Rapid Determination of the Antioxidant Capacity of Lettuce by an E‐Tongue Based on Flow Injection Coulometry

Abstract

This work proposes the use of an electronic tongue based on flow injection coulometry for the rapid determination of the antioxidant capacity of fresh lettuce. The e‐tongue consisted of a series of 16 porous carbon electrodes, each poised at a fixed potential from +100 to +850 mV. Each injection leaded to a characteristic hydrodynamic voltammogram, whose profile reflects the composition of antioxidants. The correlation between the peak area recorded by each sensor and the 1,1‐Diphenyl‐2‐picryl‐hydrazyl (DPPH) assay was maximum ín the range of potentials between +400 and 750 mV (R2>0.97). Accordingly, the charge measured provided a direct and simple index of the antioxidant capacity. The practical utility of such index was initially demonstrated by determining the best extraction conditions. This consisted in freeze‐drying of lettuce followed by methanolic extraction. Later, the e‐tongue was used to evaluate the effect of storage (one week at 5 °C) on lettuce. The e‐tongue revealed that lettuce lost up to 25 % of their initial antioxidant activity during storage. However, when lettuce samples were pre‐treated with fast cooling or vacuum cooling, the decrease of the antioxidant index was limited to 14 and 15 %. Overall, the e‐tongue is a rapid, simple and sensitive method for the determination of the antioxidant capacity of fresh lettuce samples. Indirectly, these findings suggest also that lettuce may serve as potential dietary sources of natural phenolic antioxidants.

Electrochemical Methods to Evaluate the Antioxidant Activity and Capacity of Foods: A Review

“…Several studies also focus on direct application of coulometric array detector for analysis of food antioxidants in flow injection mode. Specifically, it has been used for analysis of chlorpromazine [189], antioxidants in lettuce [190] and chili [191] extracts. Elimination of the separation step allows to identify the antioxidant capacity of large number sample in a single run within the shortest time possible.…”

Non-Extractable Polyphenols from Food By-Products: Current Knowledge on Recovery, Characterisation, and Potential Applications

“…Comparably, it allows the detection of thermosensitive compounds, and it can separate between different polyphenol classes. In this case, the phenol compounds are usually detected in negative ionisation mode [109,110]. Li et al used ESI with Q-Exactive Orbitrap MS to analyse NEPs extracted from apple pomace.…”

Benefits and Pitfalls of HPLC Coupled to Diode-Array, Charged Aerosol, and Coulometric Detections: Effect of Detection on Screening of Bioactive Compounds in Apples

“…Electrochemical detection such as coulometric detection (CD) and cyclic voltammetry is another suitable tool to determine the overall antioxidant capacity of complex plant samples [ 29 , 40 , 41 , 42 ]. CD is very sensitive to electroactive substances and enables determination of all oxidizable substances.…”