Electrochemical Determination of the "Furanic Index" in Honey

5-(hydroxymethyl)furan-2-carbaldehyde, better known as hydroxymethylfurfural (HMF),
is a well-known freshness parameter of honey: although mostly absent in fresh samples, its concentration
tends to increase naturally with aging. However, high quantities of HMF are also found in fresh
but adulterated samples or honey subjected to thermal or photochemical stresses. In addition, HMF
deserves further consideration due to its potential toxic effects on human health. The processes at the
origin of HMF formation in honey and in other foods, containing saccharides and proteins—mainly
non-enzymatic browning reactions—can also produce other furanic compounds. Among others,
2-furaldehyde (2F) and 2-furoic acid (2FA) are the most abundant in honey, but also their isomers
(i.e., 3-furaldehyde, 3F, and 3-furoic acid, 3FA) have been found in it, although in small quantities.
A preliminary characterization of HMF, 2F, 2FA, 3F, and 3FA by cyclic voltammetry (CV) led to
hypothesizing the possibility of a comprehensive quantitative determination of all these compounds
using a simple and accurate square wave voltammetry (SWV) method. Therefore, a new parameter
able to provide indications on quality of honey, named “Furanic Index” (FI), was proposed in this
contribution, which is based on the simultaneous reduction of all analytes on an Hg electrode to
ca. 1.50 V vs. Saturated Calomel Electrode (SCE). The proposed method, validated, and tested on
10 samples of honeys of different botanical origin and age, is fast and accurate, and, in the case of
strawberry tree honey (Arbutus unedo), it highlighted the contribution to the FI of the homogentisic
acid (HA), i.e., the chemical marker of the floral origin of this honey, which was quantitatively
reduced in the working conditions. Excellent agreement between the SWV and Reverse-Phase
High-Performance Liquid Chromatography (RP-HPLC) data was observed in all samples considered.