Herbal infusions bioelectrochemical polyphenolic index: Green tea – The gallic acid interference
Author: Dulce M.A. Gil and Pedro L.V. Falé and Maria L.M. Serralheiro and Maria J.F. Rebelo
An amperometric biosensor containing immobilised laccase from Trametes versicolor was used for the quantification of phenolic compounds in herbal infusions and green tea samples, from nine botanical families. The main purpose of this research was to correlate the bioelectrochemical polyphenolic index (BPI) of the samples with the total phenolic content according to the Folin–Ciocalteu spectrophotometric method (TPC), and the total antioxidant activity (TAA) measured by TEAC (Trolox Equivalent Antioxidant Capacity). A strong correlation between BPI, TPC, and TAA was obtained for 10 herbal infusion samples. However, when a green tea sample was taken into account, a decrease in the linear correlation coefficient (r2) from 0.9949 to 0.2599 and 0.5609 to 0.1086 for the relationship between BPI/TPC and BPI/TAA, respectively, was observed. Thus, we could conclude that the green tea’s matrix affects the laccase-based biosensor response. HPLC–DAD analysis showed the presence of gallic acid only in the green tea sample. The results have indicated that gallic acid inhibited the laccase activity regarding the ABTS oxidation in a concentration-dependent manner. The very strong correlation between BPI/TPC obtained for herbal infusions allow us to conclude that the laccase-based biosensor, used in this research, provides a valuable tool to obtain a valid estimation of the classical Folin–Ciocalteu index, in an uncomplicated and fast way.