Determination of total phenolic compounds in Cuban monofloral honeys by reverse flow injection analysis − Folin-Ciocalteau method

Abstract

Sugars represent approximately 80 % of the total composition of bee honey. They are the main interferers species of the Folin-Ciocalteau (FC) method for the determination of Total Phenolic Compounds (TPC). In the present work, a new combined methodology of Solid Phase Extraction (SPE) for sample preparation and Reverse Flow Injection Analysis (rFIA), with the use of FC reagent (FCR) was developed. SPE was performed with C18 BAKERBOND cartridges, while a two-channel rFIA optimized system was established for measurements. In this configuration sample and NaOH solution (0.1 molL-1) flow in two different channels, while FC reagent is injected. The detection was carried out in a flow cell located into a UV–Vis spectrophotometer at 760 nm. The results, expressed as Gallic acid equivalent (GAE), ranged from 75 to 107.9 and 215–242 mg Kg−1 for Leñatero and Guao de Costa honeys respectively used as experimental samples. Recoveries for honey samples were of 93–96 % (CV < 8 %). These results suggest that this new methodology is fast (30 injection per hour), selective, sensitive with a limit of detection of 1.49⋅10-6 molL-1 and simple, with a minimum expense of chemicals (70 μL of 7.5 % FC reagent per injection).