44ª Reunião Anual Virtual da SBQ

The banana is one of the most consumed fruits in Brazil, so that 98% of the national production is directed to the domestic market. However, the processing of this fruit generates a large amount of waste. For each ton of banana produced, approximately 4 tons of waste are generated, including peels, leaves and pseudo-stems1. Banana peels have a rich composition of phenolic compounds, such as vanillic acid (VA). This phenolic acid is the precursor of vanillin biosynthesis, which, in turn, is responsible for the vanilla aroma of several products in the food and pharmaceutical industry2. Therefore, within a biorefinery concept, these industries could reuse the VA contained in banana peels for higher added-value products. In this context, effective analytical methodologies are necessary to characterize these substrates. Thus, the objective of this work was to develop a portable, simple, sensitive, selective and low-cost electrochemical platform for the determination of VA in banana peel. The proposed sensor was based on a screen-printed carbon electrode (SPCE) modified with reduced graphene oxide (rGO), iron nanoparticles (FeNPs) and a molecularly imprinted polymer (MIP) of poly(pyrrole). For this, using a 0.50 mg mL-1 graphene oxide aqueous suspension containing 0.10 mol L-1 Na2SO4, the SPCE was modified with rGO through the application of -1.40 V until the charge of 1.0 mC was reached. Then, using a solution of 0.10 mol L-1 KCl containing 5.0×10-3 mol L-1 FeCl3, the SPCE/rGO electrode was decorated with FeNPs by applying -1.30 V until the charge of 5.0 mC was reached. For MIP preparation, 50 μL of a solution containing 3.0×10-2 mol L-1 pyrrole and 7.0×10-3 mol L-1 VA (PBS; pH 7.0) were placed on the SPCE/rGO-FeNPs electrode and electropolymerization was performed by applying three consecutive voltammetric cycles in a potential range of 0.60 to 1.20 V at 50 mV s-1. After the electropolymerization process, the electrode was inserted in a solution of ethanol-acetic acid (9:1; v:v) for 60 seconds to remove the VA template from the polymer matrix and obtain the SPCE/rGO-FeNPs-MIP electrode. This electrode was characterized by cyclic voltammetry, electrochemical impedance spectroscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy. For the rebinding experiments, 50 μL of VA solutions in different concentrations (PBS; pH 6.0) were placed on the electrode for 10 minutes. Under optimized conditions, the developed method exhibited two linear ranges from 1.0×10-9 to 1.5×10-7 mol L-1, with limit of detection and limit of quantification calculated to be 3.1×10-10 mol L-1 and 1.0×10-9 mol L-1 (n = 3), respectively. The proposed device presented excellent selectivity for the VA molecule and was successfully applied in banana peel extract sample. The quantification of VA was performed using the standard addition method and the results obtained were validated by recovery assays, where values between 98.6 and 106.7% were found.