without the necessity for surface cleaning after each measurement. Precise results are in agreement with those obtained by the Folin-Ciocalteu method.
Highlights
Phenolic compounds are a class of chemicals that have a hydroxyl functional group attached to an aromatic hydrocarbon group
The results are reported as gallic acid equivalent (GAE)
The total content of phenolic compounds can be calculated according to the formula C = (c · V )/m, where c is the concentration of gallic acid established from the calibration curve, V is the volume of tea solution, and m is the weight of tea (g)
Summary
Phenolic compounds are a class of chemicals that have a hydroxyl functional group attached to an aromatic hydrocarbon group. The largest and most studied polyphenols are the flavonoids, as catechins, which correspond to the main phenolic compound found in green and black teas [3]. Gallic acid was identified to be main free phenolic acids; the four major catechins are (−)epicatechin gallate (ECG), (−)-epigallocatechin (EGC), (−)epigallocatechin gallate (EGCG), and (−)-epicatechin (EC). These species can be associated to a reduction in the risk of cardiovascular disease and some forms of cancer, as well as the improvement of oral health and other physiological functions such as anti-hypertensive effect, body weight control, antibacterial and antivirasic activity, and so forth [1,2,3,4]. The development of analytical methods for polyphenols represents an important and exciting topic for analytical chemists
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